Subject: Re: [Sigtran] Re: M3UA Notify message

From: "TOLGA ASVEREN" <[email-masked]>
Date: Wed, 26 Feb 2003 12:12:22 +0200

Brian,

Consider the following example because it appears that you don't understand
what is involved:

AS1 RK1 = PCA/ISUP.  n = 2, k = 1.  3 ASPs: ASP1, ASP2, ASP3, 1 SGP: SGP1

AS1 is inactive.  ASP1 comes up and goes active for AS1.  SGP1 knows that
n=2 and also knows that ASP2 and ASP3 are in the ASP-DOWN state.  Until
now it has been responding to local MTP User MTP-TRANSFER requests to PCA,
SI=5 with MTP-STATUS(Inaccessible User).  Messages from the SS7 network
have been replied to with UPU(Inaccessible).  Now, SGP1 MAY decide to not
direct traffic to ASP1, but continue to respond to local MTP-TRANSFER
requests destined to AS1 with MTP-STATUS(Inaccessible User) and respond to
received SS7 messages for AS1 with UPU(Inaccessible).  If it does so, it
SHOULD withhold the NTFY(AS_Active).  If it decides to direct traffic to
ASP1, it MUST send NTFY(AS_Active) and will mark the MTP User as accessible
(and stop responding with MTP-STATUS and UPU).  The RFC cannot tell the
SGP designer what they should or should not do here because it is
intricately
involved with SS7 conformance and performance.

ASP2 and ASP3 SHOULD coordinate with ASP1 the number of active ASPs.  That
is, ASP2 and ASP3 should know that "n" are required and should take action
to establish associations, go ASP-UP and at least one of them should go
ASP-ACTIVE for AS1.  There is no way for SGP1 to "tell" an ASP to go active
for an AS, so this is something the ASPs need to do on their own.  Also,
ASP1 SHOULD wait until one of ASP2 or ASP3 is active for AS1 before
informing
the local ISUP (MTP User at PCA/SI=5) that it can start traffic.

Any questions?
[TOLGA] Sure. I don't get the reasoning behind letting wait ASPs for n of
them to be ACTIVE with a SHOULD and give freedom to SG to direct or not to
direct the traffic with MAY. For example in your example if SG decides to
direct traffic to AS with the first ACTIVE ASP, ASPs will still wait for
the nth ASP to be ACTIVE. I don't think this is a good choice. If ASPs
don't rely on an indication from SGP (NTFY), they can't know about the
decision of SGP, when it is going to direct traffic (unless this is
predetermined, which I call interpreting n as mandatory).

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From: "Brian F. G. Bidulock" <[email-masked]>
Date: Wed, 26 Feb 2003 04:53:01 -0700

TOLGA,

TOLGA ASVEREN wrote:                                                                 (Wed, 26 Feb 2003 12:12:22)

> direct the traffic with MAY.

Because M3UA cannot say what the SG "SHOULD" do with regard to the SS7
network.  It can only talk about what it "MAY" do with regard to the SS7
network.

> For example in your example if SG decides to direct traffic to AS with the
> first ACTIVE ASP, ASPs will still wait for the nth ASP to be ACTIVE. I don't
> think this is a good choice.

It is the best choice.

> If ASPs don't rely on an indication from SGP (NTFY), they can't know about
> the decision of SGP, when it is going to direct traffic (unless this is

The ASPs can reply on an indication from the SGP (NTFY) because it says
"SHOULD" in the RFC and, if the NTFY is not withheld it is a "MUST" to
send NTFY(AS_Active) when the first ASP goes active.  Therefore, the ASP
can rely upon the fact that a correct SGP will always send NTFY(AS_Active)
before or when it directs traffic.

But regardless of the SGP's decision, the ASP SHOULD still wait.  It is up
to the ASP to determine what to do with any traffic it might receive while
it is waiting (which might be none, even if the SGP "directs" traffic).

--brian

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