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Network Working Group Brian Bidulock
INTERNET-DRAFT OpenSS7 Corporation
February 21, 2004
Expires in August 2004
Correlation Id and Hearbeat Procedures (CORID)
Supporting Lossless Fail-Over between SCTP Associations
for
Signalling User Adaptation Layers
<draft-bidulock-sigtran-corid-03.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 working
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Copyright
Copyright (C) The Internet Society (2003). All Rights Reserved.
Abstract
This Internet-Draft describes Correlation Id and Heartbeat
procedures to support lossless fail-over between SCTP [RFC 2960]
associations for SS7 [Q.700] Signalling User Adaptation Protocols
[M2UA..ISUA, TUA] supporting the concept of a Routing Context or
Interface Identifier. These procedures permit lossless fail-over
between Application Server Processes (ASPs) at a Signalling Gateway
(SG) and fail-over between Signalling Gateway Processes (SGPs) and
Signalling Gateways (SGs) at an Application Server Process (ASP).
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Lossless fail-over permits these fail-overs to occur without loss or
duplication of UA-User messages.
Contents
A complete table of contents, list of illustrations and change
history appears at the end of this document.
1. Introduction
1.1. Scope
This Internet-Draft describes Correlation Id and Heartbeat (CORID)
procedures to support lossless fail-over between SCTP [RFC 2960]
associations for SS7 [Q.700] Signalling User Adaptation Protocols
[M2UA..ISUA, TUA] above MTP3 [Q.704] supporting the concept of a
Routing Context or Interface Identifier. These procedures permit
lossless fail-over between Application Server Processes (ASPs) at a
Signalling Gateway (SG) and fail-over between Signalling Gateway
Processes (SGPs) and Signalling Gateways (SGs) at an Application
Server Process (ASP). Lossless fail-over permits these fail-overs to
occur without loss or duplication of UA-User messages.
UA implementations with CORID are intended to be compatible with UA
implementations not supporting this configuration; however, the full
benefits acheived by the CORID procedures will not be realized unless
implementations at both endpoints implement CORID.
1.2. Abbreviations
AS --Application Server.
ASP --Application Server Process.
CORID --Correlation Id Extension
IANA --Internet Assigned Numbers Authority
I-D --Internet-Draft
IETF --Internet Engineering Task Force
IP --Internet Protocol.
IPSP --IP Signalling Point.
SCCP --Signalling Connection Control Part.
SCTP --Stream Control Transmission Protocol.
SG --Signalling Gateway.
SGP --Signalling Gateway Process.
SIGTRAN --IETF Signalling Transport WG
SPP --Signalling Peer Process.
SS7 --Signalling System No. 7.
SUA --SS7 SCCP-User Adpatation Layer.
TCAP --Transaction Capabilities Application Part.
TUA --SS7 TCAP-User Adaptation Layer.
UA --User Adaptation Layer.
WG --Working Group
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1.3. Terminology
CORID supplements the terminology used in the UA documents
[M2UA..ISUA, TUA] by adding the following terms:
Changeback - the MTP3 [Q.704] procedure for redirecting signalling
traffic back to a primary linkset from an alternate linkset.
Changeover - the MTP3 [Q.704] procedure for diverting signalling
traffic from a failed primary linkset to an alternate linkset.
Lossless Fail-Over - is mechanism for fail-over between SCTP [RFC
2960] associations (i.e, between ASPs, IPSPs, SGPs or SGs) that
provides for the elminitation of duplication or loss of UA-User
messages between SG and AS.
Message Duplication - a situation where multiple copies of a UA-User
message arrives at a Signalling Endpoint.
Message Loss - a situation where instances of a UA-User message is
lost in transit between Signalling Endpoints.
Message Mis-sequencing - a situation where UA-User messages that are
intended to arrive in sequence, arrive at a terminating Signalling
Endpoint in an order other than the order in which the messages
were transmitted at the originating Signalling Endpoint.
Signalling Endpoint (SEP) - in this document, a Signalling Enpoint is
an SS7 SEP [Q.700] or an Application Server.
Signalling Peer Process (SPP) - refers to an ASP, SGP or IPSP.
Signalling User Adaptation Layer (UA) - one or more of the Stream
Control Transmission Protocol (SCTP) [RFC 2960] SS7 Signalling
User Adaptation Layers [M2UA..ISUA, TUA] supporting the
Correlation Id parameter and the BEAT message.
Time-controlled Changeover - the MTP3 [Q.704] procedure for diverting
signalling traffic from a failed primary linkset to an alternate
linkset where sequence number information cannot be exchanged
between signalling points or where it is undesirable to use the
normal changeover procedures.
1.4. Overview
The existing UA [M2UA..ISUA, TUA] procedures do not include
procedures to avoid loss or duplication of messages when a UA peer
must fail-over between SCTP [RFC 2960] associations between diverse
Application Server Processes (ASPs), Signalling Gateway Processes
(SGPs), Signalling Gateways (SGs), and IP Signalling Processes
(IPSPs).
CORID provides procedures to eliminate message loss, duplication or
mis-sequencing under all failure, deactivation, recovery and
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activation scenarios. CORID provides the following capabilities that
are not provided for in the existing UA specifications:
+ Support for elimintating mis-sequencing of UA-User messages at
signalling endpoints (Application Servers or SS7 SEPs) when
diverting messages between ASPs, SGPs, SGs, or IPSPs by supporting
BEAT procedures analogous to the MTP3 [Q.704] Changeback procedure.
+ Support for eliminating duplication of UA-User messages at
signalling endpoints (Application Servers or SS7 SEPs) or SS7
endpoints across fail-over between ASPs, SGPs, SGs, or IPSPs.
+ Support for elimination of message loss of UA-User messages between
Signalling Gateways (SGs) and Application Servers (ASs) across
fail-over between ASPs, SGPs, SGs, or IPSPs.
1.4.1. Configuration
For carrier-class operation, the SS7 Signalling User Adaptation
Layers recommend that Signalling Gateways and Application Servers be
configured such that there is no single point of failure within the
SG/AS architecture or in the intervening network. The SS7 UAs also
recommend that no Application Server be configured for less than two
(2) Application Server Processes.
All of the UAs describe an override, loadsharing and broadcast
traffic mode. The UA protocols place no restrictions on the
distribution algorithm which is used for distributing traffic over
multiple Signalling Processes. Additional traffic distribution
proposals have been put forward for Load Selection [LOADSEL] and Load
Grouping [LOADGRP]
Fail-over between Application Server Processes (ASPs) and
Signalling Gateway Processes (SGPs) is not detailed in the UA
protocols [M2UA..ISUA, TUA], but it is clear that when an SCTP
association fails and the ASP transitions to the ASP-DOWN state from
the perspective of the SGP peer, the traffic which the associated ASP
was previously responsible needs to be diverted to an alternate ASP
(if available) in the same Application Server pool.
1.4.2. Conditions at Fail-Over
The details of this diversion of traffic is not specified, however,
a dichotomy exists when such fail-over occurs as a result of the loss
of an SCTP association between these Signalling Peer Processes (SPPs).
When an SPP loses its SCTP association with another SPP, and diverts
traffic towards another SPP, there exists the possibility that
messages previously destined to the peer SPP exist in several
categories, as follows:
Category (1) - Queued in the sending SPP process,
Category (2) - queued for transmission, but not yet transmitted by the
transport provider (SCTP),
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Category (3) - queued for retransmission, but not yet acknowledged by
the peer transport provider (SCTP), and,
Category (4) - acknowledged by the peer transport provider (SCTP) and
deleted from the sending transport provider's (SCTP's)
retransmission queue.
Signalling | Stream Control |
Peer Transmission Protocol
Process | (RFC 2960) |
First Transmission
| +-----------------|------------->
___ _ _ ___ _ _ | ___ _ _
| | | __ | | | | __ | | | | __ |
| | |/ \ | | |/ \ | | | |/ \ Retransmission
---->| | | |-|--->| | | |-+--->| | | |---|------------->
| | |\__/ | | |\__/ | | |\__/
___|_|_| | ___|_|_| | ___|_|_| |
Category (1) | Category (2) | Category (3) | Category (4)
------------ ------------ ------------ ------------
Queued in | Queued for | Queued for | Acked and
Signalling Transmission Acknowledgment Deleted
Peer Process | | |
Figure 1. Buffer Categories at SCTP Association Failure
These categories are illustrated in Figure 1. Note that to
retransmit categories (2) and (3) (and perhaps categories (1)) on
another link requires sent data acknowledgment or buffer retrieval
capability by the underlying transport provider.
As there is no SPP peer-to-peer acknowledgement, for messages in
Categories (3) and (4), the message might or might not have been
delivered to the peer SPP. Therefore, at the time of failure of an
SCTP association between two Signalling Peer Processes (SPPs), it is
not possible for either SPP to determine which of the messages in
categories (3) and (4) above (transmitted, but not yet acknowledged;
transmitted and acknowledged) were successfully received by the peer
before failure. Without information concerning which messages in this
category were successfully received by the peer, the SPP either risks
message loss or message duplication when it diverts traffic from the
failed association.
1.4.3. Sources of Message Loss and Duplication
If the messages from category (3) or (4) are retransmitted on an
alternate association, the SPP diverting the traffic risks message
duplication. This is because some messages of the category might
possibly have been successfully received by the peer before fail-over.
If the messages from category (3) and (4) are discarded before
diverting messages from categories (1) and (2) and then new traffic on
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an alternate association, the SPP risks message loss. This is because
some of the messages in category (3) and (4) might possibly have not
been received by the peer SPP before the association failed.
This is the dychotomy: regardless of the nature of a policy
concerning the disposition of messages at an SPP experiencing failure
to its peer, without information concerning messages successfully
received by the peer, the SPP risks message loss or duplication.
It should be possible to induce such a system to demonstrate
message loss or duplication.
Because SS7 performance requirements [Q.706] have more stringent
requirements against duplication of messages than loss of messages,
the only policy is to discard messages in category (3).
To avoid loss of messages to meet SS7 performance requirements
[Q.706] in consideration of this dichotomy, implementation cost may be
driven higher than would be the case if a procedure were established
to exchange information between the Signalling Processes on either
side of a failed association.
This Internet-Draft provides Correlation Id and Heartbeat
procedures for fail-over for the SS7 signalling UAs which will remove
the possibility of message loss or duplication in the event that an
SCTP association failure while communication between the Application
Server and Signalling Gateway is still possible.
1.4.4. Conditions at Recovery
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Signalling Application
Gateway (X) Server
/----------\__________/____________/----------\
| |_________ / _________| |
| SGP1 |... \ / ...| ASP1 |
| |_____ \ / _____| |
\----------/ \ X / \----------/
\ / \ /
/----------\_______\_/ \_/_______/----------\
| |________\_____/________| |
| SGP2 |... \ / ...| ASP2 |
| |________ \ / ________| |
\----------/ \ X / \----------/
\/ \/
. /\ /\ SCTP .
. / X \ Associations .
. / / \ \ .
