Subject: M2PA: SLC assignment

From: Amish Chana <[email-masked]>
Date: Tue, 02 Oct 2001 15:47:04 +0100

Tom and others,

Why does M2PA impose the following requirment?
"Each association must be mapped to the same Signaling Link
Code (SLC) in the client and server, so that each endpoint knows which link 
is being created at the time the SCTP association is established."

In a SS7 network with MTP2 links it is possible for each endpoint to assign 
a different SLC to each signalling link in a linkset. The ITU-T 
Recommendations does not state that each link must be mapped to the same SLC 
in both endpoints.

Regards,
Amish

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From: Patrick Lam <[email-masked]>
Date: Tue, 02 Oct 2001 10:53:41 -0700

The nature of M2PA doesn't have the concept of "link set".  Therefore, for 2 endpoints
(client and server) to identify the association between each other, they have to have
the same SLC.  While in traditional SS7, two endpoints only have to identify the
linkset between each other to facilitate the communications.

Amish Chana wrote:

> You are currently subscribed to sigtran as: [email-masked]

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From: "Brian F. G. Bidulock" <[email-masked]>
Date: Tue, 2 Oct 2001 12:53:34 -0500

Amish,

Even in SS7 nodes at both ends of the link must agree on the SLC,
otherwise changeover procedures are not possible.

--brian

Amish Chana wrote:                                          (Tue, 02 Oct 2001 15:47:04)
> You are currently subscribed to sigtran as: [email-masked]

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

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From: Al Varney <[email-masked]>
Date: Tue, 02 Oct 2001 14:19:44 -0500

At 03:47 PM 10/2/01 +0100, Amish Chana wrote:
>Code (SLC) in the client and server, so that each endpoint knows which 
>link is being created at the time the SCTP association is established."
>
>In a SS7 network with MTP2 links it is possible for each endpoint to 
>assign a different SLC to each signalling link in a linkset. The ITU-T 
>Recommendations does not state that each link must be mapped to the same 
>SLC in both endpoints.

    You are correct.  Q.704 fails to state this as a literal requirement, 
but parts of MTP (changeover) fail if the endpoints do not agree on SLC 
assignments.  Link failure is not the time to find out you have this problem.

    Fortunately, the SLT message of Q.707 will detect this (not uncommon) 
mis-match when signaling links are brought into service.

    One reason for an SLC mis-match is the criss-crossing ("frogging") of 2 
links within a linkset, typically somewhere in digital transmission 
cross-connect equipment.  The admonition in Q.707 to flag SS7 signaling 
link equipment per M.1050 doesn't seem to prevent such errors.

Al Varney  --  [email-masked]

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From: Amish Chana <[email-masked]>
Date: Tue, 02 Oct 2001 21:51:08 +0100

Thanks Al & Brian for your responses.

I just realised I've been specifyng the SLC in configuration data all along 
- except with a different name.

Amish

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