Subject: [Sigtran] SUA IG: Usage of TID labels

From: "Barry Nagelberg" <[email-masked]>
Date: Tue, 27 Apr 2004 12:32:14 -0400

Lode,

Here is some updated suggested text for the SUA IG, regarding the usage of
TID labels.

I suggest that we have some mailing list discussion, or poll, or something
on this issue, even prior to publication of the SUA IG. In spite of the fact
that SUA v16 is very unclear on the use of these labels, we're apparently
moving towards the RFC stage, and companies are moving ahead on SUA
implementation. If we're not careful, we run the risk of ending up with
incompatible implementations.

In section 4.7.2.1 (Association Setup, ASP going active):

<snip>
In the ASPAC message, the ASP optionally includes a TID and/or DRN Label
Parameter for each AS. If more than one ASP in a given AS includes a TID
and/or DRN Label Parameter, then these ASPs must specify a unique label at a
fixed position in the TID or DRN parameter. The same ASPAC message is sent
to each SG used for interworking with the SS7 network.

If an ASP does not include a TID and/or DRN Label Parameter in the ASPAC
message, then the SG MAY send a TCAP message with any TID or DRN to this
ASP.
<snip>

In section 4.7.3.1 (Routing and message distribution at the SG - TCAP
traffic):

<snip>
   a. The SG examines the bits between the 'Start' bit and the 'End' bit
   of the received TCAP transaction ID (TID). The 'Start' and 'End' bits
   are defined in the 'TID Label' parameter that was sent in the ASPAC
   message for this AS.

   b. If these bits exactly match the 'Label' field of the 'TID Label'
   parameter that was sent in the ASPAC message, then the message is sent
   to the ASP that registered for this label via the ASPAC msg.

   c. If these bits do not match the label field of any ASP in this AS,
   then the SG may discard the message.
<snip>

Barry Nagelberg

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---

From: "Brian F. G. Bidulock" <[email-masked]>
Date: Tue, 27 Apr 2004 17:08:34 -0600

Barry,

Barry Nagelberg wrote:                                                               (Tue, 27 Apr 2004 12:32:14)
> message, then the SG MAY send a TCAP message with any TID or DRN to this

I don't think that it was really the intent to have some APSs register TID or
DRN labels and some not.  I believe the intent was that all ASPs register TID
or DRN labels, or none.  Otherwise, if some register TID/DRN label and some do
not, there is an ambiguity as to where any given message will be sent.

draft-bidulock-sigtran-loadsel-02.txt describes a technique for using TID/DRN
labels across load sharing pools in a more structured way.  This draft is out
of date, so I will resubmit it shortly.  You can pull up a copy of the
outdated draft from http://www.openss7.org/sigtran01.html if you want to take
a look in the meantime.

>    then the SG may discard the message.

Discard would not be a good thing from an SS7 network perspective.  Which
SS7 message an SG discards or returns on error from the SS7 side of the
node is the business of SS7 and not SUA.  Please remove mention of discard.
More interesting is what needs to be done with the message if it is not
discarded.  Perhaps sent to any other active ASP for the RC so that the
SCCP application can deal with aborting the transaction or reseting the
connection as required by the particular SCCP application.

If you look at draft-bidulock-sigtran-loadsel-02.txt it is possible using
this approach to pend on a load selection while giving notification of
failure within a load selection to give other APSs an opportunity to sync
connection/transaction state and register for the load selection.

--brian

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