

Network Working Group                                         R. Stewart
Internet-Draft                                       Cisco Systems, Inc.
Expires: August 27, 2003                                          Q. Xie
                                                              L. Yarroll
                                                          Motorola, Inc.
                                                                 J. Wood
                                                         DoCoMo USA Labs
                                                                 K. Poon
                                                              Consultant
                                                               K. Fujita
                                                           NEC USA, Inc.
                                                               M. Tuexen
                                                       February 26, 2003


    Sockets API Extensions for Stream Control Transmission Protocol
                                 (SCTP)
                   draft-ietf-tsvwg-sctpsocket-06.txt

Status of this Memo

   This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of RFC2026.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups.  Note that
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   Internet-Drafts.

   Internet-Drafts are draft documents valid for a maximum of six months
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   The list of current Internet-Drafts can be accessed at http://
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   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html.

   This Internet-Draft will expire on August 27, 2003.

Copyright Notice

   Copyright (C) The Internet Society (2003).  All Rights Reserved.

Abstract

   This document describes a mapping of the Stream Control Transmission



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   Protocol SCTP RFC2960 [8] into a sockets API.  The benefits of this
   mapping include compatibility for TCP applications, access to new
   SCTP features and a consolidated error and event notification scheme.

Table of Contents

   1.     Introduction . . . . . . . . . . . . . . . . . . . . . . .   4
   2.     Conventions  . . . . . . . . . . . . . . . . . . . . . . .   6
   2.1    Data Types . . . . . . . . . . . . . . . . . . . . . . . .   6
   3.     UDP-style Interface  . . . . . . . . . . . . . . . . . . .   7
   3.1    3.1 Basic Operation  . . . . . . . . . . . . . . . . . . .   7
   3.1.1  socket() - UDP Style Syntax  . . . . . . . . . . . . . . .   8
   3.1.2  bind() - UDP Style Syntax  . . . . . . . . . . . . . . . .   8
   3.1.3  listen() - UDP Style Syntax  . . . . . . . . . . . . . . .   9
   3.1.4  sendmsg() and recvmsg() - UDP Style Syntax . . . . . . . .  10
   3.1.5  close() - UDP Style Syntax . . . . . . . . . . . . . . . .  11
   3.1.6  connect() - UDP Style Syntax . . . . . . . . . . . . . . .  12
   3.2    Implicit Association Setup . . . . . . . . . . . . . . . .  12
   3.3    Non-blocking mode  . . . . . . . . . . . . . . . . . . . .  13
   3.4    Special considerations . . . . . . . . . . . . . . . . . .  13
   4.     TCP-style Interface  . . . . . . . . . . . . . . . . . . .  16
   4.1    Basic Operation  . . . . . . . . . . . . . . . . . . . . .  16
   4.1.1  socket() - TCP Style Syntax  . . . . . . . . . . . . . . .  17
   4.1.2  bind() - TCP Style Syntax  . . . . . . . . . . . . . . . .  17
   4.1.3  listen() - TCP Style Syntax  . . . . . . . . . . . . . . .  18
   4.1.4  accept() - TCP Style Syntax  . . . . . . . . . . . . . . .  19
   4.1.5  connect() - TCP Style Syntax . . . . . . . . . . . . . . .  19
   4.1.6  close() - TCP Style Syntax . . . . . . . . . . . . . . . .  20
   4.1.7  shutdown() - TCP Style Syntax  . . . . . . . . . . . . . .  20
   4.1.8  sendmsg() and recvmsg() - TCP Style Syntax . . . . . . . .  21
   4.1.9  getpeername()  . . . . . . . . . . . . . . . . . . . . . .  22
   5.     Data Structures  . . . . . . . . . . . . . . . . . . . . .  23
   5.1    The msghdr and cmsghdr Structures  . . . . . . . . . . . .  23
   5.2    SCTP msg_control Structures  . . . . . . . . . . . . . . .  24
   5.2.1  SCTP Initiation Structure (SCTP_INIT)  . . . . . . . . . .  25
   5.2.2  SCTP Header Information Structure (SCTP_SNDRCV)  . . . . .  26
   5.3    SCTP Events and Notifications  . . . . . . . . . . . . . .  29
   5.3.1  SCTP Notification Structure  . . . . . . . . . . . . . . .  29
   5.4    Ancillary Data Considerations and Semantics  . . . . . . .  39
   5.4.1  Multiple Items and Ordering  . . . . . . . . . . . . . . .  39
   5.4.2  Accessing and Manipulating Ancillary Data  . . . . . . . .  39
   5.4.3  Control Message Buffer Sizing  . . . . . . . . . . . . . .  40
   6.     Common Operations for Both Styles  . . . . . . . . . . . .  42
   6.1    send(), recv(), sendto(), recvfrom() . . . . . . . . . . .  42
   6.2    setsockopt(), getsockopt() . . . . . . . . . . . . . . . .  43
   6.3    read() and write() . . . . . . . . . . . . . . . . . . . .  43
   6.4    getsockname()  . . . . . . . . . . . . . . . . . . . . . .  43
   7.     Socket Options . . . . . . . . . . . . . . . . . . . . . .  45



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   7.1    Read / Write Options . . . . . . . . . . . . . . . . . . .  46
   7.1.1  Retransmission Timeout Parameters (SCTP_RTOINFO) . . . . .  46
   7.1.2  Association Parameters (SCTP_ASSOCINFO)  . . . . . . . . .  47
   7.1.3  Initialization Parameters (SCTP_INITMSG) . . . . . . . . .  49
   7.1.4  SO_LINGER  . . . . . . . . . . . . . . . . . . . . . . . .  49
   7.1.5  SCTP_NODELAY . . . . . . . . . . . . . . . . . . . . . . .  49
   7.1.6  SO_RCVBUF  . . . . . . . . . . . . . . . . . . . . . . . .  50
   7.1.7  SO_SNDBUF  . . . . . . . . . . . . . . . . . . . . . . . .  50
   7.1.8  Automatic Close of associations (SCTP_AUTOCLOSE) . . . . .  50
   7.1.9  Set Primary Address (SCTP_SET_PRIMARY_ADDR)  . . . . . . .  50
   7.1.10 Set Peer Primary Address (SCTP_SET_PEER_PRIMARY_ADDR)  . .  51
   7.1.11 Set Adaption Layer Indicator (SCTP_SET_ADAPTION_LAYER) . .  51
   7.1.12 Enable/Disable message fragmentation
          (SCTP_DISABLE_FRAGMENTS) . . . . . . . . . . . . . . . . .  51
   7.1.13 Peer Address Parameters (SCTP_SET_PEER_ADDR_PARAMS)  . . .  51
   7.1.14 Set default send parameters (SET_DEFAULT_SEND_PARAM) . . .  52
   7.1.15 Set notification and ancillary events (SCTP_SET_EVENTS)  .  52
   7.1.16 Set/clear IPv4 mapped addresses
          (SCTP_I_WANT_MAPPED_V4_ADDR) . . . . . . . . . . . . . . .  53
   7.1.17 Set the maximum fragrmentation size (SCTP_MAXSEG)  . . . .  53
   7.2    Read-Only Options  . . . . . . . . . . . . . . . . . . . .  53
   7.2.1  Association Status (SCTP_STATUS) . . . . . . . . . . . . .  53
   7.2.2  Peer Address Information (SCTP_GET_PEER_ADDR_INFO) . . . .  54
   7.3    Ancillary Data and Notification Interest Options . . . . .  55
   8.     New Interfaces . . . . . . . . . . . . . . . . . . . . . .  58
   8.1    sctp_bindx() . . . . . . . . . . . . . . . . . . . . . . .  58
   8.2    Branched-off Association . . . . . . . . . . . . . . . . .  59
   8.3    sctp_getpaddrs() . . . . . . . . . . . . . . . . . . . . .  59
   8.4    sctp_freepaddrs()  . . . . . . . . . . . . . . . . . . . .  60
   8.5    sctp_getladdrs() . . . . . . . . . . . . . . . . . . . . .  60
   8.6    sctp_freeladdrs()  . . . . . . . . . . . . . . . . . . . .  61
   8.7    sctp_sndmsg()  . . . . . . . . . . . . . . . . . . . . . .  61
   9.     Preprocessor Constants . . . . . . . . . . . . . . . . . .  62
   10.    Security Considerations  . . . . . . . . . . . . . . . . .  63
   11.    Acknowledgments  . . . . . . . . . . . . . . . . . . . . .  64
          References . . . . . . . . . . . . . . . . . . . . . . . .  65
          Authors' Addresses . . . . . . . . . . . . . . . . . . . .  65
   A.     TCP-style Code Example . . . . . . . . . . . . . . . . . .  68
   B.     UDP-style Code Example . . . . . . . . . . . . . . . . . .  74
          Intellectual Property and Copyright Statements . . . . . .  76











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1. Introduction

   The sockets API has provided a standard mapping of the Internet
   Protocol suite to many operating systems.  Both TCP RFC793 [1] and
   UDP RFC768 [2] have benefited from this standard representation and
   access method across many diverse platforms.  SCTP is a new protocol
   that provides many of the characteristics of TCP but also
   incorporates semantics more akin to UDP.  This document defines a
   method to map the existing sockets API for use with SCTP, providing
   both a base for access to new features and compatibility so that most
   existing TCP applications can be migrated to SCTP with few (if any)
   changes.

   There are three basic design objectives:

   1)  Maintain consistency with existing sockets APIs:

      We define a sockets mapping for SCTP that is consistent with other
      sockets API protocol mappings (for instance, UDP, TCP, IPv4, and
      IPv6).

   2)  Support a UDP-style interface

      This set of semantics is similar to that defined for connection
      less protocols, such as UDP.  It is more efficient than a TCP-like
      connection-oriented interface in terms of exploring the new
      features of SCTP.

      Note that SCTP is connection-oriented in nature, and it does not
      support broadcast or multicast communications, as UDP does.

   3)  Support a TCP-style interface

      This interface supports the same basic semantics as sockets for
      connection-oriented protocols, such as TCP.

      The purpose of defining this interface is to allow existing
      applications built on connection-oriented protocols be ported to
      use SCTP with very little effort, and developers familiar with
      those semantics can easily adapt to SCTP.

      Extensions will be added to this mapping to provide mechanisms to
      exploit new features of SCTP.

   Goals 2 and 3 are not compatible, so in this document we define two
   modes of mapping, namely the UDP-style mapping and the TCP-style
   mapping.  These two modes share some common data structures and
   operations, but will require the use of two different application



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   programming models.

   A mechanism is defined to convert a UDP-style SCTP association into a
   TCP-style socket.

   Some of the SCTP mechanisms cannot be adequately mapped to existing
   socket interface.  In some cases, it is more desirable to have new
   interface instead of using existing socket calls.  This document also
   describes those new interface.










































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2. Conventions

2.1 Data Types

   Whenever possible, data types from Draft 6.6 (March 1997) of POSIX
   1003.1g are used: uintN_t means an unsigned integer of exactly N bits
   (e.g., uint16_t).  We also assume the argument data types from
   1003.1g when possible (e.g., the final argument to setsockopt() is a
   size_t value).  Whenever buffer sizes are specified, the POSIX 1003.1
   size_t data type is used.









































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3. UDP-style Interface

   The UDP-style interface has the following characteristics:

   A) Outbound association setup is implicit.

   B) Messages are delivered in complete messages (with one notable
   exception).

   C) There is a 1 to MANY relationship between socket and association.

3.1 3.1 Basic Operation

   A typical server in this model uses the following socket calls in
   sequence to prepare an endpoint for servicing requests:

   1.  socket()

   2.  bind()

   3.  listen()

   4.  recvmsg()

   5.  sendmsg()

   6.  close()

   A typical client uses the following calls in sequence to setup an
   association with a server to request services:

   1.  socket()

   2.  sendmsg()

   3.  recvmsg()

   4.  close()

   In this model, by default, all the associations connected to the
   endpoint are represented with a single socket.

   If the server or client wishes to branch an existing association off
   to a separate socket, it is required to call sctp_peeloff() and in
   the parameter specifies one of the transport addresses of the
   association.  The sctp_peeloff() call will return a new socket which
   can then be used with recv() and send() functions for message
   passing.  See Section Section 8.2 for more on branched-off



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   associations.

   Once an association is branched off to a separate socket, it becomes
   completely separated from the original socket.  All subsequent
   control and data operations to that association must be done through
   the new socket.  For example, the close operation on the original
   socket will not terminate any associations that have been branched
   off to a different socket.

   We will discuss the UDP-style socket calls in more details in the
   following subsections.

3.1.1 socket() - UDP Style Syntax

   Applications use socket() to create a socket descriptor to represent
   an SCTP endpoint.

   The syntax is,

   sd = socket(PF_INET, SOCK_SEQPACKET, IPPROTO_SCTP);

   or,

   sd = socket(PF_INET6, SOCK_SEQPACKET, IPPROTO_SCTP);

   Here, SOCK_SEQPACKET indicates the creation of a UDP-style socket.

   The first form creates an endpoint which can use only IPv4 addresses,
   while, the second form creates an endpoint which can use both IPv6
   and IPv4 addresses.

3.1.2 bind() - UDP Style Syntax

   Applications use bind() to specify which local address the SCTP
   endpoint should associate itself with.

   An SCTP endpoint can be associated with multiple addresses.  To do
   this, sctp_bindx() is introduced in section Section 8.1 to help
   applications do the job of associating multiple addresses.

   These addresses associated with a socket are the eligible transport
   addresses for the endpoint to send and receive data.  The endpoint
   will also present these addresses to its peers during the association
   initialization process, see RFC2960 [8].

   After calling bind() or sctp_bindx(), if the endpoint wishes to
   accept new associations on the socket, it must call listen() (see
   section Section 3.1.3).



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   The syntax of bind() is,

   ret = bind(int sd, struct sockaddr *addr, socklen_t addrlen);

   sd: the socket descriptor returned by socket().

   addr: the address structure (struct sockaddr_in or struct
      sockaddr_in6 RFC2553 [7]).

   addrlen: the size of the address structure.

