07-18-2021 07:47 PM
Hi Team,
I understand there are different methods/protocols to send/receive fax over IP.
If two different device supports different fax method, will fax work ?
Fax--Analog gw ( fax protocol 1) --- IP---- (fax protocol 2 ) VG
will there be need of MTP or any media resources to make fax work or this just wont work ?
Question is similar to voice call, when two endpoint speaks different codec, transcoder ensure two endpoints speak with two different codec.
Regards
Shri
07-18-2021 08:39 PM - edited 07-18-2021 08:39 PM
Hi,
Yes you can send/received FAX weather its using different protocol and coded.
if two location using Different fax protocol they can send/received FAX, thing is that both location must have connectivity between them.
For example in case you want to send FAX From your IP network (VG224) to any public network (outside network) for this you required voice gateway with SIP trunk/ E1 T1 connection to send FAX outside of your network weather its analog networks or digital using same protocol or not generally we don’t know, you will dial the number and its landed on your Gateway based on dial peer which you have configured on VG and on the dial peer we configured Voice class which indicate the codec priority, FAX work on G711 codec so codec negotiation done based on dial peer by using voice class configuration, And your service provider will take responsibility to connect your call with destination endpoint.
If using SIP gateway with cucm you can check MTP on your sip trunk profile.
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07-19-2021 11:08 PM
For example in case you want to send FAX From your IP network (VG224) to any public network (outside network) for this you required voice gateway with SIP trunk/ E1 T1 connection to send FAX outside of your network .
Can we send FAX over Analogue lines ?
you will dial the number and its landed on your Gateway based on dial peer which you have configured on VG and on the dial peer we configured Voice class which indicate the codec priority, FAX work on G711 codec so codec negotiation done based on dial peer by using voice class configuration, And your service provider will take responsibility to connect your call with destination endpoint.
If i configure Voice class configuration, can i send fax between t.38 and pass through.?
07-19-2021 11:47 PM - edited 07-19-2021 11:53 PM
Answer is No.
In modern pass through Fax works like real time Voice call while in t.38 its like gmail, Am I right ? If not pls correct.
I have given my answer based on posted question as Shri2 asking about from Ip to analog gateway as now analog gateway also works on VoIP.
Suggest your answer also so that it will be helpful for us.
07-21-2021 07:29 AM
So for successful fax for below call flow, analog gateway and SIP Gateway has to have common FAX protocol.
Fax--Analog gw --- IP---- VG-- E1
recent interviewer question , how can we make fax successful if two endpoint is using different fax protocol.
interviewee response : not possible to make fax work.
interviewer response : we can, with the help of MTP.. was surprised to hear it so wanted to confirm this from support forum.
Regards
Shrikant
07-21-2021 10:18 AM
If your ISP Is not gone support the protocol which are using, the FAX will fail. MTP has role when using DO/EO. But Never heard of using MTP for establishing connetion between multiple FAX protocols.
07-19-2021 01:12 AM
Thanks for the response Sadav, Lets consider below scenario
Fax--Analog gw ( fax protocol modem passthrough ( g711 ) --- IP---- ( t38 protocol ) VG-- E1
Will fax work in this scenario ?
07-19-2021 02:20 AM
Below is the answer for your query.
There are two conceptual methods of carrying virtually real-time fax-machine-to-fax-machine communication across packet networks:
Fax relay, in which the T.30 fax from the PSTN is demodulated at the sending gateway. The demodulated fax content is enveloped into packets, sent over the network, and remodulated into T.30 fax at the receiving end.
In addition to the methods for real-time fax transmission, a method called store-and-forward fax breaks the fax process into distinct sending and receiving processes and allows fax messages to be stored between those processes. store-and-forward fax is based on the ITU-T T.37 standard, and it also enables fax transmissions to be received from or delivered to computers rather than fax machines.
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07-19-2021 09:27 AM - edited 07-19-2021 11:09 PM
If your ISP use t.38, you need to send the FAX on t.38. if not the fax doesn't work. If pass through you need to send as pass through.
In my region t38 doesn't work. Below configuration which i use send faxes through T.38 first and fallback to passthrough in case of T.38 not available
SIP
voice service voip
fax protocol t38 fallback pass-through g711alaw
When using MGCP gateway. I use below config.
MGCP.
mgcp modem passthrough voip codec g711alaw
08-05-2021 06:50 AM
I would be hesitant to configure modem pass through. I have a way back memory of modem pass through superseding fax pass through if both were configured.
08-05-2021 07:42 AM
Never suggested to use both Modem and fax passthrough
08-05-2021 02:36 AM - edited 08-05-2021 02:40 AM
There are 2 most commonly used Fax over IP protocols T.38 and Pass-through (there are more cisco proprietary methods), from these to there are 2 variations NSE based and Protocol Based, NSE based is mainly a Cisco Thing, While Protocol based is used by most other vendors that support Fax over IP
Fax protocols themselves don't interwork over IP, nor there is a resource to interwork them but there might be a protocol fallback mechanism, meaning the fax will be attempted 1st in T38 and if it fails pass-through is attempted. it depends on which protocol the VGs are configured. With (sccp,mgcp,sip,h323) and the configuration itself..
MTPs might be used for a Fax call but not for fax protocol interworking purposes, they might be use i.e in a scenario where the VG is configured as MGCP and the PSTN gw as SIP, since the dtmf mechanisms will be different, and the fax transmission rellys on dtmf tones then the MTP might be invoked by the CUCM to interwork the dtmf relay difference.
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