FAX + VoIP - T.30 / T.38

Ok... just discovered the 2-sided discussion on Fax over IP. Some VoIP vendors indicate they have not seen any probs over their network, while some integrators have said flat out it doesn't work reliably...

SO - what's been your experience with normal FAX machines that work fine on a POTS/PSTN network... plugging them into an analog port on a VoIP gateway, and used across the VoIP LAN / WAN configuration ? here -

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is better -
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tnx for the feedback

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Phil Schuman
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I have been running analogue fax machines connected via FXS ports on a

90 site Satellite WAN (580 ms RTT) for over 3 years - they work perfectly.

The Softswitch article is complete garbage - the guy who wrote that is clueless.

Cisco Routers support T.38 and their own proprietary Fax protocol. Both work with no problems. You can run 8k G.729 and run fax over it using the command "fax rate voice" on your dial-peers. Cisco command reference:-

For >example, if the voice codec is G.711, fax transmission may occur up to

14,400 bps >because 14,400 bps is less than the 64-k voice rate. If the voice codec is G.729 (8k), >the fax transmission speed will be 7200 bps.

If you require fast fax transmission then with a well deisgned dial plan, you can create sperate dial-peers for Fax calls using a 64k codec and have your voice calls use an 8k Codec.

Check out the Cisco fax troubleshooting guide for more information on Cisco's Fax over VoIP implementation:-

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Phil Schuman wrote:

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