   If sd is an IPv4 socket, the address passed must be an IPv4 address.
   If the sd is an IPv6 socket, the address passed can either be an IPv4
   or an IPv6 address.

   Applications cannot call bind() multiple times to associate multiple
   addresses to an endpoint.  After the first call to bind(), all
   subsequent calls will return an error.

   If addr is specified as a wildcard (INADDR_ANY for an IPv4 address,
   or as IN6ADDR_ANY_INIT or in6addr_any for an IPv6 address), the
   operating system will associate the endpoint with an optimal address
   set of the available interfaces.

   If a bind() or sctp_bindx() is not called prior to a sendmsg() call
   that initiates a new association, the system picks an ephemeral port
   and will choose an address set equivalent to binding with a wildcard
   address.  One of those addresses will be the primary address for the
   association.  This automatically enables the multi-homing capability
   of SCTP.

3.1.3 listen() - UDP Style Syntax

   By default, new associations are not accepted for UDP style sockets.
   An application uses listen() to mark a socket as being able to accept
   new associations.  The syntax is,

      int listen(int socket, int backlog);
       socket  - the socket descriptor of the endpoint.
       backlog - ignored for UDP-style sockets.

   Note that UDP-style socket consumers do not need to call accept to
   retrieve new associations.  Calling accept() on a UDP-style socket
   should return EOPNOTSUPP.  Rather, new associations are accepted
   automatically, and notifications of the new associations are
   delivered via recvmsg() with the SCTP_ASSOC_CHANGE event (if these
   notifications are enabled).  Clients will typically not call listen,
   so that they can be assured that the only associations on the socket



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   will be ones they actively initiated.  Server or peer-to-peer
   sockets, on the other hand, will always accept new associations, so a
   well-written application using server UDP-style sockets must be
   prepared to handle new associations from unwanted peers.

   Also note that the SCTP_ASSOC_CHANGE event provides the association
   ID for a new association, so if applications wish to use the
   association ID as input to other socket calls, they should ensure
   that the SCTP_ASSOC_CHANGE event is enabled (it is enabled by
   default).

3.1.4 sendmsg() and recvmsg() - UDP Style Syntax

   An application uses sendmsg() and recvmsg() call to transmit data to
   and receive data from its peer.

   ssize_t sendmsg(int socket, const struct msghdr *message, int flags);

   ssize_t recvmsg(int socket, struct msghdr *message, int flags);

   socket: the socket descriptor of the endpoint.

   message: pointer to the msghdr structure which contains a single user
      message and possibly some ancillary data.  See Section 5 for
      complete description of the data structures.

   flags: No new flags are defined for SCTP at this level.  See Section
      5 for SCTP-specific flags used in the msghdr structure.

   As we will see in Section 5, along with the user data, the ancillary
   data field is used to carry the sctp_sndrcvinfo and/or the
   sctp_initmsg structures to perform various SCTP functions including
   specifying options for sending each user message.  Those options,
   depending on whether sending or receiving, include stream number,
   stream sequence number, various flags, context and payload protocol
   Id, etc.

   When sending user data with sendmsg(), the msg_name field in msghdr
   structure will be filled with one of the transport addresses of the
   intended receiver.  If there is no association existing between the
   sender and the intended receiver, the sender's SCTP stack will set up
   a new association and then send the user data (see Section 3.2 for
   more on implicit association setup).

   If a peer sends a SHUTDOWN, a SCTP_SHUTDOWN_EVENT notification will
   be delivered if that notification has been enabled, and no more data
   can be sent to that association.  Any attempt to send more data will
   cause sendmsg() to return with an ESHUTDOWN error.  Note that the



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   socket is still open for reading at this point so it is possible to
   retrieve notifications.

   When receiving a user message with recvmsg(), the msg_name field in
   msghdr structure will be populated with the source transport address
   of the user data.  The caller of recvmsg() can use this address
   information to determine to which association the received user
   message belongs.  Note that if SCTP_ASSOC_CHANGE events are disabled,
   applications must use the peer transport address provided in the
   msg_name field by recvmsg() to perform correlation to an association,
   since they will not have the association ID.

   If all data in a single message has been delivered, MSG_EOR will be
   set in the msg_flags field of the msghdr structure (see section
   Section 5.1).

   If the application does not provide enough buffer space to completely
   receive a data message, MSG_EOR will not be set in msg_flags.
   Successive reads will consume more of the same message until the
   entire message has been delivered, and MSG_EOR will be set.

   If the SCTP stack is running low on buffers, it may partially deliver
   a message.  In this case, MSG_EOR will not be set, and more calls to
   recvmsg() will be necessary to completely consume the message.  Only
   one message at a time can be partially delivered.

   Note, if the socket is a branched-off socket that only represents one
   association (see Section 3.1), the msg_name field is not used when
   sending data (i.e., ignored by the SCTP stack).

3.1.5 close() - UDP Style Syntax

   Applications use close() to perform graceful shutdown (as described
   in Section 10.1 of RFC2960 [8]) on ALL the associations currently
   represented by a UDP-style socket.

   The syntax is:

      ret = close(int sd);

       sd      - the socket descriptor of the associations to be closed.

   To gracefully shutdown a specific association represented by the
   UDP-style socket, an application should use the sendmsg() call,
   possibly passing a user specified abort code in the data field, and
   including the MSG_EOF flag in the ancillary data (see Section 5.2.2).

   If sd in the close() call is a branched-off socket representing only



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   one association, the shutdown is performed on that association only.

3.1.6 connect() - UDP Style Syntax

   An application may use the connect() call in the UDP model to
   initiate an association without sending data.

   The syntax is:

   ret = connect(int sd, const struct sockaddr *nam, socklen_t len);

   sd: the socket descriptor to have a new association added to.

   nam: the address structure (either struct sockaddr_in or struct
      sockaddr_in6 defined in RFC2553 [7]).

   len: the size of the address.


3.2 Implicit Association Setup

   Once all bind() calls are complete on a UDP-style socket, the
   application can begin sending and receiving data using the sendmsg()/
   recvmsg() or sendto()/recvfrom() calls, without going through any
   explicit association setup procedures (i.e., no connect() calls
   required).

   Whenever sendmsg() or sendto() is called and the SCTP stack at the
   sender finds that there is no association existing between the sender
   and the intended receiver (identified by the address passed either in
   the msg_name field of msghdr structure in the sendmsg() call or the
   dest_addr field in the sendto() call), the SCTP stack will
   automatically setup an association to the intended receiver.

   Upon the successful association setup a SCTP_COMM_UP notification
   will be dispatched to the socket at both the sender and receiver
   side.  This notification can be read by the recvmsg() system call
   (see Section 3.1.3).

   Note, if the SCTP stack at the sender side supports bundling, the
   first user message may be bundled with the COOKIE ECHO message
   RFC2960 [8].

   When the SCTP stack sets up a new association implicitly, it first
   consults the sctp_initmsg structure, which is passed along within the
   ancillary data in the sendmsg() call (see Section 5.2.1 for details
   of the data structures), for any special options to be used on the
   new association.



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   If this information is not present in the sendmsg() call, or if the
   implicit association setup is triggered by a sendto() call, the
   default association initialization parameters will be used.  These
   default association parameters may be set with respective
   setsockopt() calls or be left to the system defaults.

   Implicit association setup cannot be initiated by send()/recv()
   calls.

3.3 Non-blocking mode

   Some SCTP users might want to avoid blocking when they call socket
   interface function.

   Whenever the user which want to avoid blocking must call select()
   before calling sendmsg()/sendto() and recvmsg()/recvfrom(), and check
   the socket status is writable or readable.  If the socket status
   isn't writeable or readable, the user should not call sendmsg()/
   sendto() and recvmsg()/recvfrom().

   Once all bind() calls are complete on a UDP-style socket, the
   application must set the non-blocking option by a fcntl() (such as
   O_NONBLOCK).  After which the sendmsg() function returns immediately,
   and the success or failure of the data message (and possible
   SCTP_INITMSG parameters) will be signaled by the SCTP_ASSOC_CHANGE
   event with SCTP_COMM_UP or CANT_START_ASSOC.  If user data could not
   be sent (due to a CANT_START_ASSOC), the sender will also receive a
   SCTP_SEND_FAILED event.  Those event(s) can be received by the user
   calling of recvmsg().  A server (having called listen()) is also
   notified of an association up event by the reception of a
   SCTP_ASSOC_CHANGE with SCTP_COMM_UP via the calling of recvmsg() and
   possibly the reception of the first data message.

   In order to shutdown the association gracefully, the user must call
   sendmsg() with no data and with the MSG_EOF flag set.  The function
   returns immediately, and completion of the graceful shutdown is
   indicated by an SCTP_ASSOC_CHANGE notification of type
   SHUTDOWN_COMPLETE (see Section 5.3.1.1).

3.4 Special considerations

   The fact that a UDP-style socket can provide access to many SCTP
   associations through a single socket descriptor has important
   implications for both application programmers and system programmers
   implementing this API.  A key issue is how buffer space inside the
   sockets layer is managed.  Because this implementation detail
   directly affects how application programmers must write their code to
   ensure correct operation and portability, this section provides some



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   guidance to both implementors and application programmers.

   An important feature that SCTP shares with TCP is flow control:
   specifically, a sender may not send data faster than the receiver can
   consume it.

   For TCP, flow control is typically provided for in the sockets API as
   follows.  If the reader stops reading, the sender queues messages in
   the socket layer until it uses all of its socket buffer space
   allocation creating a "stalled connection".  Further attempts to
   write to the socket will block or return the error EAGAIN (for a
   non-blocking socket).  At some point, either the connection is
   closed, or the receiver begins to read again freeing space in the
   output queue.

   For TCP-style SCTP sockets (this includes sockets descriptors that
   were separated from a UDP style socket with sctp_peeloff()) the
   behavior is identical.  For UDP-style SCTP sockets, the fact that we
   have multiple associations on a single socket makes the situation
   more complicated.  If the implementation uses a single buffer space
   allocation shared by all associations, a single stalled association
   can prevent the further sending of data on all associations active on
   a particular UDP-style socket.

   For a blocking socket, it should be clear that a single stalled
   association can block the entire socket.  For this reason,
   application programmers may want to use non-blocking UDP-style
   sockets.  The application should at least be able to send messages to
   the non-stalled associations.

   But a non-blocking socket is not sufficient if the API implementor
   has chosen a single shared buffer allocation for the socket.  A
   single stalled association would eventually cause the shared
   allocation to fill, and it would become impossible to send even to
   non-stalled associations.

   The API implementor can solve this problem by providing each
   association with its own allocation of outbound buffer space.  Each
   association should conceptually have as much buffer space as it would
   have if it had its own socket.  As a bonus, this simplifies the
   implementation of sctp_peeloff().

   To ensure that a given stalled association will not prevent other
   non-stalled associations from being writable, application programmers
   should either:






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   (a) demand that the underlying implementation dedicates independent
      buffer space allotments to each association (as suggested above),
      or

   (b) verify that their application layer protocol does not permit
      large amounts of unread data at the receiver (this is true of some
      request-response protocols, for example), or

   (c) use TCP-style sockets for association which may potentially stall
      (either from the beginning, or by using sctp_peeloff before
      sending large amounts of data that may cause a stalled condition).








































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4. TCP-style Interface

   The goal of this model is to follow as closely as possible the
   current practice of using the sockets interface for a connection
   oriented protocol, such as TCP.  This model enables existing
   applications using connection oriented protocols to be ported to SCTP
   with very little effort.

   Note that some new SCTP features and some new SCTP socket options can
   only be utilized through the use of sendmsg() and recvmsg() calls,
   see Section 4.1.8.

4.1 Basic Operation

   A typical server in TCP-style model uses the following system call
   sequence to prepare an SCTP endpoint for servicing requests:

   1.  socket()

   2.  bind()

   3.  listen()

   4.  accept()

   The accept() call blocks until a new association is set up.  It
   returns with a new socket descriptor.  The server then uses the new
   socket descriptor to communicate with the client, using recv() and
   send() calls to get requests and send back responses.

   Then it calls

   5.  close()

   to terminate the association.

   A typical client uses the following system call sequence to setup an
   association with a server to request services:

   1.  socket()

   2.  connect()

   After returning from connect(), the client uses send() and recv()
   calls to send out requests and receive responses from the server.

   The client calls




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   3.  close()

   to terminate this association when done.

4.1.1 socket() - TCP Style Syntax

   Applications calls socket() to create a socket descriptor to
   represent an SCTP endpoint.

   The syntax is:

     int socket(PF_INET, SOCK_STREAM, IPPROTO_SCTP);

      or,

     int socket(PF_INET6, SOCK_STREAM, IPPROTO_SCTP);

   Here, SOCK_STREAM indicates the creation of a TCP-style socket.

   The first form creates an endpoint which can use only IPv4 addresses,
   while the second form creates an endpoint which can use both IPv6 and
   IPv4 addresses.

4.1.2 bind() - TCP Style Syntax

   Applications use bind() to pass an address to be associated with an
   SCTP endpoint to the system.  bind() allows only either a single
   address or a IPv4 or IPv6 wildcard address to be bound.  An SCTP
   endpoint can be associated with multiple addresses.  To do this,
   sctp_bindx() is introduced in Section 8.1  to help applications do
   the job of associating multiple addresses.

   These addresses associated with a socket are the eligible transport
   addresses for the endpoint to send and receive data.  The endpoint
   will also present these addresses to its peers during the association
   initialization process, see RFC2960 [8].

   The syntax is:

   int bind(int sd, struct sockaddr *addr, socklen_t addrlen);

   sd: the socket descriptor returned by socket() call.

   addr: the address structure (either struct sockaddr_in or struct
      sockaddr_in6 defined in RFC2553 [7]).






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   addrlen: the size of the address structure.

