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Modem & FAX pass-through differencies

Can anybody tell what are exact differencies in parametar setting beetween modem and fax pass-through modes (like values of static jitter buffer and so on...). In every documentation I find only value for static jitter buffer for modem (200 ms).

If both are configured globaly (as system parameter) on Cisco voice-gateways (for example - 28xx, 38xx or AS 5xxx) in which cases these two modes can cause malufunction of one of them and why?

Cisco Employee

Re: Modem & FAX pass-through differencies

When the gateways detect a data modem, both the  originating gateway and the terminating gateway switch from dynamic and  adaptive buffers to static de-jitter buffers.

The use of a static  de-jitter buffer is required for modem passthrough because the  adaptation process in a dynamic de-jitter buffer causes a retrain on the  modem connection. When the modem call is concluded, the voice ports  revert to dynamic jitter buffers.

Modem and fax passthrough are treated the same fax passthrough is just a special case of modem passthrough.

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