/ / \ \
/----------\_____/ / \ \_____/----------\
| |_______/ \_______| |
| SGPn |... ...| ASPn |
| |_______________________| |
\----------/ \----------/
Figure 2. Example (A) Configuration of ASPs and SGPs
Figure 2 illustrates an example (A) configuration of ASPs and SGPs.
In this example, the ASP and SGP are interconnected with a full-mesh
arrangement of SCTP Associations. Each ASP is interconnected to each
SGP by an association.
When a failure of the SCTP assocation occurs, it is, for example,
between `SGP1' and `ASP1' as indicated by the (X) in the Figure 2.
When a recovery occurs, it is also the SCTP association between `SGP1'
and `ASP1' that recovers.
The normal procedure for dealing with such a failure[1] is for SGP1
to mark ASP1 in the ASP-DOWN state and to redirect traffic over the
remaining ASPs in the Application Server[2].
When the SCTP association between ASP1 and SGP1 recovers and ASP1
succesfully activates for the AS using the ASP Active Procedures[3],
once ASP1 has entered the ASP-ACTIVE state for the AS, message mis-
sequencing can occur if traffic is immediately applied on the newly
active association.
The UA procedures[3] provide no detail concerning the restarting of
traffic to recovering ASPs in the AS.
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1.4.5. Sources of Message Mis-Sequencing
Because the SGPs can be experiencing different loads or other local
factors, each SGP may differ. Therefore, restoring a traffic flow to
a newly active SGP, without first ensuring that messages are purged
through the old path before the diversion, can result in message mis-
sequencing. This is example (C) illustrated in Figure 3.
_____
/ \ SGPx
| |________________
| | ______ |
| | __ |X|X| |
| |___/ \|X|X|____|_____
| | \__/|X|X| | |
| | |X|X|__ | | ASP1
| |________________| \| _______________
| | ( \ | _____ |
| NIF | ( \ | __ | | | |
| | ( \____|__/ \| | |____|___
| | SGP1 | \__/| | | |
| |________________ | | |_|_|_ |
| | ______ | | |_______________|
| | __ | | | | |
| |___/ \| | |____|_____|
| | \__/| | | |
| | |_|_|__ |
| |________________|
| |
\_____/
Figure 3. Example (C) Restoration of a Traffic Flow
Before switching traffic back to SGP1 from SGPx, SGPx is queueing
traffic from ASP1 to the SS7 network. (This queueing could either be
within the SGP or as a result of queueing within the transport
protocol.) [RFC 2960] If the traffic flow from ASP1 is switched
rapidly to SGP1, a race condition exists between messages in SGPx's
queue and messages in SGP1's queue. A rapid switch can result in mis-
sequencing.
As SGPx and SGP1 do not necessarily have to belong to the same SG
(and because there exists queuing within the transport protocol
itself), close queue synchornization between SGPx and SGP1 cannot be
expected.
CORID provides both a time-controlled and a Heartbeat procedure for
restoration of traffic to avoid mis-sequencing during restoration.
1.5. Functional Areas
The CORID procedures to avoid message loss, duplication and mis-
sequencing under these types of scenarios requires protocol parameters
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that provide a clear identification of the independent traffic flows
involved. Then, procedures are required to control the fail-over and
restoration of the identified traffic flows to avoid message loss.
The SS7 MTP3 [Q.704] provide an excellent example of the types of
procedures that can be applied to the problem of switching traffic
flows across redundant processes[4].
1.5.1. Identification of Traffic Flows
Traffic flows between Server Processes in the UAs are managed on
the basis of the Application Server to which the traffic flows
correspond. Traffic flows from SG to AS are identified by the Routing
Key or Routing Context to which they correspond[5].
An Application Server Process can be active and handling traffic
for any number or combination of traffic flows. That is, the ASP can
be actively handling traffic for any number of Application Servers.
When an SCTP [RFC 2960] association fails, it is necessary to identify
both the sequence of the last message succesfully received and
processed by the Signalling Process, as well as the traffic flow
within which that sequence applies.
Therefore, this document identifies a message in a traffic flow by
the Routing Context, Traffic Flow Id and the correlation (sequence)
number within that flow as identified by the Correlation Identifier.
The Correlation Identifier is a combination of Traffic Flow Id and
Correlation Number which is applied to all divertable traffic.
(For details on the assignment of Traffic Flow Identifiers and
Correlation numbers, see Section 4.1.2 "Correlation".)
1.5.1.1. SGP Starting New SGP-to-ASP Traffic
When traffic is originally started for a traffic flow, the first
divertable message in the traffic flow is assigned a Correlation
Number of one (1) by the sending Signalling Process. Subsequent
divertable messages within the routing context are given the
Correlation Id number of two (2), three (3), and so on.
Because SCTP is a sequenced reliable transport [RFC 2960], it is
only necessary to communicate this Correlation Id number between SPP
peers for the intial message which is sent to the peer. Each
Signalling Peer Process MUST be capable of counting the messages which
have been sent or received on the SCTP association, and assigning each
subsequent message the next sequential Correlation Id number.
1.5.1.2. SPP Diverting peer SPP Traffic
Should, for example, the association fail between the SGP and the
ASP, the SGP will recover any buffers from categories (1), (2), (3)
and (4), and immediately restart traffic, in sequence, on another
active ASP within the AS. When the SGP restarts traffic on this
alternate ASP, if the messages belong to Category (4) or (3) (i.e,
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they were transmitted on but not acknowledged by the underlying
transport, or transmitted and acknowledged), the SGP will label the
initial message sent with the Correlation Id of the message at the
time that it was originally sent. When the SGP sends tmessages from
Category (2), (1) and newly arriving traffic, the SGP will not tag the
messages with a Correlation Id, but instead will label them internally
with the next sequential Correlation Numbers for the traffic flow.
Thus, the alternate Signalling Peer Process which is receiving
diverted traffic will be able to distinguish the problematic Category
(3) and (4) messages from those which follow. When an tagged message
is received, the Signalling Peer Process is now aware that the
messages were previously sent to the normal SPP to which the SCTP
association was lost. When an untagged message arrives, the receiving
Signalling Peer Process is aware that this and subsequent messages
within the traffic flow represent previously unsent traffic.
(Detailed procedures for the tagging of messages are described in
Section 4.1.3 and 4.1.5.2.1; for diversion, Sections 4.2.2, 4.2.3 and
4.1.6.)
1.5.1.3. SPP Receiving Diverted Traffic
At the Signalling Process receiving the diverted traffic for the
Routing Context, three actions are possible (or, combinations of the
three):
(1) Ignore the Correlation Id and process the messages blind at the
risk that message duplication will occur,
(2) discard all messages tagged with a Correlation Id at the risk
of increased message loss, or,
(3) perform the procedures described in Section 4.1.5.2.2
minimizing the message duplication and loss resulting from the
diversion.
Only by performing the procedures described in Section 4.1.5.2.2
will message duplication and loss be minimized.
1.5.1.4. SPP Restoring Traffic
Should, for example, the association recover between the SGP and
ASP, the ASP will need to rebalance the load across the available SGPs
and the newly available SGP. As discussed, if the ASP switches
traffic immediately, message mis-sequencing can occur. Two procedures
are provided by CORID for restoring traffic without message mis-
sequencing: a Heartbeat procedure and a timer procedure.
The Heartbeat procedure withholds divertable traffic from the SGP
currently active for each traffic flow and sends a BEAT message on
each flow. Once the BEAT ACK is received by the ASP, the ASP is
assured that there is no divertable traffic pending on the SGP and the
traffic flow can be switched to the recovered SGP. The Heartbeat
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procedure is applicable to recovery between SGPs in the same SG as
well as SGPs in different SGs.
The Timer procedure witholds divertable traffic from the SGP
currently active for the traffic flow and waits until a timer expires.
Once the timer expires, the ASP is resonably assured that there is no
traffic pending on the SGP and the traffic flow can be switched to the
recovered SGP. The Timer procedure is applicable to recovery between
SGPs where the SGPs do not support CORID.
Restoration of traffic is described in detail in Sections 4.2.3 and
4.1.6.
1.6. Sample Configurations
A typical Example (C) configuration (multiple Signalling Gateways)
is illustrated in Figure 4. In this configuration a number of
Application Server Processes (ASPs) serving a number of Application
Servers (ASs) are connected to two Signalling Gateways (SGs). The SGs
appear as mated SS7 Signalling Transfer Points (STPs) [Q.705] to the
SS7 Network. Traffic originating at Signalling Endpoints (SEP) in the
SS7 network and directed toward SEP in the IP network (i.e.,
Application Servers) is loadshared over the STPs by the Signalling
|
SS7 IP
Network | Network
_________________ ________ _____
| | ________| ______| | / \
| | |_______| ____| ASP1 | | |
B/D-Links | | | SGP1 |________ | |________| | |
___________| STP SG1|________| | | ________ | |
/| | | |__ + | | __| | | AS1 |
/ | | SGP2 |__ + | | __| ASP2 | | |
\ / | | |________| + | | |________| | |
\ / |_________________| | | ________ | |
\ / C- | + | | __| | \_____/
X Links| | + | | __| ASP3 | _____
/ \ _|_______________ + | | |________| / \
/ \ | | ________| | | ________ | |
/ \ | | |__ + | | __| | | |
\ | | | SGP3 |__ + | | __| ASP4 | | |
__________\| STP SG2|________| + | | |________| | AS2 |
| | | |________|_| ________ | |
| | SGP4 |_______ |_____| | | |
| | |________| |______| ASP5 | | |
|_________________| SCTP |________| \_____/
| Associations
|
Figure 4. Example (C) Sample Multiple-SG Configuration
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Link Selection (SLS) [Q.704] value associated with each message.
Traffic originating at the SEP in the IP network (i.e, AS) is
loadshared over the SGs in the same fashion.
Notes for Section 1
[1] As described in the UA documents [M2UA..ISUA, TUA].
[2] For illustration purposes only, all ASPs in Figure 2 are
members of the one Application Server which is represented at
all of the SGPs.
[3] See Section 4.3.4.3 of the specific UA document [M2UA..ISUA,
TUA].
[4] See, for example, Clause 5 "Changeover", Clause 6 "Changeback",
Clause 7 "Forced Rerouting" and Clause 8 "Controlled
Rereouting" of the MTP3 specifications [Q.704].
[5] This is true for all User Adaptation layers with the exception
of M2UA [M2UA]. In M2UA, the Application Server and traffic
flows are identified by an equivalent of the Routing Key: the
Link Key, and the equivalent of the Routing Context: the
Interface Identifier. An Application Server may also represent
multiple Interface Identifiers.
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 protcol element definitions are
provided by CORID in extension to the existing protocol element
definitions for the UAs [M2UA..ISUA, TUA].
3.1. Parameters
The following subsections describe the parameters used for CORID,
their format and the message in which they are used.
3.1.1. Correlation Id
The Correlation Id parameter is used in the BEAT, BEAT ACK, ASPAC,
ASPAC ACK, and UA-User data messages. It is used here to identify
data messages sent to a peer SPP.
