[cisco-voip] recommended configuration for fax (MGCP PSTN Gateway, SCCP VG224)

[Michael Hamann]

Hello,

we are migrating a large Siemens PBX to a CUCM (9.1) environment with several
2921 MGCP (E1) PSTN gateways. We start now with the first branch offices where
we plan to have a 2901 Voice router (MGCP) with SRST configured. SRST works as
expected but we are not sure on how to provide analog lines (especially for fax
maschines) in the branch offices.

So far we plan to put VG204 and VG224 in the branch offices, configure them with
SCCP so that they can register with SRST in case of a WAN outage.

In our lab we are experiencing problems with sending and receiving faxes and I
am not sure what the best configuration is. As far as I understand T.38 protocol
based is not supported with SCCP and VGs.  So we decided to use T.38 NSE based.
Here I am not sure on how this will work with our SIP Fax Server (XCAPI
Interface confgured with T38). Since the amount of internal faxes is very low we
could use softfax in this case...

So our call flow looks like this.

Fax Maschine <-> VG224 (SCCP) <-> CUCM (9.1) <-> 2921 (MGCP/E1) <-> PSTN

Our configuration an a *VG224* looks like this:

----

voice service voip
 fax protocol t38 nse version 0 ls-redundancy 0 hs-redundancy 0 fallback
g711alaw

---

Configuration on the C2921 MGCP:

---

voice service voip
 fax protocol t38 nse version 0 ls-redundancy 1 hs-redundancy 1 fallback
pass-through g711alaw

ccm-manager fallback-mgcp
ccm-manager redundant-host XXX
ccm-manager mgcp
no ccm-manager fax protocol cisco
ccm-manager music-on-hold
ccm-manager config XXX
ccm-manager config
ccm-manager download-tones
ccm-manager sccp local GigabitEthernet0/0
!
mgcp
mgcp call-agent XXX XXX service-type mgcp version 0.1
mgcp rtp unreachable timeout 1000 action notify
mgcp modem passthrough voip mode nse
no mgcp timer receive-rtcp
mgcp sdp simple
mgcp fax t38 ecm
mgcp fax t38 inhibit
mgcp fax t38 ls_redundancy 1
mgcp fax t38 hs_redundancy 1
no mgcp fax-relay sg3-to-g3

---


show mgcp:


----
MGCP default package: mt-package
MGCP supported packages: gm-package dtmf-package trunk-package line-package
                         hs-package rtp-package atm-package ms-package
dt-package
                         mo-package mt-package sst-package fxr-package
pre-package
                         md-package
MGCP Digit Map matching order: shortest match
SGCP Digit Map matching order: always left-to-right
MGCP VoAAL2 ignore-lco-codec DISABLED
MGCP T.38 Max Fax Rate is DEFAULT
MGCP T.38 Fax is DISABLED
MGCP T.38 Fax ECM is ENABLED
MGCP T.38 Fax NSF Override is DISABLED
MGCP T.38 Fax Low Speed Redundancy: 1
MGCP T.38 Fax High Speed Redundancy: 1
MGCP Fax relay SG3-to-G3: DISABLED
MGCP Fax relay ANSam suppression: DISABLED



----

On CUCM we have disabled Cisco Fax and enabled T38 fax.

Is this configuration correct or did we now mix up T38 protocol based with T38
NSE ? A "show voice call summary" during a fax call show only a g711
connection...

Does anybody have a example configuration for our szenario ? What would be the
recommended protocolls to use in this szenario ?

Thank you and kind regards
Michael
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