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Network Working Group Brian Bidulock
INTERNET-DRAFT OpenSS7 Corporation
Expires in six months January 10, 2002
Load Selection
for
Signalling User Adaptation Layers
<draft-bidulock-sigtran-loadsel-00.txt>
Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 or RFC 2026. Internet-Drafts are
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Abstract
This Internet-Draft describes Load Selection for Signalling User
Adaptation Protocols [M3UA, SUA, TUA], which permits an Application
Server Processes (ASP) to indicate its placement within an
Application Server and permits an Signalling Gateway (SG) to
distribute traffic over ASPs in Application Servers under Application
Server Process (ASP) control.
1. Introduction
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1.1. Scope
This Internet-Draft provides parameters and associated procedures in
extension to the parameters and procedures of the Signalling User
Adaptation Layers (UAs) [M3UA, SUA, TUA], for the purpose of
permitting Application Server Process control over placement of ASPs
within Application Servers (or Load Groups [LOADGRP]) as part of the
normal procedures of these UA protocols.
UA implementations supporting Load Selection are intended to be
compatible with UA implementations not supporting Load Selection.
1.2. Terminology
Load Selection supplements the terminology used in the UA documents
[M2UA...TUA] by adding the following terms:
Load Selector (LS) - an identifier that uniquely identifies a
partition of traffic flow within an Application Server. This
identifier is only guaranteed unique within the scope of an
Application Server and MAY need to be combined with a Routing
Context to uniquely define a traffic flow at a Signalling
Gateway.
Signalling User Adaptation Layer (UA) - one or more of the Stream
Control Transmission Protocol (SCTP) [RFC 2960] SS7 Signalling
User Adaptation Layers [M3UA, SUA, TUA] supporting the concept
of a Routing Context.
1.3. Overview
UA procedures with regard to traffic distribution and ASP traffic
management provide a mechanism to select the algorithm for
coordinating state and distributing traffic over a number of
Application Server Processes (ASPs) serving an Application Server
(AS). These existing procedures provide only simplified distribution
approaches which are not amenable in the following situations:
o Connection- or Transaction-Oriented traffic flows which group the
messages corresponding to a connection or a transaction.
o Large scale systems that need to adapt to dynamic traffic loading.
o Systems that need dynamic reconfiguration under ASP control for
maintenance or fail-over purposes.
Load Selection for the Signalling User Adaptation Layers [M3UA, SUA,
TUA] permits close control over the placement and grouping of
Application Server Processes serving an Application Server that
provides for load selection placement within an Application Server: a
capability not present in the existing scheme.
Under existing UA traffic distribution, there is no mechanism which
permits an Application Server Process (ASP) to indicate which of a
number of ASPs it wishes to override in an Override AS. There is
also no mechanism which permits an ASP to indicate which traffic
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flows it wishes to process within a Load-share or Broadcast AS.
Load Selection provides the ability for the ASP itself to control its
placement within an AS, be informed of the failure of ASPs serving
other load selections within the AS, and chose to activate itself to
receive additional load selections within the AS. Load Selection
also permits grouping of ASPs within a load selection.
1.3.1. Non-Load Selection Traffic Distribution
Figure 1 illustrates the existing traffic distribution algorithm that
is used across the Signalling User Adaptation Layers.
When an SGP distributes a Signalling User Adaptation Layer message
toward the Application Server based on the Routing Key, it selects an
ASP that is active for the AS according to a Traffic Mode Type that
is associated with the AS. The Traffic Mode Type describes three
general distribution algorithms: Override, Load-share and Broadcast.
The detailed actions taken for these distribution algorithms are
described in Section 4 of the Signalling User Adaptation Layer
specifications [M3UA, SUA, TUA]; however, they can be summarized as
follows:
____
Traffic /....\
Mode Type ____|__....|
| |...|
_______ /------------------>| ASP |...|
| |---\ |_______|...|
| SGP |--\ \ ____|__....|
|_______|-\ \ \ | |...|
\ \ \ \------------>| ASP |...|
_______ \ \ \ |_______|...|
| | \ \ \ ____|__....| Application
| SGP | \ \ \ | |...| Server
|_______| \ \ \---------->| ASP |...|
\ \ |_______|...|
\ \ ____|__....|
\ \ | |...|
\ \-------->| ASP |...|
\ |_______|...|
\ ____|__....|
\ | |...|
\------>| ASP |...|
|_______|...|
|......|
\____/
Figure 1. Non-Load Selection Traffic Distribution
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Override:- When distributing messages to an Override Application
Server, the SGP selects the ASP which is active for the
Application Server. In an Override Application Server, at most
one ASP can be active for the AS at any given point in time.
The active ASP for the AS is selected.
A major limitation of the Override AS that is relieved by Load
Selection is that only one ASP can be active within an
Application Sever. This does not work when the number of ASPs
required to service an AS is greater than one.
Load-share:- When distributing messages to a Load-share Application
Server, the SGP selects one of the ASPs that are active for the
Application Server using an implementation dependent load-
sharing algorithm based on some unspecified aspect of the
traffic or static configuration data.
A major limitation of the Load-share AS is that each ASP in the
Application Server must be capable of handling any (and all)
traffic within the Load-share AS. Under the current approach
an SGP does not distinguish between ASPs in a Load-share AS
and, aside from perhaps attempting to equally distribute
traffic load over the available ASPs, it is not possible for
the ASPs to control which traffic flows it receives. This
causes management difficulties when the number of ASPs required
to service an AS is large, but the number of spare ASPs is
small.
Broadcast:- When distributing messages to a Broadcast Application
Server, the SGP sends a copy of the message to each of the ASPs
that are active for the Application Server. The ASPs
themselves decide which, if any, of the ASPs will process the
message.
A major limitation of the Broadcast AS is that each ASP
receives each message. This does not scale well when the
number of ASPs needed to service an AS is large.
Load Selection enhances the traffic distribution algorithms of the
existing Signalling User Adaptation Layers by providing ASP control
over its placement within an AS by load selection.
1.3.2. Load Selection Traffic Distribution
Figure 2 illustrates the Load Selection traffic distribution
algorithms that are used across the Signalling User Adaptation Layers
as a result of the Load Selection messages and procedures.
Load Selection introduces the concept of a Load Selector. A Load
Selector is an identifier that is used to identify a traffic flow
within (or across) Application Server(s). Signalling Gateway
Processes (SGPs) distribute traffic first over Load Selector and then
distribute traffic within the Load Selector. Each Load Selector
describes and is identified by an identifier within the Application
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Traffic Load ____
Mode Type Selection /....\
____|__....|
LS1 | |...|
_______ /------------------>| ASP |...|
| |---\ |_______|...|
| SGP |--\ \ ____|__....|
|_______|-\ \ \ LS2 | |...|
\ \ \------------>| ASP |...|
_______ \ \ |_______|...|
| | \ \ ____|__....| Application
| SGP | \ \ LS3 | |...| Server
|_______| \ \---------->| ASP |...|
\ |_______|...|
\ ____|__....|
\ | |...|
\-------->| ASP |...|
| |_______|...|
| LS4 ____|__....|
| | |...|
\-------->| ASP |...|
|_______|...|
|......|
\____/
Figure 2. Load Selection Traffic Distribution
Server. The Load Selector identifies the traffic flows that will be
distributed to ASPs associated with the Load Selector within an
Application Server.
When an SGP distributes a Signalling User Adaptation Layer message
toward an Application Server based on the Routing Key, it first
derives a Load Selector according to a UA-specific, AS-specific and
implementation-dependent load selection algorithm. This load
selection algorithm is configured at the SGP and may consist, for
example, of the Signalling Link Selection (SLS) [Q.704] value
contained in the message for distribution.
Once the SGP has determined Load Selector to which the message
corresponds, an ASP that is active for Load Selector within the AS is
selected. When multiple ASPs are active for the same Load Selection
within an AS, the SGP uses the traffic handling mode based on the
Traffic Mode Type associated with the Application Server to choose
the ASP within the load selection.[1]
Under Load Selection, the Traffic Mode Type continues to describe
three general distribution algorithms: Override, Load-share and
Broadcast. The change in the behavior of the SGP when selecting an
ASP for traffic distribution introduced by Load Selection is that the
SGP also takes into account the concept of a Load Selector. The Load
Selection procedures are summarized as follows:
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Override:- When distributing messages to an Override Application
Server, the SGP first determines the Load Selector associated
with the message. The SGP then distributes the message to the
ASP that is active for the Load Selector within the AS. In an
Override Application Server, at most one ASP can be active for
the AS within a Load Selector at any given point in time. The
active ASP associated with the Load Selector for the AS is
used.
