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Internet Engineering Task Force D. Sprague
Internet Draft R. Benedyk
Document: <draft-benedyk-sigtran-tali-01.txt> D. Brendes
Category: Informational J. Keller
Tekelec
June 2000
Transport Adapter Layer Interface
Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026.
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Abstract
This document proposes the interfaces of a Signaling Gateway, which
provides interworking between the Switched Circuit Network (SCN) and
an IP network. Since the Gateway is the central point of signaling
information, not only does it provide transportation of signaling
from one network to another, but it can also provide additional
functions such as protocol translation, security screening, routing
information, and seamless access to Intelligent Network(IN) services
on both networks.
The Transport Adapter Layer Interface (TALI) is the proposed
interface, which provides TCAP, ISUP, and MTP messaging over TCP/IP.
In addition, TALI provides SCCP Management (SCMG), MTP Primitives,
dynamic registration of circuits, and routing of call control
messages based on circuit location.
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Table of Contents
1. Introduction 4
2. Overview of the TALI Protocol 6
2.1 Traditional PSTN SS7 Networks 6
2.2 Converged SS7 Networks 8
2.3 TALI Protocol Stack Overview 9
2.3.1 An Alternate TALI Protocol Stack using the SAAL Layer 11
2.3.2 An Alternate TALI Protocol Stack using SCTP 13
2.4 Inputs to the TALI Version 1.0 State Machine 13
3. TALI Version 1.0 15
3.1 Overview of the TALI Message Structure 15
3.1.1 Types of TALI Fields 17
3.2 Detailed TALI Message Structure 18
3.2.1 TALI Peer to Peer Messages 18
3.2.1.1 Test Message (test) 18
3.2.1.2 Allow Message (allo) 18
3.2.1.3 Prohibit Message (proh) 19
3.2.1.4 Prohibit Acknowledgement Message (proa) 19
3.2.1.5 Monitor Message (moni) 19
3.2.1.6 Monitor Acknowledge Message (mona) 20
3.2.2 Service Messages 20
3.2.2.1 SCCP Service Message (sccp) 20
3.2.2.1.1 SCCP Encapsulation using TALI 22
3.2.2.2 ISUP Service Message (isot) 23
3.2.2.2.1 ISUP Encapsulation using TALI 23
3.2.2.3 MTP3 Service Message (mtp3) 24
3.2.2.3.1 MTP3 Encapsulation using TALI 25
3.2.2.4 SAAL Service Message (saal) 26
3.2.2.4.1 MTP3 and SAAL Peer to Peer Encapsulation using TALI 27
3.3 TALI Timers 28
3.3.1 T1 Timer 29
3.3.2 T2 Timer 29
3.3.3 T3 Timer 29
3.3.4 T4 Timer 29
3.3.5 Recommended Defaults and Ranges for the TALI Timers 29
3.4 TALI User Events 30
3.4.1 Management Open Socket Event 30
3.4.2 Management Close Socket Event 31
3.4.3 Management Allow Traffic Event 31
3.4.4 Management Prohibit Traffic Event 31
3.5 Other Implementation Dependent TALI Events 31
3.6 TALI States 31
3.7 TALI Version 1.0 State Machine 32
3.7.1 State Machine Concepts 32
3.7.1.1 General Protocol Rules 32
3.7.1.2 Graceful Shutdown of a Socket 33
3.7.1.3 TALI Protocol Violations 33
3.7.2 The State Machine 33
3.8 TALI 1.0 Implementation Notes 35
3.8.1 Failure on a TCP/IP Socket 36
3.8.2 Congestion on a TCP/IP Socket 36
3.9 TALI 1.0 Limitations 36
4. TALI Version 2.0 36
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4.1 Overview of TALI Version 2.0 Features 37
4.2 TALI Version Identification 39
4.3 Backwards Compatibility 41
4.3.1 Generating Protocol Violations based on Received Messages43
4.4 Overview of the TALI Message Structure 45
4.4.1 Types of TALI Fields 45
4.5 Detailed TALI Message Structures for New 2.0 Opcodes 47
4.5.1 Management Message (mgmt) 49
4.5.1.1 Routing Key Registration Primitive (rkrp) 50
4.5.1.1.1 RKRP Data Structures 53
4.5.1.1.1.1 Common Fields in all RKRP Messages 53
4.5.1.1.1.2 CIC Based Routing Key Operations 54
4.5.1.1.1.3 SCCP Routing Key Operations 58
4.5.1.1.1.4 DPC-SI, DPC and SI based Routing Key Operations 60
4.5.1.1.1.5 Default Routing Key Operations 62
4.5.1.1.1.6 Support for Multiple RKRP Registration Operations 64
4.5.1.1.1.6.1 Multiple Registrations Support 64
4.5.1.1.1.6.2 Multiple RKRP Operations in a Single Message 66
4.5.1.2 MTP3 Primitive (mtpp) 67
4.5.1.3 Socket Option Registration Primitive (sorp) 71
4.5.2 Extended Service Message (xsrv) 74
4.5.3 Special Message (spcl) 74
4.5.3.1 Special Messages Not Supported (smns) 75
4.5.3.2 Query Message (qury) 76
4.5.3.3 Reply Message (rply) 76
4.5.3.4 Unsolicited Information Message (USIM) 77
4.6 TALI Timers 77
4.7 TALI User Events 77
4.8 TALI States 78
4.9 TALI Version 2.0 State Machine 78
4.9.1 State Machine Concepts 78
4.9.1.1 General Protocol Rules 78
4.9.1.2 Graceful Shutdown of a Socket 79
4.9.1.3 TALI Protocol Violations 79
4.9.2 The State Machine 79
4.10 TALI 2.0 Specification Limitations 82
5. Success/Failure Codes 82
6. Security Considerations 83
7. References 83
8. Acknowledgments 84
9. Author's Addresses 84
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1. Introduction
This document is organized into the following 6 sections:
- Introduction to the document
- Overview of the TALI Protocol
- TALI Version 1.0
- TALI Version 2.0
- Success/Failure Codes
- Security Considerations
The following terms are used throughout this document.
Circuit Identification Code (CIC):
A field identifying the circuit being setup or released. Depending
on SI and MSU Type, this field can be 12, 14 or 32 bits.
Changeover/Changeback (co/cb):
SS7 MTP3 procedure related to link failure and re-establishment.
Far End (FE):
The remote endpoint of a socket connection.
Far End Allowed (FEA):
The FE is ready to use the socket for service PDUs.
Far End Prohibited (FEP):
The FE is not ready to use the socket for service PDUs.
Intelligent Network (IN):
A network that allows functionality to be distributed flexibly at a
variety of nodes on and off the network and allows the architecture
to be modified to control the services.
Management ATM Adaptation Layer (MAAL):
This layer is a component of SAAL. This layer maps requests and
indications between the System Management for the SG and the other
SAAL layers. MAAL includes interfaces to/from SSCOP, SSCF, and
system management. More information can be found in T1.652.
Media Gateway (MG):
A MG terminates SCN media streams, packetizes the media data, if it
is not already packetized, and delivers packetized traffic to the
packet network. It performs these functions in reverse order for
media streams flowing from the packet network to the SCN.
Media Gateway Controller (MGC):
An MGC handles the registration and management of resources at the
MG. The MGC may have the ability to authorize resource usage based
on local policy. For signaling transport purposes, the MGC serves
as a possible termination and origination point for SCN application
protocols, such as SS7 ISDN User Part and Q.931/DSS1.
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MTP3 Framing (MTP3F):
TALI does not require full MTP3 procedures support but rather uses
the MTP3 framing structure (ie: SIO, Routing Label, etc)
Near End (NE):
The local endpoint of a socket connection.
Near End Allowed (NEA):
The NE is ready to use the socket for service PDUs.
Near End Prohibited (NEP):
The NE is not ready to use the socket for service PDUs.
Q.BICC ISUP:
An ISUP+ variant that uses 32 bit CIC codes instead of 14/12 bit CIC
codes. ISUP+, or Q.BICC ISUP, is based on the Q.765.BICC
specification currently being developed in ITU Study Group 11.
Signaling ATM Adaptation Layer (SAAL):
This layer is the equivalent of MTP-2 for ATM High Speed Links
carrying SS7 Traffic as described in GR-2878-CORE [8]. SAAL
includes SSCF, SSCOP and MAAL.
Signaling Gateway (SG):
An SG is a signaling agent that receives/sends SCN native signaling
at the edge of the IP network. The SG function may relay, translate
or terminate SS7 signaling in an SS7-Internet Gateway. The SG
function may also be co-resident with the MGC/MG functions to
process SCN signaling associated with line or trunk terminations
controlled by the MG (e.g., signaling backhaul).
Service Specific Coordination Function (SSCF):
This layer is a component of SAAL. This layer maps the services
provided by the lower layers of the SAAL to the needs of a specific
higher layer user. In the case of the STP, the higher layer user is
the MTP-3 protocol, and the SSCF required is that as defined by
T1.645: SSCF for Support of Signaling at the Network Node Interface
(SSCF at the NNI). More information can be found in T1.645. SSCF
provides the interface between SSCOP and MTP3 and includes the
following functions:
- Local Retrieve of messages to support link changeover procedures
- Flow control with four levels of congestion
Switched Circuit Network (SCN):
The term SCN is used to refer to a network that carries traffic
within channelized bearers of pre-defined sizes. Examples include
Public Switched Telephone Networks (PSTNs) and Public Land Mobile
Networks (PLMNs). Examples of signaling protocols used in SCN
include Q.931, SS7 MTP Level 3 and SS7 Application/User parts.
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Service Specific Connection Oriented Protocol (SSCOP):
This layer is a component of SAAL. This layer provides reliable
point to point data transfer with sequence integrity and error
recovery by selective retransmission. Protocol layer interfaces are
described in T1.637. Aspects of the protocol include flow control,
connection control, error reporting to layer management, connection
maintenance in the prolonged absence of data transfer, local data
retrieval by the user of the SSCOP, error detection of protocol
control information and status reporting. SSCOP provides the link
layer functions that are:
- In-Sequence Delivery
- Flow Control
- Error Detection/Correction
- Keep Alive
- Local Data Retrieval
- Connection Control
- Protocol Error Detection and Recovery
Signaling Transfer Point (STP):
Packet switches that provide CCS message routing and transport. They
are stored programmed switches that use information contained in the
message in conjunction with information stored in memory to route
the message to the appropriate destination signaling point.
