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New Member


I am just wondering how much bandwidth faxing uses when going through an AS5300?

  • Other Collaboration Voice and Video Subjects
Cisco Employee

Re: Faxing

Are you talking about on the VOIP side. Are you doing fax-relay or fax-passthrough. With g.729 and fax-relay it should be about 24k a call. With fax-passthrough or fax-relay on g.711 the call will take about 80k this is assuming no rtp header compression.

Thank you,


New Member

Re: Faxing

I'd disagree to the previous answer. Fax Relay means no voice codec at all. The DSP simply turn off any codec that have been choosen, and treat fax as data. Using Fax Relay (or T.38) you can define how much BW it will consume: like 2.4k, 4.8k, 9.6k, 14.4k. Yes, you should add the overhead BW consumption to the rates above, but as you can set fax to as low as 2.4k, anything goes.

A 1700/2600/3600 gateway supports T.38 (or Fax Relay), while the ATA-186 does NOT. So, if you use the ATA-186, you are restricted to 64k (in fact 80k) fax transmissions (regardless of codecs, as, repeating, they don't affect the fax transmission).