Load-share:- When distributing messages to a Load-share Application
Server, the SGP first determines the Load Selector associated
with the message. The SGP then selects one of the active ASPs
associated with the Load Selector within the AS using an
implementation dependent load-sharing algorithm based on some
unspecified aspect of the traffic or static configuration data.
Broadcast:- When distributing messages to a Broadcast Application
Server, the SGP first determines the Load Selector associated
with the message. The SGP then selects all of the active ASPs
associated with the Load Selector within the AS and sends a
copy of the message to each ASP. (The ASPs themselves decide
which ASP(s) will process the message.)
The result of this extension is that Application Server Processes
have control over their placement within an Application Server and
can control the traffic that they receive by registering and
activating for specific Load Selectors within the AS.
1.4. Sample Configurations
2. Conventions
The keywords MUST, MUST NOT, REQUIRED, SHALL, SHALL NOT, SHOULD,
SHOULD NOT, RECOMMENDED, NOT RECOMMENDED, MAY, and OPTIONAL, when
they appear in this document, are to be interpreted as described in
[RFC 2119].
3. Protocol Elements
The following subsections describe the parameters which are added by
this extension, their format and the message in which they are used.
3.1. Parameters
Load Selection adds one new parameter: the Load Selector parameter.
3.1.1. Load Selector
The Load Selector parameter is used in the ASPAC, ASPAC ACK, ASPIA,
ASPIA ACK, and NTFY messages. It is used to identify the placement
of the ASP within an Application Server. It identifies the Load
Selector for which the ASP is registering, activating or
deactivating, or when the SG is indicating or notifying of an ASP
state change.
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The Load Selector parameter is formatted as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag = 0xXXXX | Length = 8 |
+---------------------------------+-----------------------------+
| Load Selector 1 |
+---------------------------------+-----------------------------+
\ \
/ ... /
\ \
+---------------------------------+-----------------------------+
| Load Selector n |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
EDITOR'S NOTE:- The parameter tag values shown as 0xXXXX)
above will be assigned by IANA within the common parameter
range of the SIGTRAN UAs and may change its value in further
versions of this document.
The Load Selector parameter contains the following fields:
Load Selector field: n x 32-bits (unsigned integer)
The Load Selector field is an identifier, that MUST be unique
within an Application Server and MAY be unique within an
administrative domain, that identifies the placement or Load
Selection of an ASP within an AS. This identifier in conjunction
with any Application Server identifier (i.e, Routing Context)
identifies the traffic flow for which an ASP is registering,
activating or deactivating, or for which an SG is providing
notification of an ASP or AS state change.
When the Load Selector parameter is included in the ASPAC, ASPAC ACK,
ASPIA, ASPIA ACK or NTFY message, one Routing Context representing a
single Application Server SHOULD be associated (specified or implied)
with the message.
3.2. Messages
Load Selection adds the Load Selector parameter as an OPTIONAL
parameter to be used in conjunction with the common Traffic Mode Type
in the following messages: [2]
ASPAC ASP Active message
ASPAC Ack ASP Active Ack message
ASPIA ASP Inactive message
ASPIA Ack ASP Inactive Ack message
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NTFY Notify message
3.2.1. ASP Active (ASPAC)
Load Selection supplements the ASPAC message by permitting the
following optional parameters to be included in the message:
Extension Parameters
-----------------------------------------
Load Selector Optional
The format of the resulting ASPAC message is as follows: [2]
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag = 0x000b | Length = 8 |
+- - - - - - - - - - - - - - - - -+- - - - - - - - - - - - - - -+
| Traffic Mode Type |
+---------------------------------+-----------------------------+
| Tag = 0xXXXX | Length |
+- - - - - - - - - - - - - - - - -+- - - - - - - - - - - - - - -+
\ \
/ Load Selector /
\ \
+---------------------------------+-----------------------------+
| Tag = 0x0006 | Length = 8 |
+- - - - - - - - - - - - - - - - -+- - - - - - - - - - - - - - -+
\ \
/ Routing Context /
\ \
+---------------------------------+-----------------------------+
| Tag = 0x0004 | Length |
+- - - - - - - - - - - - - - - - -+- - - - - - - - - - - - - - -+
\ \
/ Info String /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
EDITOR'S NOTE:- The parameter tag values shown as 0xXXXX)
above will be assigned by IANA within the common parameter
range of the SIGTRAN UAs and may change its value in further
versions of this document.
No other changes to the ASPAC message format are provided by this
extension.
The Load Selector parameter is used by the ASP in the ASPAC message
to indicate the range of traffic for which the ASP is activating.
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The Application Servers for which the Load Selectors apply is either
indicated in the ASPAC message by providing the associated Routing
Contexts or, if there is no Routing Context parameter in the message,
the associated Application Servers are implied by SGP and ASP
configuration data. (See Section 4.1.5 - "ASP Active Procedures".)
3.2.2. ASP Active Ack (ASPAC ACK)
Load Selection supplements the ASPAC ACK message by permitting the
following optional parameters to be included in the message:
Extension Parameters
-----------------------------------------
Load Selector Optional
The format of the resulting ASPAC ACK message is as follows: [2]
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag = 0x000b | Length = 8 |
+- - - - - - - - - - - - - - - - -+- - - - - - - - - - - - - - -+
| Traffic Mode Type |
+---------------------------------+-----------------------------+
| Tag = 0xXXXX | Length |
+- - - - - - - - - - - - - - - - -+- - - - - - - - - - - - - - -+
\ \
/ Load Selector /
\ \
+---------------------------------+-----------------------------+
| Tag = 0x0006 | Length = 8 |
+- - - - - - - - - - - - - - - - -+- - - - - - - - - - - - - - -+
\ \
/ Routing Context /
\ \
+---------------------------------+-----------------------------+
| Tag = 0x0004 | Length |
+- - - - - - - - - - - - - - - - -+- - - - - - - - - - - - - - -+
\ \
/ Info String /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
EDITOR'S NOTE:- The parameter tag values shown as 0xXXXX)
above will be assigned by IANA within the common parameter
range of the SIGTRAN UAs and may change its value in further
versions of this document.
No other changes to the ASPAC ACK message format are provided by this
extension.
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The Load Selector parameter is used by the SGP in the ASPAC ACK
message to indicate the range of traffic for which the SGP has
activated the ASP. The Application Servers for which the Load
Selectors apply is either indicated in the ASPAC message by providing
the associated Routing Contexts or, if there is no Routing Context
parameter in the message, the associated Application Servers are
implied by SGP and ASP configuration data. (See Section 4.1.5 - "ASP
Active Procedures".)
3.2.3. ASP Inactive (ASPIA)
Load Selection supplements the ASP Inactive (ASPIA) message by
permitting the following parameters to be included in the message:
Extension Parameters
-----------------------------------------
Load Selector Optional
The format of the resulting ASPIA message is as follows: [2]
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag = 0xXXXX | Length |
+- - - - - - - - - - - - - - - - -+- - - - - - - - - - - - - - -+
\ \
/ Load Selector /
\ \
+---------------------------------+-----------------------------+
| Tag = 0x0006 | Length = 8 |
+- - - - - - - - - - - - - - - - -+- - - - - - - - - - - - - - -+
\ \
/ Routing Context /
\ \
+---------------------------------+-----------------------------+
| Tag = 0x0004 | Length |
+- - - - - - - - - - - - - - - - -+- - - - - - - - - - - - - - -+
\ \
/ Info String /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
EDITOR'S NOTE:- The parameter tag values shown as 0xXXXX)
above will be assigned by IANA within the common parameter
range of the SIGTRAN UAs and may change its value in further
versions of this document.
No other changes to the ASPIA message format are provided by this
extension.
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The Load Selector parameter is used by the ASP in the ASPIA message
to indicate the range of traffic for which the ASP is deactivating.
The Application Servers for which the Load Selectors apply is either
indicated in the ASPAC message by providing the associated Routing
Contexts or, if there is no Routing Context parameter in the message,
the associated Application Servers are implied by SGP and ASP
configuration data. (See Section 4.1.6 - "ASP Inactive Procedures".)