The Correlation Id parameter is formatted as follows:
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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 = 0x0019 | Length |
+- - - - - - - - - - - - - - - -+- - - - - - - - - - - - - - - -+
| Correlation Id #1 |
+- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -+
| Correlation Id #2 |
+- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -+
\ . \
/ . /
\ . \
/ /
+- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -+
| Correlation Id #n |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The Correlation Id parameter contains one or more of the following
field:
Correlation Id field: 8-bytes
The Correlation Id field 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Correlation Number |
+- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -+
| Traffic Flow Id |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Correlation Number field: 32-bits (unsigned integer)
The Correlation Number field identifies a particular message
within a traffic flow. When the Correlation Id parameter is
included in the BEAT (ACK) or ASPAC (ACK) message, this field
identifies the last sent message for the indicated traffic flow.
When the Correlation Id parameter is included a UA-User data
message, this field identifies the Correlation Number of the
message in which it is contained.
Traffic Flow Id field: 32-bits (unsigned integer)
The Traffic Flow Id field identifies a particular indepdently
sequenced traffic flow to which the Correlation Number field value
applies. The Traffic Flow Id field identifies a traffic flow
associated with an Application Server. When used for tagging
messages or in the BEAT (ACK) or ASPAC (ACK) message for a
Loadshare AS Load Selection [LOADSEL] or Loadshare Load Group
[LOADGRP], the Traffic Flow Id field MUST identify traffic flow
(Load Selection) within an Application Server.
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For an Override or Broadcast AS (or Load Group), the Traffic Flow
Id is not required and SHOULD be coded zero (0). In this case,
the Correlation Id parameter SHOULD only contain one Correlation
Id field.
For details on Traffic Flow Id assignment, see Section 4.1.2.2.
When the Correlation Id parameter is included in the BEAT, BEAT
ACK, ASPAC, ASPAC ACK, and UA-User data messages, only one Routing
Context (or Interface Identifier) representing a single Application
Server MUST be associated (specified or implied) with the message.
3.2. Messages
3.2.1. ASP Active (ASPAC)
CORID supplements the ASPAC mesage by permitting the following
optional parameters to be included in the message:
Extension Parameters
------------------------------------------
Correlation Id Mandatory
The format of the resulting ASPAC message is as follows:
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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 = 0x000b | Length = 8 |
+- - - - - - - - - - - - - - - -+- - - - - - - - - - - - - - - -+
| Traffic Mode Type |
+-------------------------------+-------------------------------+
| Tag = 0x0006 | Length = 8 |
+- - - - - - - - - - - - - - - -+- - - - - - - - - - - - - - - -+
| Routing Context |
+-------------------------------+-------------------------------+
| Tag = 0x0001 | Length=8 |
+- - - - - - - - - - - - - - - -+- - - - - - - - - - - - - - - -+
| Interface Identifier (integer) |
+-------------------------------+-------------------------------+
| Tag = 0x0003 | Length |
+- - - - - - - - - - - - - - - -+- - - - - - - - - - - - - - - -+
\ \
/ Interface Identifier (text) /
\ \
+-------------------------------+-------------------------------+
| Tag = 0x0019 | Length |
+- - - - - - - - - - - - - - - -+- - - - - - - - - - - - - - - -+
\ \
/ Correlation Id /
\ \
+-------------------------------+-------------------------------+
| Tag = 0x0004 | Length |
+- - - - - - - - - - - - - - - -+- - - - - - - - - - - - - - - -+
\ \
/ Info String /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The Correlation Id parameter is used by the ASP in the ASPAC
message to indicate the correlation identifier for the first UA-User
message to be transmitted in each traffic flow from the Application
Server being activated to the Signalling Gateway. The Application
Servers for which the Correlation Id apply is either indicated in the
ASPAC message by providing the associated Routing Contexts (or
Interface Identifiers), or, if there is no Routing Context (or
Interface Identifier) parameter in the message, the associated
Application Servers are implied by the SGP and ASP configuration data.
When the Correlation Id parameter is present in the ASPAC message,
the message SHOULD only contain one Routing Context (or Interface
Identifier) in the Routing Context (or Interface Identifier)
parameter. When the Correlation Id parameter is not present, but
required by the SGP, the value of the Correlation Id is assumed to be
zero (0).
The ASPAC message MAY contain additional extension parameters
provided for by other extensions.
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No other changes to the ASPAC message format are provided by this
extension.
3.2.2. ASP Active Acknowledgement (ASPAC ACK)
CORID supplements the ASPAC ACK mesage by permitting the following
optional parameters to be included in the message:
Extension Parameters
------------------------------------------
Correlation Id Mandatory
The format of the resulting ASPAC ACK message is 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 = 0x000b | Length = 8 |
+- - - - - - - - - - - - - - - -+- - - - - - - - - - - - - - - -+
| Traffic Mode Type |
+-------------------------------+-------------------------------+
| Tag = 0x0006 | Length = 8 |
+- - - - - - - - - - - - - - - -+- - - - - - - - - - - - - - - -+
| Routing Context |
+-------------------------------+-------------------------------+
| Tag = 0x0001 | Length=8 |
+- - - - - - - - - - - - - - - -+- - - - - - - - - - - - - - - -+
| Interface Identifier (integer) |
+-------------------------------+-------------------------------+
| Tag = 0x0003 | Length |
+- - - - - - - - - - - - - - - -+- - - - - - - - - - - - - - - -+
\ \
/ Interface Identifier (text) /
\ \
+-------------------------------+-------------------------------+
| Tag = 0x0019 | Length |
+- - - - - - - - - - - - - - - -+- - - - - - - - - - - - - - - -+
\ \
/ Correlation Id /
\ \
+-------------------------------+-------------------------------+
| Tag = 0x0004 | Length |
+- - - - - - - - - - - - - - - -+- - - - - - - - - - - - - - - -+
\ \
/ Info String /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The Correlation Id parameter is used by the SGP in the ASPAC ACK
message to indicate the correlation identifier for the first UA-User
message to be transmitted from the Signalling Gateway to the
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Application Server being activated for each traffic flow. The
Application Servers for which the Correlation Id apply is either
indicated in the ASPAC ACK message by providing the associated Routing
Contexts (or Interface Identitifiers), or, if there is no Routing
Context or Interface Identifier parameter in the message, the
associated Application Servers are implied by the SGP and ASP
configuration data.
When the Correlation Id parameter is present in the ASPAC ACK
message, the message SHOULD only contain one Routing Context
(Interface Identifier) in the Routing Context (Interface Identifier)
parameter. When the Correlation Id parameter is not present, but
required by the ASP, the value of the Correlation Id is assumed to be
zero (0).
The ASPAC ACK message MAY contain additional extension parameters
provided for by other extensions.
No other changes to the ASPAC ACK message format are provided by
this extension.
3.2.3. Heartbeat (BEAT)
CORID supplements the BEAT message by permitting the following
optional parameters to tbe indicated in the message:
Extension Parameters
---------------------------------------------
Routing Context Conditional *1
Interface Identifier Conditional *2
Correlation Id Conditional
Note 1: The Routing Context parameter is only included in those
UAs that support Routing Context [M3UA..ISUA, TUA].
Note 2: The Interface Identifier parameter is only included in
those UAs that support Interface Identifier [M2UA].
The format of the resulting BEAT message is as follows:
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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 = 0x0006 | Length = 8 |
+- - - - - - - - - - - - - - - -+- - - - - - - - - - - - - - - -+
| Routing Context |
+-------------------------------+-------------------------------+
| Tag = 0x0001 | Length=8 |
+- - - - - - - - - - - - - - - -+- - - - - - - - - - - - - - - -+
| Interface Identifier (integer) |
+-------------------------------+-------------------------------+
| Tag = 0x0003 | Length |
+- - - - - - - - - - - - - - - -+- - - - - - - - - - - - - - - -+
\ \
/ Interface Identifier (text) /
\ \
+-------------------------------+-------------------------------+
| Tag = 0x0019 | Length |
+- - - - - - - - - - - - - - - -+- - - - - - - - - - - - - - - -+
\ \
/ Correlation Id /
\ \
+-------------------------------+-------------------------------+
| Tag = 0x0009 | Length |
+- - - - - - - - - - - - - - - -+- - - - - - - - - - - - - - - -+
\ \
/ Heartbeat Data /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The Routing Context parameter is used by the SPP in the BEAT
message to indicate the Application Server for which the message
applies when the CORID heatbeat procedures are used. The Application
Servers for which the BEAT message apply is either indicated in the
BEAT message by providing the associated Routing Contexts (or
Interface Identifier), or, if there is no Routing Context (or
Interface Identifier) paraemter in the message, the associated
Application Servers are implied by the SPP configuration data.
When the Routing Context (or Interface Identifier) is present in
the BEAT message, the message SHOULD only contain one Routing Context
(Interface Identifier) in the Routing Context (Interface Identifier)
parameter. When the Routing Context (Interface Identifier) is not
present in the BEAT message, but required by the SPP, the BEAT message
is assumed to be a normal BEAT message not supporting the procedures
of CORID an a normal BEAT ACK response MUST be generated.
The Correlation Id parameter is used by the SPP in the BEAT message
to indicate the correlation identifier for the last UA-User message
that was transmitted to the peer SPP for each traffic flow for the
given SCTP stream upon which the BEAT message is sent. The
Application Servers fro which the Correlation Id applies is either
indicated in the BEAT message by providing the associated Routing
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Context (Interface Identifier), or, if there is no Routing Context (or
Interface Identifier) parameter in the message, the associated
Application Servers are implied by the SPP configuration data.
When the Correlation Id parameter is present in the BEAT message,
the message SHOULD only contain one Routing Context (Interface
Identifier) in the Routing Context (Interface Identifier) parameter.
When the Correlation Id parameter is not present, but required by the
SPP, the value of the Correlation Id is assumed to be zero (0) for all
affected traffic flows.
The BEAT mesage MAY contain additional extension parameters
provided for by other extensions.
No other changes to the BEAT message format are provided by this
extension.
3.2.4. Heartbeat Acknowledgement (BEAT ACK)
CORID supplements the BEAT ACK message by permitting the following
optional parameters to tbe indicated in the message:
Extension Parameters
---------------------------------------------
Routing Context Conditional *1
Interface Identifier Conditional *2
Correlation Id Conditional
Note 1: The Routing Context parameter is only included in those
UAs that support Routing Context [M3UA..ISUA, TUA].
Note 2: The Interface Identifier parameter is only included in
those UAs that support Interface Identifier [M2UA].
