[Asterisk-Users] Faxing in passthrough and codec in passthrough

[T. Chan]

Dear All,

I need your advices, all you experts out there, I have spent alot of time
testing but just could not get it to work, so I need your assistance please.

I have been trying to passthrough calls with asterisk, that is, receiving
calls from customer via VOIP and then directly send the calls out to other
VOIP carriers. For example calls to India come in to my asterisk and get
routed to Carrier A who is, for example, using a Cisco VOIP gateway to
receive my calls and terminate to India.

I have 2 problems with passing throughs:

1. Faxing - when calls come into my asterisk, I don't suppose it knows if it
is a fax or not, or if there is a way to configure the Asterisk to detect
it, how should it be configured? Then the calls to India will go directly
back out via VOIP to Carrier A who , for example, uses Cisco VOIP gateways
and supports T38 faxing. The problem is that, with this passing through, all
faxes become impossible. Another scenario which is NOT a passthrough
situation is I have an Asterisk in, for example, New York and another one
in, for example, Los Angeles, we tried making faxes from New York from the
ZAP channels to Los Angeles, to be terminated via ZAP channels on ISDN
circuits. Again, it never works. Ladies and Gentlemen, how should one
configure Asterisk to make (a) faxing possible in a passthrough situation
with both endpoints cisco and asterisk in the middle and (b) faxing possible
with both asterisk as endpoints?

2. Codec negotiation - again in a passthrough situation when both endpoints
are non-asterisk, most probably cisco or quintum gateways, I can never allow
more than 1 codec, for example, g723 and g729 or with g711. For example, if
the terminating endpoint is quintum and allows only g723, the originating
endpoint is cisco and it is sending both g723 and g729, I cannot allow on my
asterisk both g723 and g729 and let it negotiate because it will not work. I
have to ONLY allow g723. However, there might be a quintum2 as a terminating
endpoint that uses g729, and if I allow both g723 and g729 on my asterisk,
both quintum and quintum2 will not work, if I allow ONLY g723 on the
asterisk, only the first quintum will work, and if I allow ONLY g729, only
quintum2 will work, I cannot send calls to both quintum and quintum2, all
other gateways, softswitches work with allowing all codecs to negotiate, but
it does not seem to work with asterisk, I tried h323 and SIP and reaping
same results. Can anyone help me to see how I could achieve that please,
thanks !!

Look forward to your assistance. Thanks

TC
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