   If sd is an IPv4 socket, the address passed must be an IPv4 address.
   Otherwise, i.e., the sd is an IPv6 socket, the address passed can
   either be an IPv4 or an IPv6 address.

   Applications cannot call bind() multiple times to associate multiple
   addresses to the endpoint.  After the first call to bind(), all
   subsequent calls will return an error.

   If addr is specified as a wildcard (INADDR_ANY for an IPv4 address,
   or as IN6ADDR_ANY_INIT or in6addr_any for an IPv6 address), the
   operating system will associate the endpoint with an optimal address
   set of the available interfaces.

   If a bind() or sctp_bindx() is not called prior to the connect()
   call, the system picks an ephemeral port and will choose an address
   set equivalent to binding with a wildcard address.  One of those
   addresses will be the primary address for the association.  This
   automatically enables the multi-homing capability of SCTP.

   The completion of this bind() process does not ready the SCTP
   endpoint to accept inbound SCTP association requests.  Until a
   listen() system call, described below, is performed on the socket,
   the SCTP endpoint will promptly reject an inbound SCTP INIT request
   with an SCTP ABORT.

4.1.3 listen() - TCP Style Syntax

   Applications use listen() to ready the SCTP endpoint for accepting
   inbound associations.

   The syntax is:

   int listen(int sd, int backlog);

   sd: the socket descriptor of the SCTP endpoint.

   backlog: this specifies the max number of outstanding associations
      allowed in the socket's accept queue.  These are the associations
      that have finished the four-way initiation handshake (see Section
      5 of RFC2960 [8]) and are in the ESTABLISHED state.  Note, a
      backlog of '0' indicates that the caller no longer wishes to
      receive new associations.







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4.1.4 accept() - TCP Style Syntax

   Applications use accept() call to remove an established SCTP
   association from the accept queue of the endpoint.  A new socket
   descriptor will be returned from accept() to represent the newly
   formed association.

   The syntax is:

   new_sd = accept(int sd, struct sockaddr *addr, socklen_t *addrlen);

   new_sd: the socket descriptor for the newly formed association.

   sd the listening socket descriptor.

   addr on return, will contain the primary address of the peer
      endpoint.

   addrlen on return, will contain the size of addr.


4.1.5 connect() - TCP Style Syntax

   Applications use connect() to initiate an association to a peer.

   The syntax is:

   int connect(int sd, const struct sockaddr *addr, socklen_t addrlen);

   sd: the socket descriptor of the endpoint.

   addr the peer's address.

   addrlen the size of the address.

   This operation corresponds to the ASSOCIATE primitive described in
   section 10.1 of RFC2960 [8].

   By default, the new association created has only one outbound stream.
   The SCTP_INITMSG option described in Section 7.1.3 should be used
   before connecting to change the number of outbound streams.

   If a bind() or sctp_bindx() is not called prior to the connect()
   call, the system picks an ephemeral port and will choose an address
   set equivalent to binding with INADDR_ANY and IN6ADDR_ANY for IPv4
   and IPv6 socket respectively.  One of those addresses will be the
   primary address for the association.  This automatically enables the
   multi-homing capability of SCTP.



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   Note that SCTP allows data exchange, similar to T/TCP RFC1644 [3],
   during the association set up phase.  If an application wants to do
   this, it cannot use connect() call.  Instead, it should use sendto()
   or sendmsg() to initiate an association.  If it uses sendto() and it
   wants to change initialization behavior, it needs to use the
   SCTP_INITMSG socket option before calling sendto().  Or it can use
   SCTP_INIT type sendmsg() to initiate an association without doing the
   setsockopt().

   SCTP does not support half close semantics.  This means that unlike
   T/TCP, MSG_EOF should not be set in the flags parameter when calling
   sendto() or sendmsg() when the call is used to initiate a connection.
   MSG_EOF is not an acceptable flag with SCTP socket.

4.1.6 close() - TCP Style Syntax

   Applications use close() to gracefully close down an association.

   The syntax is:

      int close(int sd);

        sd      - the socket descriptor of the association to be closed.

   After an application calls close() on a socket descriptor, no further
   socket operations will succeed on that descriptor.

4.1.7 shutdown() - TCP Style Syntax

   SCTP differs from TCP in that it does not have half closed semantics.
   Hence the shutdown() call for SCTP is an approximation of the TCP
   shutdown() call, and solves some different problems.  Full
   TCP-compatibility is not provided, so developers porting TCP
   applications to SCTP may need to recode sections that use shutdown().
   (Note that it is possible to achieve the same results as half close
   in SCTP using SCTP streams.)

   The syntax is:













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      int shutdown(int socket, int how);

       sd      - the socket descriptor of the association to be closed.

       how     - Specifies the type of shutdown.  The  values  are
                 as follows:

                 SHUT_RD
                       Disables further receive operations. No SCTP
                       protocol action is taken.

                 SHUT_WR
                       Disables further send operations, and initiates
                       the SCTP shutdown sequence.

                 SHUT_RDWR
                       Disables further send  and  receive  operations
                       and initiates the SCTP shutdown sequence.


   The major difference between SCTP and TCP shutdown() is that SCTP
   SHUT_WR initiates immediate and full protocol shutdown, whereas TCP
   SHUT_WR causes TCP to go into the half closed state.  SHUT_RD behaves
   the same for SCTP as TCP.  The purpose of SCTP SHUT_WR is to close
   the SCTP association while still leaving the socket descriptor open,
   so that the caller can receive back any data SCTP was unable to
   deliver (see Section 5.3.1.4 for more information).

   To perform the ABORT operation described in RFC2960 [8] section 10.1,
   an application can use the socket option SO_LINGER.  It is described
   in Section 7.1.4.

4.1.8 sendmsg() and recvmsg() - TCP Style Syntax

   With a TCP-style socket, the application can also use sendmsg() and
   recvmsg() to transmit data to and receive data from its peer.  The
   semantics is similar to those used in the UDP-style model (section
   Section 3.1.3), with the following differences:

   1) When sending, the msg_name field in the msghdr is not used to
   specify the intended receiver, rather it is used to indicate a
   different peer address if the sender does not want to send the
   message over the primary address of the receiver.  If the transport
   address given is not part of the current association, the data will
   not be sent and a SCTP_SEND_FAILED event will be delivered to the
   application if send failure events are enabled.

   2) An application must use close() to gracefully shutdown an



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   association, or use SO_LINGER option with close() to abort an
   association.  It must not use the MSG_ABORT or MSG_EOF flag in
   sendmsg().  The system returns an error if an application tries to do
   so.

4.1.9 getpeername()

   Applications use getpeername() to retrieve the primary socket address
   of the peer.  This call is for TCP compatibility, and is not
   multi-homed.  It does not work with UDP-style sockets.  See Section
   8.3 for a multi-homed/UDP-sockets version of the call.

   The syntax is:

      int getpeername(int socket, struct sockaddr *address,
                      socklen_t *len);

       sd      - the socket descriptor to be queried.

       address - On return, the peer primary address is stored in
                 this buffer. If the socket is an IPv4 socket, the
                 address will be IPv4. If the socket is an IPv6 socket,
                 the address will be either an IPv6 or IPv4
                 address.

       len     - The caller should set the length of address here.
                 On return, this is set to the length of the returned
                 address.


   If the actual length of the address is greater than the length of the
   supplied sockaddr structure, the stored address will be truncated.



















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5. Data Structures

   We discuss in this section important data structures which are
   specific to SCTP and are used with sendmsg() and recvmsg() calls to
   control SCTP endpoint operations and to access ancillary information
   and notifications.

5.1 The msghdr and cmsghdr Structures

   The msghdr structure used in the sendmsg() and recvmsg() calls, as
   well as the ancillary data carried in the structure, is the key for
   the application to set and get various control information from the
   SCTP endpoint.

   The msghdr and the related cmsghdr structures are defined and
   discussed in details in  RFC2292 [6].  Here we will cite their
   definitions from RFC2292 [6].

   The msghdr structure:

   struct msghdr {
     void      *msg_name;        /* ptr to socket address structure */
     socklen_t  msg_namelen;     /* size of socket address structure */
     struct iovec  *msg_iov;     /* scatter/gather array */
     size_t     msg_iovlen;      /* # elements in msg_iov */
     void      *msg_control;     /* ancillary data */
     socklen_t  msg_controllen;  /* ancillary data buffer length */
     int        msg_flags;       /* flags on received message */
   };

   The cmsghdr structure:

   struct cmsghdr {
     socklen_t  cmsg_len;   /* #bytes, including this header */
     int        cmsg_level; /* originating protocol */
     int        cmsg_type;  /* protocol-specific type */
                /* followed by unsigned char cmsg_data[]; */
     };

   In the msghdr structure, the usage of msg_name has been discussed in
   previous sections (see Section 3.1.3 and Section 4.1.8).

   The scatter/gather buffers, or I/O vectors (pointed to by the msg_iov
   field) are treated as a single SCTP data chunk, rather than multiple
   chunks, for both sendmsg() and recvmsg().

   The msg_flags are not used when sending a message with sendmsg().




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   If a notification has arrived, recvmsg() will return the notification
   with the MSG_NOTIFICATION flag set in msg_flags.  If the
   MSG_NOTIFICATION flag is not set, recvmsg() will return data.  See
   Section 5.3 for more information about notifications.

   If all portions of a data frame or notification have been read,
   recvmsg() will return with MSG_EOR set in msg_flags.

5.2 SCTP msg_control Structures

   A key element of all SCTP-specific socket extensions is the use of
   ancillary data to specify and access SCTP-specific data via the
   struct msghdr's msg_control member used in sendmsg() and recvmsg().
   Fine-grained control over initialization and sending parameters are
   handled with ancillary data.

   Each ancillary data item is proceeded by a struct cmsghdr (see
   Section 5.1), which defines the function and purpose of the data
   contained in in the cmsg_data[] member.

   There are two kinds of ancillary data used by SCTP: initialization
   data, and, header information (SNDRCV).  Initialization data
   (UDP-style only) sets protocol parameters for new associations.
   Section 5.2.1 provides more details.  Header information can set or
   report parameters on individual messages in a stream.  See Section
   5.2.2 for how to use SNDRCV ancillary data.

   By default on a TCP-style socket, SCTP will pass no ancillary data;
   on a UDP-style socket, SCTP will only pass SCTP_SNDRCV and
   SCTP_ASSOC_CHANGE information.  Specific ancillary data items can be
   enabled with socket options defined for SCTP; see Section 7.3.

   Note that all ancillary types are fixed length; see Section 5.4 for
   further discussion on this.  These data structures use struct
   sockaddr_storage (defined in RFC2553 [7]) as a portable, fixed length
   address format.

   Other protocols may also provide ancillary data to the socket layer
   consumer.  These ancillary data items from other protocols may
   intermingle with SCTP data.  For example, the IPv6 socket API
   definitions (RFC2292 [6] and RFC2553 [7]) define a number of
   ancillary data items.  If a socket API consumer enables delivery of
   both SCTP and IPv6 ancillary data, they both may appear in the same
   msg_control buffer in any order.  An application may thus need to
   handle other types of ancillary data besides that passed by SCTP.

   The sockets application must provide a buffer large enough to
   accommodate all ancillary data provided via recvmsg().  If the buffer



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   is not large enough, the ancillary data will be truncated and the
   msghdr's msg_flags will include MSG_CTRUNC.

5.2.1 SCTP Initiation Structure (SCTP_INIT)

   This cmsghdr structure provides information for initializing new SCTP
   associations with sendmsg().  The SCTP_INITMSG socket option uses
   this same data structure.  This structure is not used for recvmsg().

   cmsg_level    cmsg_type      cmsg_data[]
   ------------  ------------   ----------------------
   IPPROTO_SCTP  SCTP_INIT      struct sctp_initmsg

   Here is the definition of the sctp_initmsg structure:

   struct sctp_initmsg {
      uint16_t sinit_num_ostreams;
      uint16_t sinit_max_instreams;
      uint16_t sinit_max_attempts;
      uint16_t sinit_max_init_timeo;
   };

   sinit_num_ostreams: 16 bits (unsigned integer)

   This is an integer number representing the number of streams that the
   application wishes to be able to send to.  This number is confirmed
   in the SCTP_COMM_UP notification and must be verified since it is a
   negotiated number with the remote endpoint.  The default value of 0
   indicates to use the endpoint default value.

   sinit_max_instreams: 16 bits (unsigned integer)

   This value represents the maximum number of inbound streams the
   application is prepared to support.  This value is bounded by the
   actual implementation.  In other words the user MAY be able to
   support more streams than the Operating System.  In such a case, the
   Operating System limit overrides the value requested by the user.
   The default value of 0 indicates to use the endpoint's default value.

   sinit_max_attempts: 16 bits (unsigned integer)

   This integer specifies how many attempts the SCTP endpoint should
   make at resending the INIT.  This value overrides the system SCTP
   'Max.Init.Retransmits' value.  The default value of 0 indicates to
   use the endpoint's default value.  This is normally set to the
   system's default 'Max.Init.Retransmit' value.

   sinit_max_init_timeo: 16 bits (unsigned integer)



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   This value represents the largest Time-Out or RTO value (in
   milliseconds) to use inattempting a INIT.  Normally the 'RTO.Max' is
   used to limit the doubling of the RTO upon timeout.  For the INIT
   message this value MAY override 'RTO.Max'.  This value MUST NOT
   influence 'RTO.Max' during data transmission and is only used to
   bound the initial setup time.  A default value of 0 indicates to use
   the endpoint's default value.  This is normally set to the system's
   'RTO.Max' value (60 seconds).

