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Monday, December 11, 2006

Eric J Merkel Re: M23 vs M13 DS3 Muxing Thu 12/7

Actually, the M23 framing works just fine. We found the problem to be in the channel mappings on our switch. Apparently, our switch programmer started at interface 1 when he should have started at 0. The Cisco T1 controller interface starts at 1 and the switch at 0 so the SS7 signaling was mapping channels to the wrong interface. Basically interface 1 went to 2, and 2 to 3 and so on and there the COT tests would not pass. DOH!!!

After talking to several telco people, apparently even though their framing says M13 it is actually converting four DS1's into a DS2, then mapping the 7 DS2's up to the DS3 level. I guess both ADTRAN and Alcatel group them this way with the M13 option so it isn't truly doing a straight DS1 to DS3 conversion. So the M23 & M13 framing are somewhat synonymous on this equipment though that is technically they should call it M23 not M13.

FWIW, we also tried C-bit and had the same problems which took us down the path of trying to figure out why the channels weren't syncing. Just the lovely part of SS7 where signalling takes place out of band.

Thanks for everyone's suggestions.

-Eric

----- Original Message -----
From: "Adam Rothschild"
To:
Sent: Thursday, December 07, 2006 2:34 PM
Subject: Re: M23 vs M13 DS3 Muxing


> On 2006-12-07-12:32:03, Jawaid Bazyar
> wrote:
>> M23 is definitely different than M13. The 1 and 3 refer to T1 and
>> T3. In M23, it refers to T2 and T3! I don't know if anyone ever
>> deployed T2 in North America but it still exists in some places.
> [...]
>
> M23 (as opposed to c-bit parity) is most definitely a valid means of
> delivering T1 tails off a carrier's CT3 facilities. Whether or not
> you want it depends on your particular carrier's configuration.
>
> For example, on a Level(3) (formerly LGN) circuit 'round here:
>
> [email protected]> show interfaces t1-5/3/0:0
> Physical interface: t1-5/3/0:0, Enabled, Physical link is Up
> [...]
> Link-level type: Cisco-HDLC, MTU: 1504, Clocking: Internal, Speed: T1,
> Loopback: None, FCS: 16, Mode: M23,
> Framing: ESF ^^^^^^^^^
>
> Definitely worth a try if c-bit isn't working.
>
> HTH,
> -a
> _______________________________________________
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_______________________________________________
"Eat sushi frequently". - Avi
[email protected] is the human contact address.
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