Fax Help 2951 PRI MGCP with VG204 SCCP

Answered Question
Jul 27th, 2010
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Hi,


After some advice on whats best.


At the moment we have 4 x 2951's with 8 PRI ISDN to PSTN running MGCP CUCM 7.1.5


Also we have 4 x VG204 running SCCP for FAX.



There is due to be 11 remote sites in future but none now.


Im lead to believe the gateways are configured forr Fax passthrough , we are having issues with FAX inboun.


Can someone please verify if the configs are correct & if we should chage to fax relay on what that would provide


see configs below.




pasted configs


2951 PRI to PSTN

ccm-manager redundant-host 192.168.67.2
ccm-manager mgcp
no ccm-manager fax protocol cisco


!
mgcp
mgcp call-agent 192.168.67.1 service-type mgcp version 0.1
mgcp dtmf-relay voip codec all mode out-of-band
mgcp rtp unreachable timeout 1000 action notify
mgcp modem passthrough voip mode nse
mgcp modem passthrough voip codec g711alaw

mgcp package-capability rtp-package
mgcp package-capability sst-package
mgcp package-capability pre-package
no mgcp package-capability res-package
no mgcp timer receive-rtcp
mgcp sdp simple
mgcp fax t38 inhibit
mgcp rtp payload-type g726r16 static
mgcp bind control source-interface Loopback0
mgcp bind media source-interface Loopback0
!
mgcp profile default
!
sccp local Loopback0
sccp ccm 192.168.67.2 identifier 2 priority 2 version 7.0
sccp ccm 192.168.67.1 identifier 1 priority 1 version 7.0
sccp ip precedence 3
sccp



//////


VG204


stcapp ccm-group 1


stcapp
stcapp feature access-code
stcapp feature speed-dial


voice service voip


fax protocol t38 nse force ls-redundancy 0 hs-redundancy 0 fallback cisco


modem passthrough nse codec g711alaw



voice-card 0


!


archive


log config


  hidekeys


ccm-manager fax protocol cisco ----is this correct -?????
ccm-manager config server 192.168.67.1
ccm-manager config
ccm-manager sccp local FastEthernet0/0
ccm-manager sccp
sccp local FastEthernet0/0


sccp ccm 192.168.67.1 identifier 1 priority 1 version 7.0


sccp ccm 192.168.67.2 identifier 2 priority 2 version 7.0


sccp


dial-peer voice 500 pots

service stcapp

port 0/0

!

dial-peer voice 501 pots

service stcapp

port 0/1

!

dial-peer voice 502 pots

service stcapp

port 0/2

Correct Answer by Michael Hanes about 6 years 12 months ago

Your situation has a few answers and can get somewhat confusing with the various fax transport mechanisms and switchovers used by Cisco gateways so please bear with me and let me know if you need any clarifications.


Your MGCP voice gateways are configured for what we commonly refer to as NSE-based passthrough (because Cisco NSE messages are used to switch from voice mode to passthrough) or simply modem passthrough. Do not be confused by the term "modem passthrough" though as it also carries fax traffic as well.


Your SCCP voice gateways are configured for modem passthrough AND NSE-based T.38 fax relay. This could possibly cause problems with your inbound faxes as this SCCP gateway will try a T.38 switchover but the MGCP voice gateway is not configured for T.38.  Typically we recommend T.38 for FoIP but many customers also run passthrough. I will leave the decision up to you and run you through the config changes for each scenario:


Scenario 1: Modem Passthrough


Your MGCP gateway configs are fine. On your SCCP voice gateway please remove the line "fax protocol t38 nse force ls-redundancy 0 hs-redundancy 0 fallback cisco" under voice service voip. Now both of your gateways are configured correctly for NSE-based passthrough. In regards to your question about "ccm-manager fax protocol cisco", I believe this only applies to MGCP voice gateways. If you wanted to configure cisco fax relay for SCCP you would do this under voice service voip and not with this command.



Scenario 2: NSE-based T.38 Fax Relay


Configure "no mgcp fax t38 inhibit" and "mgcp fax t38 gateway force" on your MGCP voice gateway and remove the modem passthrough commands. On the SCCP voice gateway remove the command "modem passthrough nse codec g711alaw" from under voice service voip.


In regards to what is best, the simplest solution would be to change to passthrough. However, T.38 is the de facto standard and what is recommended in the design guides. Just be aware that with SCCP voice gateways you must use Cisco's NSE-based T.38 which has a non-standards compliant switchover so it only works between Cisco products. I hope this helps.


-David

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shaftstri Tue, 07/27/2010 - 13:26
User Badges:

Thanks David,

Greta response and greatly Appreciated.

Correct Answer
Michael Hanes Tue, 07/27/2010 - 08:32
User Badges:
  • Cisco Employee,

Your situation has a few answers and can get somewhat confusing with the various fax transport mechanisms and switchovers used by Cisco gateways so please bear with me and let me know if you need any clarifications.


Your MGCP voice gateways are configured for what we commonly refer to as NSE-based passthrough (because Cisco NSE messages are used to switch from voice mode to passthrough) or simply modem passthrough. Do not be confused by the term "modem passthrough" though as it also carries fax traffic as well.


Your SCCP voice gateways are configured for modem passthrough AND NSE-based T.38 fax relay. This could possibly cause problems with your inbound faxes as this SCCP gateway will try a T.38 switchover but the MGCP voice gateway is not configured for T.38.  Typically we recommend T.38 for FoIP but many customers also run passthrough. I will leave the decision up to you and run you through the config changes for each scenario:


Scenario 1: Modem Passthrough


Your MGCP gateway configs are fine. On your SCCP voice gateway please remove the line "fax protocol t38 nse force ls-redundancy 0 hs-redundancy 0 fallback cisco" under voice service voip. Now both of your gateways are configured correctly for NSE-based passthrough. In regards to your question about "ccm-manager fax protocol cisco", I believe this only applies to MGCP voice gateways. If you wanted to configure cisco fax relay for SCCP you would do this under voice service voip and not with this command.



Scenario 2: NSE-based T.38 Fax Relay


Configure "no mgcp fax t38 inhibit" and "mgcp fax t38 gateway force" on your MGCP voice gateway and remove the modem passthrough commands. On the SCCP voice gateway remove the command "modem passthrough nse codec g711alaw" from under voice service voip.


In regards to what is best, the simplest solution would be to change to passthrough. However, T.38 is the de facto standard and what is recommended in the design guides. Just be aware that with SCCP voice gateways you must use Cisco's NSE-based T.38 which has a non-standards compliant switchover so it only works between Cisco products. I hope this helps.


-David

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