5.2.2 SCTP Header Information Structure (SCTP_SNDRCV)

   This cmsghdr structure specifies SCTP options for sendmsg() and
   describes SCTP header information about a received message through
   recvmsg().

   cmsg_level    cmsg_type      cmsg_data[]
   ------------  ------------   ----------------------
   IPPROTO_SCTP  SCTP_SNDRCV    struct sctp_sndrcvinfo

   Here is the definition of sctp_sndrcvinfo:

   struct sctp_sndrcvinfo {
      uint16_t sinfo_stream;
      uint16_t sinfo_ssn;
      uint16_t sinfo_flags;
      uint32_t sinfo_ppid;
      uint32_t sinfo_context;
      uint32_t sinfo_timetolive;
      uint32_t sinfo_tsn;
      uint32_t sinfo_cumtsn;
      sctp_assoc_t sinfo_assoc_id;
   };


   sinfo_stream: 16 bits (unsigned integer)

   For recvmsg() the SCTP stack places the message's stream number in
   this value.  For sendmsg() this value holds the stream number that
   the application wishes to send this message to.  If a sender
   specifies an invalid stream number an error indication is returned
   and the call fails.

   sinfo_ssn: 16 bits (unsigned integer)

   For recvmsg() this value contains the stream sequence number that the
   remote endpoint placed in the DATA chunk.  For fragmented messages
   this is the same number for all deliveries of the message (if more
   than one recvmsg() is needed to read the message).  The sendmsg()



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   call will ignore this parameter.

   sinfo_ppid: 32 bits (unsigned integer)

   This value in sendmsg() is an opaque unsigned value that is passed to
   the remote end in each user message.  In recvmsg() this value is the
   same information that was passed by the upper layer in the peer
   application.  Please note that byte order issues are NOT accounted
   for and this information is passed opaquely by the SCTP stack from
   one end to the other.

   sinfo_context: 32 bits (unsigned integer)

   This value is an opaque 32 bit context datum that is used in the
   sendmsg() function.  This value is passed back to the upper layer if
   a error occurs on the send of a message and is retrieved with each
   undelivered message (Note: if a endpoint has done multiple sends, all
   of which fail, multiple different sinfo_context values will be
   returned.  One with each user data message).

   sinfo_flags: 16 bits (unsigned integer)

   This field may contain any of the following flags and is composed of
   a bitwise OR of these values.



























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     recvmsg() flags:

       MSG_UNORDERED - This flag is present when the message was sent
                       non-ordered.

     sendmsg() flags:

       MSG_UNORDERED - This flag requests the un-ordered delivery of the
                       message.  If this flag is clear the datagram is
                       considered an ordered send.

       MSG_ADDR_OVER - This flag, in the UDP model, requests the SCTP
                       stack to override the primary destination address
                       with the address found with the sendto/sendmsg
                       call.

       MSG_ABORT     - Setting this flag causes the specified association
                       to abort by sending an ABORT message to the peer
                       (UDP-style only). The ABORT chunk will contain an
                       error cause 'User Initiated Abort' with cause code 12.
                       The cause specific information of this error cause is
                       provided in msg_iov.

       MSG_EOF       - Setting this flag invokes the SCTP graceful shutdown
                       procedures on the specified association. Graceful
                       shutdown assures that all data enqueued by both
                       endpoints is successfully transmitted before closing
                       the association (UDP-style only).

   sinfo_timetolive: 32 bit (unsigned integer)

   For the sending side, this field contains the message time to live in
   milliseconds.  The sending side will expire the message within the
   specified time period if the message as not been sent to the peer
   within this time period.  This value will override any default value
   set using any socket option.  Also note that the value of 0 is
   special in that it indicates no timeout should occur on this message.

   sinfo_tsn: 32 bit (unsigned integer)

   For the receiving side, this field holds a TSN that was assigned to
   one of the SCTP Data Chunks.

   sinfo_cumtsn: 32 bit (unsigned integer)

   This field will hold the current cumulative TSN as known by the
   underlying SCTP layer.  Note this field is ignored when sending and
   only valid for a receive operation when sinfo_flags are set to



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   MSG_UNORDERED.

   sinfo_assoc_id: sizeof (sctp_assoc_t)

   The association handle field, sinfo_assoc_id, holds the identifier
   for the association announced in the SCTP_COMM_UP notification.  All
   notifications for a given association have the same identifier.
   Ignored for TCP-style sockets.

   A sctp_sndrcvinfo item always corresponds to the data in msg_iov.

5.3 SCTP Events and Notifications

   An SCTP application may need to understand and process events and
   errors that happen on the SCTP stack.  These events include network
   status changes, association startups, remote operational errors and
   undeliverable messages.  All of these can be essential for the
   application.

   When an SCTP application layer does a recvmsg() the message read is
   normally a data message from a peer endpoint.  If the application
   wishes to have the SCTP stack deliver notifications of non-data
   events, it sets the appropriate socket option for the notifications
   it wants.  See Section 7.3 for these socket options.  When a
   notification arrives, recvmsg() returns the notification in the
   application-supplied data buffer via msg_iov, and sets
   MSG_NOTIFICATION in msg_flags.

   This section details the notification structures.  Every notification
   structure carries some common fields which provides general
   information.

   A recvmsg() call will return only one notification at a time.  Just
   as when reading normal data, it may return part of a notification if
   the msg_iov buffer is not large enough.  If a single read is not
   sufficient, msg_flags will have MSG_EOR clear.  The user MUST finish
   reading the notification before subsequent data can arrive.

5.3.1 SCTP Notification Structure

   The notification structure is defined as the union of all
   notification types.









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    union sctp_notification {
     struct {
       uint16_t sn_type;             /* Notification type. */
       uint16_t sn_flags;
       uint32_t sn_length;
       } sn_header;
       struct sctp_assoc_change sn_assoc_change;
       struct sctp_paddr_change sn_padr_change;
       struct sctp_remote_error sn_remote_error;
       struct sctp_send_failed sn_send_failed;
       struct sctp_shutdown_event sn_shutdown_event;
       struct sctp_adaption_event sn_adaption_event;
       struct sctp_rcv_pdapi_event sn_rcv_pdapi_event;
    };


   sn_type: 16 bits (unsigned integer)

   The following list describes the SCTP notification and event types
   for the field sn_type.

   SCTP_ASSOC_CHANGE: This tag indicates that an association has either
      been opened or closed.  Refer to Section 5.3.1.1 for details.

   SCTP_PEER_ADDR_CHANGE: This tag indicates that an address that is
      part of an existing association has experienced a change of state
      (e.g.  a failure or return to service of the reachability of a
      endpoint via a specific transport address).  Please see Section
      5.3.1.2 for data structure details.

   SCTP_REMOTE_ERROR: The attached error message is an Operational Error
      received from the remote peer.  It includes the complete TLV sent
      by the remote endpoint.  See Section 5.3.1.3 for the detailed
      format.

   SCTP_SEND_FAILED: The attached datagram could not be sent to the
      remote endpoint.  This structure includes the original
      SCTP_SNDRCVINFO that was used in sending this message i.e.  this
      structure uses the sctp_sndrecvinfo per Section 5.3.1.4.

   SCTP_SHUTDOWN_EVENT: The peer has sent a SHUTDOWN.  No further data
      should be sent on this socket.

   SCTP_ADAPTION_INDICATION: This notification holds the peers indicated
      adaption layer.  Please see Section 5.3.1.6.






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   SCTP_PARTIAL_DELIVERY_EVENT: This notification is used to tell a
      receiver that the partial delivery has been aborted.  This may
      indicate the association is about to be aborted.  Please see
      Section 5.3.1.7

   All standard values for sn_type flags are greater than 2^15.  Values
   from 2^15 and down are reserved.

   sn_flags: 16 bits (unsigned integer)

   These are notification-specific flags.

   sn_length: 32 bits (unsigned integer)

   This is the length of the whole sctp_notification structure including
   the sn_type, sn_flags, and sn_length fields.

5.3.1.1 SCTP_ASSOC_CHANGE

   Communication notifications inform the ULP that an SCTP association
   has either begun or ended.  The identifier for a new association is
   provided by this notification.  The notification information has the
   following format:

     struct sctp_assoc_change {
        uint16_t sac_type;
        uint16_t sac_flags;
        uint32_t sac_length;
        uint16_t sac_state;
        uint16_t sac_error;
        uint16_t sac_outbound_streams;
        uint16_t sac_inbound_streams;
        sctp_assoc_t sac_assoc_id;
        uint8_t  sac_info[0];
     };

   sac_type:

   It should be SCTP_ASSOC_CHANGE.

   sac_flags: 16 bits (unsigned integer)

   Currently unused.

   sac_length: 32 bits (unsigned integer)

   This field is the total length of the notification data, including
   the notification header.



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   sac_state: 16 bits (signed integer)

   This field holds one of a number of values that communicate the event
   that happened to the association.  They include:

     Event Name           Description
     ----------------     ---------------
     SCTP_COMM_UP         A new association is now ready
                          and data may be exchanged with this
                          peer.

     SCTP_COMM_LOST       The association has failed.  The association
                          is now in the closed state.  If SEND FAILED
                          notifications are turned on, a SCTP_COMM_LOST
                          is followed by a series of SCTP_SEND_FAILED
                          events, one for each outstanding message.

     SCTP_RESTART         SCTP has detected that the peer has restarted.

     SCTP_SHUTDOWN_COMP   The association has gracefully closed.

     SCTP_CANT_STR_ASSOC  The association failed to setup. If non blocking
                          mode is set and data was sent (in the udp mode),
                          a SCTP_CANT_STR_ASSOC is followed by a series of
                          SCTP_SEND_FAILED events, one for each outstanding
                          message.

   sac_error:  16 bits (signed integer)

   If the state was reached due to a error condition (e.g.
   SCTP_COMM_LOST) any relevant error information is available in this
   field.  This corresponds to the protocol error codes defined in
   RFC2960 [8].

   sac_outbound_streams:  16 bits (unsigned integer)

   sac_inbound_streams:  16 bits (unsigned integer)

   The maximum number of streams allowed in each direction are available
   in sac_outbound_streams and sac_inbound streams.

   sac_assoc_id: sizeof (sctp_assoc_t)

   The association id field, holds the identifier for the association.
   All notifications for a given association have the same association
   identifier.  For TCP style socket, this field is ignored.

   sac_data: variable



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   If the sac_state is SCTP_COMM_LOST and an ABORT chunk was received
   for this association, sac_data[] contains the complete ABORT chunk as
   defined in the SCTP specification RFC2960 [8] section 3.3.7.

5.3.1.2 SCTP_PEER_ADDR_CHANGE

   When a destination address on a multi-homed peer encounters a change
   an interface details event is sent.  The information has the
   following structure:


       struct sctp_paddr_change {
          uint16_t spc_type;
          uint16_t spc_flags;
          uint32_t spc_length;
          struct sockaddr_storage spc_aaddr;
          int spc_state;
          int spc_error;
          sctp_assoc_t spc_assoc_id;
        }

   spc_type:

   It should be SCTP_PEER_ADDR_CHANGE.

   spc_flags: 16 bits (unsigned integer)

   Currently unused.

   spc_length: 32 bits (unsigned integer)

   This field is the total length of the notification data, including
   the notification header.

   spc_aaddr: sizeof (struct sockaddr_storage)

   The affected address field, holds the remote peer's address that is
   encountering the change of state.

   spc_state:  32 bits (signed integer)

   This field holds one of a number of values that communicate the event
   that happened to the address.  They include:








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     Event Name           Description
     ----------------     ---------------
     SCTP_ADDR_AVAILABLE  This address is now reachable.

     SCTP_ADDR_UNREACHABL The address specified can no
                          longer be reached.  Any data sent
                          to this address is rerouted to an
                          alternate until this address becomes
                          reachable.

     SCTP_ADDR_REMOVED    The address is no longer part of
                          the association.

     SCTP_ADDR_ADDED      The address is now part of the
                          association.

     SCTP_ADDR_MADE_PRIM  This address has now been made
                          to be the primary destination address.

   spc_error:  32 bits (signed integer)

   If the state was reached due to any error condition (e.g.
   SCTP_ADDR_UNREACHABL) any relevant error information is available in
   this field.

   spc_assoc_id: sizeof (sctp_assoc_t)

   The association id field, holds the identifier for the association.
   All notifications for a given association have the same association
   identifier.  For TCP style socket, this field is ignored.

5.3.1.3 SCTP_REMOTE_ERROR

   A remote peer may send an Operational Error message to its peer.
   This message indicates a variety of error conditions on an
   association.  The entire ERROR chunk as it appears on the wire is
   included in a SCTP_REMOTE_ERROR event.  Please refer to the SCTP
   specification RFC2960 [8] and any extensions for a list of possible
   error formats.  SCTP error notifications have the format:












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   struct sctp_remote_error {
       uint16_t sre_type;
       uint16_t sre_flags;
       uint32_t sre_length;
       uint16_t sre_error;
       sctp_assoc_t sre_assoc_id;
       uint8_t sre_data[0];
   };


   sre_type:

   It should be SCTP_REMOTE_ERROR.

   sre_flags: 16 bits (unsigned integer)

   Currently unused.

   sre_length: 32 bits (unsigned integer)

   This field is the total length of the notification data, including
   the notification header and the contents of sre_data.

   sre_error: 16 bits (unsigned integer)

   This value represents one of the Operational Error causes defined in
   the SCTP specification, in network byte order.

   sre_assoc_id: sizeof (sctp_assoc_t)

   The association id field, holds the identifier for the association.
   All notifications for a given association have the same association
   identifier.  For TCP style socket, this field is ignored.

   sre_data: variable

   This contains the ERROR chunk as defined in the SCTP specification
   RFC2960 [8] section 3.3.10.

5.3.1.4 SCTP_SEND_FAILED

   If SCTP cannot deliver a message it may return the message as a
   notification.








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   struct sctp_send_failed {
      uint16_t ssf_type;
      uint16_t ssf_flags;
      uint32_t ssf_length;
      uint32_t ssf_error;
      struct sctp_sndrcvinfo ssf_info;
      sctp_assoc_t ssf_assoc_id;
      uint8_t ssf_data[0];
   };


   ssf_type:

   It should be SCTP_SEND_FAILED.

