Subject: OFFLIST: SUA Issue #14 (was, SUA v8 : SUA CO message parameters)

From: Verwimp Gery <[email-masked]>
Date: Tue, 23 Oct 2001 11:24:18 +0200

Brian,

Don't overreact. The point I was making is that in ITU-T, one cannot predict
which bit will be used where, because it depends on local agreements (e.g.
four hops => consec. bits 1,2,3 and 4 of the SLS or bits 1,2,1,2 or whatever
scheme). And what the paragraphs don't say, is that the STP MAY change the
SLS to obtain a better loadsharing.

Remark that in the figure nodes B and C cannot use the second least
significant bit anymore for loadsharing if every node connected to it uses
the same scheme. So some additional measures are taken, e.g. "A" uses
another SLS bit or the opposite 0,1 decision with the same bit based on DPC,
or any node "X" connected to the same STP-pair makes opposite/other SLS
decisions). Which makes rotation a moot point.

This being said, I saw no compelling reason why the two SGs couldn't come
out with a different SLS. It's also transparent to the ASP; even when
keeping the sequence control the same, another SLS may come out depending on
SG. A different route = a different ballgame.

But I'm sure you know all this, too. You can expect the same of me, even if
I over-simplify things sometimes (I'm not a native English speaker ;)

Regards,

____________________________

Gery Verwimp
> SIEMENS ATEA
> ICN D CS D5
> Tel. : +32 14 25 3424
Fax : +32 14 25 3212
mailto:[email-masked]
____________________________________

-----Original Message-----
From: Brian F. G. Bidulock [mailto:[email-masked]]
Sent: maandag 22 oktober 2001 21:43
To: sigtran
Subject: Re: SUA Issue #14 (was, SUA v8 : SUA CO message parameters)

Gery,

Verwimp Gery wrote:                                       (Mon, 22 Oct 2001
12:26:43)
> 
> SLS rotation is only specified in ANSI. In ITU-T networks, there's no such
> thing. Perhaps you should read up on the ITU specs ;) We have to support
> both, don't we ?
> 

In ITU an STP uses a fixed bit-number in the incoming SLS to determine the
linkset in a combined linkset.  As bit numbers change along the path, this
has the same effect as SLS rotation.  In the ANSI network, the STP always
examines the same bit number and rotates the SLS.  In ITU networks, the
bit number which is use to select linkset changes from STP to STP.  The two
procedures have the same effect and are quite similar.  ANSI has the
advantage
that bit numbers do not need to be assigned to STPs.

Neither method requires any particular support in either M3UA or SUA except
that M3UA and SUA must select the proper SLS value on outgoing messages.
In-sequence delivery is something which is done by the SS7 network and is
transparent to the SEP.  The SEP need only assign the same outgoing SLS for
all messages that it wants delivered to the distant end in sequence.  This
is
the same for ANSI and ITU networks.

I suggest you read ANSI T1.111.5 7.3 and particuarly 7.3.1.  You will find
the
same format of section describing the same thing in Q.705 A.3 with
particular attention to A.3.2.  There is, in fact, little difference between
the ANSI approach and the ITU approach.  The ITU approach uses different
bit positions at each node without rotating the SLS.  The ANSI approach uses
the same bit position at each node and rotates the SLS.  Both approaches
yeild the same result.

Anyone who has worked with MTP in both environments knows this.

There is "such a thing in ITU". :P

It would assist the process if one doesn't spread misinformation about SS7.

--brian

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

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From: "Brian F. G. Bidulock" <[email-masked]>
Date: Tue, 23 Oct 2001 04:55:58 -0500

Gery,

Verwimp Gery wrote:                                       (Tue, 23 Oct 2001 11:24:18)
> SLS to obtain a better loadsharing.

Wrong.  Unlike IETF RFCs in the ANSI/ITU specs, anything not explicitly
permitted is not permitted.  That is, the STP MUST NOT change SLS.

> This being said, I saw no compelling reason why the two SGs couldn't come

Changing SLS will destroy the QOS of the connection.  That is compelling
enough for me.

> I over-simplify things sometimes (I'm not a native English speaker ;)

You need to work on your understanding of SS7.

--brian

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

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