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Default Fax Protocol Cisco and T.38 - Send/Receive Issue

Unanswered Question
Feb 7th, 2012
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I have 2 gateways, one is a 2811 & the other is a 2911. The 2811 runs "advipservicesk9-mz.124-24.T3" and 2911 runs "universalk9-mz.SPA.151-4.M2" with IPBase,Security & UC. I have configured a fax machine on both the routers fxs ports. The routers are across a WAN and there is a gk in between. When I send a fax it fails and I noticed that the 2811 uses CISCO FAX CODEC & the 2911 uses T.38 CODEC. These are the default codecs for both the IOS. I am trying to configure the 2911 to use the cisco fax codec but, seems like the command is not supported anymore. The reason I want to use cisco fax protocol is because all the other routers on the network uses it thus is easier to change the NEW router that all the other older routers.


voice services voip

fax protocol cisco


Has anyone encountered this issue? Kindly share you experience or work around.

Thank you.

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Overall Rating: 5 (1 ratings)
rushan_2 Fri, 02/24/2012 - 01:03
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Recently we have upgraded our 2800 series to 2900 with PVDM3. Our previous fax configuration use to be on CISCO protocol but due to PVDM3 are not able to configure CISCO protocol for FAX and we have to use T.38. After configuring T.38 we noticed the  BW it consumes is 128kbps for 1 FAX call where else the CISCO protocol use to only consume 16kbps. Is there a way we could bring down the BW to 16kbps?

I have tried tuning the FAX-RELAY speed but it does not seem to help. The issue I am facing is, I have a gatekeeper and it is configured with BW limit and we only want to allow 2 X g729 calls = 32kbps. How can I achieve this with the new T.38 protocol.

Please Help.




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