   The flag value will take one of the following values



   SCTP_DATA_UNSENT  - Indicates that the data was never put on
                       the wire.

   SCTP_DATA_SENT    - Indicates that the data was put on the wire.
                       Note that this does not necessarily mean that the
                       data was (or was not) successfully delivered.


   ssf_length: 32 bits (unsigned integer)

   This field is the total length of the notification data, including
   the notification header and the payload in ssf_data.

   ssf_error: 16 bits (unsigned integer)

   This value represents the reason why the send failed, and if set,
   will be a SCTP protocol error code as defined in RFC2960 [8] section
   3.3.10.

   ssf_info: sizeof (struct sctp_sndrcvinfo)

   The original send information associated with the undelivered
   message.

   ssf_assoc_id: sizeof (sctp_assoc_t)

   The association id field, sf_assoc_id, holds the identifier for the
   association.  All notifications for a given association have the same
   association identifier.  For TCP style socket, this field is ignored.



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   ssf_data: variable length

   The undelivered message, exactly as delivered by the caller to the
   original send*() call.

5.3.1.5 SCTP_SHUTDOWN_EVENT

   When a peer sends a SHUTDOWN, SCTP delivers this notification to
   inform the application that it should cease sending data.

       struct sctp_shutdown_event {
           uint16_t sse_type;
   	uint16_t sse_flags;
           uint32_t sse_length;
           sctp_assoc_t sse_assoc_id;
       };

   sse_type

   It should be SCTP_SHUTDOWN_EVENT

   sse_flags: 16 bits (unsigned integer)

   Currently unused.

   sse_length: 32 bits (unsigned integer)

   This field is the total length of the notification data, including
   the notification header.  It will generally be sizeof (struct
   sctp_shutdown_event).

   sse_flags: 16 bits (unsigned integer)

   Currently unused.

   sse_assoc_id: sizeof (sctp_assoc_t)

   The association id field, holds the identifier for the association.
   All notifications for a given association have the same association
   identifier.  For TCP style socket, this field is ignored.

5.3.1.6 SCTP_ADAPTION_INDICATION

   When a peer sends a Adaption Layer Indication parameter , SCTP
   delivers this notification to inform the application that of the
   peers requested adaption layer.





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       struct sctp_adaption_event {
           uint16_t sai_type;
   	uint16_t sai_flags;
           uint32_t sai_length;
           uint32_t sai_adaptation_bits;
           sctp_assoc_t sai_assoc_id;
       };

   sai_type

   It should be SCTP_ADAPTION_INDICATION

   sai_flags: 16 bits (unsigned integer)

   Currently unused.

   sai_length: 32 bits (unsigned integer)

   This field is the total length of the notification data, including
   the notification header.  It will generally be sizeof (struct
   sctp_adaption_event).

   sai_adaption_bits: 32 bits (unsigned integer)

   This field holds the bit array sent by the peer in the adaption layer
   indication parameter.  The bits are in network byte order.

   sai_assoc_id: sizeof (sctp_assoc_t)

   The association id field, holds the identifier for the association.
   All notifications for a given association have the same association
   identifier.  For TCP style socket, this field is ignored.

5.3.1.7 SCTP_PARTIAL_DELIVERY_EVENT

   When a receiver is engaged in a partial delivery of a message this
   notification will be used to indicate various events.

       struct sctp_rcv_pdapi_event {
           uint16_t pdapi_type;
   	uint16_t pdapi_flags;
           uint32_t pdapi_length;
   	uint32_t pdapi_indication;
           sctp_assoc_t pdapi_assoc_id;
       };

   pdapi_type




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   It should be SCTP_PARTIAL_DELIVERY_EVENT

   pdapi_flags: 16 bits (unsigned integer)

   Currently unused.

   pdapi_length: 32 bits (unsigned integer)

   This field is the total length of the notification data, including
   the notification header.  It will generally be sizeof (struct
   sctp_rcv_pdapi_event).

   pdapi_indication: 32 bits (unsigned integer)

   This field holds the indication being sent to the application
   possible values include:

   SCTP_PARTIAL_DELIVERY_ABORTED

   pdapi_assoc_id: sizeof (sctp_assoc_t)

   The association id field, holds the identifier for the association.
   All notifications for a given association have the same association
   identifier.  For TCP style socket, this field is ignored.

5.4 Ancillary Data Considerations and Semantics

   Programming with ancillary socket data contains some subtleties and
   pitfalls, which are discussed below.

5.4.1 Multiple Items and Ordering

   Multiple ancillary data items may be included in any call to
   sendmsg() or recvmsg(); these may include multiple SCTP or non-SCTP
   items, or both.

   The ordering of ancillary data items (either by SCTP or another
   protocol) is not significant and is implementation-dependent, so
   applications must not depend on any ordering.

   SCTP_SNDRCV items must always correspond to the data in the msghdr's
   msg_iov member.  There can be only a single SCTP_SNDRCV info for each
   sendmsg() or recvmsg() call.

5.4.2 Accessing and Manipulating Ancillary Data

   Applications can infer the presence of data or ancillary data by
   examining the msg_iovlen and msg_controllen msghdr members,



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   respectively.

   Implementations may have different padding requirements for ancillary
   data, so portable applications should make use of the macros
   CMSG_FIRSTHDR, CMSG_NXTHDR, CMSG_DATA, CMSG_SPACE, and CMSG_LEN.  See
   RFC2292 [6] and your SCTP implementation's documentation for more
   information.  Following is an example, from RFC2292 [6],
   demonstrating the use of these macros to access ancillary data:

   struct msghdr   msg;
   struct cmsghdr  *cmsgptr;

   /* fill in msg */

   /* call recvmsg() */

   for (cmsgptr = CMSG_FIRSTHDR(&msg); cmsgptr != NULL;
        cmsgptr = CMSG_NXTHDR(&msg, cmsgptr)) {
        if (cmsgptr->cmsg_level == ... && cmsgptr->cmsg_type == ... ) {
           u_char  *ptr;

           ptr = CMSG_DATA(cmsgptr);
           /* process data pointed to by ptr */
        }
   }


5.4.3 Control Message Buffer Sizing

   The information conveyed via SCTP_SNDRCV events will often be
   fundamental to the correct and sane operation of the sockets
   application.  This is particularly true of the UDP semantics, but
   also of the TCP semantics.  For example, if an application needs to
   send and receive data on different SCTP streams, SCTP_SNDRCV events
   are indispensable.

   Given that some ancillary data is critical, and that multiple
   ancillary data items may appear in any order, applications should be
   carefully written to always provide a large enough buffer to contain
   all possible ancillary data that can be presented by recvmsg().  If
   the buffer is too small, and crucial data is truncated, it may pose a
   fatal error condition.

   Thus it is essential that applications be able to deterministically
   calculate the maximum required buffer size to pass to recvmsg().  One
   constraint imposed on this specification that makes this possible is
   that all ancillary data definitions are of a fixed length.  One way
   to calculate the maximum required buffer size might be to take the



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   sum the sizes of all enabled ancillary data item structures, as
   calculated by CMSG_SPACE.  For example, if we enabled
   SCTP_SNDRCV_INFO and IPV6_RECVPKTINFO RFC2292 [6], we would calculate
   and allocate the buffer size as follows:

   size_t total;
   void *buf;

   total = CMSG_SPACE(sizeof (struct sctp_sndrcvinfo)) +
           CMSG_SPACE(sizeof (struct in6_pktinfo));

   buf = malloc(total);

   We could then use this buffer for msg_control on each call to
   recvmsg() and be assured that we would not lose any ancillary data to
   truncation.



































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6. Common Operations for Both Styles

6.1 send(), recv(), sendto(), recvfrom()

   Applications can use send() and sendto() to transmit data to the peer
   of an SCTP endpoint.  recv() and recvfrom() can be used to receive
   data from the peer.

   The syntax is:

   ssize_t send(int sd, connst void *msg, size_t len, int flags);
   ssize_t sendto(int sd, const void *msg, size_t len, int flags,
                  const struct sockaddr *to, int tolen);
   ssize_t recv(int sd, void *buf, size_t len, int flags);
   ssize_t recvfrom(int sd, void *buf, size_t len, int flags,
                    struct sockaddr *from, int *fromlen);

     sd      - the socket descriptor of an SCTP endpoint.
     msg     - the message to be sent.
     len     - the size of the message or the size of buffer.
     to      - one of the peer addresses of the association to be
               used to send the message.
     tolen   - the size of the address.
     buf     - the buffer to store a received message.
     from    - the buffer to store the peer address used to send the
               received message.
     fromlen - the size of the from address
     flags   - (described below).

   These calls give access to only basic SCTP protocol features.  If
   either peer in the association uses multiple streams, or sends
   unordered data these calls will usually be inadequate, and may
   deliver the data in unpredictable ways.

   SCTP has the concept of multiple streams in one association.  The
   above calls do not allow the caller to specify on which stream a
   message should be sent.  The system uses stream 0 as the default
   stream for send() and sendto().  recv() and recvfrom() return data
   from any stream, but the caller can not distinguish the different
   streams.  This may result in data seeming to arrive out of order.
   Similarly, if a data chunk is sent unordered, recv() and recvfrom()
   provide no indication.

   SCTP is message based.  The msg buffer above in send() and sendto()
   is considered to be a single message.  This means that if the caller
   wants to send a message which is composed by several buffers, the
   caller needs to combine them before calling send() or sendto().
   Alternately, the caller can use sendmsg() to do that without



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   combining them.  recv() and recvfrom() cannot distinguish message
   boundaries.

   In receiving, if the buffer supplied is not large enough to hold a
   complete message, the receive call acts like a stream socket and
   returns as much data as will fit in the buffer.

   Note, the send and recv calls, when used in the UDP-style model, may
   only be used with branched off socket descriptors (see Section 8.2).

   Note, if an application calls a send function with no user data and
   no ancillary data the SCTP implementation should reject the request
   with an appropriate error message.  An implementation is NOT allowed
   to send a Data chunk with no user data RFC2960 [8].

6.2 setsockopt(), getsockopt()

   Applications use setsockopt() and getsockopt() to set or retrieve
   socket options.  Socket options are used to change the default
   behavior of sockets calls.  They are described in Section 7

   The syntax is:

   ret = getsockopt(int sd, int level, int optname, void *optval,
                    size_t *optlen);
   ret = setsockopt(int sd, int level, int optname, const void *optval,
                    size_t optlen);

     sd      - the socket descript.
     level   - set to IPPROTO_SCTP for all SCTP options.
     optname - the option name.
     optval  - the buffer to store the value of the option.
     optlen  - the size of the buffer (or the length of  the option
               returned).


6.3 read() and write()

   Applications can use read() and write() to send and receive data to
   and from peer.  They have the same semantics as send() and recv()
   except that the flags parameter cannot be used.

   Note, these calls, when used in the UDP-style model, may only be used
   with branched off socket descriptors (see Section 8.2).

6.4 getsockname()

   Applications use getsockname() to retrieve the locally-bound socket



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   address of the specified socket.  This is especially useful if the
   caller let SCTP chose a local port.  This call is for where the
   endpoint is not multi-homed.  It does not work well with multi-homed
   sockets.  See Section 8.5 for a multi-homed version of the call.

   The syntax is:

   int getsockname(int socket, struct sockaddr *address,
                   socklen_t *len);

     sd      - the socket descriptor to be queried.

     address - On return, one locally bound address (chosen by
               the SCTP stack) is stored in this buffer. If the
               socket is an IPv4 socket, the address will be IPv4.
               If the socket is an IPv6 socket, the address will
               be either an IPv6 or IPv4 address.

     len     - The caller should set the length of address here.
               On return, this is set to the length of the returned
               address.


   If the actual length of the address is greater than the length of the
   supplied sockaddr structure, the stored address will be truncated.

   If the socket has not been bound to a local name, the value stored in
   the object pointed to by address is unspecified.























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7. Socket Options

   The following sub-section describes various SCTP level socket options
   that are common to both models.  SCTP associations can be
   multi-homed.  Therefore, certain option parameters include a
   sockaddr_storage structure to select which peer address the option
   should be applied to.

   For the UDP-style sockets, an sctp_assoc_t structure (association ID)
   is used to identify the the association instance that the operation
   affects.  So it must be set when using this model.

   For the TCP-style sockets and branched off UDP-style sockets (see
   Section 8.2) this association ID parameter is ignored.  In the cases
   noted below where the parameter is ignored, an application can pass
   to the system a corresponding option structure similar to those
   described below but without the association ID parameter, which
   should be the last field of the option structure.  This can make the
   option setting/getting operation more efficient.  If an application
   does this, it should also specify an appropriate optlen value (i.e.
   sizeof (option parameter) - sizeof (struct sctp_assoc_t)).

   Note that socket or IP level options is set or retrieved per socket.
   This means that for UDP-style sockets, those options will be applied
   to all associations belonging to the socket.  And for TCP-style
   model, those options will be applied to all peer addresses of the
   association controlled by the socket.  Applications should be very
   careful in setting those options.

   sctp_opt_info()

   For some implementations getsockopt() is read-only, so a new
   interface will be needed when information must be passed both in to
   and out of the SCTP stack.  The syntax for scpt_opt_info() is,

   int sctp_opt_info(int sd,
                     sctp_assoc_t id,
                     int opt,
                     void *arg,
                     size_t *size);

   For UDP-style sockets, id specifies the association to query.  For
   TCP-style sockets, id is ignored.

   opt specifies which SCTP socket option to get.  It can any socket
   option currently supported that requests information (either read/
   write options or read only) such as:




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   SCTP_RTOINFO
   SCTP_ASSOCINFO
   SCTP_SET_PRIMARY_ADDR
   SCTP_SET_PEER_PRIMARY_ADDR
   SCTP_SET_PEER_ADDR_PARAMS
   SCTP_STATUS
   SCTP_GET_PEER_ADDR_INFO

   arg is an option-specific structure buffer provided by the caller.
   See Section 8.5) subsections for more information on these options
   and option-specific structures.

   sctp_opt_info() returns 0 on success, or on failure returns -1 and
   sets errno to the appropriate error code.

