Subject: Re: [Sigtran] [m3ua]-AS-SG

From: "TOLGA ASVEREN" <[email-masked]>
Date: Tue, 4 Mar 2003 07:58:04 +0200

Brian,

My point with my explanation why each SGP can be identified only with SCTP
addressing from ASP point of view was not to propose implicitly to put a
parameter or to define a procedure to do otherwise. IMO, there is no need
for this. Just form two SCTP associations -one for each SGP-, I don't think
this is terribly bad.
Still some comments below.

    Tolga

Barry.Nagelberg,

[email-masked] wrote:
(Mon, 03 Mar 2003 13:08:15)
> "Brian F. G. Bidulock" <[email-masked]>
> Sent by: [email-masked]
>  03/03/2003 12:37 PM
>  Please respond to bidulock
>
>
>         To:     [email-masked]
>         cc:     [email-masked]
>         Subject:        Re: [Sigtran] [m3ua]-AS-SG
>
>
> Barry.Nagelberg,
>
> [email-masked] wrote: (Mon, 03 Mar 2003 11:18:26)
> > Brian,
> >
> > OK, I agree with you that a parameter to identify the SG could be
> selected
> > on an implementation-dependent basis. This, however, would destroy the
> > concept of  interoperability.
>
> How so?
>
> [BN] - Because both the ASP and the SGP must be aware that the chosen
> parameter is being used to identify the SG.

I don't think so...  Why would the ASP need to know that the SGP is
using SLS, for example, to select the SG?
[TOLGA]If ASP is communicating via multiple SGs, it should be able to
select the SG it wants, reachability of a specific destination might be
different via each of them. This basically also rules out any possiblity to
use SLS for that purpose. Imagine the scenario where ASP1 uses SG1 and SG2.
PC-A is reachable via SG1 but not via SG2. And let's furthermore assume one
wants to use just SGP1 for both SG1 and SG2. Now there is one association
between SGP1 and ASP1 -O.K. this won't work, but the point is to show that
it won't work with one association-. ASP1 wants to send messages to PC-A
and because it is reachable via SG1 and because SGP1 is part of SG1 it
sends the messages to it. Now let's assume SGP1 is doing loadsharing based
on SLS to decide for which SG (SG1 or SG2) the message is intended for. In
such a case messages with SLS values matching SG2 will be dropped.
Now, one might argue that when one speaks of SGP, it also includes level3
logic (MTP3) not just M3UA-SGP stack (this is how I see it and IMO also how
RFC sees it and please note the above example does not interprete SGP in
that way). In such a case, by definition, one SGP can't be part of multiple
SGs(countability argument in your message, I agree). I believe, not to take
this into account was one of the reasons, why this thread was triggered.
Then one might ask, why I can't use one association for multiple SGPs? The
above explanation will be still a valid answer I think (just with the
modification that there are now two SGPs -SGP1 and SGP2-, which are part of
SG1 and SG2). And as indicated at the beginning of this message, I don't
think it is a good idea to introduce some new parameters/mechanism to
reduce number of SCTP associations, when we want to use multiple MTP3
entities for SS7 connectivity(IMO, multiple SG scenario is not a good
choice with ASP/SGP model anyway, but discussing this belongs not to this
thread)

>
> >
> > Furthermore, I don't understand why you say that there is a "lack of a
> > practical purpose" for an SGP to serve multiple SGs. I contend that is
> the
> > same reason why the RFC allows an ASP to serve mutiple ASs.
>
> What makes the SG different from each other (particularly when the same
> set
> of SGP belong to the same SGs)?
>
> [BN] - I don't understand what you mean.

To count something normally requires cardinality based on some
distinguishing
feature.  For tangible objects this is time-space coordinates.  What is it
for SG?  What is distinguishes one SG from another so that we can say that
there are two and not just one?  Fermi spin?

--brian

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

From: "Brian F. G. Bidulock" <[email-masked]>
Date: Mon, 3 Mar 2003 23:47:49 -0700

TOLGA,

TOLGA ASVEREN wrote:                                                                 (Tue, 04 Mar 2003 07:58:04)
> different via each of them.

Where does it say that in the RFC?  (That the AS SHOULD be able to select
an SG???)

> This basically also rules out any possiblity to use SLS for that purpose.

I don't see it ruled out at all.  I personaly don't think that it would be
terribly useful, but it is not ruled out.

> Imagine the scenario where ASP1 uses SG1 and SG2.  PC-A is reachable via SG1
> but not via SG2.

Who says this has to happen?  The reachability of all remote point codes via
SG1 and SG2 could be identical.  Don't assume that they are mated STPs.

> And let's furthermore assume one wants to use just SGP1 for
> both SG1 and SG2. Now there is one association between SGP1 and ASP1 -O.K.
> this won't work, but the point is to show that it won't work with one
> association-. ASP1 wants to send messages to PC-A and because it is
> reachable via SG1 and because SGP1 is part of SG1 it sends the messages to
> it. Now let's assume SGP1 is doing loadsharing based on SLS to decide for
> which SG (SG1 or SG2) the message is intended for. In such a case messages
> with SLS values matching SG2 will be dropped.  Now, one might argue that
> when one speaks of SGP, it also includes level3 logic (MTP3) not just
> M3UA-SGP stack (this is how I see it and IMO also how RFC sees it and please
> note the above example does not interprete SGP in that way). In such a case,
> by definition, one SGP can't be part of multiple SGs(countability argument
> in your message, I agree).

I asked how to count them.  Do you believe that they must be different in SS7
routing to count them?  I appears so.  I don't see where it says that in the
RFC either.

> I believe, not to take this into account was one of the reasons, why this
> thread was triggered.  Then one might ask, why I can't use one association
> for multiple SGPs?

How do you count SGPs?  It think an SGP is the process at the SGP end of an
association; an ASP the process at the ASP end of the association.  But that
has little bearing on how many SGs an SGP belongs to.  An SG is a logical
thing.  We did not say that there was a 1:1 relationship between SGP and SG
(if we did it might be easier to count SGs, but all of that sort of thing
was moved to an "operational" appendix and made into a simple example, by
our A-Ds I might add.)

> The above explanation will be still a valid answer I think (just with the
> think it is a good idea to introduce some new parameters/mechanism to reduce
> number of SCTP associations, when we want to use multiple MTP3 entities for
> SS7 connectivity(IMO, multiple SG scenario is not a good choice with ASP/SGP
> model anyway, but discussing this belongs not to this thread)

There were those that wanted to restrict the architecture more for clarity and
simplicity (I wan't one of them) but that idea got appendicitis.  You can try
putting these restrictions back in the IG, but the IG will never make it past
draft anyway.

--brian