The format of the resulting BEAT ACK message is as follows:
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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 = 0x0006 | Length = 8 |
+- - - - - - - - - - - - - - - -+- - - - - - - - - - - - - - - -+
| Routing Context |
+-------------------------------+-------------------------------+
| Tag = 0x0001 | Length=8 |
+- - - - - - - - - - - - - - - -+- - - - - - - - - - - - - - - -+
| Interface Identifier (integer) |
+-------------------------------+-------------------------------+
| Tag = 0x0003 | Length |
+- - - - - - - - - - - - - - - -+- - - - - - - - - - - - - - - -+
\ \
/ Interface Identifier (text) /
\ \
+-------------------------------+-------------------------------+
| Tag = 0x0019 | Length |
+- - - - - - - - - - - - - - - -+- - - - - - - - - - - - - - - -+
\ \
/ Correlation Id /
\ \
+-------------------------------+-------------------------------+
| Tag = 0x0009 | Length |
+- - - - - - - - - - - - - - - -+- - - - - - - - - - - - - - - -+
\ \
/ Heartbeat Data /
\ \
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
The Routing Context parameter is used by the SPP in the BEAT ACK
message to indicate the Application Server for which the message
applies when the CORID heatbeat procedures are used. The Application
Servers for which the BEAT ACK message apply is either indicated in
the BEAT ACK message by providing the associated Routing Contexts (or
Interface Identifier), or, if there is no Routing Context (or
Interface Identifier) paraemter in the message, the associated
Application Servers are implied by the SPP configuration data.
When the Routing Context (or Interface Identifier) is present in
the BEAT ACK message, the message SHOULD only contain one Routing
Context (Interface Identifier) in the Routing Context (Interface
Identifier) parameter. When the Routing Context (Interface
Identifier) is not present in the BEAT message, but required by the
SPP, the BEAT message is assumed to be a normal BEAT message not
supporting the procedures of CORID an a normal BEAT ACK response MUST
be generated.
The Correlation Id parameter is used by the SPP in the BEAT ACK
message if it appeared in the BEAT message. In this case, the
Correlation Id parameter that the SPP places in the BEAT ACK message
MUST be the same as that in the corrsponding received BEAT message.
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When the Correlation Id parameter is present in the BEAT ACK
message, the message SHOULD only contain one Routing Context
(Interface Identifier) in the Routing Context (Interface Identifier)
parameter.
The BEAT ACK mesage MAY contain additional extension parameters
provided for by other extensions.
No other changes to the BEAT ACK message format are provided by
this extension.
4. Procedures
CORID provides the following procedures in extension to the
procedures of the UAs [M2UA..ISUA, TUA].
4.1. Traffic Handling
In some circumstances, the SPP must treat traffic differently than
normal in fitting with the CORID procedures. This traffic handling is
described in the sections below:
4.1.1. Classification
Divertable messages are any UA-User messages destined for an
Application Server. Divertable messages are UA-User data and some
management (non-ASP management) messages that have an explicit or
implied Routing Context (Interface Identifier) and have strict
requirements preventing loss, duplication or mis-sequencing. All SSNM
messages containing an explicit or implied Routing Context SHALL be
classified as divertable, with the exception of DAUD which SHOULD be
classified as divertable between ASPs or SGPs belonging to the same
SG, and SHOULD be classified as non-divertable between SGs. UA-User
messages that qualify as divertable messages in addition to SSNM are
listed in Table 1. Although some messages in some message classes
might be considered as non-divertable, all messages in the message
classes listed in Table 1 SHALL be treated as divertable.
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Table 1. Divertable Messages by UA
+------+----------+----------+--------+
| UA | Class | Msg | Notes |
+------+----------+----------+--------+
| M2UA | MAUP | Data | |
| | | Data Ack | |
+------+----------+----------+--------+
| M3UA | Transfer | DATA | |
+------+----------+----------+--------+
| | CL | CLDT | Note 1 |
| | | CLDR | |
| +----------+----------+--------+
| | CO | CORE | |
| SUA | | COAK | |
| | | CODT | |
| | | RESRE | |
| | | RESCO | |
| | | RELRE | |
+------+----------+----------+--------+
| | TCM | TUNI | |
| | | TQRY | Note 2 |
| | | TCNV | |
| | | TRSP | |
| | +----------+--------+
| | | TUAB | |
| | | TPAB | |
| TUA | | TNOT | |
| +----------+----------+--------+
| | CHM | CINV | Note 3 |
| | | CRES | |
| | +----------+--------+
| | | CERR | |
| | | CREJ | |
| | | CCAN | |
+------+----------+----------+--------+
| | SSNM | DUNA | |
| | | DAVA | Note 4 |
| All | | SCON | |
| | | DUPU | |
| | +----------+--------+
| | | DAUD | Note 5 |
+------+----------+----------+--------+
Note 1: All those marked "Return on Error".
Note 2: All those without components or marked
"Return on Error".
Note 3: All those in operation class 1, 2 or 3.
Note 4: All those with implied Routing Context or
containing explicit Routing Context
parameters in the message.
Note 5: See Section 4.1.1.
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4.1.2. Correlation
Each independent traffic flow for a given Application Server as
identified by a Routing Context (Interface Identifier) MUST be
correlated using a Correlation Id. The Correlation Id consists of a
Correlation Number and a traffic flow identifier. The Correlation
Number is used to number each message within the given traffic flow.
4.1.2.1. Assignment of Correlation Ids
To accomodate all combinations of traffic modes at AS and SG,
divertable messages are correlated by independent traffic flow. That
is, each sent divertable message is labelled with a traffic flow
identifier and a Correlation Number for the AS that is incremented for
each message sent for the traffic flow. In the same fashion, each
received divertable message is labelled with the identity of the
traffic flow on which it was received and a Correlation Number for the
AS that is incremented for each message received on that traffic flow.
An SPP maintains two correlation counters for each traffic flow for
each AS: for each traffic flow, one counter tracks the Correlation
Number of messages sent to the AS and the other tracks the Correlation
Number of messages received from the AS. Before traffic is started
for an AS on a traffic flow, these counters are set to zero (0). The
first divertable message for the AS on the flow MUST then be assigned
a coorrelation number of one (1); and subsequent divertable messages,
the Correlation Number of two (2), three (3), and so forth.
Whenever traffic is started for the AS (using the ASP Active
Procedures), the correlation counters SHALL be synchronized by
exchanging correlation numbers and traffic flow identifiers in the
Correlation Id parameter in the ASPAC and ASPAC ACK messages. For new
traffic, the Correlation Number MUST zero (0); for restarting traffic,
it is SHOULD be the Correlation Number of the last message
transferred. (See Section 4.2.3.)
4.1.2.2. Assignment of Traffic Flow Ids
Traffic Flow Ids SHALL identify a switchable traffic flow within an
Application Server. The Traffic Flow Id value SHALL be assigned by
the sending SPP[1].
Traffic Flow Ids assigned by an SPP and MUST be communicated to the
peer SPP in an ASPAC or ASPAC ACK message.
For traffic distributions that do not loadshare (i.e, Override and
Broadcast), the Traffic Flow Id field is not required and MAY be set
to zero (0). In this case, the Correlation Id parameter in the BEAT,
BEAT ACK, ASPAC or ASPAC ACK message SHOULD only contain one
Correlation Id field (see Section 3.1.1).
Following are rules for the assignment of Traffic Flow Ids at an
SPP:
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(i) If an SPP belongs to a regular Override or Broadcast AS, no
Traffic Flow Id need be assigned or included by the SPP in the
Correlation Id parameter.
(ii) If an SPP belongs to a regular Loadshare AS, a Traffic Flow Id
is assigned and included in the Correlation Id parameter. The
Traffic Flow Id Id assigned MUST unambiguously identify the
traffic flow within the AS.
(iii) If an SPP belongs to a Load Selector [LOADSEL], a Traffic Flow
Id is assigned and included in the Correlation Id parameter
regardless of the Traffic Mode Type of the AS. The Traffic
Flow Id assigned MUST unambiguously identify the the Load
Selection within the AS.[2]
(iv) If an SPP belongs to a Load Group [LOADGRP], a Traffic Flow Id
is assigned and included in the Correlation Id for a Loadshare
AS or Load Group. An assigned Traffic Flow Id MUST
unambiguously identify the Load Selection within the AS. For a
non-loadshare AS and Load Group, no Traffic Flow Id need be
assigned or included in the Correlation Id parameter.[3]
4.1.3. Tagging
Each sent or received message for an AS is labelled when it is
first sent or received. The message is labelled with the traffic flow
id associated with the SPP to or from which the message was sent or
received, and the correlation number assigned within the traffic flow
(see Section 4.1.2.1).
Tagged messages contain a Correlation Id parameter: an untagged
message is tagged by adding a Correlation Id parameter to the message.
When a message is tagged, it SHALL be tagged with the same values of
the traffic flow id (if required) and Correlation Number with which it
was originally labelled.
Although each message is labelled with a traffic flow id and
correlation number, the message is not necessarily tagged with the
Correlation Id parameter when the message is sent. Messages for an AS
that are sent for the first time MUST NOT be tagged. Messages
retransmitted MUST be tagged.
4.1.4. Buffering
To support CORID and SPP will have to, under some circumstances,
buffer messages. When divering traffic, the SPP requires buffers to
hold unsent messages awaiting diversion; when sending traffic, the SPP
requires buffers to hold local copies of sent messages in the event of
failure.
4.1.4.1. SPP witholding unsent messages
CORID procedures require that an SPP at times withhold AS traffic.
To perform this, the SPP allocates a diversion buffer and places in
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the buffer all subsequent messages that would otherwise be sent to the
SPP for the AS.
4.1.4.2. Local copies of sent messages
To reduce loss of messages, an SPP SHOULD buffer messages until it
can be assured that the peer SPP has received and processed the
message. When a message is sent to an SPP supporting CORID a local
copy of the message MUST be kept until it is discarded in accordance
with a CORID procedure.[4]
(i) A local copy SHOULD NOT be discarded when it is acknowledged by
the peer SCTP.
(ii) a local copy SHOULD NOT be discarded until the sending SPP is
confident that the peer SPP has received and processed the
message.
(iii) To ensure that stale messages do not propagate through the
system, an SPP SHOULD NOT keep local copies of sent messages
for longer than a maximum lifetime T(lifetime). Any local
coppies of sent messages that are older (measured from the
moment at which they were sent to the peer SPP) than
T(lifetime) SHOULD be discarded.
4.1.5. Message Handling
The SPP supporting CORID handles tagged and untagged messages
differently.
4.1.5.1. Untagged Messages
Under some circumstances, an SPP will send or receive untagged
messages. Untagged messages (see Section 4.1.3) are messages which do
not contain a Correlation Id parameter.
4.1.5.1.1. SPP sending untagged messages
An SPP sends untagged messages to a peer SPP whenever the message
is being sent for an Application Server for the first time. All
divertable messages which have been transmitted for the first time
MUST NOT be sent tagged.
Local copies of untagged messages awaiting acknowledgement or
expiry are labelled with the Routing Context (Interface Identifier)
for the Application Server to which they were sent, the traffic flow
id of the SPP to which they were sent, and the Correlation Number of
the message. The Correlation Number with which a message is labelled
MUST be the next sequential Correlation Number for the AS and traffic
flow. These labels can be used later to tag a message that is marked
for diversion.
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4.1.5.1.2. SPP receiving untagged messages
When an SPP receives an untagged message, it associates with the
message the next sequential Correlation Number for the Routing Context
(Interface Identifier) and traffic flow id for which the message was
received. Untagged messages are received in order and MAY be
processed when received. The SPP SHOULD keep track of the Correlation
Ids that have been processed for the AS.