   All options that support specific settings on an association by
   filling in either an association id variable or a sockaddr_storage
   SHOULD also support setting of the same value for the entire endpoint
   (i.e.  future associations).  To accomplish this the following logic
   is used when setting one of these options:

   a) If an address is specified via a sockaddr_storage that is included
      in the structure the address is used to lookup the association and
      the settings are applied to the specific address (if appropriate)
      or to the entire association.

   b) If an association identification is filled in but not a
      sockaddr_storage (if present) the association is found using the
      association identification and the settings should be applied to
      the entire association (since a specific address is specified).
      Note this also applies to options that hold an association
      identification in their structure but do not have a
      sockaddr_storage field.

   c) If neither the sockaddr_storage  or association identification is
      set i.e.  the sockadd_storage is set to all 0's (INADDR_ANY) and
      the association identification is 0, the settings are a default
      and to be applied to the endpoint (all future associations).


7.1 Read / Write Options

7.1.1 Retransmission Timeout Parameters (SCTP_RTOINFO)

   The protocol parameters used to initialize and bound retransmission
   timeout (RTO) are tunable.  See RFC2960 [8] for more information on
   how these parameters are used in RTO calculation.  The peer address
   parameter is ignored for TCP style socket.



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   The following structure is used to access and modify these
   parameters:

   struct sctp_rtoinfo {
       sctp_assoc_t          srto_assoc_id;
       uint32_t              srto_initial;
       uint32_t              srto_max;
       uint32_t              srto_min;
   };
     srto_initial    - This contains the initial RTO value.
     srto_max and srto_min - These contain the maximum and minimum bounds
                             for all RTOs.
     srto_assoc_id   - (UDP style socket) This is filled in the application,
                       and identifies the association for this query. If
                       this parameter is missing (on a UDP style socket),
                       then the change effects the entire endpoint.

   All parameters are time values, in milliseconds.  A value of 0, when
   modifying the parameters, indicates that the current value should not
   be changed.

   To access or modify these parameters, the application should call
   getsockopt or setsockopt() respectively with the option name
   SCTP_RTOINFO.

7.1.2 Association Parameters (SCTP_ASSOCINFO)

   This option is used to both examine and set various association and
   endpoint parameters.

   See RFC2960 [8] for more information on how this parameter is used.
   The peer address parameter is ignored for TCP style socket.

   The following structure is used to access and modify this parameters:

















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   struct sctp_assocparams {
      sctp_assoc_t    sasoc_assoc_id;
      uint16_t        sasoc_asocmaxrxt;
      uint16_t        sasoc_number_peer_destinations;
      uint32_t        sasoc_peer_rwnd;
      uint32_t        sasoc_local_rwnd;
      uint32_t        sasoc_cookie_life;
   };
     sasoc_asocmaxrxt - This contains the maximum retransmission attempts
                        to make for the association.

     sasoc_number_peer_destinations - This is the number of destination
                                      address that the peer considers
                                      valid.
     sasoc_peer_rwnd - This holds the current value of the peers
                       rwnd (reported in the last SACK) minus any
                       outstanding data (i.e. data inflight).
     sasoc_local_rwnd - This holds the last reported rwnd that was
                        sent to the peer.
     sasoc_cookie_life - This is the associations cookie life value
                         used when issuing cookies.
     sasoc_assoc_id   - (UDP style socket) This is filled in the application,
                        and identifies the association for this query.

   This information may be examined for either the endpoint or a
   specific association.  To examine a endpoints default parameters the
   association id (sasoc_assoc_id) should must be set to the value '0'.
   The values of the sasoc_peer_rwnd is meaningless when examining
   endpoint information.

   The values of the sasoc_asocmaxrxt and sasoc_cookie_life may be set
   on either an endpoint or association basis.  The rwnd and destination
   counts (sasoc_number_peer_destinations,
   sasoc_peer_rwnd,sasoc_local_rwnd) are NOT settable and any value
   placed in these is ignored.

   To access or modify these parameters, the application should call
   getsockopt or setsockopt() respectively with the option name
   SCTP_ASSOCINFO.

   The maximum number of retransmissions before an address is considered
   unreachable is also tunable, but is address-specific, so it is
   covered in a separate option.  If an application attempts to set the
   value of the association maximum retransmission parameter to more
   than the sum of all maximum retransmission parameters, setsockopt()
   shall return an error.  The reason for this, from RFC2960 [8] section
   8.2:




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   Note: When configuring the SCTP endpoint, the user should avoid
   having the value of 'Association.Max.Retrans' larger than the
   summation of the 'Path.Max.Retrans' of all the destination addresses
   for the remote endpoint.  Otherwise, all the destination addresses
   may become inactive while the endpoint still considers the peer
   endpoint reachable.

7.1.3 Initialization Parameters (SCTP_INITMSG)

   Applications can specify protocol parameters for the default
   association initialization.  The structure used to access and modify
   these parameters is defined in Section 5.2.1).  The option name
   argument to setsockopt() and getsockopt() is SCTP_INITMSG.

   Setting initialization parameters is effective only on an unconnected
   socket (for UDP-style sockets only future associations are effected
   by the change).  With TCP-style sockets, this option is inherited by
   sockets derived from a listener socket.

7.1.4 SO_LINGER

   An application using the TCP-style socket can use this option to
   perform the SCTP ABORT primitive.  The linger option structure is:

   struct  linger {
       int     l_onoff;                /* option on/off */
       int     l_linger;               /* linger time */
   };

   To enable the option, set l_onoff to 1.  If the l_linger value is set
   to 0, calling close() is the same as the ABORT primitive.  If the
   value is set to a negative value, the setsockopt() call will return
   an error.  If the value is set to a positive value linger_time, the
   close() can be blocked for at most linger_time ms.  If the graceful
   shutdown phase does not finish during this period, close() will
   return but the graceful shutdown phase continues in the system.

   Note, this is a socket level option NOT an SCTP level option.  So
   when setting SO_LINGER you must specify a level of SOL_SOCKET in the
   setsockopt() call.

7.1.5 SCTP_NODELAY

   Turn on/off any Nagle-like algorithm.  This means that packets are
   generally sent as soon as possible and no unnecessary delays are
   introduced, at the cost of more packets in the network.  Expects an
   integer boolean flag.




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7.1.6 SO_RCVBUF

   Sets receive buffer size.  For SCTP TCP-style sockets, this controls
   the receiver window size.  For UDP-style sockets, this controls the
   receiver window size for all associations bound to the socket
   descriptor used in the setsockopt() or getsockopt() call.  The option
   applies to each association's window size separately.  Expects an
   integer.

7.1.7 SO_SNDBUF

   Sets send buffer size.  For SCTP TCP-style sockets, this controls the
   amount of data SCTP may have waiting in internal buffers to be sent.
   This option therefore bounds the maximum size of data that can be
   sent in a single send call.  For UDP-style sockets, the effect is the
   same, except that it applies to all associations bound to the socket
   descriptor used in the setsockopt() or getsockopt() call.  The option
   applies to each association's window size separately.  Expects an
   integer.

7.1.8 Automatic Close of associations (SCTP_AUTOCLOSE)

   This socket option is applicable to the UDP-style socket only.  When
   set it will cause associations that are idle for more than the
   specified number of seconds to automatically close.  An association
   being idle is defined an association that has NOT sent or received
   user data.  The special value of '0' indicates that no automatic
   close of any associations should be performed.  The option expects an
   integer defining the number of seconds of idle time before an
   association is closed.

7.1.9 Set Primary Address (SCTP_SET_PRIMARY_ADDR)

   Requests that the peer mark the enclosed address as the association
   primary.  The enclosed address must be one of the association's
   locally bound addresses.  The following structure is used to make a
   set primary request:

   struct sctp_setprim {
       sctp_assoc_t            ssp_assoc_id;
       struct sockaddr_storage ssp_addr;
   };
     ssp_addr            The address to set as primary
     ssp_assoc_id        (UDP style socket) This is filled in by the
                         application, and identifies the association
                         for this request.

   This functionality is optional.  Implementations that do not support



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   this functionality should return EOPNOTSUPP.

7.1.10 Set Peer Primary Address (SCTP_SET_PEER_PRIMARY_ADDR)

   Requests that the local SCTP stack use the enclosed peer address as
   the association primary.  The enclosed address must be one of the
   association peer's addresses.  The following structure is used to
   make a set peer primary request:

   struct sctp_setpeerprim {
       sctp_assoc_t            sspp_assoc_id;
       struct sockaddr_storage sspp_addr;
   };

     sspp_addr           The address to set as primary
     sspp_assoc_id       (UDP style socket) This is filled in by the
                         application, and identifies the association
                         for this request.


7.1.11 Set Adaption Layer Indicator (SCTP_SET_ADAPTION_LAYER)

   Requests that the local endpoint set the specified Adaption Layer
   Indication parameter for all future INIT and INIT-ACK exchanges.

       struct sctp_setadaption {
           u_int32_t   ssb_adaption_ind;
       };

       ssb_adaption_ind    The adaption layer indicator that will be included
                           in any outgoing Adaption Layer Indication
                           parameter.


7.1.12 Enable/Disable message fragmentation (SCTP_DISABLE_FRAGMENTS)

   This option is a on/off flag.  If enabled no SCTP message
   fragmentation will be performed.  Instead if a message being sent
   exceeds the current PMTU size, the message will NOT be sent and
   instead a error will be indicated to the user.

7.1.13 Peer Address Parameters (SCTP_SET_PEER_ADDR_PARAMS)

   Applications can enable or disable heartbeats for any peer address of
   an association, modify an address's heartbeat interval, force a
   heartbeat to be sent immediately, and adjust the address's maximum
   number of retransmissions sent before an address is considered
   unreachable.  The following structure is used to access and modify an



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   address's parameters:

   struct sctp_paddrparams {
       sctp_assoc_t            spp_assoc_id;
       struct sockaddr_storage spp_address;
       uint32_t                spp_hbinterval;
       uint16_t                spp_pathmaxrxt;
   };

     spp_assoc_id    - (UDP style socket) This is filled in the application,
                       and identifies the association for this query.
     spp_address     - This specifies which address is of interest.
     spp_hbinterval  - This contains the value of the heartbeat interval,
                       in milliseconds.  A value of 0, when modifying the
                       parameter, specifies that the heartbeat on this
                       address should be disabled. A value of UINT32_MAX
                       (4294967295), when modifying the parameter,
                       specifies that a heartbeat should be sent
                       immediately to the peer address, and the current
                       interval should remain unchanged.
     spp_pathmaxrxt  - This contains the maximum number of
                       retransmissions before this address shall be
                       considered unreachable.


   To read or modify these parameters, the application should call
   sctp_opt_info() with the SCTP_SET_PEER_ADDR_PARAMS option.

7.1.14 Set default send parameters (SET_DEFAULT_SEND_PARAM)

   Applications that wish to use the sendto() system call may wish to
   specify a default set of parameters that would normally be supplied
   through the inclusion of ancillary data.  This socket option allows
   such an application to set the default sctp_sndrcvinfo structure.
   The application that wishes to use this socket option simply passes
   in to this call the sctp_sndrcvinfo structure defined in Section
   5.2.2) The input parameters accepted by this call include
   sinfo_stream, sinfo_flags, sinfo_ppid, sinfo_context,
   sinfo_timetolive.  The user must provide the sinfo_assoc_id field in
   to this call if the caller is using the UDP model.

7.1.15 Set notification and ancillary events (SCTP_SET_EVENTS)

   This socket option is used to specify various notifications and
   ancillary data the user wishes to receive.  Please see Section 7.3)
   for a full description of this option and its usage.





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7.1.16 Set/clear IPv4 mapped addresses (SCTP_I_WANT_MAPPED_V4_ADDR)

   This socket option is a boolean flag which turns on or off mapped V4
   addresses.  If this option is turned on and the socket is type
   PF_INET6, then IPv4 addresses will be mapped to V6 representation.
   If this option is turned off, then no mapping will be done of V4
   addresses and a user will receive both PF_INET6 and PF_INET type
   addresses on the socket.

   By default this option is turned on.

7.1.17 Set the maximum fragrmentation size (SCTP_MAXSEG)

   This socket option specifies the maximum size to put in any outgoing
   SCTP chunk.  If a message is larger than this size it will be
   fragmented by SCTP into the specified size.  Note that the underlying
   SCTP implementation may fragment into smaller sized chunks when the
   PMTU of the underlying association is smaller than the value set by
   the user.

7.2 Read-Only Options

7.2.1 Association Status (SCTP_STATUS)

   Applications can retrieve current status information about an
   association, including association state, peer receiver window size,
   number of unacked data chunks, and number of data chunks pending
   receipt.  This information is read-only.  The following structure is
   used to access this information:

   struct sctp_status {
       sctp_assoc_t    sstat_assoc_id;
       int32_t         sstat_state;
       uint32_t        sstat_rwnd;
       uint16_t        sstat_unackdata;
       uint16_t        sstat_penddata;
       uint16_t        sstat_instrms;
       uint16_t        sstat_outstrms;
       uint32_t        sstat_fragmentation_point;
       struct sctp_paddrinfo sstat_primary;
   };

     sstat_state    - This contains the association's current state one
                      of the following values:

   		     SCTP_CLOSED
   		     SCTP_BOUND
   		     SCTP_LISTEN



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   		     SCTP_COOKIE_WAIT
   		     SCTP_COOKIE_ECHOED
   		     SCTP_ESTABLISHED
   		     SCTP_SHUTDOWN_PENDING
   		     SCTP_SHUTDOWN_SENT
   		     SCTP_SHUTDOWN_RECEIVED
   		     SCTP_SHUTDOWN_ACK_SENT


     sstat_rwnd     - This contains the association  peer's current
                      receiver window size.
     sstat_unackdata - This is the number of unacked data chunks.
     sstat_penddata  - This is the number of data chunks pending receipt.
     sstat_primary   - This is information on the current primary peer
                       address.
     sstat_assoc_id  - (UDP style socket) This holds the an identifier for the
                       association.  All notifications for a given association
                       have the same association identifier.

     sstat_instrms   - The number of streams that the peer will
                       be using inbound.

     sstat_outstrms  - The number of streams that the endpoint is
                       allowed to use outbound.

     sstat_fragmentation_point - The size at which SCTP fragmentation
                                 will occur.