3.2.4. ASP Inactive Ack (ASPIA ACK)
Load Selection supplements the ASP Inactive Ack (ASPIA ACK) message
by permitting the following parameters to be included in the message:
Extension Parameters
-----------------------------------------
Load Selector Optional
The format of the resulting ASPIA ACK message is as follows: [2]
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag = 0xXXXX | Length |
+- - - - - - - - - - - - - - - - -+- - - - - - - - - - - - - - -+
\ \
/ Load Selector /
\ \
+---------------------------------+-----------------------------+
| Tag = 0x0006 | Length = 8 |
+- - - - - - - - - - - - - - - - -+- - - - - - - - - - - - - - -+
\ \
/ Routing Context /
\ \
+---------------------------------+-----------------------------+
| Tag = 0x0004 | Length |
+- - - - - - - - - - - - - - - - -+- - - - - - - - - - - - - - -+
\ \
/ Info String /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
EDITOR'S NOTE:- The parameter tag values shown as 0xXXXX)
above will be assigned by IANA within the common parameter
range of the SIGTRAN UAs and may change its value in further
versions of this document.
No other changes to the ASPIA ACK message format are provided by this
extension.
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The Load Selector parameter is used by the SGP in the ASPIA ACK
message to indicate the range of traffic for which the SGP has
deactivated the ASP. The Application Servers for which the Load
Selectors apply is either indicated in the ASPAC message by providing
the associated Routing Contexts or, if there is no Routing Context
parameter in the message, the associated Application Servers are
implied by SGP and ASP configuration data. (See Section 4.1.6 - "ASP
Inactive Procedures".)
3.2.5. Error (ERR)
Load Selection supplements the Error (ERR) message by adding the
following values to the common mandatory Error Code parameter in the
ERR message:
0xYY Invalid Load Selector
EDITOR'S NOTE:- The Error Code value shown as 0xYY) above
will be assigned by IANA as a value of the common Error Code
parameter for SIGTRAN UAs and may change its value in further
versions of this document.
These new error codes are interpreted as follows: [2]
The "Invalid Load Selector" error would be sent in an ERR message if
the SG determines that one or more Load Selectors in the Load
Selector parameter provided by the ASP is invalid, is not
configured, or cannot be supported.
No other changes to the ERR message or Error Code parameter format
are provided by this extension. See Section 4 for extension
procedures associated with the ERR message.
3.2.6. Notify (NTFY)
Load Selector supplements the Notify (NTFY) message by permitting the
following parameters to be included in the message:
Extension Parameters
-----------------------------------------
Load Selector Optional
The format of the resulting NTFY message is as follows: [2]
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag = 0x000d | Length = 8 |
+- - - - - - - - - - - - - - - - -+- - - - - - - - - - - - - - -+
| Status Type | Status Information |
+---------------------------------+-----------------------------+
| Tag = 0x0012 | Length = 8 |
+- - - - - - - - - - - - - - - - -+- - - - - - - - - - - - - - -+
| ASP Identifier |
+---------------------------------+-----------------------------+
| Tag = 0xXXXX | Length |
+- - - - - - - - - - - - - - - - -+- - - - - - - - - - - - - - -+
\ \
/ Load Selector /
\ \
+---------------------------------+-----------------------------+
| Tag = 0x0006 | Length = 8 |
+- - - - - - - - - - - - - - - - -+- - - - - - - - - - - - - - -+
\ \
/ Routing Context /
\ \
+---------------------------------+-----------------------------+
| Tag = 0x0004 | Length |
+- - - - - - - - - - - - - - - - -+- - - - - - - - - - - - - - -+
\ \
/ Info String /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
EDITOR'S NOTE:- The parameter tag values shown as 0xXXXX)
above will be assigned by IANA within the common parameter
range of the SIGTRAN UAs and may change its value in further
versions of this document.
No other changes to the NTFY message format are provided by this
extension.
The Load Selector parameter is used by the SGP in the NTFY message to
indicate the traffic load positions which led to or have contributed
to the change in state of an associated Application Server when
sending a NTFY message that indicates and Application Server state
change. The Application Servers for which the Load Selectors apply
is either indicated in the NTFY message by providing the associated
Routing Contexts or, if there is not Routing Context parameter in the
message, the associated Application Servers are implied by SGP and
ASP configuration data. (See Section 4.1.7 - "Notification
Procedures".)
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4. Procedures
Load Selection provides for an additional level of control over the
traffic distribution patterns within an Application Server. Load
Selection provides the Load Selector parameter which may be
optionally included in the ASPAC, ASPAC ACK, ASPIA, ASPIA ACK and
NTFY messages. In addition, it provides procedures for use of the
Load Selector parameter in association with these messages.
4.1. AS and ASP State Maintenance
In addition to the SGP maintaining the state of each remote ASP in
each Application Server that the ASP is configured to receive
traffic, under Load Selection, SGP MAY also maintain the state of
each remote ASP in each Load Selector within an Application server
that the ASP is configured to receive traffic. Aside from the
procedures described in Section 4.1.7 "Notification Procedures", no
management procedures are provided by Load Selection for maintaining
the state of a Load Selector within an Application Server. The Load
Selector state is maintained separate from the ASP and AS states.
4.1.1. ASP State
Load Selection uses the existing UA [M3UA, SUA, TUA] definitions and
procedures with regard to ASP State.
4.1.2. AS State
The state of the Application Server is maintained in the Signalling
User Adaptation Layer on the SGPs. The state of the Application
Server changes due to ASP state transitions. The possible states of
an Application Server using Load Selection are:
AS-DOWN: The Application Server is unavailable. This state
implies that all related ASPs are in the ASP-DOWN
state for this AS. Initially, the AS will be in this
state. An Application Server is in the AS-DOWN state
when it is removed from a configuration.
AS-INACTIVE: The Application Server is available but no
application traffic is active (i.e, one or more
related ASPs are in the ASP-INACTIVE state, but there
is no ASP in the ASP-ACTIVE state). The recovery
timer T(r) is not running or has expired.
AS-ACTIVE: The Application Server is available and application
traffic is active. This state implies that there is
at least one ASP in the ASP-ACTIVE state within the
AS.
AS-PENDING: An active ASP has transition to ASP-INACTIVE or ASP-
DOWN and it was the last remaining active ASP for a
Load Selector in the AS. A recovery timer T(r)
SHOULD be started and all incoming signalling
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messages SHOULD be queue by the SGP for each of the
Load Selectors for which there is no ASP in the ASP-
ACTIVE state. If an ASP becomes ASP-ACTIVE for each
Load Selector in the AS before T(r) expires, the AS
is moved to the AS-ACTIVE state and all the queued
messages for the Load Selector will be sent to the
newly active ASPs on each Load Selector.
4.1.3. ASP Up Procedures
When an SGP receives an ASP Up messages from an ASP and the ASP is
configured at the SGP in one or more Load Selectors associated with
one or more Application Servers, if the ASP is not already in the
ASP-INACTIVE state for the associated Application Servers, the SGP
moves the ASP into the ASP-INACTIVE state for the configured Load
Selectors within the associated Application Servers. In any event,
the SGP responds with an ASP Up Ack message.
If the ASP transition to the ASP-INACTIVE state within these Load
Selectors results in a state change in the associated Application
Servers, the SGP moves the Application Server to the AS-INACTIVE
state. If the ASP transition to the ASP-INACTIVE state for the given
Load Selectors within an associated Application Server results in a
change in state of the AS (or the Load Selectors associated with the
AS), the SGP also follows the "Notification Procedures" (described in
Section 4.1.7) for the Application Server.
Otherwise, the "ASP Up Procedures" described by the UAs [3] apply
also to Load Selection.
4.1.4. ASP Down Procedures
When an SGP receives an ASP Down messages from an ASP and the ASP is
configured at the SGP in one or more Load Selectors associated with
one or more Application Servers, if the ASP is not already in the
ASP-DOWN state for the associated Application Servers, the SGP moves
the ASP to the ASP-DOWN state for the configured Load Selectors
within the associated Application Servers. In any event, the SGP
responds with an ASP Down Ack.
If the ASP transition to the ASP-DOWN state within these Load
Selectors results in a state change in the associated Application
Servers, the SGP moves the Application Server to the AS-DOWN state.
Otherwise, the "ASP Down Procedures" described by the UAs [3] apply
also to Load Selection.
4.1.5. ASP Active Procedures
When an ASP wishes to activate for a set of Load Selectors associated
with an Application Server, it includes the Load Selector parameter
in the ASPAC message.
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When an SGP receives and ASPAC message requesting activation for a
set of Load Selectors within an AS or the SG otherwise activates the
ASP for a set of Load Selectors within an AS, the SG sends an ASPAC
ACK message including the Load Selectors for which the ASP has been
activated. If the SGP is responding to an ASP that included Load
Selectors in the ASPAC message, the SG MUST include the Load
Selectors in the response ASPAC ACK message.