2. Overview of the TALI Protocol
2.1 Traditional PSTN SS7 Networks
The traditional PSTN SS7 network consists of 3 types of devices
connected via dedicated SS7 signaling links.
The 3 primary device types for PSTN networks are:
* SSP: Signaling Service Point. These nodes act as endpoints in
the SS7 network, originating SS7 messages as users attempt to
place phone calls. These nodes contain interfaces into the SS7
data network and the SS7 voice network.
* STP: Signaling Transfer Point. These nodes act primarily as
switches, switching SS7 traffic from node to node throughout the
network until it reaches another endpoint. An important feature
of each STP is to provide SS7 network management functionality
that allows messages to be delivered even when links and devices
fail. STPs also sometimes provide database type services, such as
Global Title Translations and Local Number Portability.
* SCP: Signaling Control Point. These nodes act as databases. These
nodes contain stored data that is used to turn SS7 Queries into
SS7 Replies.
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There are 3 primary types of dedicated SS7 signaling links:
* 56Kbps SS7 (DS0, V35, OCU) links. These links implement the MTP-1
and MTP-2 protocols as defined in [1].
* DS1 High Speed Links. These links use the SAAL protocol to
provide an alternative to 56Kbps SS7 links that is based on newer,
faster technology. These links implement the SS7 protocol as
defined in [8].
* E1 Links.
Figure 1 provides an overview of the traditional PSTN network. In
this network, any of the links can be implemented via either 56
Kbps, DS1, or E1 links.
^
/ \
/SCP\
/-----\
/ \
/ \
/ \
/ \
/---\ +---+ +---+ /---\
| SSP |-----|STP|----|STP|-----| SSP |
\---/ \ /+-+-+\ /+-+-+ \ / \---/
\/ | \/ | \/
/\ | /\ | /\
/---\ / \+-+-+/ \+-+-+ / \ /---\
| SSP |/----|STP|----|STP|/----| SSP |
\---/ +---+ +---+ \---/
\ /
\ /
\ /
\ ^ /
\/ \/
/SCP\
/-----\
Figure 1: The Traditional PSTN Network
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2.2 Converged SS7 Networks
In the converged SS7 network, SS7 devices will reside on both the
traditional PSTN network (with dedicated 56 Kbps and DS1 links) and
on the IP network (with Ethernet links based on IP protocol). The
services of SSPs, STPs, and SCPs can be provided by new types of
devices that reside on IP networks. The IP network is not intended
to completely replace the PSTN, rather devices on the 2 types of
networks must be able to communicate with one another and convert
from 1 lower layer protocol to the other.
Signaling Gateways are new devices that may also function as an STP
in the converged network. SGs provide interfaces to:
* devices on the SCN (traditional SSPs, STPs, and SCPs)
* other SGs
* new devices on the IP network
SGs also continue to perform STP functions such as SS7 network
management and some database services (such as GTT and LNP).
New devices on the IP network include:
* Media Gateway Controllers. In addition to other functions, these
devices control Media Gateways and perform call processing.
* Media Gateways. In addition to other functions, these devices
control voice circuits that are used to carry telephone calls.
MGs + MGCs combine to provide the functionality of traditional
SSPs.
* IP based SCPs. The database services that are related to SS7 can
be moved onto devices on the IP network.
Figure 2 provides an overview of the converged SS7 network.
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^ ----- +---+
/ \ // \\---------------------|SG |
/SCP\----| SCN | +---+ +---+
/-----\ \\ //---------------|SG | |
----- \ +---+ |
/ | \ | |
/ | \ -----
/ | /---\ // \\
/ | | SSP | | IP |
/ | \---/ \\ //
/ | | / ----- \
/ | +---+ / | \ ^
/ | |MG |\ +---+ | \/ \
/ | +---+ \ |MGC| +---+ /SCP\
/ | \ +---+ |MGC| /-----\
/ /---\ +---+ \ | +---+
/ | SSP |----|MG |\ \ | /
/ \---/ +---+ \\ \ ----- /
/ \ // \\ +---+
/---\ +---+ \| IP |----|ISP|
| SSP |------------|MG |----- \\ // +---+
\---/ +---+ -----
Figure 2: The Converged SS7 Network
In theory, the TALI protocol can be used between 2 nodes to carry
SS7 traffic across TCP/IP. Some of the areas that TALI could be
used include:
- For SG to SG communication across IP
- For SG to MGC communication across IP
- For SG to IP based SCP communication across IP
- For communication between multiple IP based SCPs
- For communication between multiple MGCs
- For communication between MGCs and MGs
- For other IP devices such as DNS, Policy Servers, etc.
In reality, the communication between MGCs, or between MGC and MG is
probably better suited to using other protocols. With respect to
the Signaling Gateway implementation, the TALI protocol is used to
carry SS7 traffic:
- For SG to SG communication
- For SG to MGC communication
- For SG to IP based SCP communication
2.3 TALI Protocol Stack Overview
The Transport Adapter Layer Interface is the proposed interface that
provides SCCP, ISUP, and MTP messaging encapsulation within a TCP/IP
packet between two switching elements. In addition, TALI provides
SCCP Management (SCMG), MTP Primitives, dynamic registration of
circuits, and routing of call control messages based on circuit
location.
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The major purpose of the TALI protocol is to provide a bridge
between the SS7 Signaling Network and applications that reside
within an IP network. Figure 3 provides a simple illustration that
highlights the protocol stacks used for transport of SS7 MSUs on
both the SS7 side and the IP side of the SG.
SS7 traffic SS7 traffic
via 56Kbps links via TALI
+-----------+ +----+ +--------+
|Traditional| | SG | | IP |
|SS7 Devices|<------>| |<-------->| Devices|
+-----------+ +----+ +--------+
SS7 SS7, TALI, TCP/IP
protocol stack protocol stack
+---------------+ +---------------+
|SS7 application| |SS7 application|
|layer | |layer |
+-------+-------+ +-------+-------+
| TCAP | ISUP | | TCAP | ISUP |
+-------+ | +-------+ |
| SCCP | | | SCCP | |
+-------+-------+ +-------+-------+
| MTP3 | | MTP3F |
+---------------+ +---------------+
| MTP2 | | TALI |
+---------------+ +---------------+
| MTP1 | | TCP |
| (& phy. | +---------------+
| layer) | | IP |
+---------------+ +---------------+
| MAC |
| (& phy. |
| layer) |
+---------------+
Figure 3: TALI Protocol to carry SS7 over TCP/IP
From Figure 3, several observations can be made:
* The TALI layer is used when transferring SS7 over IP.
* When SS7 traffic is carried over a IP network, the MTP2 and
MTP1 layers of a traditional 56 Kbps link are replaced by the
TALI, TCP, IP, and MAC layers
* The TALI layer sits on top of the TCP layer.
* The TALI layer sits below the various SS7 layers (MTP3, SCCP/TCAP,
ISUP, and applications). The data from these SS7 layers is
carried as the data portion of TALI service data packets.
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Some of the facts concerning the TALI protocol which are important
to understanding how TALI works that are not evident from Figure 3
include the following:
* Each TALI connection is provided over a single TCP socket.
* The standard Berkeley sockets interface to the TCP is used by
the TALI layer to provide connection oriented service from
endpoint to peer endpoint.
* TCP sockets are based on a Client/Server architecture; one end
of the TALI connection must be defined as the 'server side', the
other end is a 'client'.
* The client/server roles are important only in bringing up the
TCP connection between the 2 endpoint, once the connection is
established both ends use the same Berkeley sockets calls (send,
recv) to transfer data.
* The TCP socket must be connected before the 2 TALI endpoints can
begin communicating.
* TALI provides user control over each TALI connection that is
defined. This control:
* Allows the user to control when each TALI connection will be
made
* Allows the user to control when each TALI connection is allowed
to carry SS7 traffic
* Allows the user to control the graceful shutdown of each socket
* TALI provides Peer to Peer messages. These messages originate
from the TALI layer of one endpoint of the connection and are
terminated at the TALI layer of the other endpoint. Peer to Peer
messages are used:
* To provide test and watchdog maintenance messages
* To control the ability of each socket to carry SS7 service
messages
* TALI provides Service messages. These messages originate from the
layer above the TALI layer of one endpoint of the connection and
are transferred to and terminated at the layer above the TALI
layer of the other endpoint.
* The service messages provide several different ways to
encapsulate the SS7 messages (SCCP/TCAP, ISUP, and other MTP3
layer data) across the TCP/IP connection.
* As we will see later, different Service opcodes are used to
communicate across the TALI socket exactly how each SS7 message
has been encapsulated.
* A set of TALI timers is defined. These timers are used to
correctly implement the TALI state machine.
2.3.1 An Alternate TALI Protocol Stack using the SAAL Layer
This section presents a different, slightly more complex, TALI
protocol stack that can be used in place of the protocol stack in
the previous section.
Figure 3 in the previous section provided a simple illustration that
highlighted the basic TALI protocol stack that can be used to
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transport SS7 MSUs between 56 Kbps links on the SS7 side of an SG
and the IP devices.
Figure 4 below illustrates an alternate TALI protocol stack that
includes the SAAL layer as part of the data transferred across the
TCP/IP connection.