   To access these status values, the application calls getsockopt()
   with the option name SCTP_STATUS.  The sstat_assoc_id parameter is
   ignored for TCP style socket.

7.2.2 Peer Address Information (SCTP_GET_PEER_ADDR_INFO)

   Applications can retrieve information about a specific peer address
   of an association, including its reachability state, congestion
   window, and retransmission timer values.  This information is
   read-only.  The following structure is used to access this
   information:











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   struct sctp_paddrinfo {
       sctp_assoc_t    spinfo_assoc_id;
       struct sockaddr_storage spinfo_address;
       int32_t         spinfo_state;
       uint32_t        spinfo_cwnd;
       uint32_t        spinfo_srtt;
       uint32_t        spinfo_rto;
       uint32_t        spinfo_mtu;
   };

     spinfo_address   - This is filled in the application, and contains
                        the peer address of interest.

    On return from getsockopt():

     spinfo_state     - This contains the peer addresses's state (either
                        SCTP_ACTIVE or SCTP_INACTIVE).
     spinfo_cwnd      - This contains the peer addresses's current congestion
                        window.
     spinfo_srtt      - This contains the peer addresses's current smoothed
                        round-trip time calculation in milliseconds.
     spinfo_rto       - This contains the peer addresses's current
                        retransmission timeout value in milliseconds.
     spinfo_mtu       - The current P-MTU of this address.
     spinfo_assoc_id  - (UDP style socket) This is filled in the application,
                        and identifies the association for this query.

   To retrieve this information, use sctp_opt_info() with the
   SCTP_GET_PEER_ADDR_INFO options.

7.3 Ancillary Data and Notification Interest Options

   Applications can receive per-message ancillary information and
   notifications of certain SCTP events with recvmsg().

   The following optional information is available to the application:

   1.  SCTP_SNDRCV: Per-message information (i.e.  stream number, TSN,
       SSN, etc.  described in Section 5.2.2)

   2.  SCTP_ASSOC_CHANGE: (described in Section 5.3.1.1)

   3.  SCTP_PEER_ADDR_CHANGE: (described in Section 5.3.1.2)

   4.  SCTP_REMOTE_ERROR: (described in Section 5.3.1.3)

   5.  SCTP_SEND_FAILED: (described in Section 5.3.1.4)




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   6.  SCTP_SHUTDOWN_EVENT: (described in Section 5.3.1.5)

   7.  SCTP_ADAPTION_INDICATION: (described in Section 5.3.1.6)

   8.  SCTP_PARTIAL_DELIVERY_EVENT: (described in Section 5.3.1.7)

   To receive any ancillary data or notifications, first the application
   registers it's interest by calling the SCTP_SET_EVENTS setsockopt()
   with the following structure.

   struct sctp_event_subscribe{
       u_int8_t sctp_data_io_event;
       u_int8_t sctp_association_event;
       u_int8_t sctp_address_event;
       u_int8_t sctp_send_failure_event;
       u_int8_t sctp_peer_error_event;
       u_int8_t sctp_shutdown_event;
       u_int8_t sctp_partial_delivery_event;
       u_int8_t sctp_adaption_layer_event;
   };

   sctp_data_io_event - Setting this flag to 1 will cause the reception
   of SCTP_SNDRCV information on a per message basis.  The application
   will need to use the recvmsg() interface so that it can receive the
   event information contained in the msg_control field.  Please see
   Section 5.2 for further details.  Setting the flag to 0 will disable
   reception of the message control information.

   sctp_association_event - Setting this flag to 1 will enable the
   reception of association event notifications.  Setting the flag to 0
   will disable association event notifications.  For more information
   on event notifications please see Section 5.3.

   sctp_address_event - Setting this flag to 1 will enable the reception
   of address event notifications.  Setting the flag to 0 will disable
   address event notifications.  For more information on event
   notifications please see Section 5.3.

   sctp_send_failure_event - Setting this flag to 1 will enable the
   reception of send failure event notifications.  Setting the flag to 0
   will disable send failure event notifications.  For more information
   on event notifications please see Section 5.3.

   sctp_peer_error_event - Setting this flag to 1 will enable the
   reception of peer error event notifications.  Setting the flag to 0
   will disable peer error event notifications.  For more information on
   event notifications please see Section 5.3.




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   sctp_shutdown_event - Setting this flag to 1 will enable the
   reception of shutdown event notifications.  Setting the flag to 0
   will disable shutdown event notifications.  For more information on
   event notifications please see Section 5.3.

   sctp_partial_delivery_event - Setting this flag to 1 will enable the
   reception of partial delivery notifications.  Setting the flag to 0
   will disable partial delivery event notifications.  For more
   information on event notifications please see Section 5.3.

   sctp_adaption_layer_event - Setting this flag to 1 will enable the
   reception of adaption layer notifications.  Setting the flag to 0
   will disable adaption layer event notifications.  For more
   information on event notifications please see Section 5.3.

   An example where an application would like to receive data io events
   and association events but no others would be as follows:

   {
      struct sctp_event_subscribe event;

      memset(&event,0,sizeof(event));

      event.sctp_data_io_event = 1;
      event.sctp_association_event = 1;

      setsockopt(fd, IPPROTO_SCTP, SCTP_SET_EVENT, &event, sizeof(event));
   }

   Note that for UDP-style SCTP sockets, the caller of recvmsg()
   receives ancillary data and notifications for ALL associations bound
   to the file descriptor.  For TCP-style SCTP sockets, the caller
   receives ancillary data and notifications for only the single
   association bound to the file descriptor.

   By default a UDP-style socket has sctp_data_io_event and
   sctp_association_event on and all other options off.














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8. New Interfaces

   Depending on the system, the following interface can be implemented
   as a system call or library function.

8.1 sctp_bindx()

   The syntax of sctp_bindx() is,

   int sctp_bindx(int sd, struct sockaddr_storage *addrs, int addrcnt,
                  int flags);

   If sd is an IPv4 socket, the addresses passed must be IPv4 addresses.
   If the sd is an IPv6 socket, the addresses passed can either be IPv4
   or IPv6 addresses.

   A single address may be specified as INADDR_ANY or IN6ADDR_ANY, see
   Section 3.1.2 for this usage.

   addrs is a pointer to an array of one or more socket addresses.  Each
   address is contained in a struct sockaddr_storage, so each address is
   a fixed length.  The caller specifies the number of addresses in the
   array with addrcnt.

   On success, sctp_bindx() returns 0.  On failure, sctp_bindx() returns
   -1, and sets errno to the appropriate error code.

   For SCTP, the port given in each socket address must be the same, or
   sctp_bindx() will fail, setting errno to EINVAL.

   The flags parameter is formed from the bitwise OR of zero or more of
   the following currently defined flags:

   SCTP_BINDX_ADD_ADDR

   SCTP_BINDX_REM_ADDR

   SCTP_BINDX_ADD_ADDR directs SCTP to add the given addresses to the
   association, and SCTP_BINDX_REM_ADDR directs SCTP to remove the given
   addresses from the association.  The two flags are mutually
   exclusive; if both are given, sctp_bindx() will fail with EINVAL.  A
   caller may not remove all addresses from an association; sctp_bindx()
   will reject such an attempt with EINVAL.

   An application can use sctp_bindx(SCTP_BINDX_ADD_ADDR) to associate
   additional addresses with an endpoint after calling bind().  Or use
   sctp_bindx(SCTP_BINDX_REM_ADDR) to remove some addresses a listening
   socket is associated with so that no new association accepted will be



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   associated with those addresses.  If the endpoint supports dynamic
   address a SCTP_BINDX_REM_ADDR or SCTP_BINDX_ADD_ADDR may cause a
   endpoint to send the appropriate message to the peer to change the
   peers address lists.

   Adding and removing addresses from a connected association is
   optional functionality.  Implementations that do not support this
   functionality should return EOPNOTSUPP.

8.2 Branched-off Association

   After an association is established on a UDP-style socket, the
   application may wish to branch off the association into a separate
   socket/file descriptor.

   This is particularly desirable when, for instance, the application
   wishes to have a number of sporadic message senders/receivers remain
   under the original UDP-style socket but branch off those associations
   carrying high volume data traffic into their own separate socket
   descriptors.

   The application uses sctp_peeloff() call to branch off an association
   into a separate socket (Note the semantics are somewhat changed from
   the traditional TCP-style accept() call).

   The syntax is:

   new_sd = sctp_peeloff(int sd, sctp_assoc_t *assoc_id);

      the new socket descriptor representing the branched-off
      association.

      the original UDP-style socket descriptor returned from the
      socket() system call (see Section 3.1.1).

      the specified identifier of the association that is to be branched
      off to a separate file descriptor (Note, in a traditional
      TCP-style accept() call, this would be an out parameter, but for
      the UDP-style call, this is an in parameter).


8.3 sctp_getpaddrs()

   sctp_getpaddrs() returns all peer addresses in an association.  The
   syntax is,

     int sctp_getpaddrs(int sd, sctp_assoc_t id,
                        struct sockaddr_storage **addrs);



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   On return, addrs will point to a dynamically allocated array of
   struct sockaddr_storages, one for each peer address.  The caller
   should use sctp_freepaddrs() to free the memory.  addrs must not be
   NULL.

   If sd is an IPv4 socket, the addresses returned will be all IPv4
   addresses.  If sd is an IPv6 socket, the addresses returned can be a
   mix of IPv4 or IPv6 addresses.

   For UDP-style sockets, id specifies the association to query.  For
   TCP-style sockets, id is ignored.

   On success, sctp_getpaddrs() returns the number of peer addresses in
   the association.  If there is no association on this socket,
   sctp_getpaddrs() returns 0, and the value of *addrs is undefined.  If
   an error occurs, sctp_getpaddrs() returns -1, and the value of *addrs
   is undefined.

8.4 sctp_freepaddrs()

       sctp_freepaddrs() frees all resources allocated by
       sctp_getpaddrs(). Its syntax is,

       void sctp_freepaddrs(struct sockaddr_storage *addrs);

       addrs is the array of peer addresses returned by sctp_getpaddrs().


8.5 sctp_getladdrs()

   sctp_getladdrs() returns all locally bound address on a socket.  The
   syntax is,

       int sctp_getladdrs(int sock, sctp_assoc_t id,
                          struct sockaddr_storage **ss);


   On return, addrs will point to a dynamically allocated array of
   struct sockaddr_storages, one for each local address.  The caller
   should use sctp_freeladdrs() to free the memory.  addrs must not be
   NULL.

   If sd is an IPv4 socket, the addresses returned will be all IPv4
   addresses.  If sd is an IPv6 socket, the addresses returned can be a
   mix of IPv4 or IPv6 addresses.

   For UDP-style sockets, id specifies the association to query.  For
   TCP-style sockets, id is ignored.



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   If the id field is set to the value '0' then the locally bound
   addresses are returned without regard to any particular association.

   On success, sctp_getladdrs() returns the number of local addresses
   bound to the socket.  If the socket is unbound, sctp_getladdrs()
   returns 0, and the value of *addrs is undefined.  If an error occurs,
   sctp_getladdrs() returns -1, and the value of *addrs is undefined.

8.6 sctp_freeladdrs()

       sctp_freeladdrs() frees all resources allocated by
       sctp_getladdrs(). Its syntax is,

       void sctp_freeladdrs(struct sockaddr_storage *addrs);

       addrs is the array of peer addresses returned by sctp_getladdrs().


8.7 sctp_sndmsg()

   An implementation may provide a library function (or possibly system
   call) to assist the user with the advanced features of SCTP.

       sctp_sendmsg(). Its syntax is,

       void sctp_sendmsg(int s, const void *msg, size_t len,
                         uint32_t ppid,
   		      uint32_t flags,
   		      uint16_t stream_no,
   		      uint32_t timetolive,
   		      uint32_t context)


       s          - is the socket descriptor
       msg        - is the message to be sent.
       len        - is the length of the message.
       ppid       - is the same as sinfo_ppid (see section 5.2.2)
       flags      - is the same as sinfo_flags (see section 5.2.2)
       stream_no  - is the same as sinfo_stream (see section 5.2.2)
       timetolive - is the same as sinfo_timetolive (see section 5.2.2)
       context    - is the same as sinfo_context (see section 5.2.2)










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9. Preprocessor Constants

   For application portability it is desireable to define pre-processor
   constants for determination if sctp is present and supports various
   features.  The following pre-processor constants should be defined in
   a include file, sctp.h.

   HAVE_SCTP - If this constant is defined to 1, then an implementation
      of SCTP is available.

   HAVE_KERNEL_SCTP - If this constant is defined to 1, then a kernel
      SCTP implementation is available through the sockets interface.

   HAVE_SCTP_PRSCTP - If this constant is defined to 1, then the SCTP
      implementation supports the partial reliablility extension to
      SCTP.

   HAVE_SCTP_ADDIP - If this constant is defined to 1, then the SCTP
      implementation supports the dynamic address extension to SCTP.

   HAVE_SCTP_CANSET_PRIMARY - If this constant is defined to 1, then the
      SCTP implementation supports the ability to request setting of the
      remote primary address.

   HAVE_SCTP_SAT_NETWORK_CAPABILITY - If this constant is defined to 1,
      then the SCTP implementation supports the satellite network
      extension to SCTP.
























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10. Security Considerations

   Many TCP and UDP implementations reserve port numbers below 1024 for
   privileged users.  If the target platform supports privileged users,
   the SCTP implementation SHOULD restrict the ability to call bind() or
   sctp_bindx() on these port numbers to privileged users.

