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Fax Protocol Compatability

I'm fairly new to VoIP and have only just started dealing with fax protocols so please bare with me.

At one of our clients we have replaced quiet a few 3925 and 2921 ISR at their remote sites over the last 6 months. We have noticed on the new devices running the new IOS that the cisco fax protocol is not support and we have to configure T.38. I did a quick check at what fax protocol all the voice gateways and vg224's are configured with and it looks like we have a mix of protocols in our network.

e.g.

Site A:

2921 H323 voice gateway and a analogue fax plugged into a vg224 using stcapp

Voice gateway fax protocol config:

fax protocol t38 version 0 ls-redundancy 0 hs-redundancy 0 fallback pass-through g711alaw
modem passthrough nse codec g711alaw

VG224 Config:

fax protocol t38 nse ls-redundancy 0 hs-redundancy 0 fallback pass-through g711alaw
modem passthrough nse codec g711alaw

Site B:

2921 H323 voice gateway with a analogue fax plugged into a fxs card using stcapp:
fax protocol cisco

Head Office:

The H323 2851 voice gateway at head office:
fax protocol cisco


vg224 using stcapp  with our head office faxes connected:
fax protocol t38 nse force ls-redundancy 0 hs-redundancy 0 fallback cisco
modem passthrough nse codec g711ulaw

All our analogue ports on either our vg224s or FXS ports are using stcapp and are registered to the call manager so internal fax to fax communication in most cases goes internally over the wan link rather than over the external pstn lines. Now I have a number of questions regarding the fax protocols:

1. In the case of the first site, should the fax protocol configuration on the vg224 match that of the gateway. As you can see the gateway does not have nse configured?
2. At some of the other remote sites they have T.38 NSE force configured. Will these sites still be able to fax to a site with just t.38 with no nse and t.38 with nse but no force command configured?
3. Is the modem passthrough command even needed as the fax protocol command specifies the passthrough?
4. Faxes aren't used too regularily so we only get calls reporting fax issues sparodically. Given the 3 configurations above, in what situations will faxes work and when will they fail (e.g. first site to HO, second site to HO, first site faxing to second site.)
5. What is the best option to go from here, should we configure all gateways and vg224s with:
fax protocol t38 nse ls-redundancy 0 hs-redundancy 0 fallback pass-through g711alaw ?
fax protocol t38 nse force ls-redundancy 0 hs-redundancy 0 fallback pass-through g711alaw ?
fax protocol t38 version 0 ls-redundancy 0 hs-redundancy 0 fallback pass-through g711alaw ?
fax protocol t38 nse version 0 ls-redundancy 0 hs-redundancy 0 fallback pass-through g711alaw ?
fax protocol t38 nse force version 0 ls-redundancy 0 hs-redundancy 0 fallback pass-through g711alaw?

Everyone's tags (3)
1 REPLY

Fax Protocol Compatability

Personally there is many ways and options, that I don't feel comfortable giving an option. But Michael Hanes wrote a forum here about this and it might help you out.

https://supportforums.cisco.com/docs/DOC-14470

HTH

Regards,

Yosh

HTH Regards, Yosh
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