If the Load Selectors included in an ASPAC message contains invalid
information or indicates an unsupported Load Selector, or a Load
Selector parameter required by the SGP is missing, the SGP replies to
the ASPAC message with an ERR("Invalid/Unsupported/Missing Load
Selector") message and takes no further action with regard to AS or
ASP state.
The Application Servers associated with the Load Selectors is
indicated in the ASPAC (ACK) message by Routing Context or, when the
Routing Context parameter is missing from the ASPAC (ACK) message, is
implied by ASP and SGP configuration data. When the Load Selector
parameter is included in the ASPAC (ACK) message, the Routing Context
parameter or implicit configuration data SHOULD be associated with a
single Application Server.
If the ASP transition to the ASP-ACTIVE state for the given Load
Selectors within an associated Application Server results in a change
in state of the AS (or the Load Selectors associated with the AS),
the SGP follows the "Notification Procedures" (described in Section
4.1.7) for the Application Server.
Otherwise, the "ASP Active Procedures" described by the UAs [3] apply
also to Load Selection.
4.1.6. ASP Inactive Procedures
When an ASP wishes to deactivate for a set of Load Selectors
associated with an Application Server, it includes the Load Selector
parameter in the ASPIA message.
When an SGP receives an ASPIA message requesting deactivation for a
set of Load Selectors within an AS or the SG otherwise deactivates
the ASP for a set of Load Selectors within an AS, the SG sends an
ASPIA ACK message including the Load Selectors for which the ASP has
been deactivated. If the SGP is responding to an ASP that included
Load Selectors in the ASPIA message, the SG MUST include the Load
Selectors in the response ASPIA ACK message.
If the SGP receives an ASPIA message from an ASP that is active for a
set of Load Selectors associated with the Application Server for
which the ASP is requesting deactivation, and the Load Selector
parameter is not present in the ASPIA message, the SGP will interpret
this as a request to deactivate the ASP for all the Load Selectors
associated with the Application Server for which the ASP is active.
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If the Load Selectors included in an ASPAC message contains invalid
information or indicates an unsupported Load Selector, the SGP
replies to the ASPAC message with an ERR("Invalid/Unsupported/Missing
Load Selector") message and takes no further action with regard to AS
or ASP state.
The Application Servers associated with the Load Selectors is
indicated in the ASPIA (ACK) message by Routing Context or, when the
Routing Context parameter is missing from the ASPIA (ACK) message, is
implied by ASP and SGP configuration data. When the Load Selector
parameter is included in the ASPIA (ACK) message, the Routing Context
parameter or implicit configuration data SHOULD be associated with a
single Application Server.
If the ASP transition to the ASP-INACTIVE state for the given Load
Selectors within an associated Application Server results in a change
in state of the AS (or the Load Selectors associated with the AS),
the SGP follows the "Notification Procedures" (described in Section
4.1.7) for the Application Server.
Otherwise, the "ASP Inactive Procedures" described by the UAs [3]
apply also to Load Selection.
4.1.7. Notify Procedures
4.1.7.1. AS State Change
When an ASP makes a state transition and is configured for a set of
Load Selectors in one or more Application Servers, the ASP state
transition may result in a change to the state of the associated
Application Servers, or Load Selectors within those AS, at the SGP.
When a recovery timer T(r) expires, the associated Application Server
will transition from the AS-PENDING state to the AS-INACTIVE state.
Whenever an AS changes state, or the condition of the AS Load
Selectors perpetuating the current AS state changes, the SGP MUST
notify all ASPs not in the ASP-DOWN state configured for the
Application Server by sending a Notify (NTFY) message to each
indicating the state of the Application Server in the Status
Information field of the Status parameter in the NTFY message.
When an Application Server is configured for Load Selection, the SGP
MUST also include a list of Load Selectors for which the Application
Server is configured that caused the AS state change or is
perpetuating the AS state.
The SGP includes the Routing Context that identifies the Application
Server for which the NTFY message is being sent. If, however, the
ASP is not configured for more than one Application Sever, the
Routing Context MAY be excluded from the message as it is implied by
configuration data.
Otherwise, the "Notification Procedures" described by the UAs [3]
apply also to Load Selection.
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Examples are given in Section 5.
4.1.7.2. ASP Override
Whenever an ASP becomes active for a Load Selector in an Override
Application Server, the Load Selector MUST be placed in a NTFY
message with a Status Information indicating "Alternate ASP active in
AS", along with the Routing Context for the associated AS and any ASP
Identifier associated with the ASP for which the notification is
being given.
Otherwise, the "Notification Procedures" described by the UAs [3]
apply also to Load Selection.
4.1.8. Registration Procedures
There is no specific registration procedure for Load Selection. It
can be conceived that the REG REQ and REG RSP message could be used
with extensions to the Routing Key that would permit the SGP to
return both a Routing Context and a Load Selector associated with a
given Routing Key. Such a Routing Key could include load selection
key fields such a Signalling Link Selection (SLS) [Q.704] for M3UA
[M3UA], Destination Local Reference (DLR) [Q.713] for SUA [SUA], and
Destination Transaction Id [Q.773] for TUA [TUA]. A registration
procedure is not currently described for Load Selection; however, a
registration procedure may be added to later revisions of this draft.
Otherwise, the "Registration Procedures" described by the UAs [3]
apply also to Load Selection.
4.2. Interworking Procedures
Load Selection supports the ASP Extension procedures described in
ASPEXT [ASPEXT] and defines the following ASP Extension value:
1 Load Selection Extension [LOADSEL]
The following procedres may be used where the ASPEXT procedures are
not used:
Whenever an ASP receives an ASPIA ACK not containing a Load Selector
parameter in response to an ASPAC containing the parameter, the ASP
will assume that the the SGP or IPSP does not support Load Selection
and MUST fall back to the non-Load Selection UA procedures.
5. Examples
Figure 3 illustrates the example configuration that is used for all
the examples in this section. The example configuration consist of:
o Two SGs (SG1 and SG2) acting as STPs in the SS7 network and
consisting (for example) of a single SGP. Each SG is connected to
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each of the ASPs in the example configuration.
o Four ASPs (ASP1, ASP2, ASP3 and ASP4). Each ASP is connected to
both of the SGs in the example configuration.
o One Application Server (AS1). The Traffic Mode Type of the
Application Server is different in each example.
o Three Load Selectors (LS1 and LS2) associated with the Application
Server. The traffic that corresponds to each Load Selectors is
different in each example.
SCTP
Associations ________ _________
_________ ............| | / \
| |..: .......| ASP1 | | AS1 |
| |..... : |________| | |
________| SG1 |....: : | ......... |
/| |...:: : ________ | : : |
\ / |_________| :::..:......| | | : LS1 : |
\ / | :: :......| ASP2 | | :.......: |
\ / | :: :: |________| | |
X | :: :: | |
/ \ | :: :: ________ | |
/ \ ____|____ ::...::.....| | | |
/ \ | |..:....::.....| ASP3 | | ......... |
_______\| |..:.....:: |________| | : : |
| SG2 |..:......: | : LS2 : |
| |..:..... ________ | :.......: |
|_________| :....:......| | | |
:......| ASP4 | | |
|________| \_________/
Figure 3. Example Configuration
5.1.1. Initialization
Figure 4 illustrates the common initialization procedure use for all
of the examples. Each ASP establishes an SCTP Association with SG1
and sends and ASP Up message to which it receives and ASP Up
response. The ASPs are not statically configured to serve specific
AS or LS within the AS, so no Notify messages are received. The same
sequence of messages are also exchanged with SG2.
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SG1 SG2 ASP1 ASP2 ASP3 ASP4 AS1
: : : : : : :
:<----:-Establish Association------>: : : : :
:<----:-ASPUP-----------------------: : : : :
:-----:-ASPUP ACK------------------>: : : : :
: : : : : : :
:<----:-Establish Association-------:---->: : : :
:<----:-ASPUP-----------------------:-----: : : :
:-----:-ASPUP ACK-------------------:---->: : : :
: : : : : : :
:<----:-Establish Association-------:-----:---->: : :
:<----:-ASPUP-----------------------:-----:-----: : :
:-----:-ASPUP ACK-------------------:-----:---->: : :
: : : : : : :
:<----:-Establish Association-------:-----:-----:---->: :
:<----:-ASPUP-----------------------:-----:-----:-----: :
:-----:-ASPUP ACK-------------------:-----:-----:---->: :
: : : : : : :
: : (Same message exchange for SG2) : : : :
: : : : : : :
Figure 4. Example - Initialization
5.2. M3UA with Override AS and Load Selection based on CIC
This example is for an M3UA configuration with the Application Server
(AS1) configured with a Traffic Mode Type of Override. The
Application Server (AS1) has associated with it a Routing Key (RK1)
that consists of a Destination Point Code that corresponds to the AS1
(MGC1) point code (PC1), an Originating Point Code that corresponds
to a remote MGC2 point code (PC2), and the SI value for ISUP (SI=5).