4.1.5.2. Tagged Messages
Under some circumstances, an SPP will send or receive tagged
messages. Tagged messages (see Section 4.1.3) are messages which
contain a Correlation Id parameter.
4.1.5.2.1. SPP sending tagged messages
An SPP sends tagged traffic whenever it sends traffic that is
marked for diversion. That is, whenever an SPP sends divertable
messages to an SPP other than the original SPP for which those
messages were labelled, the SPP MUST tag the message with the
Correlation Id parameter that contains the labelled traffic flow id
(if required) and Correlation Number.
In addition, when a ASP becomes active for a Broadcast AS, an SGP
MUST tag the first message in each traffic flow towards the ASP to
allow the ASP to synchronize its entry into the Broadcast AS.
4.1.5.2.2. SPP receiving tagged messages
The handling of tagged messages is the mechanism that provides for
the reduction of message loss, duplication and mis-sequencing. An SPP
receiving divertable messages containing a Correlation Id parameter
SHALL perform the following actions:
(i) The SPP determines (by implementation-dependent means [5])
whether the message has already been processed for the AS.
(ii) If the message has not already been processed for the AS, it is
processed as normal.
(iii) If the message has already been processed for the AS, it is
discarded.
(iv) If, as a result of some failure, the SPP cannot determine with
any certainly whether the tagged message has been processed
for the AS, or not, the SPP MUST discard the message[6].
4.1.5.3. Heartbeat Messages
Under some circumstances, an SPP will send or receive BEAT messages
with the intention of pushing the messages on the stream on which the
BEAT message is sent.
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4.1.5.3.1. SPP sending BEAT messages
An SPP sends BEAT messages whenever it witholds traffic to or from
an AS in preparation for diversion. That is, whenever an SPP
withholds divertable messages, the SPP MUST send a BEAT message with
an implied Application Server or explicit Routing Context (Interface
Identifier) plus the Correlation Id parameter with the Traffic Flow
Ids for a particularl stream, on each stream used by the AS for which
traffic is being diverted.
4.1.5.3.2. SPP receiving BEAT messages
The handling of BEAT messages is the mechanism that provide for the
reduction of message loss, duplication and mis-sequencing during
diversion between active SPP. An SPP receiving a BEAT message
containing an explicit or implied Routing Context (Interface
Identifier) and Correlation Id parameter on a stream other than stream
zero (0) SHALL perform the following actions:
(i) The SPP will wait until any internal queue of messages for the
Application Server indicated by the Routing Context (Interface
Identifier) and the traffic flows indicated by the Correlation
Id parameter in the BEAT message have drained.
(ii) If the SGP can determine the traffic flows in the SS7 network
which require changeback, the SPP MAY then initiate a
changeback procedure [Q.704] to the SS7 network and await
completion of the changeback procedure.
(iii) Once internal message queues for the Application server have
drained (i.e. all messages for the indicated Application Server
have been processed), and any changeback procedure to the SS7
network has completed at an SGP, the SPP will respond with a
BEAT ACK message which contains the Routing Context (Interface
Identifier) parameter, the Correlation Id parameter unchanged,
and the opqaue information contained in the Heatbeat Data
parameter of the BEAT message. (This BEAT ACK message may be
sent on any stream.)
4.1.6. Diversion
When an SPP supporting CORID wishes to reroute traffic from one SPP
or AS to another, it performs a diversion.
4.1.6.1. SPP diverting traffic from a failed, deactivated or overridden
peer SPP
When diverting traffic due to a failed, deactivated or overridden
peer SPP, the diverting SPP will be in one of the following
situations:
(i) no alternate SPP exists,
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(ii) an alternate SPP exists in the same AS or SG,
(iii) an alternate SPP exists in a different AS or SG.
4.1.6.1.1. Alternate SPP in same AS or SG, or No Alternate SPP
When an SPP diverts AS traffic away from a failed, deactivated or
overridden peer SPP to an alternate peer SPP in the same AS or SG, the
SPP SHALL perform the following actions:
(i) The SPP tags (see Section 4.1.3) each untagged message that is
marked for diversion.
(ii) If an alternate SPP is available (active for the AS), the SPP
sends the messages marked for divertion to the alternate SPP.
(iii) If no alternate SPP exists (the AS is AS-PENDING), the SPP
buffers the marked messages in a buffer used for buffering
messages while the AS is in the AS-PENDING state.
(iv) The SPP then diverts AS traffic, beginning with traffic
withheld for the AS, to the alternate SPP or AS-PENDING buffer.
This procedure corresponds to the Sequenced Changeover procedure
used by the SS7 MTP [Q.704].
4.1.6.1.2. Alternate SPP in different AS or SG
When an SPP diverts AS traffic away from a failed or deactivated
peer SPP to an alternate peer SPP in a different AS or SG, the SPP
SHALL perform the following actions:
(i) The SPP starts timer T(divert) and continues buffering AS
traffic until the timer expires.
(ii) When T(divert) expires, and the failed or deactivated SPP has
not recovered, the SPP continues with the following actions:
(iii) The SPP discards all tagged messages and messages marked for
diversion.
(iv) The SPP starts AS traffic, beginning with the contents of the
diversion buffer, to the alternate SPP.[7]
This procedure corresponds to the Time-Controlled Changeover
procedure used by the SS7 MTP [Q.704].
4.1.6.2. SPP diverting traffic from an active peer SPP
When an SPP wishes to divert AS traffic away from an active peer
SPP, the SPP SHALL perform the following actions:
(i) The SPP witholds and buffers AS traffic for the SPP from which
the traffic is being diverted.
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(ii) The SPP sends a BEAT message with the associated Routing
Context (Interface Identifier) and the Traffic Flow Ids being
diverted in the Correlation Id parameter, plus a unique
identifier[8] in the Heartbeat Data parameter on each SCTP
stream on which the traffic being withheld for diversion was
previously sent. The Correlation Id parameter SHOULD only
contain the Traffic Flow Ids that correspond to traffic flows
on the SCTP stream upon which the particular BEAT message is
sent. If the Application Server is not implied by the SCTP
association, the BEAT message must also contain the Routing
Context (Interface Identifier) coresponding to the Application
Server.
(iii) The SPP starts a timer T(restore).
(iv) If the SPP receives the BEAT ACK message(s) for the concerned
Application Server that contain the unique identifier(s) in the
Heartbeat Data parameter before timer T(restore) expires, the
SPP diverts the traffic, beginning with the withheld traffic,
to the target SPP and cancels the T(restore) timer.
(v) If the timer T(restore) expires, the diverting SPP diverts
traffic, beginning with the withheld traffic, to the target
SPP.
(vi) If an SPP receives a BEAT ACK message(s) for the concerned
Application Server containing a unique identifier for which the
timer T(restore) has already expired, the SPP ignores the
message.
The purpose of this BEAT procedure is to avoid mis-sequencing by
ensuring that all messages sent for the AS to the old SPP have been
processed before messages are sent to the new SPP. This avoids races
between (and possible mis-sequencing of) messages sent on the old SPP
and messages sent on the new SPP.
This procedure corresponds to the Changeback procedure used by the
SS7 MTP [Q.704].
4.2. ASP Management Procedures
CORID extends the ASP Management procedures of the UAs with the
following procedures:
4.2.1. ASP Down Procedures
CORID extends the ASP Down procedures of the UAs as follows:
4.2.1.1. SPP detecting loss of SCTP association
When an SPP receives an SCTP COMMUNICATION LOST or RESTART
indication and there are Application Servers active for the
association, the SPP SHALL perform the following actions with regard
to active AS traffic for the association:
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(i) The SPP witholds AS traffic for the peer SPP in a diversion
buffer.
(ii) The SPP marks for diversion all local copies of AS messages
already sent to the peer SPP.
(iii) The SPP then SHALL perform the actions described in Section
4.1.6.1.
4.2.1.2. ASP sending ASPDN
An ASP MUST NOT send an ASPDN message until it has completed the
ASP Inactive Procedures with the intended SGP for every AS.
4.2.1.3. SGP or IPSP receiving ASPDN
An SGP or IPSP, upon rreceiving an ASPDN message from an ASP-ACTIVE
ASP, MUST perform the ASP Inactive Procedures with regard to CORID
(see Section 4.2.2.2) for every AS for which the ASP is ASP-ACTIVE and
then complete the ASPDN procedures.
4.2.1.4. ASP receiving ASPDN ACK
An SGP or IPSP, upon receiving an unsolicited ASPDN ACK message
from an active SGP, MUST perform the ASP Inactive Procedures with
regard to CORID (see Section 4.2.2.3) for every AS for which the ASP
is ASP-ACTIVE and then complete the ASPDN ACK procedures.
4.2.2. ASP Inactive Procedures
CORID extends the ASP Inactive procedures of the UAs as follows:
4.2.2.1. ASP sending ASPIA
When an ASP wishes to deactivate an Application Server with an SGP,
the ASP SHALL perform the following actions for traffic pertaining to
the AS:
(i) The ASP withholds sending AS traffic to the SGP or IPSP.
(ii) The ASP stops processing AS traffic recevied from the SGP or
IPSP. Any messages received for the Application Server after
the last processed message MAY be discarded.
(iii) The ASP starts a T(divert) timer.
(iv) The ASP SHALL perform the applicable UA ASP Inactive
Procedures[9].
4.2.2.2. SGP receiving ASPIA or sending ASPIA ACK
An SGP receiving an ASPIA message for an AS, or wishing to send an
unsolicited ASPIA ACK to deactivate an AS, SHALL perform the following
actions for the traffic pertaining to each AS for which deactivation
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is performed:
(i) The SGP withholds sending AS traffic to the ASP.
(ii) The SGP stops processing AS traffic received from the ASP. Any
messages received for the AS at the SGP after receiving the
ASPIA message MUST be discarded.
(iii) The SGP marks for diversion all local copies of AS messages
sent to the ASP.
(iv) The SGP then SHALL perform the actions described in Section
4.1.6.1.
(v) The ASP SHALL perform the applicable UA ASP Inactive
Procedures[9].
4.2.2.3. ASP receiving ASPIA ACK
Upon receiving an ASPIA ACK message the ASP SHALL perform the
following actions for the traffic pertaining to the AS identified by
the Routing Context (Interface Identifier) in the received ASPIA ACK
message or implied by the SCTP association on which the ASPIA ACK
message was received:
(i) The T(divert) timer is cancelled (if running).
(ii) The ASP marks for diversion any local copies of AS messages
sent to the SGP.
(iii) The ASP then SHALL perform the actions described in Section
4.1.6.1.
(iv) The ASP SHALL perform the applicable UA ASP Inactive
Procedures[9].
4.2.2.4. T(divert) timer expiry
If the T(divert) timer expires before receiving an ASPIA ACK for
the AS, the ASP SHALL perform the actions described in Section
4.2.2.3.
4.2.3. ASP Active Procedures
CORID extends the ASP Active procedures of the UAs as follows:
4.2.3.1. ASP sending ASPAC
When an ASP wishes to activate an Application Server for an SGP,
the ASP SHALL perform the following actions for traffic pertaining to
the AS:
(i) The ASP determines the Correlation Number of the last message
sent to this SGP for the AS for each traffic flow.