SS7 traffic SS7 traffic
via DS1 links via TALI
+-----------+ +----+ +--------+
|Traditional| | SG | | IP |
|SS7 Devices|<------>| |<-------->| Devices|
+-----------+ +----+ +--------+
SS7 DS1 SS7, TALI, TCP/IP
protocol stack protocol stack
+-----------------+ +-----------------+
| SS7 application | | SS7 application |
| layer | | layer |
+--------+--------+ +--------+--------+
| TCAP | ISUP | | TCAP | ISUP |
+--------+ | +--------+ |
| SCCP | | | SCCP | |
+--------+--------+ +--------+--------+
| SAAL | | SAAL |
|(SSCF,MAAL,SSCOP)| |(SSCF,MAAL,SSCOP)|
+-----------------+ +-----------------+
| AAL5 | | TALI |
+-----------------+ +-----------------+
| ATM | | TCP |
| (& phy. | +-----------------+
| layer) | | IP |
+-----------------+ +-----------------+
| MAC |
| (& phy. |
| layer) |
+-----------------+
Figure 4: An Alternate TALI Protocol Stack with SAAL
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The following bullets provide a discussion regarding the differences
between these 2 protocol stacks, the reasons for having 2 protocol
stacks, and the advantages of each:
* When the TALI protocol stack is implemented without the SAAL
layer, as in Figure 3, the SEQUENCE NUMBER of the SS7 MSU is NOT
part of the data transferred across the TCP/IP connection. In 56
Kbps SS7 links, the MTP2 header contains an 8 bit sequence number
for each MSU. The sequence number is used to preserve message
sequencing and to support complex SS7 procedures involving MSU
retrieval during link changeover and changeback. As indicated in
Figure 3, the MTP2 header is NOT part of the data transferred
across the TCP/IP connection. The TALI protocol stack without
SAAL still guarantees correct sequencing of SS7 data (this
sequencing is provided by sequence numbers in the TCP layer),
however that protocol stack can not support SS7 changeover and
changeback procedures.
* When the TALI protocol stack is implemented with the SAAL layer,
as in Figure 4, the SEQUENCE NUMBER of the SS7 MSU IS part of the
data transferred across TCP/IP. In SS7 DS1 links, the SSCOP
trailer contains a 24 bit sequence number for each MSU. This 24
bit sequence number serves the same purposes as the 8 bit SS7
sequence number. As indicated in Figure 4, the SSCOP trailer IS
part of the data transferred across the TCP/IP connection. The
protocol stack in Figure 4 can support SS7 changeover and
changeback procedures.
* Implementing the TALI protocol with SAAL therefore provides
support for SS7 co/cb and data retrieval and can help to minimize
MSU loss as SS7 links are deactivated. However, implementing SAAL
is not a trivial matter. The SAAL layer consists of 3 sublayers
(SSCF, SSCOP, and MAAL), one of which (SSCOP) is quite involved.
It is envisioned that most SS7 to TCP/IP applications will NOT
choose to implement SAAL.
2.3.2 An Alternate TALI Protocol Stack using SCTP
The TALI protocol is dependent on a reliable transport layer below
it. At the initial design of TALI, TCP was the only reliable,
proven transport layer. Simple Control Transport Protocol (SCTP) is
currently being designed as a transport later specifically for
signalling. Once SCTP is a proven and accepted transport protocol,
SCTP can then be used in place of TCP as shown in Figures 3 and 4.
2.4 Inputs to the TALI Version 1.0 State Machine
Figure 5 illustrates the inputs that affect the TALI State Machine.
Inputs to the state machine include:
* Management events (ie: requests from the human user of the TALI
connection) to control the operation of a particular TALI session.
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* TALI messages received from the Peer. These messages include peer
to peer messages as well as service data messages.
* Events from the User of the TALI layer. The user is the layer
above TALI in the protocol stack, either the SS7 or SAAL layer.
* Implementation Dependent Events. Each implementation must provide
inputs into the TALI state machine such as:
* Socket Events
* TALI protocol violations. The TALI state machine must detect
protocol violations and act accordingly.
* Timer events.
+====+ +============+
| | +---------+ +-------------+ | |
|User| | Service | | Mgmt. Open | | MANAGEMENT |
|Part|<-->| Message | | Mgmt. Close |<-->| |
| | | | | Mgmt. Proh. | | |
| | +---------+ | Mgmt. Allow | +============+
+====+ ^ +-------------+
| ^
| |
v v
+========================================================+
| TALI State Machine |
+========================================================+
^ ^ ^ ^
| | | |
| | | |
v | | |
+---------+ +-----------------+ +-----------+ +------------+
| Received| | Connection est. | | Protocol | | T1 Expired |
| 'test' | | Connection lost | | Violation | | T2 Expired |
| 'allo' | | | | | | T3 Expired |
| 'proh' | +-----------------+ +-----------+ | T4 Expired |
| 'proa' | ^ ^ +------------+
| 'moni' | | | ^
| 'mona' | | | |
| or | | | |
| Service | | | |
| Message | +========================================+
+---------+ | IMPLEMENTATION |
^ | DEPENDENT |
| +========================================+
|
v
+============+
| PEER |
| |
+============+
Figure 5: Overview of Inputs to the TALI 1.0 State Machine
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3. TALI Version 1.0
This chapter provides the states, messages, message exchange rules
and state machine that must be implemented to provide a TALI version
1.0 protocol layer.
3.1 Overview of the TALI Message Structure
Table 2 provides a summary of the messages and message structure
used in TALI version 1.0.
+------------------------------------------------------------------+
| OCTET | DESCRIPTION | SIZE | VALUE | TYPE |
+------------------------------------------------------------------+
| 0..3 | SYNC | 4 Octets | | 4 byte |
| | | | | ASCII |
+------------------------------------------------------------------+
| | TALI | | 'TALI' | |
+------------------------------------------------------------------+
| 4..7 | OPCODE | 4 Octets | | 4 byte |
| | | | | ASCII |
+------------------------------------------------------------------+
| | Test Service | | 'test' | |
| | Allow Service | | 'allo' | |
| | Prohibit Service | | 'proh' | |
| | Prohibit Service Ack | | 'proa' | |
| | Monitor Socket | | 'moni' | |
| | Monitor Socket Ack | | 'mona' | |
| | SCCP Service | | 'sccp' | |
| | ISUP Service over TALI | | 'isot' | |
| | MTP3 Service over TALI | | 'mtp3' | |
| | Service over SAAL | | 'saal' | |
+------------------------------------------------------------------+
| 8..9 | LENGTH | 2 Octets | | integer |
| | (least significant | | | |
| | byte first) non-0 | | | |
| | if Service or | | | |
| | Socket monitor message| | | |
+------------------------------------------------------------------+
| 10..X | DATA PAYLOAD | variable | | variable |
+------------------------------------------------------------------+
Table 2: Message Structure for TALI 1.0
Table 3 indicates the valid values of the LENGTH field for each
version 1.0 opcode. The LENGTH field is always an indication of the
# of bytes contained in the DATA PAYLOAD portion of a general TALI
message.
Sprague et al Informational - December 2000 15
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+------------------------------------------------------------------+
| OPCODE | VALID LENGTH VALUES | COMMENTS |
+------------------------------------------------------------------+
| test | 0 bytes | |
+------------------------------------------------------------------+
| allo | 0 bytes | |
+------------------------------------------------------------------+
| proh | 0 bytes | |
+------------------------------------------------------------------+
| proa | 0 bytes | |
+------------------------------------------------------------------+
| moni | 0-200 bytes | A maximum length is provided so |
| | | that the maximum ethernet frame |
| | | size is not exceeded. |
+------------------------------------------------------------------+
| mona | 0-200 bytes | Mona reply length and content must|
| | | match the original moni (with the |
| | | exception of the opcode) |
+------------------------------------------------------------------+
| sccp | 12-265 bytes | These are the valid sizes for the |
| | | SCCP-ONLY portions of SCCP UDT |
| | | MSUs |
+------------------------------------------------------------------+
| isot | 11-273 bytes | The length is the number of octets|
| | | in the MTP3 and higher layer(s) of|
| | | the SS7 MSU. This length includes|
| | | the SIO byte and all bytes in the |
| | | SIF (Service Information Field) |
| | | field. The MTP3 routing label is |
| | | part of the SIF field. |
+------------------------------------------------------------------+
| mtp3 | 11-280 bytes | The length is the number of octets|
| | | in the MTP3 and higher layer(s) of|
| | | the SS7 MSU. This length includes|
| | | the SIO byte and all bytes in the |
| | | SIF (Service Information Field) |
| | | field. The MTP3 routing label is |
| | | part of the SIF field. |
+------------------------------------------------------------------+
| saal | 11-280 bytes | The length is the number of octets|
| | | in the MTP3 and higher layer(s) of|
| | | the SS7 MSU. This length includes|
| | | the SIO byte and all bytes in the |
| | | SIF (Service Information Field) |
| | | field. The MTP3 routing label is |
| | | part of the SIF field. Seven (7) |
| | | octets of SSCOP trailer is added |
| | | to the message. The SSCOP trailer|
| | | bytes are also included in the |
| | | length. |
+------------------------------------------------------------------+
Table 3: Valid Length Fields for Each Opcode in TALI 1.0
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3.1.1 Types of TALI Fields
Several field types are used in the general TALI message structure.
+------------------------------------------------------------------+
|Field Type | Implementation Notes for that Type |
+------------------------------------------------------------------+
|4 byte | * 4 byte ASCII text strings are used to define the |
|ASCII text | sync code and the opcode of the basic TALI message.|
| | * These fields are case sensitive, the coding for |
| | each sync and opcode literal needs to match the |
| | case specified in Table 2. |
| | * The standard ASCII conversion table is used to |
| | transform each character into a byte. |
| | * The order of the ASCII characters is important. |
| | The first character in the string must be the |
| | first character transmitted across the wire. |
| | * For example, if the string being encoded is 'abCD',|
| | the order of the bytes as they are transferred |
| | over the wire must be: |
| | 1st byte: 0x61 ('a') 3rd byte: 0x43 ('C') |
| | 2nd byte: 0x62 ('b') 4th byte: 0x44 ('D') |
| | * The software for each implementation should be |
| | written in a manner that accounts for the required |
| | byte order of transmission (ie: the Big Endian/ |
| | Little Endian characteristics of the processor |
| | need to be dealt with in the software. |
+------------------------------------------------------------------+
|Integer | * A 1, 2 or 4 byte field to be treated as an integer |
| | value. Integer fields should be transmitted Least |
| | Significant Byte first across the wire. |
| | * The software for each implementation should be |
| | written in a manner that accounts for the required |
| | byte order of transmission (ie: the Big Endian/ |
| | Little Endian characteristics of the processor |
| | need to be dealt with in the software. |
+------------------------------------------------------------------+
|Variable | * The definition of the message structure for this |
| | field is governed by other specifications. |
| | * For example, when transferring MTP3 service data |
| | via a 'mtp3' opcode, the DATA PAYLOAD begins with |
| | the SIO byte of the MTP3 routing label. The |
| | structure for the entire DATA PAYLOAD is governed |
| | by the MTP3 message structure defined in [1]. |
+------------------------------------------------------------------+
|X byte | * ASCII text fields of sizes other than 4 bytes |
|ASCII text | should be supported according to the same rules |
| | presented for the 4 byte ASCII text fields. For |
| | instance, an 8 byte string such as 'ab01cd23' could|
| | be used, where the 'a' would be the first byte of |
| | the field transmitted out the wire. |
+------------------------------------------------------------------+
Table 4: Implementation Notes for each Type of TALI field
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3.2 Detailed TALI Message Structure
3.2.1 TALI Peer to Peer Messages
The following subsections provide more information regarding the
TALI Peer to Peer messages that are implemented in version 1.0. The
TALI peer to peer messages originate at the TALI layer of 1 end of
the socket connection (the near end) and are terminated at the TALI
layer of the far end of the connection.