The Load Selectors (LS1 and LS2) correspond to two sets of CIC values
which correspond to two different trunk groups between MGC1 and MGC2
(TG1 and TG2).
5.2.1. Activation
Figure 5 illustrates activation of the ASPs for Load Selectors within
the Override Application Server. The sequence of events is as
follows:
(1) ASP1 sends an ASP Active message to SG1 identifying Load
Selector LS1 within Application Server AS1/RC1 and receives an
acknowledgment and a notification. Data is transferred
between the SG and ASP1 for Load Selection LS1 within AS1.
(2) ASP2 sends an ASP Active message to SG1 identifying Load
Selector LS2 within Application Server AS1/RC1 and receives an
acknowledgment and a notification. ASP1 also receives
notification that AS1/RC1 is active for LS2. Data is
transferred between the SG and ASP2 for Load Selection LS2
within AS1.
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(3) ASP3 sends an ASP Inactive message to SG1 identifying Load
Selector LS1 within Application Server AS1/RC1 and receives an
acknowledgment and a notification.
(4) ASP4 sends an ASP Inactive message to SG1 identifying Load
Selector LS1 and LS2 within Application Server AS1/RC1 and
receives an acknowledgment and a notification.
(5) The same exchange is repeated for SG2.
SG1 SG2 ASP1 ASP2 ASP3 ASP4 AS1
: : : : : : :
:<----:-ASPAC(LS1/RC1)--------------: : : : :
:-----:-ASPAC ACK(LS1/RC1)--------->: : : : :
:-----:-NTFY(AS_Act)(LS1/RC1)------>: : : : (LS1) :
: : : : : : :
:<----:-DATA----------------------->:<----:-----:-----:-------->:
: : : : : : :
:<----:-ASPAC(LS2/RC1)--------------:-----: : : :
:-----:-ASPAC ACK(LS2/RC1)----------:---->: : : :
:-----:-NTFY(AS_Act)(LS1,LS2/RC1)-->: : : : :
:-----:-NTFY(AS_Act)(LS1,LS2/RC1)---:---->: : : (LS2) :
: : : : : : :
:<----:-DATA------------------------:---->:<----:-----:-------->:
: : : : : : :
:<----:-ASPIA(LS1/RC1)--------------:-----:-----: : :
:-----:-ASPIA ACK(LS1/RC1)----------:-----:---->: : :
:-----:-NTFY(AS_Act)(LS1,LS2/RC1)---:-----:---->: : :
: : : : : : :
:<----:-ASPIA(LS1,LS2/RC1)----------:-----:-----:-----: :
:-----:-ASPIA ACK(LS1,LS2/RC1)------:-----:-----:---->: :
:-----:-NTFY(AS_Act)(LS1,LS2/RC1)---:-----:-----:---->: :
: : : : : : :
: : (Same message exchange for SG2) : : : :
: : : : : : :
Figure 5. M3UA Example - Activation
5.2.2. Failure of ASP1
Figure 6 illustrates the failure of ASP1. The sequence of events is
as follows:
(1) Data for LS1 within AS1 is exchanged between SG1 and ASP1.
Data for LS2 within AS1 is exchanged between SG1 and ASP2.
(2) Communication is lost between SG1 and ASP1. ASP2, ASP3, and
ASP4 are notified of the failure of ASP1 and the change of
state of AS1 to AS-PENDING for LS1. Data for LS2 in AS1 is
unaffected.
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(3) ASP4 (spare) responds to the AS-PENDING notification and
activates for LS1 in AS1/RC1. ASP2, ASP3 and ASP4 receive an
AS-ACTIVE notification. Data for LS1 in AS1 is now exchanged
with ASP4.
SG1 SG2 ASP1 ASP2 ASP3 ASP4 AS1
: : : : : : :
: : : : : : (LS1) :
:<----:-DATA----------------------->:<----:-----:-----:-------->:
: : : : : : :
:<----:-COMM LOST----------XXXX-----: : : : :
:-----:-NTFY(ASP Fail)(ASP1)--------:---->: : : :
:-----:-NTFY(ASP Fail)(ASP1)--------:-----:---->: : :
:-----:-NTFY(ASP Fail)(ASP1)--------:-----:-----:---->: :
:-----:-NTFY(AS_Pending)(LS1/RC1)---:---->: : : :
:-----:-NTFY(AS_Pending)(LS1/RC1)---:-----:---->: : :
:-----:-NTFY(AS_Pending)(LS1/RC1)---:-----:-----:---->: :
: : : : : : :
:<----:-ASPAC(LS1/RC1)--------------:-----:-----:-----: :
:-----:-ASPAC ACK(LS1/RC1)----------:-----:-----:---->: :
:-----:-NTFY(AS_Active)(LS1,LS2/RC1):---->: : : :
:-----:-NTFY(AS_Active)(LS1,LS2/RC1):-----:---->: : :
:-----:-NTFY(AS_Active)(LS1,LS2/RC1):-----:-----:---->: :
: : : : : : (LS1) :
:<----:-DATA------------------------:-----:-----:---->:<------->:
: : : : : : :
Figure 6. M3UA Example - Failure of ASP1
5.2.3. Sparing
Figure 7 illustrates a sparing situation where one ASP takes over
traffic from another so that the original ASP can be taken out of
service. The sequence of events is as follows:
(1) Data for LS1 in AS1 is exchange between SG1 and ASP1.
(2) ASP4 (spare) activates for LS1 in AS1 and receives and
acknowledgment. ASP4 has overridden ASP1 and a notification
is sent to ASP1 that indicates that ASP4 in now the "Alternate
ASP Active for AS".
(3) Data for LS1 in AS1 is now being exchanged between SG1 and
ASP4.
(4) ASP1 can now be taken down and out of service.
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SG1 SG2 ASP1 ASP2 ASP3 ASP4 AS1
: : : : : : :
: : : : : : (LS1) :
:<----:-DATA----------------------->:<----:-----:-----:-------->:
:<----:-DATA----------------------->:<----:-----:-----:-------->:
: : : : : : :
:<----:-ASPAC(LS1/RC1)--------------:-----:-----:-----: :
:-----:-ASPAC ACK(LS1/RC1)----------:-----:-----:---->: :
:-----:-NTFY(Alt ASP)(ASP4)-------->: : : : :
: : : : : : (LS1) :
:<----:-DATA------------------------:-----:-----:---->:<------->:
:<----:-DATA------------------------:-----:-----:---->:<------->:
: : : : : : :
Figure 7. M3UA Example - Sparing
5.3. SUA with Load-share AS and Load Selection based on GT
This example is for an SUA configuration with the Application Server
(AS1) configured with a Traffic Mode Type of Load-share. The
Application Server (AS1) has associated with it (RK1) that consists
of Destination Point Code and Subsystem Number that corresponds to
the AS1 (HLR1) point code (PC1). The Load Selectors (LS1 and LS2)
correspond to two sets of Global Titles which correspond to Mobile
and GSTN numbering.
5.3.1. Activation
Figure 8 illustrates activation of the ASPs for Load Selectors within
the Load-share Application Server. The sequence of events is as
follows:
(1) ASP1 sends an ASP Active message to SG1 identifying Load
Selector LS1 within Application Server AS1/RC1 and receives an
acknowledgment and a notification. Data is transferred
between the SG and ASP1 for Load Selection LS1 within AS1.
(2) ASP2 sends an ASP Active message to SG1 identifying Load
Selector LS2 within Application Server AS1/RC1 and receives an
acknowledgment and a notification. ASP1 also receives
notification that AS1/RC1 is active for LS2. Data is
transferred between the SG and ASP2 for Load Selection LS2
within AS1.
(3) ASP3 sends an ASP Active message to SG1 identifying Load
Selector LS1 within Application Server AS1/RC1 and receives an
acknowledgment and a notification. Data is load-shared
between the SG and ASP1 and ASP3 for Load Selection LS1 within
AS1.
(4) ASP4 sends an ASP Inactive message to SG1 identifying Load
Selector LS1 and LS2 within Application Server AS1/RC1 and
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receives an acknowledgment and a notification.
