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DS-3 framing ( M13/CBIT Framing issue)

Unanswered Question


Just wondering if someone knows anything about the framing issues when Telco ( Any one) gives you a DS-3 and if framing on their end is configured as M13 but on the ATM interface on your Router the framing is configured as C-Bit.

Any document referring to these kind of issues, or personal experience will be of great help as to why there are problems.



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jeffreymcnamara Thu, 11/09/2006 - 13:14
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Telco would only use M13 if T1 slots are provisioned on the DS3, if they are you need to match the framing format in the interface, this is normal config for channelized DS3.

Normally if you ordered a DS3 with C-bit, your interface provides framing, telco sends it as unframed.

pciaccio Fri, 11/10/2006 - 03:57
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If your T-3 is provisioned for M-13 and you want to use it for ATM, then it is provisioned wrong. You need C-Bit for ATM. M-13 is used if you are going to channelize the T-3 into 28 T-1's (using a M-13 mux or similiar). C-Bit is a clear pipe (non-channelized).ATM uses a non-channelized pipe...


You see we want Telco to set the T-3 framing as C-bit but there are some parts of Canada where Telco can only give you M13 framing. So when we have Telco sending us M13 framing and we have configured C-bit framing on our end routers, then we have seen some instances where there are problems but on some cases it works fine.

Not sure what cisco thinks of this issue.



pciaccio Fri, 11/10/2006 - 06:27
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You probably have to terminate the T-3 to a demux or some other device (T-3 CSU) that takes the M-13 and hands off a HSSI. I'm pretty sure that you cannot terminate a C-bit T-3 directly to the router.

shakir.muhammadi Tue, 10/30/2007 - 10:33
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We have a situation where we wanted telco to deliver an ATM based DS-3 but because their multiplexer at the site can only offered M13 framing, we end up using a multiplexer to convert it to HSSI. However we are seeing frame PVC flapping every now and then, telco tried so many test and couldn't find anything wrong with the circuit. The PVC flaps is still a problem. Anybody has experienced this type of problem? any way to resolve it?


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