   Similarly unprevledged users should not be able to set protocol
   parameters which could result in the congestion control algorithm
   being more aggressive than permitted on the public Internet.  These
   parameters are:

   struct sctp_rtoinfo

   If an unprivileged user inherits a UDP-style socket with open
   associations on a privileged port, it MAY be permitted to accept new
   associations, but it SHOULD NOT be permitted to open new
   associations.  This could be relevant for the r* family of protocols.

































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11. Acknowledgments

   The authors wish to thank Kavitha Baratakke, Mike Bartlett, Jon
   Berger, Scott Kimble, Renee Revis, and many others on the TSVWG
   mailing list for contributing valuable comments.

   A special thanks to Phillip Conrad, for his suggested text, quick and
   constructive insights, and most of all his persistent fighting to
   keep the interface to SCTP usable for the application programmer.










































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References

   [1]  Postel, J., "Transmission Control Protocol", STD 7, RFC 793,
        September 1981.

   [2]  Postel, J., "User Datagram Protocol", STD 6, RFC 768, August
        1980.

   [3]  Braden, B., "T/TCP -- TCP Extensions for Transactions Functional
        Specification", RFC 1644, July 1994.

   [4]  Bradner, S., "The Internet Standards Process -- Revision 3", BCP
        9, RFC 2026, October 1996.

   [5]  Bradner, S., "Key words for use in RFCs to Indicate Requirement
        Levels", BCP 14, RFC 2119, March 1997.

   [6]  Stevens, W. and M. Thomas, "Advanced Sockets API for IPv6", RFC
        2292, February 1998.

   [7]  Gilligan, R., Thomson, S., Bound, J. and W. Stevens, "Basic
        Socket Interface Extensions for IPv6", RFC 2553, March 1999.

   [8]  Stewart, R., Xie, Q., Morneault, K., Sharp, C., Schwarzbauer,
        H., Taylor, T., Rytina, I., Kalla, M., Zhang, L. and V. Paxson,
        "Stream Control Transmission Protocol", RFC 2960, October 2000.


Authors' Addresses

   Randall R. Stewart
   Cisco Systems, Inc.
   8725 West Higgins Road
   Suite 300
   Chicago, IL  60631
   USA

   Phone:
   EMail: rrs@cisco.com


   Qiaobing Xie
   Motorola, Inc.
   1501 W. Shure Drive, #2309
   Arlington Heights, IL  60004
   USA

   Phone:



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   EMail: qxie1@email.mot.com


   La Monte H.P. Yarroll
   Motorola, Inc.
   1501 W. Shure Drive, IL-2315
   Arlington Heights, IL  60004
   USA

   Phone:
   EMail: piggy@acm.org


   Jonathan Wood
   DoCoMo USA Labs
   181 Metro Drive, Suite 300
   San Jose, CA  95110
   USA

   Phone:
   EMail: jonwood@speakeasy.net


   Kacheong Poon
   Consultant

   Milpitas, CA


   Phone:
   EMail: kcpoon@yahoo.com


   Ken Fujita
   NEC USA, Inc.
   10080 Wolfe Road, Suite SW3-350
   Cupertino, CA  95014
   USA

   Phone:
   EMail: fken@ccrl.sj.nec.com


   Michael Tuexen

   Germany

   Phone:



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   EMail: tuexen@fh-muenster.de


















































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Appendix A. TCP-style Code Example

   The following code is a simple implementation of an echo server over
   SCTP.  The example shows how to use some features of TCP-style IPv4
   SCTP sockets, including:

   o  Opening, binding, and listening for new associations on a socket;

   o  Enabling ancillary data

   o  Enabling notifications

   o  Using ancillary data with sendmsg() and recvmsg()

   o  Using MSG_EOR to determine if an entire message has been read

   o  Handling notifications


   #include <stdio.h>
   #include <sys/types.h>
   #include <sys/socket.h>
   #include <netinet/in.h>
   #include <arpa/inet.h>
   #include <stdlib.h>
   #include <unistd.h>
   #include <netinet/sctp.h>
   #include <sys/uio.h>

   #define BUFLEN  100

   static void
   handle_event(void *buf)
   {
           struct sctp_assoc_change *sac;
           struct sctp_send_failed *ssf;
           struct sctp_paddr_change *spc;
           struct sctp_remote_error *sre;
           union sctp_notification *snp;
           char addrbuf[INET6_ADDRSTRLEN];
           const char *ap;
           struct sockaddr_in *sin;
           struct sockaddr_in6 *sin6;

           snp = buf;

           switch (snp->sn_header.sn_type) {
           case SCTP_ASSOC_CHANGE:



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                   sac = &snp->sn_assoc_change;
                   printf("^^^ assoc_change: state=%hu, error=%hu, instr=%hu "
                       "outstr=%hu\n", sac->sac_state, sac->sac_error,
                       sac->sac_inbound_streams, sac->sac_outbound_streams);
                   break;
           case SCTP_SEND_FAILED:
                   ssf = &snp->sn_send_failed;
                   printf("^^^ sendfailed: len=%hu err=%d\n", ssf->ssf_length,
                       ssf->ssf_error);
                   break;

           case SCTP_PEER_ADDR_CHANGE:
                   spc = &snp->sn_paddr_change; /* mt changed */
                   if (spc->spc_aaddr.ss_family == AF_INET) {
                     sin = (struct sockaddr_in *)&spc->spc_aaddr;
                     ap = inet_ntop(AF_INET, &sin->sin_addr,
                                    addrbuf, INET6_ADDRSTRLEN);
                   } else {
                     sin6 = (struct sockaddr_in6 *)&spc->spc_aaddr;
                     ap = inet_ntop(AF_INET6, &sin6->sin6_addr,
                                    addrbuf, INET6_ADDRSTRLEN);
                   }
                   printf("^^^ intf_change: %s state=%d, error=%d\n", ap,
                          spc->spc_state, spc->spc_error);
                   break;
           case SCTP_REMOTE_ERROR:
                   sre = &snp->sn_remote_error;
                   printf("^^^ remote_error: err=%hu len=%hu\n",
                       ntohs(sre->sre_error), ntohs(sre->sre_len));
                   break;
           case SCTP_SHUTDOWN_EVENT:
                   printf("^^^ shutdown event\n");
                   break;
           default:
                   printf("unknown type: %hu\n", snp->sn_header.sn_type);
                   break;
           }
   }

   static void *
   sctp_recvmsg(int fd, struct msghdr *msg, void *buf, size_t *buflen,
       ssize_t *nrp, size_t cmsglen)
   {
           ssize_t nr = 0, nnr = 0;
           struct iovec iov[1];

           *nrp = 0;
           iov->iov_base = buf;



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   	iov->iov_len = *buflen;
           msg->msg_iov = iov;
           msg->msg_iovlen = 1;


           for (;;) {
   #ifndef MSG_XPG4_2
   #define MSG_XPG4_2 0
   #endif
                   msg->msg_flags = MSG_XPG4_2;
                   msg->msg_controllen = cmsglen;

                   nnr = recvmsg(fd, msg, 0);
                   if (nnr <= 0) {
                           /* EOF or error */
                           *nrp = nr;
                           return (NULL);
                   }
   		nr += nnr;

                   if ((msg->msg_flags & MSG_EOR) != 0) {
                           *nrp = nr;
                           return (buf);
                   }

                   /* Realloc the buffer? */
                   if (*buflen == nr) {
                           buf = realloc(buf, *buflen * 2);
                           if (buf == 0) {
                                   fprintf(stderr, "out of memory\n");
                                   exit(1);
                           }
                           *buflen *= 2;
                   }

                   /* Set the next read offset */
                   iov->iov_base = (char *)buf + nr;
                   iov->iov_len = *buflen - nr;

           }
   }

   static void
   echo(int fd, int socketModeUDP)
   {
           ssize_t nr;
           struct sctp_sndrcvinfo *sri;
           struct msghdr msg[1];



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           struct cmsghdr *cmsg;
           char cbuf[sizeof (*cmsg) + sizeof (*sri)];
           char *buf;
           size_t buflen;
           struct iovec iov[1];
           size_t cmsglen = sizeof (*cmsg) + sizeof (*sri);

           /* Allocate the initial data buffer */
           buflen = BUFLEN;
           if (!(buf = malloc(BUFLEN))) {
                   fprintf(stderr, "out of memory\n");
                   exit(1);
           }

           /* Set up the msghdr structure for receiving */
           memset(msg, 0, sizeof (*msg));
           msg->msg_control = cbuf;
           msg->msg_controllen = cmsglen;
           msg->msg_flags = 0;
           cmsg = (struct cmsghdr *)cbuf;
           sri = (struct sctp_sndrcvinfo *)(cmsg + 1);

           /* Wait for something to echo */
           while (buf = sctp_recvmsg(fd, msg, buf, &buflen, &nr, cmsglen)) {

                   /* Intercept notifications here */
                   if (msg->msg_flags & MSG_NOTIFICATION) {
                           handle_event(buf);
                           continue;
                   }

                   iov->iov_base = buf;
                   iov->iov_len = nr;
                   msg->msg_iov = iov;
                   msg->msg_iovlen = 1;

                   printf("got %u bytes on stream %hu:\n", nr,
                       sri->sinfo_stream);
                   write(0, buf, nr);

                   /* Echo it back */
                   msg->msg_flags = MSG_XPG4_2;
                   if (sendmsg(fd, msg, 0) < 0) {
                           perror("sendmsg");
                           exit(1);
                   }
           }




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           if (nr < 0) {
                   perror("recvmsg");
           }
   	if(socketModeUDP == 0)
   	  close(fd);
   }

   int main()
   {
           int lfd, cfd;
           int onoff = 1;
           struct sockaddr_in sin[1];

           if ((lfd = socket(AF_INET, SOCK_STREAM, IPPROTO_SCTP)) == -1) {
                   perror("socket");
                   exit(1);
           }

           sin->sin_family = AF_INET;
           sin->sin_port = htons(7);
           sin->sin_addr.s_addr = INADDR_ANY;
           if (bind(lfd, (struct sockaddr *)sin, sizeof (*sin)) == -1) {
                   perror("bind");
                   exit(1);
           }

           if (listen(lfd, 1) == -1) {
                   perror("listen");
                   exit(1);
           }

           /* Wait for new associations */
           for (;;) {
   	        struct sctp_event_subscribe event;
                   if ((cfd = accept(lfd, NULL, 0)) == -1) {
                           perror("accept");
                           exit(1);
                   }

                   /* Enable all events */
   		event.sctp_data_io_event = 1;
   		event.sctp_association_event = 1;
                   event.sctp_address_event = 1;
                   event.sctp_send_failure_event = 1;
                   event.sctp_peer_error_event = 1;
                   event.sctp_shutdown_event = 1;
                   event.sctp_partial_delivery_event = 1;
                   event.sctp_adaption_layer_event = 1;



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                   if (setsockopt(cfd, IPPROTO_SCTP,
   		    SCTP_SET_EVENTS, &event,
   		    sizeof(event)) != 0) {
   		    perror("setevent failed");
                       exit(1);
                   }
                   /* Echo back any and all data */
                   echo(cfd,0);
           }
   }









































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Appendix B. UDP-style Code Example

   The following code is a simple implementation of an echo server over
   SCTP.  The example shows how to use some features of UDP-style IPv4
   SCTP sockets, including:

   o  Opening and binding of a socket;

   o  Enabling ancillary data

   o  Enabling notifications

   o  Using ancillary data with sendmsg() and recvmsg()

   o  Using MSG_EOR to determine if an entire message has been read

   o  Handling notifications

   Note most functions defined in Appendix A are reused in this example.

   int main()
   {
           int fd;
           int onoff = 1;
   	int idleTime = 2;
           struct sockaddr_in sin[1];
   	struct sctp_event_subscribe event;

           if ((fd = socket(AF_INET, SOCK_SEQPACKET, IPPROTO_SCTP)) == -1) {
   	  perror("socket");
   	  exit(1);
           }

           sin->sin_family = AF_INET;
           sin->sin_port = htons(7);
           sin->sin_addr.s_addr = INADDR_ANY;
           if (bind(fd, (struct sockaddr *)sin, sizeof (*sin)) == -1) {
   	  perror("bind");
   	  exit(1);
           }

   	/* Enable all notifications and events */
   	event.sctp_data_io_event = 1;
   	event.sctp_association_event = 1;
           event.sctp_address_event = 1;
           event.sctp_send_failure_event = 1;
           event.sctp_peer_error_event = 1;
           event.sctp_shutdown_event = 1;



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           event.sctp_partial_delivery_event = 1;
           event.sctp_adaption_layer_event = 1;
           if (setsockopt(fd, IPPROTO_SCTP,
   	    SCTP_SET_EVENTS, &event,
   	    sizeof(event)) != 0) {
   	    perror("setevent failed");
               exit(1);
           }
   	/* Set associations to auto-close in 2 seconds of
   	 * inactivity
   	 */
   	if (setsockopt(fd, IPPROTO_SCTP, SCTP_AUTOCLOSE,
   		       &idleTime, 4) < 0) {
   	  perror("setsockopt SCTP_AUTOCLOSE");
   	  exit(1);
   	}

           /* Allow new associations to be accepted */
           if (listen(fd, 0) < 0) {
             perror("listen");
             exit(1);
           }

           /* Wait for new associations */
           while(1){
   	  /* Echo back any and all data */
   	  echo(fd,1);
           }
   }






















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Intellectual Property Statement

   The IETF takes no position regarding the validity or scope of any
   intellectual property or other rights that might be claimed to
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Full Copyright Statement

   Copyright (C) The Internet Society (2003).  All Rights Reserved.

   This document and translations of it may be copied and furnished to
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   The limited permissions granted above are perpetual and will not be
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   TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
   BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION



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   HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
   MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.


Acknowledgement

   Funding for the RFC Editor function is currently provided by the
   Internet Society.











































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