(5) The same exchange is repeated for SG2.
SG1 SG2 ASP1 ASP2 ASP3 ASP4 AS1
: : : : : : :
:<----:-ASPAC(LS1/RC1)--------------: : : : :
:-----:-ASPAC ACK(LS1/RC1)--------->: : : : :
:-----:-NTFY(AS_Act)(LS1/RC1)------>: : : : :
: : : : : : (LS1) :
:<----:-DATA----------------------->:<----:-----:-----:-------->:
: : : : : : :
:<----:-ASPAC(LS2/RC1)--------------:-----: : : :
:-----:-ASPAC ACK(LS2/RC1)----------:---->: : : :
:-----:-NTFY(AS_Act)(LS1,LS2/RC1)-->: : : : :
:-----:-NTFY(AS_Act)(LS1,LS2/RC1)---:---->: : : :
: : : : : : (LS2) :
:<----:-DATA------------------------:---->:<----:-----:-------->:
: : : : : : :
:<----:-ASPAC(LS1/RC1)--------------:-----:-----: : :
:-----:-ASPAC ACK(LS1/RC1)----------:-----:---->: : :
:-----:-NTFY(AS_Act)(LS1,LS2/RC1)---:-----:---->: : :
: : : : : : (LS1) :
:<----:-DATA----------------------->:<----:-----:-----:-------->:
:<----:-DATA------------------------:-----:---->:<----:-------->:
: : : : : : :
:<----:-ASPIA(LS1,LS2/RC1)----------:-----:-----:-----: :
:-----:-ASPIA ACK(LS1,LS2/RC1)------:-----:-----:---->: :
:-----:-NTFY(AS_Act)(LS1,LS2/RC1)---:-----:-----:---->: :
: : : : : : :
: : (Same message exchange for SG2) : : : :
: : : : : : :
Figure 8. SUA Example - Activation
5.3.2. Failure of ASP1 and ASP2
Figure 9 illustrates the failure of ASP1 followed by the failure of
ASP2. The sequence of events is as follows:
(1) Data for LS1 within AS1 is load-shared between ASP1 and ASP3.
Data for LS2 within AS1 is exchanged with ASP2.
(2) Communication is lost between SG1 and ASP1. ASP2, ASP3, and
ASP4 are notified of the failure of ASP1. Data for LS1 in AS1
is directed toward ASP3 only. Data for LS2 in AS1 is
unaffected.
(3) Communication is lost between SG1 and ASP2. ASP3 and ASP4 are
notified of the failure of ASP1 as well of the AS1 state
change to AS-PENDING. Data for LS2 is queued at the SG.
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(4) ASP4 (spare) responds to the AS-PENDING notification and
activates for LS2 in AS1/RC1. ASP3 and ASP4 receive an AS-
ACTIVE notification. Data for LS2 in AS1 is now exchanged
with ASP4.
SG1 SG2 ASP1 ASP2 ASP3 ASP4 AS1
: : : : : : :
: : : : : : (LS1) :
:<----:-DATA----------------------->:<----:-----:-----:-------->:
:<----:-DATA------------------------:-----:---->:<----:-------->:
: : : : : : (LS2) :
:<----:-DATA------------------------:---->:<----:-----:-------->:
: : : : : : :
:<----:-COMM LOST----------XXXX-----: : : : :
:-----:-NTFY(ASP Fail)(ASP1)--------:---->: : : :
:-----:-NTFY(ASP Fail)(ASP1)--------:-----:---->: : :
:-----:-NTFY(ASP Fail)(ASP1)--------:-----:-----:---->: :
: : : : : : (LS1) :
:<----:-DATA------------------------:-----:---->:<----:-------->:
:<----:-DATA------------------------:-----:---->:<----:-------->:
: : : : : : :
:<----:-COMM LOST----------XXXX-----:-----: : : :
:-----:-NTFY(ASP Fail)(ASP2)--------:-----:---->: : :
:-----:-NTFY(ASP Fail)(ASP2)--------:-----:-----:---->: :
:-----:-NTFY(AS_Pending)(LS2/RC1)---:-----:---->: : :
:-----:-NTFY(AS_Pending)(LS2/RC1)---:-----:-----:---->: :
: : : : : : :
:<----:-ASPAC(LS2/RC1)--------------:-----:-----:-----: :
:-----:-ASPAC ACK(LS2/RC1)----------:-----:-----:---->: :
:-----:-NTFY(AS_Active)(LS2/RC1)----:-----:---->: : :
:-----:-NTFY(AS_Active)(LS2/RC1)----:-----:-----:---->: :
: : : : : : (LS2) :
:<----:-DATA------------------------:-----:-----:---->:<------->:
: : : : : : :
Figure 9. SUA Example - Failure of ASP1 and ASP2
5.3.3. Sparing
Figure 10 illustrates a sparing situation where one ASP takes over
traffic from another so that the original ASP can be taken out of
service. The sequence of events is as follows:
(1) Data for LS1 in AS1 is load-shared between SG1 and ASP1 and
ASP3.
(2) ASP4 (spare) activates for LS1 in AS1 and receives and
acknowledgment. Data for LS1 in AS1 is now being load-shared
between SG1 and ASP1, ASP3 and ASP4.
(3) ASP1 deactivates for LS1 in AS1 and receives and
acknowledgment but no notification.
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(4) Data or LS1 in AS1 is now load-shared between SG1 and ASP3 and
ASP4.
(5) ASP1 can now be taken down and out of service.
SG1 SG2 ASP1 ASP2 ASP3 ASP4 AS1
: : : : : : :
: : : : : : (LS1) :
:<----:-DATA----------------------->:<----:-----:-----:-------->:
:<----:-DATA------------------------:-----:---->:<----:-------->:
: : : : : : :
:<----:-ASPAC(LS1/RC1)--------------:-----:-----:-----: :
:-----:-ASPAC ACK(LS1/RC1)----------:-----:-----:---->: :
: : : : : : (LS1) :
:<----:-DATA----------------------->:<----:-----:-----:-------->:
:<----:-DATA------------------------:-----:---->:<----:-------->:
:<----:-DATA------------------------:-----:-----:---->:<------->:
: : : : : : :
:<----:-ASPIA(LS1/RC1)--------------: : : : :
:-----:-ASPIA ACK(LS1/RC1)--------->: : : : :
: : : : : : (LS1) :
:<----:-DATA------------------------:-----:---->:<----:-------->:
:<----:-DATA------------------------:-----:-----:---->:<------->:
: : : : : : :
Figure 10. SUA Example - Sparing
5.4. TUA with Broadcast AS and Load Selection based on DID
This example is for an TUA configuration with the Application Server
(AS1) configured with a Traffic Mode Type of Broadcast. The
Application Server (AS1) has associated with it (RK1) that consists
of Destination Point Code and Subsystem Number that corresponds to
the AS1 (HLR1) point code (PC1). The Load Selectors (LS1 and LS2)
correspond to two sets of Dialog Ids which correspond to even and odd
Dialog Ids.
5.4.1. Activation
Figure 11 illustrates activation of the ASPs for Load Selectors
within the Broadcast Application Server. The sequence of events is
as follows:
(1) ASP1 sends an ASP Active message to SG1 identifying Load
Selector LS1 within Application Server AS1/RC1 and receives an
acknowledgment and a notification. Data is transferred
between the SG and ASP1 for Load Selection LS1 within AS1.
The initial Data Messages for LS1 within AS1 are tagged with a
Correlation Id.
(2) ASP2 sends an ASP Active message to SG1 identifying Load
Selector LS2 within Application Server AS1/RC1 and receives an
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acknowledgment and a notification. ASP1 also receives
notification that AS1/RC1 is active for LS2. Data is
transferred between the SG and ASP2 for Load Selection LS2
within AS1. The initial Data Messages for LS2 within AS1 are
tagged with a Correlation Id.
(3) ASP3 sends an ASP Active message to SG1 identifying Load
Selector LS1 within Application Server AS1/RC1 and receives an
acknowledgment and a notification. Data is broadcast the SG
and ASP1 and ASP3 for Load Selection LS1 within AS1. The
initial Data Messages for LS1 within AS1 are tagged with a
Correlation Id.
(4) ASP4 sends an ASP Inactive message to SG1 identifying Load
Selector LS1 and LS2 within Application Server AS1/RC1 and
receives an acknowledgment and a notification.
(5) The same exchange is repeated for SG2.