3.2.1.1 Test Message (test)
The 'test' message is used by a TALI implementation to query the
remote end of the TALI connection with respect to the willingness of
the remote end to carry SS7 service data. This message asks the
other end: are you ready to carry service data? This message is
sent periodically by each TALI implementation based on a T1 timer
interval. Upon receiving 'test', a TALI implementation must reply
with either 'proh' or 'allo' to indicate the nodes willingness to
carry SS7 service data over that TALI connection.
+------------------------------------------------------------------+
| Octets | Field Name | Description |
+------------------------------------------------------------------+
| 0..3 | SYNC | 'TALI' |
+------------------------------------------------------------------+
| 4..7 | OPCODE | 'test' |
+------------------------------------------------------------------+
| 8..9 | LENGTH | Length = 0 |
+------------------------------------------------------------------+
3.2.1.2 Allow Message (allo)
The 'allo' message is sent in reply to a 'test' query, or in
response to some internal implementation event, to indicate that a
TALI implementation IS willing to carry SS7 service data over the
TALI session. This message informs the far end that SS7 traffic can
be transmitted on the socket. 'allo' is one of the 2 possible
replies to a 'test' message. Before SS7 traffic can be carried over
a socket, both ends of the connection need to send 'allo' messages.
+------------------------------------------------------------------+
| Octets | Field Name | Description |
+------------------------------------------------------------------+
| 0..3 | SYNC | 'TALI' |
+------------------------------------------------------------------+
| 4..7 | OPCODE | 'allo' |
+------------------------------------------------------------------+
| 8..9 | LENGTH | Length = 0 |
+------------------------------------------------------------------+
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3.2.1.3 Prohibit Message (proh)
The 'proh' message is sent in reply to a 'test' query, or in
response to some internal implementation event, to indicate that a
TALI implementation is NOT willing to carry SS7 service data over
the TALI session. This message informs the far end that SS7 traffic
can not be transmitted on the socket. 'proh' is one of the 2
possible replies to a 'test' message. As long as 1 end of the
connection remains in the 'prohibited' state, SS7 traffic can not be
carried over the socket.
+------------------------------------------------------------------+
| Octets | Field Name | Description |
+------------------------------------------------------------------+
| 0..3 | SYNC | 'TALI' |
+------------------------------------------------------------------+
| 4..7 | OPCODE | 'proh' |
+------------------------------------------------------------------+
| 8..9 | LENGTH | Length = 0 |
+------------------------------------------------------------------+
3.2.1.4 Prohibit Acknowledgement Message (proa)
The 'proa' message is sent by a TALI implementation each time a
'proh' is received from the far end. This message is sent to
indicate to the far end that his 'prohibit' message was received
correctly and will be acted on accordingly.
+------------------------------------------------------------------+
| Octets | Field Name | Description |
+------------------------------------------------------------------+
| 0..3 | SYNC | 'TALI' |
+------------------------------------------------------------------+
| 4..7 | OPCODE | 'proa' |
+------------------------------------------------------------------+
| 8..9 | LENGTH | Length = 0 |
+------------------------------------------------------------------+
3.2.1.5 Monitor Message (moni)
The 'moni' message provides a generic ECHO capability that can be
used by each TALI implementation as that implementation sees fit. A
TALI version 1.0 implementation does not have to originate a 'moni'
message to be compliant with the 1.0 specification. The primary
intent of this message is to provide a way for the TALI layer to
test the round-trip message transfer time on a socket. A 'mona'
message must be sent in reply to each received 'moni' message. The
DATA portion of a 'moni' message is vendor implementation dependent.
The DATA portion of each 'mona' reply must exactly match the DATA
portion of the 'moni' that is replied to. Regardless of whether an
implementation chooses to send 'moni' or not, 'mona' must be sent in
response to each 'moni' in order to remain compliant with the TALI
protocol.
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+------------------------------------------------------------------+
| Octets | Field Name | Description |
+------------------------------------------------------------------+
| 0..3 | SYNC | 'TALI' |
+------------------------------------------------------------------+
| 4..7 | OPCODE | 'moni' |
+------------------------------------------------------------------+
| 8..9 | LENGTH | Length |
+------------------------------------------------------------------+
| 10..X | DATA PAYLOAD| Vendor Dependent |
+------------------------------------------------------------------+
3.2.1.6 Monitor Acknowledge Message (mona)
As mentioned above, the 'mona' must be sent in reply to each
received 'moni'. The contents of the 'mona' DATA area must match
the DATA area of the received 'moni' message.
+------------------------------------------------------------------+
| Octets | Field Name | Description |
+------------------------------------------------------------------+
| 0..3 | SYNC | 'TALI' |
+------------------------------------------------------------------+
| 4..7 | OPCODE | 'mona' |
+------------------------------------------------------------------+
| 8..9 | LENGTH | Length |
+------------------------------------------------------------------+
| 10..X | DATA PAYLOAD| Vendor Dependent |
+------------------------------------------------------------------+
3.2.2 Service Messages
The following subsections provide more information regarding the
TALI Service messages that are implemented in version 1.0. TALI
Service messages are used to carry SS7 MSUs across the IP network.
The information in this section includes details with respect to how
to encapsulate SS7 MSUs into TCP/IP frames using each of the TALI
service opcodes. The TALI service messages originate at the layer
above TALI, are transported across the IP network via a TALI service
message, and are delivered to the layer above TALI at the far end of
the TALI connection.
3.2.2.1 SCCP Service Message (sccp)
The 'sccp' opcode is used to deliver SS7 MSUs with a Service
Indicator of 3 (SCCP) over a TALI connection. This opcode is only
used on TALI protocol stacks that are implemented without SAAL. The
MTP3 layer of the SS7 MSU is NOT part of the data transferred across
TCP/IP for this opcode; the data portion of the TALI 'sccp' message
begins with the first byte of the SCCP data area in the SS7 MSU
(after the MTP3 routing label). The first byte in the SCCP data
area is an SCCP message type field.
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Several restrictions on the SCCP messages that this TALI opcode can
carry exist. These restrictions are as follows:
* SCCP messages contain an SCCP message type field. The SCCP
messages that are supported by TALI 1.0 implementations are
limited to Class 0 and Class 1 SCCP messages with a message type
field of either:
* UDT
* UDTS
* XUDT
* XUDTS
* SCCP messages must contain a Point Code in the 'calling party'
area in order to be transferred across the TCP/IP connection as a
'sccp' message. An implementation may choose to modify the
original SCCP MSU to add an appropriate calling party point code
before transmission across TALI if desired.
* SCCP messages must contain a Point Code in the 'called party' area
in order to be transferred across the TCP/IP connection as a
'sccp' message. An implementation may choose to modify the
original SCCP MSU to add an appropriate called party point code
before transmission across TALI if desired.
* The encoding of the SS7 SCCP MSUs, as they are transmitted across
TALI via 'sccp', should remain compliant with the ANSI
specifications (T1.112 and T1.114) that apply to the SCCP and TCAP
portions of the message respectively.
NOTE 1: SCCP Subsystem Management for the IP based SCP's is
supported via this 'sccp' opcode. SS7 SCCP Management messages are
controlled by an SCMG SS7 process. SCMG sends the management
messages via SCCP UNITDATA (UDT) messages. Therefore, the SCMG
messages can be sent across the TALI connection.
NOTE 2: 'sccp' TALI messages will not include the MTP3 header and
therefore will not retain the original DPC/OPC of the SS7 MSU. Each
TALI implementation needs to consider if/how to provide this DPC/OPC
information in the SCCP portion of the message. For example the DPC
can be replicated to the point code in the SCCP Called Party Address
area and the OPC can be replicated to the point code in the SCCP
Calling Party Address area.
+------------------------------------------------------------------+
| Octets | Field Name | Description |
+------------------------------------------------------------------+
| 0..3 | SYNC | 'TALI' |
+------------------------------------------------------------------+
| 4..7 | OPCODE | 'sccp' |
+------------------------------------------------------------------+
| 8..9 | LENGTH | Length |
+------------------------------------------------------------------+
| 10..X | SCCP Data | SCCP data starting at the first byte after|
| | | the Layer 3 Routing Label (data does not |
| | | include the SIO or Routing Label) |
+------------------------------------------------------------------+
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3.2.2.1.1 SCCP Encapsulation using TALI
When an SCCP MSU arrives at an SG from a 56 Kbps or DS1 link and is
routed within the SG for transmission to an IP device, the SG
performs the following processing on the SS7 MSU:
* discards the MTP Layer 2 information, CRC and flags
* places the DPC from MTP Layer 3 into the Called Party Address
field of the SCCP layer; the Calling Party Address field is
created if it does not exist and then filled
* places the OPC from MTP Layer 3 into the Calling Party Address
field of the SCCP layer if there is no Calling Party Point Code
* places the modified SCCP and unchanged TCAP data in the service
payload area of the TALI packet
* The SYNC field is set
* The OPCODE is set to 'sccp'
* The LENGTH is set to the number of octets in the SERVICE field
Once the fully formed 'sccp' TALI packet is created, it is handed to
the TCP socket layer and transmitted. The transmission process will
add TCP, IP and MAC header information.
