[cisco-voip] fax and modem relay

[Nick Matthews]

Hi Eric,

You can configure both passthrough and T38 on MGCP simultaneously.

The call will switch over to passthrough a hair before T38 because
passthrough kicks off on the ANSAM/2100Hz tone.  When the DIS is
received, it will switch over to T38.  If T38 negotiates successfully,
it will take preference over passthrough.  If both are configured, it
will try to negotiate T38, but if the other side will not negotiate
it, it will stay in modem passthrough.

In the case that your remote gateway is only configured for T38, the
call will not switch over to passthrough on the 2100Hz tone, but will
then switch over to T38 on the DIS.  You would configure just T38 on
the remote site, and passthrough + T38 on the main site.


-nick

On Tue, Apr 14, 2009 at 2:33 PM, Eric Pedersen <eric.pedersen at sait.ca> wrote:
> Running CM 6.1(2) and MGCP to our gateways.
>
>
>
> We are turning up a remote site with limited bandwidth to our main campus so
> I am investigating the use of fax and modem relay at this site.  I have some
> questions, if someone has experience with this:
>
>
>
> Does CM negotiate the selection of passthrough or relay between endpoints,
> and is this taken into account for bandwidth calculations between locations?
>
>
>
> Our main campus PRIs for pstn calls are configured for fax passthrough.  The
> remote site router will be configured for relay.  For calls to or from the
> PSTN, can I force the selection of relay?  I don’t want to switch all our
> calls to relay, just to the remote site.
>
>
>
> Thanks,
>
> Eric
>
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