Subject: [Sigtran] M3UA: Inter-AS communication via SG

From: "Srivats P." <[email-masked]>
Date: Fri, 14 Feb 2003 11:48:50 +0500

All,

Does the SIGTRAN/M3UA Architecture allow inter-AS
communication via the SG? (ASes are at point code
granularity). e.g. if AS1 is 1-1-1, AS2 is 2-2-2,
and SG is 3-3-3 ... can 1-1-1 talk to 2-2-2 via the
SG ?

If yes, when AS1 becomes inaccessible to SG, does
the SG send a DUNA(1-1-1) to 2-2-2 alongwith the
TFPs it sends into the SS7 network ?

If yes, is it correct to send a DUNA(*) to all ASPs
on SS7 network isolation. When I say "SS7 Isolation",
I mean no SS7 SP/STP is accessible to the SG, but
AS(es) at point code granularity are.

Regards,
Srivats P.

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From: "Brian F. G. Bidulock" <[email-masked]>
Date: Fri, 14 Feb 2003 00:15:24 -0700

Srivats,

Srivats P. wrote:                                                                  (Fri, 14 Feb 2003 11:48:50)
> and SG is 3-3-3 ... can 1-1-1 talk to 2-2-2 via the

Yes.

> TFPs it sends into the SS7 network ?

That would depend on whether the SG supports such routing keys and such
routes.  Although an SS7 platform will often support multiple point
codes, it will not necessarily support MTP transfer or MTP management
between them.  But such a thing is sometimes done, although it doesn't
have much practical use in a real network.

> AS(es) at point code granularity are.

It is almost never correct to send DUNA(*) to all ASPs when using point
code granularity routing keys when the SG acts as an STP and one intends
to carry SCCP over M3UA.  This is because the STP has its own point code
(and possibly alias point code) which are still available to all active
AS.  Of importance would be the GTT function at the STP which is
addressable by applications at the AS.  Although one doesn't normally
route traffic between point code on a single platform, transferring
traffic between SCCP users via SCCP is required.

Instead the SG should send DUNA for each of the unavailable destinations
as they become unavailable.  Also, DUNA corresponds to MTP-PAUSE.  There
is no MTP-PAUSE(*).  Individual MTP-PAUSE primitives are delivered.

In the backhaul case, where the AS Point Code is the same as the SG's
point code (SEP instead of STP) then DUNA(*) is usable.

In section 3.4.1 it says:

                 ...  A mask value equal (or greater than) the
   number of bits in the PC indicates that the entire network
   appearance is affected - this is used to indicate network
   isolation to the ASP.

But in section 4.6 second paragraph it says:

   When the SG discovers SS7 network isolation, the SGPs send an
   indication to all concerned available ASPs (i.e., ASPs in the ASP-
   ACTIVE state) using DUNA messages for the concerned destinations.

So, I think its clear that you send DUNAs for the affected destinations
to concerned ASPs rather than just sending DUNA(*) whenever a partition
occurs.

--brian

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