Since the routing information from MTP Layer 3 is placed in the SCCP
part of the outgoing message, no routing information needs to be
saved by the SG.
SS7 MSU
| Layer 3 | Layer 2 |
| | |
+----+---+-----+-----+-------+---+--+---+---+---+---+----+
|Flag|FCS|TCAP |SCCP |Routing|SIO|LI|FIB|FSN|BIB|BSN|Flag|
| | |Layer|Layer| Label | | | | | | | |
+----+---+-----+-----+-------+---+--+---+---+---+---+----+
| |
| |
| |
TALI +-----------+---+------+----+
Packet | Service |LEN|Opcode|SYNC|
+-----------+---+------+----+
| |
| |
| |
+---------------------------+------+------+------+
IP | TALI Packet |TCP | IP | MAC |
Packet | |Header|Header|Header|
+---------------------------+------+------+------+
Figure 6: Encapsulation of SCCP MSUs using the TALI 'sccp' opcode
Sprague et al Informational - December 2000 22
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When an 'sccp' TALI packet is received on by an SG from an IP
device, the SG performs the following processing on the 'sccp'
packet:
* validates the TALI header
* Allocates space for a new SS7 message
* Regenerates the SIO with the Sub-Service Field set to National
Network, priority of zero (0), Service Indicator set to SCCP
* extracts the SCCP/TCAP data from the SERVICE area and places it in
the new SS7 message
* sets the DPC to the SCCP Called Party Point Code
* sets the OPC to the SCCP Calling Party Point Code
* randomly generates the SLS
Once the 'sccp' packet is transformed back into a normal SS7 MSU,
the MSU is routed within the SG according to the normal SS7 routing
procedures.
3.2.2.2 ISUP Service Message (isot)
The 'isot' opcode is used to deliver SS7 MSUs with a Service
Indicator of 5 (ISUP) over a TALI connection. This opcode is only
used on TALI protocol stacks that are implemented without SAAL. The
MTP3 layer of the SS7 MSU IS part of the data transferred across
TCP/IP for this opcode; the data portion of the TALI 'isot' message
begins with the SIO byte of the MTP3 header in the SS7 MSU.
+------------------------------------------------------------------+
| Octets | Field Name | Description |
+------------------------------------------------------------------+
| 0..3 | SYNC | 'TALI' |
+------------------------------------------------------------------+
| 4..7 | OPCODE | 'isot' |
+------------------------------------------------------------------+
| 8..9 | LENGTH | Length |
+------------------------------------------------------------------+
| 10..X | ISUP Data | Raw ISUP data starting at the Layer 3 SIO |
| | | field. |
+------------------------------------------------------------------+
3.2.2.2.1 ISUP Encapsulation using TALI
When an ISUP MSU arrives at an SG from a 56 Kbps or DS1 link and is
routed within the SG to a IP device, the SG performs the following
processing on the SS7 MSU:
* discards the MTP Layer 2 information, CRC and flags
* places MTP Layer 3 into the SERVICE payload area of the TALI
packet
* The SYNC field is set
* The OPCODE is set to 'isot'
* The LENGTH is set to the number of octets in the SERVICE field
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Once the fully formed 'isot' TALI packet is created, it is handed to
the TCP socket layer and transmitted. The transmission process will
add TCP, IP and MAC header information.
Since the routing information is placed in the TALI Packet, no
routing information needs to be saved by the SG.
SS7 MSU
| Layer 3 | Layer 2 |
| | |
+----+---+----+----+---+-------+---+--+---+---+---+---+----+
|Flag|FCS|ISUP|Msg.|CIC|Routing|SIO|LI|FIB|FSN|BIB|BSN|Flag|
| | |Part|Type| |Label | | | | | | | |
+----+---+----+----+---+-------+---+--+---+---+---+---+----+
| /
| /
| |
TALI +-----------------------+---+------+----+
Packet | Service |LEN|Opcode|SYNC|
+-----------------------+---+------+----+
| /
| ---------
| /
+----------------------------+------+------+------+
IP | TALI Packet |TCP | IP | MAC |
Packet | |Header|Header|Header|
+----------------------------+------+------+------+
Figure 7: Encapsulation of ISUP MSUs using the TALI 'isot' opcode
When an 'isot' TALI packet is received on an SG from an IP device,
the SG performs the following processing on the 'isot' packet:
* validates the TALI header
* Allocates space for a new SS7 message
* extracts the MTP Layer 3 data from the SERVICE area and places it
in the new SS7 message
Once the 'isot' packet is transformed back into a normal SS7 MSU,
the MSU is routed within the SG according to the normal SS7 routing
procedures.
3.2.2.3 MTP3 Service Message (mtp3)
The 'mtp3' opcode is used to deliver SS7 MSUs with a Service
Indicator of 0-2, 4, 6-15 (non-SCCP, non-ISUP) over a TALI
connection. This opcode is only used on TALI protocol stacks that
are implemented without SAAL. The MTP3 layer of the SS7 MSU IS part
of the data transferred across TCP/IP for this opcode; the data
portion of the TALI 'mtp3' message begins with the SIO byte of the
MTP3 header in the SS7 MSU.
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+------------------------------------------------------------------+
| Octets | Field Name | Description |
+------------------------------------------------------------------+
| 0..3 | SYNC | 'TALI' |
+------------------------------------------------------------------+
| 4..7 | OPCODE | 'mtp3' |
+------------------------------------------------------------------+
| 8..9 | LENGTH | Length |
+------------------------------------------------------------------+
| 10..X | Layer 3 MSU | Raw MSU data starting at the Layer 3 SIO |
| | Data | field. |
+------------------------------------------------------------------+
3.2.2.3.1 MTP3 Encapsulation using TALI
When an SS7 MSU with SI=0-2,4,6-15 arrives at an SG from a 56 Kbps
or DS1 link and is routed within the SG to an IP device, the SG
performs the following processing on the SS7 MSU:
* discards the MTP Layer 2 information, CRC and flags
* places MTP Layer 3 into the SERVICE payload area of TALI packet
* The SYNC field is set
* The OPCODE is set to 'mtp3'
* The LENGTH is set to the number of octets in the SERVICE field
Once the fully formed 'mtp3' TALI packet is created, it is handed to
the TCP socket layer and transmitted. The transmission process will
add TCP, IP and MAC header information.
SS7 MSU
| Layer 3 | Layer 2 |
| | |
+----+---+-----------+-------+---+--+---+---+---+---+----+
|Flag|FCS|Other Layer|Routing|SIO|LI|FIB|FSN|BIB|BSN|Flag|
| | |3 Data |Label | | | | | | | |
+----+---+-----------+-------+---+--+---+---+---+---+----+
| /
| ------
| /
TALI +----------------+---+------+----+
Packet | Service |LEN|Opcode|SYNC|
+----------------+---+------+----+
| /
| --
| /
+----------------------------+------+------+------+
IP | TALI Packet |TCP | IP | MAC |
Packet | |Header|Header|Header|
+----------------------------+------+------+------+
Figure 8: Encapsulation of SS7 MSUs with SI!=3,5,13 using 'mtp3'
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When an 'mtp3' TALI packet is received by an SG from an IP device,
the SG performs the following processing on the 'mtp3' packet:
* validates the TALI header
* Allocates space for a new SS7 message
* extracts the MTP Layer 3 data from the SERVICE area and places it
in the new SS7 message
Once the 'mtp3' packet is transformed back into a normal SS7 MSU,
the MSU is routed within the SG according to the normal SS7 routing
procedures.
3.2.2.4 SAAL Service Message (saal)
The 'saal' opcode is used to deliver SS7 MSUs with any Service
Indicator over a TALI connection. This opcode is only used on TALI
protocol stacks that are implemented with SAAL. The 'saal' opcode
is also used to transmit SAAL peer to peer packets (SSCF peer to
peer packets and SSCOP peer to peer packets other than SS7 service
data) over a TALI connection.
When used to transfer SS7 MSUs, the MTP3 layer of the SS7 MSU IS
part of the data transferred across TCP/IP for this opcode; the data
portion of the TALI 'saal' message begins with the SIO byte of the
MTP3 header in the SS7 MSU and ends with the last byte of the SSCOP
trailer.
When used to transfer SSCF/SSCOP peer to peer messages the data
portion of the TALI 'saal' message includes the entire SSCOP PDU.
+------------------------------------------------------------------+
| Octets | Field Name | Description |
+------------------------------------------------------------------+
| 0..3 | SYNC | 'TALI' |
+------------------------------------------------------------------+
| 4..7 | OPCODE | 'saal' |
+------------------------------------------------------------------+
| 8..9 | LENGTH | Length |
+------------------------------------------------------------------+
| 10..X | Layer 3 | Raw MSU data starting at the Layer 3 SIO |
| | Data | field. |
+------------------------------------------------------------------+
| (X+1) | SSCOP | Zero (0) to three (3) octets of padding |
| ..Y | Trailer | plus 4 octets for the trailer data. The |
| | | total length of the Layer 3 Data and the |
| | | SSCOP trailer must be a multiple of 4. |
+------------------------------------------------------------------+
or
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+------------------------------------------------------------------+
| Octets | Field Name | Description |
+------------------------------------------------------------------+
| 0..3 | SYNC | 'TALI' |
+------------------------------------------------------------------+
| 4..7 | OPCODE | 'saal' |
+------------------------------------------------------------------+
| 8..9 | LENGTH | Length |
+------------------------------------------------------------------+
| 10..X | SAAL Peer | Raw SSCF/SSCOP peer to peer packets are |
| | to Peer | also transferred over the TALI connection |
| | message | using this 'saal' opcode. |
+------------------------------------------------------------------+
3.2.2.4.1 MTP3 and SAAL Peer to Peer Encapsulation using TALI
When an SS7 MSU (with any SI) arrives at an SG from a 56 Kbps or DS1
link and is routed within the SG for transmission to an IP device,
the SG performs the following processing on the SS7 MSU:
* discards the MTP Layer 2 information, CRC and flags
* the MSU is passed from an MTP3 processing software layer to the
SSCF and SSCOP layers (the SAAL layers). These layers convert the
SS7 MSU into an SSCOP PDU. Part of this conversion includes
adding an SSCOP trailer.