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(ii) If the ASP has not sent a message to the SGP for the traffic
flow, the Correlation Number zero (0) is used.
(iii) If the ASP has sent messages to the SGP for the traffic flow,
but cannot determine the Correlation Number of the last message
sent due to local failure, the Correlation Number zero (0) is
used.
(iv) The ASP includes the Correlation Number(s) determined above in
the Correlation Id parameter in the ASPAC message used to
active the AS. (See Section 3.1.1.)
(v) The ASP SHALL perform the applicable UA ASP Active
Procedures[10].
4.2.3.2. SGP receiving ASPAC
When an SGP receives an ASPAC message for an Application Server,
the SGP SHALL perform the following actions with regard to traffic for
the AS:
(i) The SGP sets the Correlation Number of the next received
message from the ASP for each traffic flow to the value,
contained in the Correlation Id parameter in the ASPAC ACK
message, plus one (1).
(ii) The SGP determines the Correlation Number of the last message
sent to this ASP for each traffic flow.
(iii) If the SGP has not sent a message to the ASP for a traffic
flow, the Correlation Number zero (0) is used.
(iv) If the SGP has sent messages to the ASP for a traffic flow, but
cannot determine the Correlation Number of the last message
sent due to local failure, the Correlation Number zero (0) is
used.
(v) The SGP includes the Correlation Number(s) determined above in
the Correlation Id parameter in the ASPAC ACK message used to
acknowledge activation of the AS. (See Section 3.1.1.)
(vi) The SGP SHALL perform the applicable UA ASP Active
Procedures[10], including the sending of ASPIA ACK.
(vii) The SGP then SHALL perform the actions described in Section
4.1.6.2.
4.2.3.3. ASP receiving ASPAC ACK
When an ASP receives an expected ASPAC ACK message for an
Application Server, the ASP SHALL perform the following actions with
regard to AS traffic:
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(i) The ASP sets the Correlation Number of the next received
message from the SGP for each traffic flow to the value,
contained in the Correlation Id parameter in the ASPAC ACK
message, plus one (1).
(ii) The ASP SHALL perform the applicable UA ASP Active
Procedures[10].
(iii) The ASP then SHALL perform the actions described in Section
4.1.6.2.
If an ASP receives an unexpected ASPAC ACK (i.e, one for which no
ASPAC was sent and the ASP is already in the ASP-ACTIVE state for the
AS), then the ASP SHALL ignore the message for the purposes of CORID.
The ASP SHALL, however, perform the applicable UA ASP Active
Procedures[10].
4.3. Interworking Procedures
Because the CORID procedures provided here rely upon close
synchronization of Correlation Number between SPP, if one of the SPP
does not support these CORID procedures, neither SPP is able to take
advantage of the full benefits of the procedures. The SPP supporting
CORID MAY fall back to the interworking procedures provided in this
section, or to procedures based on the original (non-CORID) UA
procedures.
A peer SPP that does not support the CORID procedures can either be
identified by local configuration information, the ASP Extenstions
[ASPEXT] procedure, or at ASP Activation time. The lack of support
for CORID can be determined at ASP Activation time when the peer SPP
does not place a Correlation Id parameter (as it MUST if both peers
support CORID) in the ASPAC (ACK) message.
When interworking to an SPP that does not support CORID, the SPP
supporting CORID SHALL perform all of the procedures as though the
peer SPP supported CORID with the following exceptions:
(i) The SPP MUST NOT send messages marked for diversion and tagged
to the peer SPP not supporting CORID. All such messages MAY be
discarded.
(ii) When diverting traffic between a failed, deactivated or
overriden peer SPP and an alternate peer SPP not supporting
CORID, the actions described in Section 4.1.6.1.2 MUST always
be used instead of the procedures in Section 4.1.6.1.1, except
when there is no alternate SPP.
(iii) When diverting traffic from an active peer SPP not supporting
CORID, the actions described in Section 4.1.6.2 SHALL be
followed with the exception of Section 4.1.6.2(ii), (iv) and
(vi), which MUST NOT be performed.
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(iv) The SPP MUST NOT place a Correlation Id parameter in the ASPAC
or ASPAC ACK. So, the actions described in Sections
4.2.3.1(i)-(iv), 4.2.3.2(i)-(v) and 4.2.3.3(i)-(ii) do not
apply.
(v) The SPP MUST NOT place a Routing Context (Interface Identifier)
paramete rin the BEAT or BEAT ACK. So, the actions described
in Sections 4.1.6.2(ii), (iv), and (vi) do not apply.
Notes for Section 4
[1] That is, the Traffic Flow Id will be assigned by the SPP
sending the message. Traffic Flow Ids are only used to
determine whether messages belong to the same traffic flow,
therefore, the Traffic Flow Id need only uniquely identify a
traffic flow within an Application Server at the sending SPP.
[2] IMPLEMENTATION NOTE:- A simple way to assign the Traffic Flow
Id when performing Load Selection [LOADSEL] is to simply assign
the same value to the Traffic Flow Id as is assigned to the
Load Selector.
[3] IMPLEMENTATION NOTE:- A simple way to assign the Traffic Flow
Id when performing Load Grouping [LOADGRP] is to simply assign
the same value to the Traffic Flow Id as is assigned to the
Load Selector or Load Group Identifier.
[4] IMPLEMENTATION NOTE:- A simple way to meet the requirements
for keeping local copies of messages is to keep a local copy of
all messages sent to an SPP supporting CORID until a fixed
buffer allocation is exceeded, or until the local copy lifetime
expires. T(lifetime) and buffer capacity can then be adjusted
to ensure that local copies of messages are not discarded too
early resulting in message loss during fail-over.
[5] IMPLEMENTATION NOTE:- Determining which messages have already
been processed for the AS may require some ASP-to-ASP or SGP-
to-SGP synchronization that is outside the scope of the UA
documents [M2UA..ISUA, TUA] and also outside the scope of this
document.
If the received traffic flow id matches that of the SPP on
which the message was received, this might be a simple matter
of comparing the correlation number of the message to the
Correlation Number of the last message processed for the
Application Server.
[6] IMPLEMENTATION NOTE:- The reason for discarding tagged
messages at the receiver for which it cannot be determined with
any certainty whether the message was processed for the AS or
not is because, for SS7, message loss is preferrable to message
duplication [Q.706].
[7] IMPLEMENTATION NOTE:- When restarting traffic with the
contents of the diversion buffer, it might be necessary to
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reassign Routing Context (Interface Identifier) values within
the messages if the Routing Context (Interface Identifier)
values were assigned before buffering, and if the Routing
Context (Interface Identifier) values associated with the AS
traffic for the alternate SPP are different than the Routing
Context (Interface Identifier) values associated with the same
AS traffic for the failed SPP.
[8] IMPLEMENTATION NOTE:- Although the unique identifier placed in
the Heartbeat Data is implementation dependent, a useful
identifier would be the tuple formed by the Routing Context
(Interface Identifier), Correlation Id corresponding to the
last message(s) sent to the SPP from which the included traffic
flows are to be diverted.
[9] For the "ASP Inactive Procedures", see Section 4.3.4.4 of the
specific UA document [M2UA..ISUA, TUA].
[10] For the "ASP Active Procedures", see Section 4.3.4.3 of the
specific UA document [M2UA..ISUA, TUA].
5. Examples
5.1. Example Configuration
5.2. Initialization
Figure 5 illustrates the initialization sequence that is used for
all of the examples .
SGP1 SGP2 ASP1 ASP2 ASP3 ASP4 AS1
: : : : : : :
(1) :<----:-Establish Association------>: : : : :
:<----:-ASPUP-----------------------: : : : :
:-----:-ASPUP ACK------------------>: : : : :
: : : : : : :
(2) :<----:-Establish Association-------:--->: : : :
:<----:-ASPUP-----------------------:----: : : :
:-----:-ASPUP ACK-------------------:--->: : : :
: : : : : : :
(3) :<----:-Establish Association-------:----:--->: : :
:<----:-ASPUP-----------------------:----:----: : :
:-----:-ASPUP ACK-------------------:----:--->: : :
: : : : : : :
(4) :<----:-Establish Association-------:----:----:--->: :
:<----:-ASPUP-----------------------:----:----:----: :
:-----:-ASPUP ACK-------------------:----:----:--->: :
: : : : : : :
(5) : : (Same message exchange for SGP2) : : : :
: : : : : : :
Figure 5. Initialization for Examples
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The sequence of events in the exmaple illustrated in Figure 5 is as
follows:
(1) ASP1 establishes an SCTP association to SGP1 and sends an ASUP
message. SGP1 responds with an ASPUP ACK.
(2) ASP2 establishes an SCTP association to SGP1 and sends an ASUP
message. SGP1 responds with an ASPUP ACK.
(3) ASP3 establishes an SCTP association to SGP1 and sends an ASUP
message. SGP1 responds with an ASPUP ACK.
(4) ASP4 establishes an SCTP association to SGP1 and sends an ASUP
message. SGP1 responds with an ASPUP ACK.
(5) ASP1 establishes an SCTP association to SGP2 and sends an ASUP
message. SGP2 responds with an ASPUP ACK. ASP2 establishes an
SCTP association to SGP2 and sends an ASUP message. SGP2
responds with an ASPUP ACK. ASP3 establishes an SCTP
association to SGP2 and sends an ASUP message. SGP2 responds
with an ASPUP ACK. ASP4 establishes an SCTP association to
SGP2 and sends an ASUP message. SGP2 responds with an ASPUP
ACK.
5.3. Starting Traffic
These are examples of starting traffic.
5.3.1. Initial Startup
Figure 6 illustrates an example of an ASP joining a Loadshare
Application Server.
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SGP1 SGP2 ASP1 ASP2 ASP3 ASP4 AS1
: : : : : : :
(1) :<----:--ASPAC (RC1)----------------: : : : :
: : : : : : :
(2) :-----:--ASPAC ACK (RC1)----------->: : : : :
: : : : : : :
:<====:==DATA=======================: : : : :
: : : : : : :
(3) :-----:--NTFY (RC1,AS-ACTIVE)------>: : : : :
:-----:--NTFY (RC1,AS-ACTIVE)-------:--->: : : :
:-----:--NTFY (RC1,AS-ACTIVE)-------:----:--->: : :
:-----:--NTFY (RC1,AS-ACTIVE)-------:----:----:--->: :
: : : : : : :
:=====:=DATA=======================>: : : : :
: : : : : : :
(4) : :<-ASPAC (RC1)----------------: : : : :
: : : : : : :
(5) : :--ASPAC ACK (RC1)----------->: : : : :
: : : : : : :
: :<=DATA=======================: : : : :
: : : : : : :
(6) : :--NTFY (RC1,AS-ACTIVE)------>: : : : :
: :--NTFY (RC1,AS-ACTIVE)-------:--->: : : :
: :--NTFY (RC1,AS-ACTIVE)-------:----:--->: : :
: :--NTFY (RC1,AS-ACTIVE)-------:----:----:--->: :
: : : : : : :
: :==DATA======================>: : : : :
: : : : : : :
: : : : : : :
Figure 6. Example - Initial Startup
The sequence of events in the exmaple illustrated in Figure 6 is as
follows:
(1) ASP1 sends an ASPAC message to SGP1 contining the Routing
Context (Interface Identifier) corresponding to AS1 (RC1 or
IID1). Because ASP1 has never sent traffic to SGP1 for AS1,
the initial value of all Correlation Numbers for each traffic
flow activated is zero (0) and the Correlation Id parameter
need not be included in the ASPAC message. (See Section
4.2.3.1.)
