Subject: [Sigtran] RFC 3332: Traffic Flow

From: John McLaine <[email-masked]>
Date: Tue, 22 Oct 2002 02:53:46 -0700 (PDT)

Hi,
Please clarify me the term "traffic flow" in the
following paragraph from the "ASP Active Procedures"
Section.

"Whenever an ASP in a Broadcast mode AS becomes
ASP-ACTIVE, the SGP MUST tag the first DATA message
broadcast in each traffic flow with a unique
Correlation Id parameter.  The purpose of this Id is
to
 permit the newly active ASP to synchronize its
processing of traffic in each traffic flow with the
other ASPs in the broadcast group."

Does it mean:
1) Only first DATA message to the newASP be tagged?
Or
2) Only first DATA message to each STREAM to the ASP
be tagged?
or what else?

One more question please:
Suppose ASP1 is already ACTIVE in BROADCAST mode AS
and processing the traffic. Now ASP2 becomes ACTIVE in
the AS. SO now, should the Correlation Id be sent (by
SGP) only to ASP2 or both (ASP1 and ASP2).

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From: "Brian F. G. Bidulock" <[email-masked]>
Date: Tue, 22 Oct 2002 22:39:44 -0600

John,

draft-bidulock-sigtran-corid-00.txt identifies traffic flows as follows:

1.4.1.  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, Load Id, Stream Id and the sequence number
   within that flow as identified by the Correlation Identifier.  The
   Correlation Identifier is a combination of traffic flow identifier
   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".

So, traffic flows are really meant to be independent flows of traffic which
have an internal requirement on sequence.  For M3UA, this is equivalent to the
traffic flows as identified in the Changeback proceedure in Q.704 Clause 6.

In broadcast procedure, the ASP needs to know where in each independent
sequential flow (i.e, stream) of messages it is joining the AS.  This is so
that it can exchange information with its peer ASPs to coordinate its entry
into the broadcast group.

Because this is rather implementation dependent at the ASP, one way that the
SG can ensure that it is tagging the correct messages is to:

a)  ensure that all messages that belong to one SCTP stream to an ASP in a
    broadcast AS are also transmitted exclusively within one stream to other
    ASPs in the broadcast AS.

b)  tag the first data message in each stream to the newly joining ASP.

If a given ASP needs finer granularity control than this (unlikely), it would
have to expose its internal implementation details to the SG.

I was hoping that we could clarify this point before the draft went to RFC, as
there was a fair number of requests for clarification and quite some
discussion on the list; however, as the original authors of the draft were
stricken from the authors list and therefore not consulted on final edits,
changes never made it into the RFC.  If you need any more information, I
suggest you consult one of the many "editors" of the document.  You will find
their contact information towards the end of the document.

--brian

John McLaine wrote:                                   (Tue, 22 Oct 2002 02:53:46)

-- 
Brian F. G. Bidulock
[email-masked]
http://www.openss7.org/