* the SSCOP PDU (whether it is a peer to peer SAAL message or SS7
MSU in an SSCOP PDU) is copied into the SERVICE payload area of
the TALI packet
* The SYNC field is set
* The OPCODE is set to 'saal'
* The LENGTH is set to the number of octets in the SERVICE field
Once the fully formed 'saal' TALI packet is created, it is handed to
the TCP socket layer and transmitted. The transmission process will
add TCP, IP and MAC header information.
Since the routing information is placed in the TALI Packet, no
routing information needs to be saved by the SG.
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SS7 MSU
| Layer 3 | Layer 2 |
| | |
+----+---+-----------+-------+---+--+---+---+---+---+----+
|Flag|FCS|Other Layer|Routing|SIO|LI|FIB|FSN|BIB|BSN|Flag|
| | |3 Data |Label | | | | | | | |
+----+---+-----------+-------+---+--+---+---+---+---+----+
| |
| |
| |
+-------+-----------------------+
|SSCOP | Service |
|Trailer| |
+-------+-----------------------+
| |
+-------+-----------------------+---+------+----+
|Service with SSCOP Trailer |LEN|Opcode|SYNC|
+-------+-----------------------+---+------+----+
| /
| -----------------
| /
+----------------------------+------+------+------+
| TALI Packet |TCP | IP | MAC |
| |Header|Header|Header|
+----------------------------+------+------+------+
Figure 9: Encapsulation of SAAL PDUs using the TALI 'saal' opcode
When an 'saal' TALI packet is received at the SG from an IP device,
the SG performs the following processing on the 'saal' packet:
* validates the TALI header
* Allocates space for a new SSCOP PDU message
* extracts the SSCOP PDU data from the SERVICE area and places it in
the new SSCOP PDU message
Once the 'saal' packet is transformed back into a normal DS1 SSCOP
PDU, the SSCOP PDU is passed to the SAAL layer for receive
processing. If the SSCOP PDU is a peer to peer pdu, it is processed
completely in the appropriate SAAL layer. If the SSCOP PDU is an
SS7 MSU, the MSU is transformed back to a normal SS7 MSU and is
routed within the SG according to the normal SS7 routing procedures.
3.3 TALI Timers
Version 1.0 of the TALI specification defined 4 TALI timers that are
used as part of the TALI state machine. These timers are
generically named 'T1' through 'T4'. Brief descriptions of each
timer are provided in the following subsections. Timer expiration
events for each of the T1-T4 timers appear as inputs to the TALI
state machine. For exact processing of each timer (when to
start/stop, how to process timer expirations), refer to the TALI
state machine.
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Both ends of the TALI connection have there own T1-T4 timers. The
T1-T4 timer values can be set on each end of the connection
independent of the settings on the far end. For each timer, a
default value and range is recommended in the following sections.
3.3.1 T1 Timer
The T1 timer represents the time interval between the origination of
a 'test' message at each TALI implementation. Each time T1 expires,
the TALI implementation should send a 'test'.
3.3.2 T2 Timer
The T2 timer represents the amount of time that the Peer has to
return an 'allo' or a 'proh' in response to a 'test'. If the far
end fails to reply with 'allo' or 'proh' before T2 expires, the
sender of the 'test' treats the T2 expiration as a protocol
violation. Note that T2 must be < T1 in order for these timers to
work as designed.
3.3.3 T3 Timer
The T3 timer controls how long the near end should continue to
process Service Data that is received from the far end after a
Management Prohibit Traffic Event has occurred (at the near end).
This timer is used when a transition from NEA-FEA (both ends allowed
to send service data) to NEP-FEA (only far end willing to send
service data) occurs. On that transition, it is reasonable to
expect that the far end needs some amount of time to adjust its TALI
state machine and divert service data traffic away from this socket.
The T3 timer controls the amount of time the far end has to divert
traffic.
3.3.4 T4 Timer
The T4 timer represents the time interval between the origination of
a 'moni' message at each TALI implementation. Each time T4 expires,
the TALI implementation should send a 'moni'.
3.3.5 Recommended Defaults and Ranges for the TALI Timers
The following table provides the recommended default and
configurable range for each TALI timer.
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+------------------------------------------------------------------+
|Name| Min | Max |Default| Description |
+------------------------------------------------------------------+
| T1 | 100ms | 60sec | 4 sec | Send test PDU timer |
+------------------------------------------------------------------+
| T2 | 100ms | 60sec | 3 sec | Response timer for an allo or proh |
| | | | | response to test message. |
+------------------------------------------------------------------+
| T3 | 100ms | 60sec | 5 sec | Timer controls how long to process |
| | | | | rcvd serv data after an NE |
| | | | | transition from NEA to NEP. System |
| | | | | is waiting for a proa response to |
| | | | | the first proh send when NE |
| | | | | transitions from NEA to NEP. |
+------------------------------------------------------------------+
| T4 | 100ms | 60sec |10 sec | Send moni PDU timer |
+------------------------------------------------------------------+
Table 5: Timers
NOTE: The value of T1 must be at least one (1) millisecond greater
than T2. This is to prevent the system from a lockup in the T1
expired condition. If T1 is equal or less than T2, it will expire
and restart T2 and not enforce responses to the test message.
Enforcement of minimum and maximum timer values is implementation
dependent.
3.4 TALI User Events
Each TALI implementation must provide several user event controls
over the behavior of the TALI state machine for each TALI
connection. The user interface to provide these capabilities is
implementation specific.
3.4.1 Management Open Socket Event
The 'mgmt open socket' event, together with the 'mgmt close socket'
event, allows the user to control when each defined TALI connection
will form a TCP socket connection. When 'open socket' for a
particular TALI connection occurs, the TALI connection should begin
trying to form a TCP socket connection to the peer.
The steps that are taken to connect are dependent on the
client/server role of that end of the TALI connection. The exact
steps to perform these tasks are implementation dependent and may
differ based on the TCP stack being used.
In general, TALI clients form socket connections by using the BSD
sockets calls:
Socket()
Bind()
Connect()
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In general, TALI servers form socket connections by using the BSD
sockets calls:
Socket()
Bind()
Listen()
Accept()
3.4.2 Management Close Socket Event
The 'mgmt close socket' event can be issued by the user when it is
desired that the TCP socket for a TALI socket, be closed
immediately, or discontinue its attempts to connect to the peer.
After acting on 'close socket', the TALI connection will not be
established until 'mgmt open socket' is issued.
3.4.3 Management Allow Traffic Event
The 'mgmt allow traffic' event, together with the 'mgmt prohibit
traffic' event, allows the user to control when each defined TALI
connection will be willing to carry SS7 service data over that
particular TALI connection. When 'mgmt allow traffic' is issued,
the TALI implementation becomes willing to carry service data. The
TALI state for the near end should transition to NEA (near end
allowed) if the connection is already established.
3.4.4 Management Prohibit Traffic Event
The 'mgmt prohibit traffic' event is the opposite of 'allow
traffic'. When 'mgmt prohibit traffic' is issued, the TALI
implementation becomes un-willing to carry SS7 service data over
that particular TALI connection. The TALI state for the near end
should transition to NEP (near end prohibited) if the connection is
already established.
3.5 Other Implementation Dependent TALI Events
In addition to timers, each TALI implementation needs to be able to
detect, and react accordingly, for the following events:
* Connection Established. When the TCP socket connection is
initially established the TALI state machine must be notified.
* Connection Lost. When the TCP socket connection is lost, due to
socket errors during reads/writes, the TALI state machine must be
notified.
* Protocol Violations. Any violation of the TALI protocol as
discussed in 3.7.1.3.
3.6 TALI States
The TALI version 1.0 specification is based on a state machine that
considers 6 TALI states. Each end of the TALI connection maintains
its own TALI state.
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+------------------------------------------------------------------+
| Name | Description |
+------------------------------------------------------------------+
| OOS | The TALI connection is out of service. This usually|
| | corresponds to a user event to 'close' the socket, |
| | or a user event to 'deactivate the SS7 link'. |
+------------------------------------------------------------------+
| Connecting | The TALI layer is attempting to establish a TCP |
| | socket connection to the peer. Servers are |
| | 'accepting', clients are 'connecting'. |
+------------------------------------------------------------------+
| NEP-FEP | The TCP socket connection is established. Neither |
| | side of the connection is ready to use the socket |
| | for service PDUs. |
+------------------------------------------------------------------+
| NEP-FEA | The TCP socket connection is established. The NE is|
| | not ready to use the socket for service PDUs. The |
| | FE is ready to use the socket for service PDUs. |
+------------------------------------------------------------------+
| NEA-FEP | The TCP socket connection is established. The NE is|
| | ready to use the socket for service PDUs. The FE is|
| | not ready to use the socket for service PDUs. |
+------------------------------------------------------------------+
| NEA-FEA | The TCP socket connection is established. Both |
| | sides are ready to use the socket for service PDUs. |
| | This is the only state where normal bi-directional |
| | SS7 data transfer occurs. |
+------------------------------------------------------------------+
Table 6: TALI States
3.7 TALI Version 1.0 State Machine
This section provides the state machine that must be followed by
each TALI implementation in order to be compliant with this
specification.
3.7.1 State Machine Concepts
Before presenting the actual state machine, several concepts are
discussed.
3.7.1.1 General Protocol Rules
1. Neither side can send service data unless both sides are allowed.
2. Each side initializes to the prohibited state for both near end
and far end.
3. State changes between the NEx-FEx states are signaled with either
an 'allo' or 'proh'.
4. Each side can poll the far end's state with a 'test'. Upon
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sending 'test', T1 and T2 should always be restarted.
5. Each side polls the far end with a 'test' every T1 expiration.
6. The reply to a 'test' is based on the state of the near end only.
7. The reply to a 'test' is either 'allo' or 'proh'.
8. A far end signals the last service PDU has been transmitted with
either a 'proh' or a 'proa'.
9. Upon receiving a 'proh', the receiver must always reply with
'proa'.
10. The NE cannot gracefully close a socket unless a 'proh' is sent
and 'proa' is received.
11. On the transition from NEA to NEP, after sending a 'proh', the
near end must continue to process received service data until a
'proa' is received or until a T3 timer expires.