(2) SGP1 sends an ASPAC ACK message to SGP1 in response. Because
SGP1 has never send traffic to ASP1 for AS1, the initial value
of all Corrleation Numbers for each traffic flow activated is
zero (0) and the Corredlation Id parameter need not be included
in the ASPAC message. (See Section 4.2.3.2.)
Test.
(3)
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(4)
(5)
(6)
(7)
5.3.2. Joining a Broadcast
Figure 7 illustrates an example of an ASP joining a Broadcast
Application Server.
SGP1 SGP2 ASP1 ASP2 ASP3 ASP4 AS1
: : : : : : :
(1) :<----:-Establish Association------>: : : : :
:<----:-ASPUP-----------------------: : : : :
:-----:-ASPUP ACK------------------>: : : : :
: : : : : : :
(2) :<----:-Establish Association-------:--->: : : :
:<----:-ASPUP-----------------------:----: : : :
:-----:-ASPUP ACK-------------------:--->: : : :
: : : : : : :
(3) :<----:-Establish Association-------:----:--->: : :
:<----:-ASPUP-----------------------:----:----: : :
:-----:-ASPUP ACK-------------------:----:--->: : :
: : : : : : :
(4) :<----:-Establish Association-------:----:----:--->: :
:<----:-ASPUP-----------------------:----:----:----: :
:-----:-ASPUP ACK-------------------:----:----:--->: :
: : : : : : :
: : (Same message exchange for SGP2) : : : :
: : : : : : :
Figure 7. Example - Joining a Broadcast AS
The sequence of events in the exmaple illustrated in Figure 7 is as
follows:
(1)
(2)
(3)
(4)
(5)
(6)
(7)
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5.4. Fail-Over, Deactivation and Blocking
These are examples of fail-over, deactivation and blocking.
5.4.1. Association Recovery - Loadshare
Figure 8 illustrates an example of SCTP association recovery in a
Loadshare Application Server.
SGP1 SGP2 ASP1 ASP2 ASP3 ASP4 AS1
: : : : : : :
(1) :<----:-Establish Association------>: : : : :
:<----:-ASPUP-----------------------: : : : :
:-----:-ASPUP ACK------------------>: : : : :
: : : : : : :
(2) :<----:-Establish Association-------:--->: : : :
:<----:-ASPUP-----------------------:----: : : :
:-----:-ASPUP ACK-------------------:--->: : : :
: : : : : : :
(3) :<----:-Establish Association-------:----:--->: : :
:<----:-ASPUP-----------------------:----:----: : :
:-----:-ASPUP ACK-------------------:----:--->: : :
: : : : : : :
(4) :<----:-Establish Association-------:----:----:--->: :
:<----:-ASPUP-----------------------:----:----:----: :
:-----:-ASPUP ACK-------------------:----:----:--->: :
: : : : : : :
: : (Same message exchange for SGP2) : : : :
: : : : : : :
Figure 8. Example - Association Recovery
The sequence of events in the exmaple illustrated in Figure 8 is as
follows:
(1)
(2)
(3)
(4)
(5)
(6)
(7)
5.4.2. Assocation Failure - Override
Figure 9 illustrates an example of SCTP association failure in an
Override Application Server.
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SGP1 SGP2 ASP1 ASP2 ASP3 ASP4 AS1
: : : : : : :
(1) :<----:-Establish Association------>: : : : :
:<----:-ASPUP-----------------------: : : : :
:-----:-ASPUP ACK------------------>: : : : :
: : : : : : :
(2) :<----:-Establish Association-------:--->: : : :
:<----:-ASPUP-----------------------:----: : : :
:-----:-ASPUP ACK-------------------:--->: : : :
: : : : : : :
(3) :<----:-Establish Association-------:----:--->: : :
:<----:-ASPUP-----------------------:----:----: : :
:-----:-ASPUP ACK-------------------:----:--->: : :
: : : : : : :
(4) :<----:-Establish Association-------:----:----:--->: :
:<----:-ASPUP-----------------------:----:----:----: :
:-----:-ASPUP ACK-------------------:----:----:--->: :
: : : : : : :
: : (Same message exchange for SGP2) : : : :
: : : : : : :
Figure 9. Example - Assocation Failure
The sequence of events in the exmaple illustrated in Figure 9 is as
follows:
(1)
(2)
(3)
(4)
(5)
(6)
(7)
5.4.3. Deactivation - Loadshare
This is an example of deactivation of an ASP in a Loadshare
Application Server.
5.4.4. Management Blocking - Override
Figure 10 illustrates an example of management blocking of an SGP
in an Override Application Server.
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SGP1 SGP2 ASP1 ASP2 ASP3 ASP4 AS1
: : : : : : :
(1) :<----:-Establish Association------>: : : : :
:<----:-ASPUP-----------------------: : : : :
:-----:-ASPUP ACK------------------>: : : : :
: : : : : : :
(2) :<----:-Establish Association-------:--->: : : :
:<----:-ASPUP-----------------------:----: : : :
:-----:-ASPUP ACK-------------------:--->: : : :
: : : : : : :
(3) :<----:-Establish Association-------:----:--->: : :
:<----:-ASPUP-----------------------:----:----: : :
:-----:-ASPUP ACK-------------------:----:--->: : :
: : : : : : :
(4) :<----:-Establish Association-------:----:----:--->: :
:<----:-ASPUP-----------------------:----:----:----: :
:-----:-ASPUP ACK-------------------:----:----:--->: :
: : : : : : :
: : (Same message exchange for SGP2) : : : :
: : : : : : :
Figure 10. Example - Deactivation
The sequence of events in the exmaple illustrated in Figure 10 is
as follows:
(1)
(2)
(3)
(4)
(5)
(6)
(7)
5.5. Recovery
These are examples of recovery.
5.5.1. Association Recovery - Loadshare
Figure 11 illustrates an example of the recovery of an ASP in a
Loadshare Application Server.
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SGP1 SGP2 ASP1 ASP2 ASP3 ASP4 AS1
: : : : : : :
(1) :<----:-Establish Association------>: : : : :
:<----:-ASPUP-----------------------: : : : :
:-----:-ASPUP ACK------------------>: : : : :
: : : : : : :
(2) :<----:-Establish Association-------:--->: : : :
:<----:-ASPUP-----------------------:----: : : :
:-----:-ASPUP ACK-------------------:--->: : : :
: : : : : : :
(3) :<----:-Establish Association-------:----:--->: : :
:<----:-ASPUP-----------------------:----:----: : :
:-----:-ASPUP ACK-------------------:----:--->: : :
: : : : : : :
(4) :<----:-Establish Association-------:----:----:--->: :
:<----:-ASPUP-----------------------:----:----:----: :
:-----:-ASPUP ACK-------------------:----:----:--->: :
: : : : : : :
: : (Same message exchange for SGP2) : : : :
: : : : : : :
Figure 11. Example - Association Recovery
The sequence of events in the exmaple illustrated in Figure 11 is
as follows:
(1)
(2)
(3)
(4)
(5)
(6)
(7)
5.5.2. AS-Pending Recovery
Figure 12 illustrates an example of the recovery of an ASP for an
AS in the AS-PENDING state.
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SGP1 SGP2 ASP1 ASP2 ASP3 ASP4 AS1
: : : : : : :
(1) :<----:-Establish Association------>: : : : :
:<----:-ASPUP-----------------------: : : : :
:-----:-ASPUP ACK------------------>: : : : :
: : : : : : :
(2) :<----:-Establish Association-------:--->: : : :
:<----:-ASPUP-----------------------:----: : : :
:-----:-ASPUP ACK-------------------:--->: : : :
: : : : : : :
(3) :<----:-Establish Association-------:----:--->: : :
:<----:-ASPUP-----------------------:----:----: : :
:-----:-ASPUP ACK-------------------:----:--->: : :
: : : : : : :
(4) :<----:-Establish Association-------:----:----:--->: :
:<----:-ASPUP-----------------------:----:----:----: :
:-----:-ASPUP ACK-------------------:----:----:--->: :
: : : : : : :
: : (Same message exchange for SGP2) : : : :
: : : : : : :
Figure 12. Example - AS-PENDING Recovery
The sequence of events in the exmaple illustrated in Figure 12 is
as follows:
(1)
(2)
(3)
(4)
(5)
(6)
(7)
5.6. Interworking
These are examples of interworking between nodes not supporting
CORID with nodes supporting CORID.
5.6.1. ASP does not Support CORID
Figure 13 illustrates an example where the ASP does not support
CORID, but the SGP does.
B. Bidulock Version 0.3 Page 43
Internet Draft UA CORID February 21, 2004
SGP1 SGP2 ASP1 ASP2 ASP3 ASP4 AS1
: : : : : : :
(1) :<----:-Establish Association------>: : : : :
:<----:-ASPUP-----------------------: : : : :
:-----:-ASPUP ACK------------------>: : : : :
: : : : : : :
(2) :<----:-Establish Association-------:--->: : : :
:<----:-ASPUP-----------------------:----: : : :
:-----:-ASPUP ACK-------------------:--->: : : :
: : : : : : :
(3) :<----:-Establish Association-------:----:--->: : :
:<----:-ASPUP-----------------------:----:----: : :
:-----:-ASPUP ACK-------------------:----:--->: : :
: : : : : : :
(4) :<----:-Establish Association-------:----:----:--->: :
:<----:-ASPUP-----------------------:----:----:----: :
:-----:-ASPUP ACK-------------------:----:----:--->: :
: : : : : : :
: : (Same message exchange for SGP2) : : : :
: : : : : : :
Figure 13. Example - Interworking
The sequence of events in the exmaple illustrated in Figure 13 is
as follows:
(1)
(2)
(3)
(4)
(5)
(6)
(7)
6. Security
CORID does not introduce any new security risks or considerations
that are not already inherent in the UA [M2UA..ISUA, TUA] Please see
the SIGTRAN Secuirty document [SIGSEC] for security considerations and
recommendations that are applicable to each of these UAs.
7. IANA Considerations
CORID redefines the format of the Correlation Id parameter for
M2UA, M3UA, SUA and TUA. CORID also redifines the ASPAC and ASPAC ACK
messages to include the Correlation Id parameter as a mandatory
parameter of those messages.
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8. Timers
Following are the RECOMMENDED timer values:
T(divert) 0.5-2 seconds
T(restore) 0.5-2 seconds
T(lifetime) implementation dependent
0. Revision History
This section provides historical information on the changes made to
this draft. This section will be removed from the document when the
document is finalized.
