FAX compatible query

[Shri2]

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

[Sadav Ansari]

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.

Pls rate all useful post!!

Pls rate if its “Helpful”. If this answered your question pls click “Accept as Solution”.

[Nithin Eluvathingal]

---

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.?

[Sadav Ansari]

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.

[Shri2]

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

[Nithin Eluvathingal]

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. 

[Shri2]

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 ?

[Sadav Ansari]

Below is the answer for your query.

Fax Services over IP Networks

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.

• Fax pass-through, in which modulated fax information from the PSTN is passed in-band end-to-end over a voice speech path in an IP network. The following two pass-through techniques are possible:
  • The configured voice codec is used for the fax transmission. This technique works only when the configured codec is G.711 with no voice activity detection (VAD) and no echo cancellation (EC), or when the configured codec is a clear-channel codec or G.726/32. Low bit-rate codecs cannot be used for fax transmissions.
  • The gateway dynamically changes the codec from the codec configured for voice to G.711 with no VAD and no EC for the duration of the fax session. This method is specifically referred to as codec upspeed or fax pass-through with upspeed.

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.

Pls rate all useful post!!

Pls rate if its “Helpful”. If this answered your question pls click “Accept as Solution”.

[Nithin Eluvathingal]

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

[Elliot Dierksen]

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.

[Nithin Eluvathingal]

Never suggested  to use both Modem and fax passthrough 

[Nuno Melo]

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.