SG1 SG2 ASP1 ASP2 ASP3 ASP4 AS1
: : : : : : :
:<----:-ASPAC(LS1/RC1)--------------: : : : :
:-----:-ASPAC ACK(LS1/RC1)--------->: : : : :
:-----:-NTFY(AS_Act)(LS1/RC1)------>: : : : :
: : : : : : (LS1) :
:<----:-DATA-(CorrId)-------------->:<----:-----:-----:-------->:
: : : : : : :
:<----:-ASPAC(LS2/RC1)--------------:-----: : : :
:-----:-ASPAC ACK(LS2/RC1)----------:---->: : : :
:-----:-NTFY(AS_Act)(LS1,LS2/RC1)-->: : : : :
:-----:-NTFY(AS_Act)(LS1,LS2/RC1)---:---->: : : :
: : : : : : (LS2) :
:<----:-DATA-(CorrId)---------------:---->:<----:-----:-------->:
: : : : : : :
:<----:-ASPAC(LS1/RC1)--------------:-----:-----: : :
:-----:-ASPAC ACK(LS1/RC1)----------:-----:---->: : :
:-----:-NTFY(AS_Act)(LS1,LS2/RC1)---:-----:---->: : :
: : : : : : (LS1) :
:<----:-DATA-(CorrId)---------------:-----:---->:<----:-------->:
: : : : : : :
:<----:-ASPIA(LS1,LS2/RC1)----------:-----:-----:-----: :
:-----:-ASPIA ACK(LS1,LS2/RC1)------:-----:-----:---->: :
:-----:-NTFY(AS_Act)(LS1,LS2/RC1)---:-----:-----:---->: :
: : : : : : :
: : (Same message exchange for SG2) : : : :
: : : : : : :
Figure 11. TUA Example - Activation
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Internet Draft UA Load Selection January 10, 2002
5.4.2. Failure of ASP1 and ASP2
Figure 12 illustrates the failure of ASP1 followed by the failure of
ASP2. The sequence of events is as follows:
(1) Data for LS1 within AS1 is broadcast to ASP1 and ASP3. Data
for LS2 within AS1 is exchanged with ASP2.
(2) Communication is lost between SG1 and ASP1. ASP2, ASP3, and
ASP4 are notified of the failure of ASP1. Data for LS1 in AS1
is directed toward ASP3 only. Data for LS2 in AS1 is
unaffected.
(3) Communication is lost between SG1 and ASP2. ASP3 and ASP4 are
notified of the failure of ASP1 as well of the AS1 state
change to AS-PENDING. Data for LS2 is queued at the SG.
(4) ASP4 (spare) responds to the AS-PENDING notification and
activates for LS2 in AS1/RC1. ASP3 and ASP4 receive an AS-
ACTIVE notification. Data for LS2 in AS1 is now exchanged
with ASP4. Initial DATA messages for LS2 in AS1 are tagged
with a Correlation Id.
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Internet Draft UA Load Selection January 10, 2002
SG1 SG2 ASP1 ASP2 ASP3 ASP4 AS1
: : : : : : :
: : : : : : (LS1) :
:<----:-DATA----------------------->:<----:---->:<----:-------->:
:<----:-DATA----------------------->:<----:---->:<----:-------->:
: : : : : : (LS2) :
:<----:-DATA------------------------:---->:<----:-----:-------->:
: : : : : : :
:<----:-COMM LOST----------XXXX-----: : : : :
:-----:-NTFY(ASP Fail)(ASP1)--------:---->: : : :
:-----:-NTFY(ASP Fail)(ASP1)--------:-----:---->: : :
:-----:-NTFY(ASP Fail)(ASP1)--------:-----:-----:---->: :
: : : : : : (LS1) :
:<----:-DATA------------------------:-----:---->:<----:-------->:
:<----:-DATA------------------------:-----:---->:<----:-------->:
: : : : : : :
:<----:-COMM LOST----------XXXX-----:-----: : : :
:-----:-NTFY(ASP Fail)(ASP2)--------:-----:---->: : :
:-----:-NTFY(ASP Fail)(ASP2)--------:-----:-----:---->: :
:-----:-NTFY(AS_Pending)(LS2/RC1)---:-----:---->: : :
:-----:-NTFY(AS_Pending)(LS2/RC1)---:-----:-----:---->: :
: : : : : : :
:<----:-ASPAC(LS2/RC1)--------------:-----:-----:-----: :
:-----:-ASPAC ACK(LS2/RC1)----------:-----:-----:---->: :
:-----:-NTFY(AS_Active)(LS2/RC1)----:-----:---->: : :
:-----:-NTFY(AS_Active)(LS2/RC1)----:-----:-----:---->: :
: : : : : : (LS2) :
:<----:-DATA-(CorrId)---------------:-----:-----:---->:<------->:
: : : : : : :
Figure 12. TUA Example - Failure of ASP1
5.4.3. Sparing
Figure 13 illustrates a sparing situation where one ASP takes over
traffic from another so that the original ASP can be taken out of
service. The sequence of events is as follows:
(1) Data for LS1 in AS1 is broadcast from SG1 to ASP1 and ASP3.
(2) ASP4 (spare) activates for LS1 in AS1 and receives and
acknowledgment. Data for LS1 in AS1 is now being broadcast
from SG1 to ASP1, ASP3 and ASP4. Initial data for LS1 in AS1
is tagged with a Correlation Id.
(3) ASP1 deactivates for LS1 in AS1 and receives and
acknowledgment but no notification.
(4) Data or LS1 in AS1 is now broadcast from SG1 to ASP3 and ASP4.
(5) ASP1 can now be taken down and out of service.
B. Bidulock Version 0.0 Page 29
Internet Draft UA Load Selection January 10, 2002
SG1 SG2 ASP1 ASP2 ASP3 ASP4 AS1
: : : : : : :
: : : : : : (LS1) :
:<----:-DATA----------------------->:<----:-----:-----:-------->:
:<----:-DATA------------------------:-----:---->:<----:-------->:
: : : : : : :
:<----:-ASPAC(LS1/RC1)--------------:-----:-----:-----: :
:-----:-ASPAC ACK(LS1/RC1)----------:-----:-----:---->: :
: : : : : : (LS1) :
:<----:-DATA----------------------->:<----:-----:-----:-------->:
:<----:-DATA------------------------:-----:---->:<----:-------->:
:<----:-DATA-(CorrId)---------------:-----:-----:---->:<------->:
: : : : : : :
:<----:-ASPIA(LS1/RC1)--------------: : : : :
:-----:-ASPIA ACK(LS1/RC1)--------->: : : : :
: : : : : : (LS1) :
:<----:-DATA------------------------:-----:---->:<----:-------->:
:<----:-DATA------------------------:-----:-----:---->:<------->:
: : : : : : :
Figure 13. TUA Example - Sparing
6. Security
Load Selection does not introduce any new security risks or
considerations that are not already inherent in the UA [M3UA, SUA,
TUA] Please see the "Security" sections of M3UA, SUA and TUA [M3UA,
SUA, TUA] for security considerations and recommendations that are
applicable to each of these UAs.
7. IANA Considerations
Load Selection adds the following parameter tag value (described in
Section 3) to the Common Parameter numbering range for M3UA, SUA and
TUA [M3UA, SUA, TUA].
0xXXXX Load Selector
EDITOR'S NOTE:- The Load Selector tag value shown throughout
this document as 0xXXXX) will be assigned by IANA within the
common parameter range of the SIGTRAN UAs and may change its
value in further versions of this document.
Load Selection adds the following value to the Error Code parameter
(described in Section 3 and 4) for M3UA, SUA and TUA [M3UA, SUA,
TUA].
B. Bidulock Version 0.0 Page 30
Internet Draft UA Load Selection January 10, 2002
0xYY Invalid Load Selector
EDITOR'S NOTE:- The Error Code value shown throughout this
document as 0xYY) will be assigned by IANA as a value of the
common Error Code parameter for SIGTRAN UAs and may change
its value in further versions of this document.
Acknowledgments
The authors would like to thank Ken Morneault, Barry Nagelberg,
Benjamin J. Wilson, Jacques Rajchgod, Greg Sidebottom and Gery
Verwimp for their valuable comments and suggestions.
Notes
[1] Another draft: UA Load Grouping [LOADGRP], provides for
selection of Load Distribution methods within a Load Selector.
The draft [LOADGRP] refers to a group of ASPs within the same
traffic load selection as a Load Group and associates a Load
Distribution with the load group that can be: Override, Load-
share or Broadcast. Load Selection is applicable both to the
normal Traffic Mode Type of an AS, as well as to the Load
Distribution within a Load Group.