0.3. Changes from Version 0.2 to Version 0.3
+ updated references, version number and dates.
0.2. Changes from Version 0.1 to Version 0.2
+ added list of abbreviations.
+ moved change history.
+ updated version numbers and dates.
+ updated references.
+ split reference sections.
+ updated security section.
+ moved notes to end of document.
0.1. Changes from Version 0.0 to Version 0.1
+ added change history,
+ updated version numbers and dates,
+ updated acknowledgements,
+ corrected section reference typos,
+ added postscript diagrams,
+ changed most SSNM messages to divertable,
+ updated interworking to perform timed diversion on recovery,
+ update Traffic Flow Id to be a simple unique identifier, no longer
containing a stream identifier,
+ updated author's address.
0.0. Version 0.0
The initial version of this document.
0.0.0. Change Log
$Log: draft-bidulock-sigtran-corid-03.txt,v $
Revision 0.9.2.1 2004/03/16 07:06:06 brian
- Added older drafts in pdf and txt form.
Revision 0.8.2.2 2003/08/01 12:23:15 brian
Added abbreviations, updated format.
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Internet Draft UA CORID February 21, 2004
R. References
R.1. Normative References
[RFC 2960] Stewart, R., Xie, Q., Morneault, K., Sharp, C.,
Schwarzbauer, H. J., Taylor, T., Rytina, I., Kalla, H., Zhang, L.
and Paxson, V., "Stream Control Transmission Protocol (SCTP),"
RFC 2960, The Internet Society (February 2000).
[M2UA] Morneault, K., Dantu, R., Sidebottom, G., Bidulock, B. and
Heitz, J., "Signaling System 7 (SS7) Message Transfer Part 2
(MTP2) - User Adaptation Layer," RFC 3331, Internet Engineering
Task Force - Signalling Transport Working Group (September,
2002).
[M3UA] Sidebottom, G., Morneault, K. and Pastor-Balbas, J., (eds),
"Signaling System 7 (SS7) Message Transfer Part 3 (MTP3) - User
Adaptation Layer (M3UA)," RFC 3332, Internet Engineering Task
Force - Signalling Transport Working Group (September, 2002).
[SUA] Loughney, J., Sidebottom, G., Coene, L., Verwimp, G., Keller,
J. and Bidulock, B., "SS7 SCCP-User Adaptation Layer (SUA),"
draft-ietf-sigtran-sua-16.txt, Internet Engineering Task Force -
Signalling Transport Working Group (December 11, 2003). Work In
Progress.
[ISUA] Bidulock, B., "SS7 ISUP-User Adaptation Layer (ISUA)," <draft-
bidulock-sigtran-isua-02.txt>, Internet Engineering Task Force -
Signalling Transport Working Group (February 21, 2004). Work In
Progress.
[RFC 2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels," RFC 2119 - BCP 14, The Internet Society
(March 1997).
[ASPEXT] Bidulock, B., "Application Server Process (ASP) Extension
Framework," <draft-bidulock-sigtran-aspext-03.txt>, Internet
Engineering Task Force - Signalling Transport Working Group
(February 21, 2004). Work In Progress.
[SIGSEC] Loughney, J., Tuexen, M. and Pastor-Balbas, J., "Security
Considerations for SIGTRAN Protocols," <draft-ietf-sigtran-
security-03.txt>, Internet Engineering Task Force - Signalling
Transport Working Group (June 29, 2003). Work In Progress.
R.2. Informative References
[Q.700] ITU, "Introduction to CCITT Signalling System No. 7," ITU-T
Recommendation Q.700, ITU-T Telecommunication Standardization
Sector of ITU, Geneva (March 1993). (Previously "CCITT
Recommendation")
[TUA] Bidulock, B., "SS7 TCAP-User Adaptation Layer (TUA)," <draft-
B. Bidulock Version 0.3 Page 46
Internet Draft UA CORID February 21, 2004
bidulock-sigtran-tua-03.txt>, Internet Engineering Task Force -
Signalling Transport Working Group (February 21, 2004). Work In
Progress.
[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")
[LOADSEL] Bidulock, B., "Load Selection Extension for Signalling User
Adaptation Layers (LOADSEL)," <draft-bidulock-sigtran-
loadsel-03.txt>, Internet Engineering Task Force - Signalling
Transport Working Group (February 21, 2004). Work In Progress.
[LOADGRP] Bidulock, B., "Load Grouping Extension for Signalling User
Adaptation Layers (LOADGRP)," <draft-bidulock-sigtran-
loadgrp-03.txt>, Internet Engineering Task Force - Signalling
Transport Working Group (February 21, 2004). Work In Progress.
[Q.706] ITU, "Signalling System No. 7 - Message Transfer Part
Signalling Performance," ITU Recommendation Q.706, ITU-T
Telecommunication Standardization Sector of ITU, Geneva (March
1993). (Previously "CCITT Recommendation")
[Q.705] ITU, "Signalling System No. 7 - Signalling Network
Structure," ITU-T Recommendation Q.705, ITU-T Telecommunication
Standardization Sector of ITU, Geneva (March 1993). (Previously
"CCITT Recommendation")
Acknowledgments
The authors would like to thank Tolga Asveren, Ken Morneault, Greg
Sidebottom, John Loughney, Sandeep Mahajan, Barry Nagelberg, and Nitin
Vairagare for their valuable comments and suggestions.
Author's Addresses
Brian Bidulock Phone: +1-780-490-1141
OpenSS7 Corporation Email: [email protected]
1469 Jeffreys Crescent URL: http//www.openss7.org/
Edmonton, AB T6L 6T1
Canada
This draft expires August 2004.
B. Bidulock Version 0.3 Page 47
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List of Tables
Table 1. Divertable Messages by UA .............................. 22
List of Illustrations
Figure 1. Buffer Categories at SCTP Association Failure ......... 5
Figure 2. Example (A) Configuration of ASPs and SGPs ............ 7
Figure 3. Example (C) Restoration of a Traffic Flow ............. 8
Figure 4. Example (C) Sample Multiple-SG Configuration .......... 11
Figure 5. Initialization for Examples ........................... 35
Figure 6. Example - Initial Startup ............................. 37
Figure 7. Example - Joining a Broadcast AS ...................... 38
Figure 8. Example - Association Recovery ........................ 39
Figure 9. Example - Assocation Failure .......................... 40
Figure 10. Example - Deactivation ............................... 41
Figure 11. Example - Association Recovery ....................... 42
Figure 12. Example - AS-PENDING Recovery ........................ 43
Figure 13. Example - Interworking ............................... 44
Table of Contents
Status of this Memo ............................................. 1
Copyright ....................................................... 1
Abstract ........................................................ 1
Contents ........................................................ 2
1 Introduction .................................................. 2
1.1 Scope ....................................................... 2
1.2 Abbreviations ............................................... 2
1.3 Terminology ................................................. 3
1.4 Overview .................................................... 3
1.4.1 Configuration ............................................. 4
1.4.2 Conditions at Fail-Over ................................... 4
1.4.3 Sources of Message Loss and Duplication ................... 5
1.4.4 Conditions at Recovery .................................... 6
1.4.5 Sources of Message Mis-Sequencing ......................... 8
1.5 Functional Areas ............................................ 8
1.5.1 Identification of Traffic Flows ........................... 9
1.6 Sample Configurations ....................................... 11
Notes for Section 1 ............................................. 12
2 Conventions ................................................... 12
3 Protocol Elements ............................................. 12
3.1 Parameters .................................................. 12
3.1.1 Correlation Id ............................................ 12
3.2 Messages .................................................... 14
3.2.1 ASP Active (ASPAC) ........................................ 14
3.2.2 ASP Active Acknowledgement (ASPAC ACK) .................... 16
3.2.3 Heartbeat (BEAT) .......................................... 17
3.2.4 Heartbeat Acknowledgement (BEAT ACK) ...................... 19
4 Procedures .................................................... 21
4.1 Traffic Handling ............................................ 21
4.1.1 Classification ............................................ 21
4.1.2 Correlation ............................................... 23
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4.1.3 Tagging ................................................... 24
4.1.4 Buffering ................................................. 24
4.1.5 Message Handling .......................................... 25
4.1.6 Diversion ................................................. 27
4.2 ASP Management Procedures ................................... 29
4.2.1 ASP Down Procedures ....................................... 29
4.2.2 ASP Inactive Procedures ................................... 30
4.2.3 ASP Active Procedures ..................................... 31
4.3 Interworking Procedures ..................................... 33
Notes for Section 4 ............................................. 34
5 Examples ...................................................... 35
5.1 Example Configuration ....................................... 35
5.2 Initialization .............................................. 35
5.3 Starting Traffic ............................................ 36
5.3.1 Initial Startup ........................................... 36
5.3.2 Joining a Broadcast ....................................... 38
5.4 Fail-Over, Deactivation and Blocking ........................ 39
5.4.1 Association Recovery - Loadshare .......................... 39
5.4.2 Assocation Failure - Override ............................. 39
5.4.3 Deactivation - Loadshare .................................. 40
5.4.4 Management Blocking - Override ............................ 40
5.5 Recovery .................................................... 41
5.5.1 Association Recovery - Loadshare .......................... 41
5.5.2 AS-Pending Recovery ....................................... 42
5.6 Interworking ................................................ 43
5.6.1 ASP does not Support CORID ................................ 43
6 Security ...................................................... 44
7 IANA Considerations ........................................... 44
8 Timers ........................................................ 45
0 Revision History .............................................. 45
0.3 Changes from Version 0.2 to Version 0.3 ..................... 45
0.2 Changes from Version 0.1 to Version 0.2 ..................... 45
0.1 Changes from Version 0.0 to Version 0.1 ..................... 45
0.0 Version 0.0 ................................................. 45
0.0.0 Change Log ................................................ 45
R References .................................................... 46
R.1 Normative References ........................................ 46
R.2 Informative References ...................................... 46
Acknowledgments ................................................. 47
Author's Addresses .............................................. 47
List of Tables .................................................. 48
List of Illustrations ........................................... 48
Table of Contents ............................................... 48
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Full Copyright Statement
Copyright (C) The Internet Society (2003). All Rights Reserved.
This document and translations of it may be copied and furnished to
others, and derivative works that comment on or otherwise explain it
or assist in its implementation may be prepared, copied, published and
distributed, in whole or in part, without restriction of any kind,
provided that the above copyright notice and this paragraph are
included on all such copies and derivative works. However, this
document itself may not be modified in any way, such as by removing
the copyright notice or references to the Internet Society or other
Internet organizations, except as needed for the purpose of developing
Internet standards in which case the procedure for copyrights defined
in the Internet Standards process must be followed, or as required to
translate into languages other than English.
The limited permission granted above are perpetual and will not be
revoked by the Internet Society or its successors or assigns.
This document and the information contained herein is provided on
an "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
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
MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Acknowledgement
Funding for the RFC Editor function is currently provided by the
Internet Society.
B. Bidulock Version 0.3 Page 50
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