3.7.1.2 Graceful Shutdown of a Socket
The state table treats a management request to close the socket as a
'hard' shutdown. That is, it will close the socket immediately
regardless of the current state. Therefore, the correct steps to
ensure a graceful shutdown of a socket (from the NEA_FEP or NEA_FEA
states) is:
1. Management issues a Management Prohibit Traffic Event on the
socket.
2. Management will wait for T3 to expire.
3. Management can then issue a Close Socket Event on the socket.
3.7.1.3 TALI Protocol Violations
Each TALI implementation must detect when violations of the TALI
protocol have occurred and react accordingly. Protocol violations
include:
* Invalid sync code in a received message
* Invalid length field in a received message
* Not receiving an 'allo' or 'proh', in response to the origination
of a 'test' , before the T2 timer expires
* Receiving Service Messages on a prohibited socket.
* TCP Socket errors û Connection Lost
In the state machine that follows, State/Event combinations that
should be treated as protocol violations are indicated via a 'PV' in
the state/event cell. All of the 'PV' events are then processed as
per the 'Protocol Violation' row in the table.
3.7.2 The State Machine
Internal Data required for State Machine:
boolean sock_allowed. This flag indicates whether the NE is allowed
to carry Service Messages.
Initial Conditions:
sock_allowed = FALSE
state = OOS
no timers running
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+------------------------------------------------------------------+
| State| OOS |Connecting| NEP-FEP | NEP-FEA | NEA-FEP | NEA-FEA |
|Event | | | | | | |
+------------------------------------------------------------------+
|T1 Exp. | | |Send test|Send test|Send test|Send test|
| | | |Start T1 |Start T1 |Start T1 |Start T1 |
| | | |Start T2 |Start T2 |Start T2 |Start T2 |
+------------------------------------------------------------------+
|T2 Exp. | | | PV | PV | PV | PV |
+------------------------------------------------------------------+
|T3 Exp. | | | PV | PV | | |
+------------------------------------------------------------------+
|T4 Exp. | | |Send moni|Send moni|Send moni|Send moni|
| | | |Start T4 |Start T4 |Start T4 |Start T4 |
+------------------------------------------------------------------+
|Rcv test| | |Send proh|Send proh|Send allo|Send allo|
+------------------------------------------------------------------+
|Rcv allo| | | Stop T2 | Stop T2 | Stop T2 | Stop T2 |
| | | | NEP-FEA | | NEA-FEA | |
+------------------------------------------------------------------+
|Rcv proh| | | Stop T2 | Stop T2 | Stop T2 | Stop T2 |
| | | |Send proa|Send proa|Send proa|Flush or |
| | | | | NEP-FEP | | reroute |
| | | | | | |Send proa|
| | | | | | | NEA-FEP |
+------------------------------------------------------------------+
|Rcv proa| | | Stop T3 | Stop T3 | | |
+------------------------------------------------------------------+
|Rcv moni| | |Convert |Convert |Convert |Convert |
| | | | to mona | to mona | to mona | to mona |
| | | |Send mona|Send mona|Send mona|Send mona|
+------------------------------------------------------------------+
|Rcv mona| | |Implemen-|Implemen-|Implemen-|Implemen-|
| | | |tation |tation |tation |tation |
| | | |dependent|dependent|dependent|dependent|
+------------------------------------------------------------------+
|Rcv | | | PV |If T3 run| PV |Process |
| Service| | | | Process | | |
| | | | |Else PV | | |
+------------------------------------------------------------------+
|Connect.| | Start T1 | | | | |
|Estab. | | Start T2 | | | | |
| | | Start T4 | | | | |
| | |(if non-0)| | | | |
| | |if sock_ | | | | |
| | | allowed | | | | |
| | | = TRUE | | | | |
| | | send allo| | | | |
| | | send test| | | | |
| | | NEA-FEP | | | | |
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| | |else | | | | |
| | | send proh| | | | |
| | | send test| | | | |
| | | NEP-FEP | | | | |
+------------------------------------------------------------------+
|Connect.| | | PV | PV | PV | PV |
|Lost | | | | | | |
+------------------------------------------------------------------+
|Protocol| | |Stop all |Stop all |Stop all |Stop all |
|Violat. | | | timers | timers | timers | timers |
| | | |Close the|Close the|Close the|Close the|
| | | | socket | socket | socket | socket |
| | | |Connect- |Connect- |Connect- |Connect- |
| | | | ing | ing | ing | ing |
+------------------------------------------------------------------+
|Mgmt. |Open | | | | | |
|Open |socket| | | | | |
|Socket |Conne-| | | | | |
| | cting| | | | | |
+------------------------------------------------------------------+
|Mgmt. | |Close the |Stop all |Stop all |Stop all |Stop all |
|Close | | socket | timers | timers | timers | timers |
|Socket | |OOS |Close the|Close the|Close the|Close the|
| | | | socket | socket | socket | socket |
| | | |OOS |OOS |OOS |OOS |
+------------------------------------------------------------------+
|Mgmt. |sock_ |sock_allo-|sock_all-|sock_all-|sock_all-|sock_all-|
|Prohibit|allow-| wed=FALSE| owed= | owed= | owed= | owed= |
|Socket |ed = | | FALSE | FALSE | FALSE | FALSE |
| |FALSE | | | |send proh|send proh|
| | | | | |start t3 |start t3 |
| | | | | | NEP-FEP | NEP-FEA |
| | | | | | | |
+------------------------------------------------------------------+
|Mgmt. |sock_ |sock_allo-|sock_all-|sock_all-|sock_all-|sock_all-|
|Allow |allow-| wed=TRUE | owed= | owed= | owed= | owed= |
|Traffic |ed = | | TRUE | FALSE | TRUE | TRUE |
| |TRUE | |send allo|send allo| | |
| | | | NEA-FEP | NEA-FEA | | |
+------------------------------------------------------------------+
|User |reject| reject | reject | reject | reject | send |
|Part |data | data | data | data | data | data |
|Msgs. | | | | | | |
+------------------------------------------------------------------+
Table 7: TALI 1.0 State Machine
3.8 TALI 1.0 Implementation Notes
Several aspects of the expected TALI 1.0 implementation have not
been specifically addressed in the state machine or previous text
(or else they were presented but will be reiterated here). These
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implementation notes in some cases have to do with the expected
behavior of the software layer above the TALI layer.
3.8.1 Failure on a TCP/IP Socket
* The failure to read or write from a TCP socket shall be detected
and generate a connection lost event.
3.8.2 Congestion on a TCP/IP Socket
* Message streams can be monitored for congestion via implementation
dependent methods.
* One possible definition of congestion for the previous requirement
might be when a TCP socket is blocked.
3.9 TALI 1.0 Limitations
Several limitations with the TALI 1.0 specification and
implementation are identified:
* For SCCP traffic, only UDT and XUDT Class 0 and Class 1 traffic
should be managed by this protocol.
* When the MTP3 Routing Label is not part of the data transmitted
across the wire, priority zero (0) traffic is used for all
traffic when the SIO is regenerated.
4. TALI Version 2.0
Version 2.0 of the TALI specification provides several additions to
the Version 1.0 specification. The 2.0 additions are provided by
introducing three new TALI opcodes. The basic functionality and
most of the details of the TALI 1.0 implementation are NOT changed
by the 2.0 additions.
The table below provides a summary of the messages and message
structure used in TALI version 2.0.
+------------------------------------------------------------------+
| OCTET | DESCRIPTION | SIZE | VALUE | TYPE |
+------------------------------------------------------------------+
| 0..3 | SYNC | 4 Octets | | 4 byte ASCII |
+------------------------------------------------------------------+
| | TALI | | 'TALI' | |
+------------------------------------------------------------------+
| 4..7 | OPCODE | 4 Octets | | 4 byte ASCII |
+------------------------------------------------------------------+
| | Test Service | | 'test' | |
| | Allow Service | | 'allo' | |
| | Prohibit Service | | 'proh' | |
| | Prohibit Service Ack| | 'proa' | |
| | Monitor Socket | | 'moni' | |
| | Monitor Socket Ack | | 'mona' | |
| | SCCP Service | | 'sccp' | |
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| | ISUP Service o/TALI | | 'isot' | |
| | MTP3 Service o/TALI | | 'mtp3' | |
| | Service o/SAAL | | 'saal' | |
| | Management Message | | 'mgmt' | |
| | Extended Service Msg| | 'xsrv' | |
| | Special Message | | 'spcl' | |
+------------------------------------------------------------------+
| 8..9 | LENGTH | 2 Octets | | integer |
| | (least significant | | | |
| | byte first) non-0 | | | |
| | if Service or | | | |
| | Socket monitor msg | | | |
+------------------------------------------------------------------+
| 10..X | DATA PAYLOAD | variable | | variable |
+------------------------------------------------------------------+
Due to the minimal amount of change from 1.0, this chapter will only
provide:
* Detailed information regarding how a TALI implementation can
identify itself as a 2.0 vs. a 1.0 implementation
* Detailed information regarding how to provide backward
compatibility for a connection to a far end that is only TALI 1.0
capable
* Detailed information regarding the new 2.0 opcodes
* Detailed information regarding any other changes to the
information presented in previous sections that need to
be implemented in order to be 2.0 compatible.
Therefore, readers of this chapter should read this from the point
of view of modifying an existing TALI 1.0 implementation to support
the new 2.0 features.
4.1 Overview of TALI Version 2.0 Features
A small number of changes to a 1.0 TALI implementation are required
to support 2.0. Figure 10 illustrates the inputs that affect the
2.0 TALI State Machine. The reader may notice that the only
differences from the inputs for 1.0 are as follows:
Three new TALI opcodes can be sent/received between a TALI node and
its peer. The new opcodes are:
* 'mgmt'
* 'xsrv'
* 'spcl'
Three new User Part capabilities need to be supported by the layer
of code above the TALI layer in each implementation. The user part
needs to provide support for 'mgmt', 'xsrv', and 'spcl' data.
