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Beginner

Fax Passthrough using NSE (via ITSP and Rightfax)

I have a customer who has the following setup:

SIP Provider => MPLS => CUBE (SIP) => CCM (SIP)       - cube set for passthu using NSE

     CCM (MGCP) => VG224                                            - set for passthu using NSE

     CCM (SIP)      => Cisco RightFax                                - set for T38 with passthru failover (realize it is protocol xfer)

     CCM (MGCP) => Router with tieline to PBX                 - set for passthu using NSE

- all g711ulay with no vad (and default 20ms samples for lack of a better term)

Testing, minimal, currently works from:

       - PSTN to VG224 (both ways)

       - Rightfax to VG224 (both ways)

Questions

1. PSTN=> VG224

     - capture shows initial g711u negotiated  (see attached flow graphic form wireshark)

     - as expected, vg224 sending NSE to switch and provider ignore (no RTP 192 ack ever)

     - fax still goes through, only doing 1-2 pages

     - working in both directions even though see Cisco side always trying NSE switch unsuccessfully

Q1: why does this work?

Q2: Will it work consistently for large faxes or faxes that have images?

Q3: since NSE does not work, can I assume no switch to 10ms sample: what impact to quality?

2. Rightfax to VG224

    - same thing here, NSE is ignored as expected

    - but fax still worked in both directions

I am asking becuase this is not yet in production and our sample faxes have been 1 to 2 pages and also we are not yet doing any volume.

Design :

- T38 from Rightfax <=> ITSP (works fine)

- would love to do T38 across board but ITP does not support T38 re-invite for PSTN bound faxes

       o and I am told Cisco will not re-invite of not on terminating side (Rightfax does)

- just provided this for big picture (anticipating recommendations)

Summary

- just why are the passthroughs working for flows that are terminating on non-Cisco gear

    - associated concern about reliability

    - associated concern about fax quality

Thank you!

Andy

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Enthusiast

Fax Passthrough using NSE (via ITSP and Rightfax)

Hey Andrew,

Yes, as long as a simple audio path is open between the 2 endpoints, with good transmition quality, fax should work. This is a best effort transmition, since it will be handled as a regular voice call.

Please take a look at this post, is extremely useful for fax environments:

https://supportforums.cisco.com/docs/DOC-25210

HTH

--
Jorge Armijo

Please remember to rate helpful responses and identify helpful or correct answers.

-- Jorge Armijo Please remember to rate helpful responses and identify helpful or correct answers.

View solution in original post

5 REPLIES 5
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Enthusiast

Fax Passthrough using NSE (via ITSP and Rightfax)

Hi,

Please remember that Passthrough NSE is Cisco Proprietary, ITSP will never send back NSE events 192 or 193. Unless the ITSP uses Cisco equipment

Right Fax uses t.38 Protocol Based as well as most ITSP, that's why you have faxes working between ITSP and Right Fax.

In call flows were Cisco Devices and ITSP's are involved, you better use a Protocol Based configuration.

Faxes that are working, those are not making switchover, since NSE is Cisco proprietary, most likely faxes are working because there is an open path between the Cisco Device and the Service Provider using g711ulaw, where there is no audio compression and the tones are going on the RTP directly, commonly named passthrough.

If your Carrier does not support t.38 Protocol based, what they accept?

You can’t trust on passthrough only, since the fax transmitions will depend on the delay, jitter and basically, the network performance. That's why t.38 is the most popular in SIP environments; it encapsulates the tones and those are sent OOB.

This is my humble opinion

--
Jorge Armijo

Please remember to rate helpful responses and identify helpful or correct answers.

-- Jorge Armijo Please remember to rate helpful responses and identify helpful or correct answers.
Highlighted
Beginner

Fax Passthrough using NSE (via ITSP and Rightfax)

Thanks for the reply Jorge.

So from what you are saying, as long as I have a g711ulaw path, really a simple voice path/voice codecs with no packet degredation, the fax call will complete and terminate fine.  This includes the fact that packetzation remains at 20ms as opposed to 10ms.

Yes, I would love to do T38 all the way through but I am limited by ITSP T.38 support.  They have had this passthrough-nse method for a year (NSE to non-Cisco endpoints) with no issues.  My CMR records show 4.4+ MOS scores so hope that remains. 

Last item is that MGCP only supports NSE based switch to passthrough.  :-(

Andy

Highlighted
Enthusiast

Fax Passthrough using NSE (via ITSP and Rightfax)

Hey Andrew,

Yes, as long as a simple audio path is open between the 2 endpoints, with good transmition quality, fax should work. This is a best effort transmition, since it will be handled as a regular voice call.

Please take a look at this post, is extremely useful for fax environments:

https://supportforums.cisco.com/docs/DOC-25210

HTH

--
Jorge Armijo

Please remember to rate helpful responses and identify helpful or correct answers.

-- Jorge Armijo Please remember to rate helpful responses and identify helpful or correct answers.

View solution in original post

Highlighted
Beginner

Fax Passthrough using NSE (via ITSP and Rightfax)

Jorge - Hope you are having a happy holiday break!

Consistent with your post, it seems that the passthrough NSE messages go unacknowledged but this does not impact the fax which succeeds anyhow (so no explicit voice to fax switch).  So for clarity:

NSE is used for:

1. switch to g711ulaw

2.  no vad

3.  if v34, disabling echo cancellation  (we are not supporting anyway)

4.  setting sample/packetization from 20ms to 10ms

5. increasing jitter buffers

5. pretty much using a voice codec with some optimizations

Since we have non-Cisco endpoints and this is ignored...

1. the lack of passthru NSE acknowledgement does not adversely impact fax delivery (anecdotely supported assumption - wireshark trace graph sure does help understand)

2. we are already at g711u, no vad, 20ms packetization (default voice in our enterprise including to SIP provider)

3. penalty is 20ms and default jitter buffers: both are non-impacting at this time (yes, realize network degredation may cause failure)

I ended up setting Rightfax to 'g711 passthrough only' and all  the flows seem to be ok (full scale testng to come).

Thanks!

Highlighted
Enthusiast

Fax Passthrough using NSE (via ITSP and Rightfax)

Hi Andrew!

Thanks for the reply.

Great to hear that all seems to be working so far, hopefully all will work like a charm on full testing

It's always a pleasure to help, and thanks for the great rating!!

--
Jorge Armijo

Please remember to rate helpful responses and identify helpful or correct answers.

-- Jorge Armijo Please remember to rate helpful responses and identify helpful or correct answers.
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