[2] For a detailed description of these messages, see Section 3 of
the M3UA, SUA or TUA specifications cited under "References"
[M3UA, SUA, TUA].
[3] For a detailed description of these procedures, see Section 4 of
the M3UA, SUA and TUA specifications cited under "References"
[M3UA, SUA, TUA].
[4] EXAMPLE:- An ASP (e.g, ASP-1) moving to state ASP-INACTIVE
within a Load Selector (e.g, LS-1) results in the state of the
AS moving to AS-PENDING. The SGP sends NTFY("Application Server
Pending") with "LS-1" in the Load Selector parameter in the
Notify message. If immediately after (and before T(r) expires)
another ASP (e.g, ASP-2) moves to state ASP-INACTIVE within
another Load Selector (e.g, LS-2) resulting the state of the AS
being "held" in the AS-PENDING state, the SGP sends
NTFY("Application Server Pending") again, but this time includes
both "LS-1" and "LS-2" in the Load Selector parameter in the
Notify message.
EXAMPLE:- When all ASPs are inactive for a Load Selector within
an Override AS, the AS will transition to the AS-PENDING state.
The SGP will send a NTFY("Application Server Pending") message
B. Bidulock Version 0.0 Page 31
Internet Draft UA Load Selection January 10, 2002
to all ASPs configured for the Application Server that are not
in the ASP-DOWN state. This message should include in the Load
Selector parameter the Load Selectors in which there is no ASP
in the ASP-ACTIVE state for the AS.
References
M3UA.
G. Sidebottom, J. Pastor-Balbes, I. Rytina, G. Mousseau, L. Ong,
H. J. Schwarzbauer, K. Gradischnig, K. Morneault, M. Kalla, N.
Glaude, B. Bidulock and N. Glaude, "SS7 MTP3-User Adaptation
Layer (M3UA)," <draft-ietf-sigtran-m3ua-10.txt>, Internet
Engineering Task Force - Signalling Transport Working Group
(November, 2001). Work In Progress.
SUA.
J. Loughney, G. Sidebottom, G. Mousseau, S. Lorusso, L. Coene,
G. Verwimp, J. Keller, F. E. Gonzalez, W. Sully, S. Furniss and
B. Bidulock, "SS7 SCCP-User Adaptation Layer (SUA)," <draft-
ietf-sigtran-sua-09.txt>, Internet Engineering Task Force -
Signalling Transport Working Group (June 15, 2001). Work In
Progress.
TUA.
B. Bidulock, "SS7 TCAP-User Adaptation Layer (TUA)," <draft-
bidulock-sigtran-tua-00.txt>, Internet Engineering Task Force -
Signalling Transport Working Group (January 2002). Work In
Progress.
LOADGRP.
B. Bidulock, "Load Grouping Extension for Signalling User
Adaptation Layers (LOADGRP)," <draft-bidulock-sigtran-
loadgrp-00.txt>, Internet Engineering Task Force - Signalling
Transport Working Group (January 2002). Work In Progress.
RFC 2960.
R. Stewart, Q. Xie, K. Morneault, C. Sharp, H. J. Schwarzbauer,
T. Taylor, I. Rytina, H. Kalla, L. Zhang and V. Paxson, "Stream
Control Transmission Protocol (SCTP)," RFC 2960, The Internet
Society (February 2000).
Q.704.
ITU, "Message Transfer Part - Signalling Network Functions and
Messages," ITU-T Recommendation Q.704, ITU-T Telecommunication
Standardization Sector of ITU, Geneva (March 1993). (Previously
"CCITT Recommendation")
RFC 2119.
S. Bradner, "Key words for use in RFCs to Indicate Requirement
Levels," RFC 2119 - BCP 14, Internet Engineering Task Force
(March 1997).
Q.713.
ITU, "Signalling Connection Control Part Formats and Codes,"
B. Bidulock Version 0.0 Page 32
Internet Draft UA Load Selection January 10, 2002
ITU-T Recommendation Q.713, ITU-T Telecommunication
Standardization Sector of ITU, Geneva (March 1993). (Previously
"CCITT Recommendation")
Q.773.
ITU, "Signalling System No. 7 - Transaction Capabilities Formats
and Encoding," ITU-T Recommendation Q.773, ITU-T
Telecommunication Standardization Sector of ITU, Geneva (March
1993). (Previously "CCITT Recommendation")
ASPEXT.
B. Bidulock, "Application Server Process (ASP) Extension
Framework," <draft-bidulock-sigtran-aspext-00.txt>, Internet
Engineering Task Force - Signalling Transport Working Group
(January 2002). Work In Progress.
LOADSEL.
B. Bidulock, "Load Selection Extension for Signalling User
Adaptation Layers (LOADSEL)," <draft-bidulock-sigtran-
loadsel-00.txt>, Internet Engineering Task Force - Signalling
Transport Working Group (January 2002). Work In Progress.
Author's Addresses
Brian Bidulock Phone: +1-972-839-4489
OpenSS7 Corporation Email: bidulock@openss7.org
4701 Preston Park Boulevard URL: http://www.openss7.org/
Suite 424
Plano, TX 75093
USA
This draft expires July, 2002.
B. Bidulock Version 0.0 Page 33
Internet Draft UA Load Selection January 10, 2002
List of Illustrations
Figure 1 Non-Load Selection Traffic Distribution ............. 3
Figure 2 Load Selection Traffic Distribution ................. 5
Figure 3 Example Configuration ............................... 19
Figure 4 Example - Initialization ............................ 20
Figure 5 M3UA Example - Activation ........................... 21
Figure 6 M3UA Example - Failure of ASP1 ...................... 22
Figure 7 M3UA Example - Sparing .............................. 23
Figure 8 SUA Example - Activation ............................ 24
Figure 9 SUA Example - Failure of ASP1 and ASP2 .............. 25
Figure 10 SUA Example - Sparing .............................. 26
Figure 11 TUA Example - Activation ........................... 27
Figure 12 TUA Example - Failure of ASP1 ...................... 29
Figure 13 TUA Example - Sparing .............................. 30
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Table of Contents
1 Introduction ............................................... 1
1.1 Scope .................................................... 2
1.2 Terminology .............................................. 2
1.3 Overview ................................................. 2
1.3.1 Non-Load Selection Traffic Distribution ................ 3
1.3.2 Load Selection Traffic Distribution .................... 4
1.4 Sample Configurations .................................... 6
2 Conventions ................................................ 6
3 Protocol Elements .......................................... 6
3.1 Parameters ............................................... 6
3.1.1 Load Selector .......................................... 6
3.2 Messages ................................................. 7
3.2.1 ASP Active (ASPAC) ..................................... 8
3.2.2 ASP Active Ack (ASPAC ACK) ............................. 9
3.2.3 ASP Inactive (ASPIA) ................................... 10
3.2.4 ASP Inactive Ack (ASPIA ACK) ........................... 11
3.2.5 Error (ERR) ............................................ 12
3.2.6 Notify (NTFY) .......................................... 12
4 Procedures ................................................. 14
4.1 AS and ASP State Maintenance ............................. 14
4.1.1 ASP State .............................................. 14
4.1.2 AS State ............................................... 14
4.1.3 ASP Up Procedures ...................................... 15
4.1.4 ASP Down Procedures .................................... 15
4.1.5 ASP Active Procedures .................................. 15
4.1.6 ASP Inactive Procedures ................................ 16
4.1.7 Notify Procedures ...................................... 17
4.1.8 Registration Procedures ................................ 18
4.2 Interworking Procedures .................................. 18
5 Examples ................................................... 18
5.1.1 Initialization ......................................... 19
5.2 M3UA with Override AS and Load Selection based on CIC .... 20
5.2.1 Activation ............................................. 20
5.2.2 Failure of ASP1 ........................................ 21
5.2.3 Sparing ................................................ 22
5.3 SUA with Load-share AS and Load Selection based on GT .... 23
5.3.1 Activation ............................................. 23
5.3.2 Failure of ASP1 and ASP2 ............................... 24
5.3.3 Sparing ................................................ 25
5.4 TUA with Broadcast AS and Load Selection based on DID .... 26
5.4.1 Activation ............................................. 26
5.4.2 Failure of ASP1 and ASP2 ............................... 28
5.4.3 Sparing ................................................ 29
6 Security ................................................... 30
7 IANA Considerations ........................................ 30
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Copyright Statement
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This document and translations of it may be copied and furnished to
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The limited permission 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
HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
MECHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
B. Bidulock Version 0.0 Page 36
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