Re: [Technical Errata Reported] RFC3331 (1425)

 
I'm getting confused about this discussion about the SDT and SDL
identifiers (not helped by something discarding half of the emails).

Why should M2UA know anything about ISUP CIC values when attempting
to allocate a singalling link?
In many cases the timeslot on a TDM link used for signalling
isn't allocated a CIC number.

I would have thought that any values used here have local
significance to the M2UA server (ie the TDM side) and be
used to determine which TDM timeslot to use.
So the SDTI would select between the physical hardware
units that run MTP2, and the SDLI would select a port.
This would mean that both values might be 32 bit numbers.

We used (a slightly modified) M2UA to link MTP3 to MTP2 on
some of our cards. One difference/problem was the registration
procedures because the MTP2 code was reponsible for allocating
the TDM timslot on an internal link to a local TDM switch,
which has to be switched to the desired external port/timeslot
by the management code. So we needed to return an identifier
back to the M2UA client :-(

> It does not "admit up to 32 significant bits".  You see,
> the Signalling Data Link Identifier is not just some value
> invented for the purpose of M2UA.  It happens to be the value
> that is used by SS7 MTP Level 3 for identifying the signalling
> link facility, where it is defined as a Circuit Identification
> Code.  Now, for ITU-T based SS7 variants, the Circuit
> Identification Code is a value only significant to 12-bits.  For
> ANSI (24-bit point code) derived variants, a Circuit Identification
> Code can be significant to 14-bits.
> 
> Now, the "Far, Far, Away" national variant could have 16-bit CICs.

16 bit CICs could easily be in use in international links.

	David

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