More information about the 3 new opcodes is provided in individual
sections in this chapter. However, a brief description of the
purpose of each of these opcodes is as follows:
* 'mgmt' û This opcode is intended to allow MANAGEMENT data, or data
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that will manage the operation of the device, to pass between the
TALI endpoints. Examples of this management data include:
* configuration data, such as which SS7 traffic streams a peer
would like to receive over a specific socket
* SS7 Network Management data, such as information regarding point
code (un)availability and congestion.
* Enabling/disabling various socket options, such as options
regarding which messages are supported, or how to format data.
* 'xsrv' û Extended Service Opcodes. It is envisioned that the TALI
protocol could be extended to carry other types of traffic that
are not covered by the 1.0 service data opcodes ('sccp', 'isot',
'mtp3', or 'saal'). By defining a new 'xsrv' service opcode, the
TALI protocol is opened up to the possibility of being used for
other types of data transport.
* 'spcl' û Special services. It is envisioned that vendors may want
to build special services into their TALI implementations that are
only activated when the implementation is connected to other
equipment implementing the same special services. This opcode is
intended to provide a general means to discover more information
regarding who the TALI session is connected to, and a means to
enable special features based on the vendor/implementation on the
far end.
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+====+ +---------+ +============+
| | | Service | +-------------+ | |
|User| | Message,| | Mgmt. Open | | MANAGEMENT |
|Part|<-->| MGMT, | | Mgmt. Close |<-->| |
| | | XSRV, | | Mgmt. Proh. | | |
| | | SPCL | | Mgmt. Allow | +============+
+====+ +---------+ +-------------+
^ ^
| |
v v
+========================================================+
| TALI State Machine |
+========================================================+
^ ^ ^ ^
| | | |
v | | |
+---------+ | | |
| Received| +-----------------+ +-----------+ +------------+
| 'test', | | Connection est. | | Protocol | | T1 Expired |
| 'allo', | | Connection lost | | Violation | | T2 Expired |
| 'proh', | | | | | | T3 Expired |
| 'proa', | +-----------------+ +-----------+ | T4 Expired |
| 'moni', | ^ ^ +------------+
| 'mona', | | | ^
| 'mgmt', | | | |
| 'xsrv', | | | |
| 'spcl', | | | |
| or | +========================================+
| Service | | IMPLEMENTATION |
| Message | | DEPENDENT |
+---------+ +========================================+
^
|
v
+============+
| PEER |
| |
+============+
Figure 10: Overview of Inputs to the TALI 2.0 State Machine
4.2 TALI Version Identification
The TALI 1.0 specification did not provide a simple means to perform
TALI version identification. However, the general purpose 'moni'
message from 1.0 can be used to solve this problem in 2.0.
Recall from 1.0 that the 'moni' message was very loosely defined in
the 1.0 spec:
* The primary purpose of the 'moni' message was to provide a general
purpose ECHO capability. It was envisioned that an important task
that the ECHO capability could provide would be to measure Round
Trip TALI/TALI processing time.
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* The data portion of the 'moni' message could be from 0-200 bytes
long. The use of the data area was completely implementation
specific.
* There were no requirements that an implementation ever send a
'moni'.
* If an implementation did send 'moni', it should use the T4 timer
to control the frequency of the outgoing 'moni'.
* The receiver of the 'moni' should not make any assumptions as to
the data portion of the 'moni'. The receiver should simply
convert the 'moni' into a 'mona' and return the message with the
same data portion.
TALI 2.0 implementations should use the 'moni' message to provide
version identification as per the following bullets:
* The primary purpose of the 'moni' message is now twofold:
* To provide version identification
* To continue to provide a general purpose ECHO capability that
can be used to measure Round Trip time or perform other
implementation specific tasks.
* The data portion of the 'moni' message is now divided into 2
portions
* A portion dedicated to version identification, 12 bytes long,
with a specific format that must be followed
* Followed by a free format section that can be used in a
completely implementation specific manner.
* The overall length of the data portion for a 'moni' should still
not exceed 200 bytes. This is required to maintain backward
compatibility with 1.0 implementations that may check for a
maximum length of 200 bytes on the 'moni' opcode.
* If a TALI implementation wants to identify itself as a version 2.0
node, it must send a 'moni' encoded as per Table 8. Every 'moni'
it sends should conform to the encoding in Table 8. The version
label should not change from 'moni' to 'moni'. The data following
the version label can change from 'moni' to 'moni' and can
continue to be used for RTT calculations, or other purposes.
* If a TALI implementation is trying to determine if the far end of
the TALI connection has implemented version 2.0, the
implementation must examine any received 'moni' messages that
arrive from the far end and see if they conform to the new
stricter 'moni' encoding in Table 8. On receiving 'moni', a TALI
2.0 node will compare the 12 bytes of data in the VER LABEL field
with a list of predetermined strings to determine the
functionality of the TALI node it is connected to. If the data
doesn't match any of the predetermined strings, the Far End is
assumed to be a TALI 1.0 node.
* Each TALI implementation must assume that the far end of the
connection is a 1.0 implementation until an arriving 'moni'
announces that the far end supports TALI version 2.0. If a 'moni'
never arrives, the implementation knows the far end has
implemented version 1.0 of the specification.
* TALI 1.0 implementations can receive newly encoded 'moni' messages
and simply ignore the data. The 1.0 implementations will continue
to operate as if the far end is always a 1.0 node (ignore the data
Sprague et al Informational - December 2000 40
draft-benedyk-sigtran-tali-01 June 2000
portion of the 'moni', convert 'moni' to 'mona', and return the
'mona').
* The next section provides more information regarding backwards
compatibility (2.0 implementations connected to devices that
implemented version 1.0 of the specification).
+------------------------------------------------------------------+
| Octets | Field Name | Description | Field Type |
+------------------------------------------------------------------+
| 0..3 | SYNC | 'TALI' |4 byte ASCII|
+------------------------------------------------------------------+
| 4..7 | OPCODE | 'moni' |4 byte ASCII|
+------------------------------------------------------------------+
| 8..9 | LENGTH | Length (includes the version | Integer |
| | | label and data fields) | |
+------------------------------------------------------------------+
| 10..21 | Ver. Label | 'vers xxx.yyy' | 12 byte |
| | See note | | ASCII |
+------------------------------------------------------------------+
| 22..X | DATA | Vendor Dependent | Variable |
| | | Maximum length of this | |
| | | message (as coded in octets 8| |
| | | -9, and stored in bytes 10-X)| |
| | | should not exceed 200 bytes. | |
+------------------------------------------------------------------+
Table 8: Version Control 'moni' Message
NOTE: xxx.yyy = provides the Major and Minor release number of the
TALI specification being implemented.
001.000 = Tali version 1.0
002.000 = Tali version 2.0 // this specification.
002.001 = Tali version 2.1 // a minor change to 2.0
003.000 = Tali version 3.0
and so on.
The 'vers 002.000' field is an 12 byte field of field type 'ascii
text'. As such, 'v' should be the first byte of the field that is
transmitted out the wire.
4.3 Backwards Compatibility
As part of adding new functionality to the TALI specification,
backwards compatibility from TALI version 2.0 to version 1.0 is
required. Backwards compatibility is important since TALI 2.0 nodes
may be connected to far ends that only support version 1.0; it is
important that these 2 implementations continue to inter-operate,
and that the 2.0 node falls back to supporting only 1.0 opcodes in
this situation.
The previous section described how a TALI 2.0 implementation can use
the 'moni' it sends to identify itself as a 2.0 node and how it can
use the 'moni' it receives to determine if the far end is also a 2.0
node. In addition to the discussion in the previous section, the
Sprague et al Informational - December 2000 41
draft-benedyk-sigtran-tali-01 June 2000
following bullets provide details regarding how backwards
compatibility must be achieved:
* As documented in the version 1.0 specification, TALI 1.0
implementations that receive TALI messages with 'mgmt', 'xsrv',
and 'spcl' opcodes will treat the message as a Protocol Violation
(invalid opcode received). The Protocol Violation will cause the
socket to be dropped immediately.
* It is therefore required that a 2.0 implementation only send
'mgmt', 'xsrv', and 'spcl' opcodes, after it has used a received
'moni' message to determine that the far end is a 2.0 (or later)
implementation and has identified itself as a 2.0 (or later)
implementation.
* Each TALI 2.0 implementations must use the 'moni' as described in
the previous section to identify themselves as 2.0, and to learn
if the far end is 2.0.
* Each TALI 2.0 implementation should maintain a variable as part of
its state machine, 'far_end_version'. The 'far_end_version'
should be initialized to 1.0 when the socket is established. Each
time a 2.0 implementation receives 'moni', it should update the
'far_end_version' variable. If the 'moni' did not contain a
version label, the 'far_end_version' should be reset to 1.0. If
the 'moni' did contain a version label for 2.0 (or a later
version), the 'far_end_version' should be set accordingly.
* Each time a 2.0 implementation receives a new 2.0 opcode ('mgmt',
'xsrv', and 'spcl') from the far end, it should examine the
'far_end_version'. If the 'far_end_version' indicates the far end
is a 1.0 implementation, the received TALI message should be
treated as a Protocol Violation (invalid opcode). If the
'far_end_version' is 2.0 (or later), the 2.0 implementation should
process the received 'mgmt/xsrv/spcl' according to that nodes
capabilities for that opcode.
* Each time a 2.0 implementation receives a request to send a TALI
message with a 2.0 opcode ('mgmt/xsrv/spcl') from a higher layer
of software, it should examine the 'far_end_version'. If the
'far_end_version' indicates the far end is a 1.0 implementation,
the request to send the 2.0 opcode should be denied or ignored (an
implementation decision) and the 2.0 opcode must NOT be sent to
the far end. If the 'far_end_version' indicates the far end is
2.0 (or later), the request can be satisfied and the TALI message
with the 2.0 opcode can be sent to the far end.
* Each TALI 2.0 implementation can provide a varying level of
support for each of the three new 2.0 opcodes ('mgmt/xsrv/spcl').
In other words, an implementation may wish to only support SOME OF
the primitives within the new opcodes. The level of support for
each 2.0 opcode ('mgmt/xsrv/spcl') is independent of the other two
2.0 opcodes.
* The basic message structure for TALI messages using the new 2.0
opcodes is presented in Table 9.
* The minimal level o |
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