Commonly supported Fax/Modem call flows

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Jun 20, 2012 3:28 AM
Jun 20th, 2012

Introduction

With the number of faxing protocols supported by Cisco devices and Service Providers, it is easy to get confused with all the possibilities. The important point to note is that in a fax call flow, all the devices on VoIP need to utilize the same faxing protocol for a fax call to be successful as faxing protocols cannot be transcoded unlike audio calls.

A fax call first sets up as an audio call and then switches over to a fax call. Two of the most common switchover mechanisms are NSE (Cisco propriety) and protocol based (Standards) switchover. Just like the faxing protocols, the switchover mechanism also needs to be the same in a fax call flow.

This document lists the most commonly encountered faxing call flows Cisco customers open TAC SRs for along with a baseline configuration that should be present on the gateways.

Fax Call Flows

A. Telco – PRI – GW – FXS – Fax/Modem

     [No FoIP protocols involved]

voice service pots
fax rate disable

B. Telco – PRI – GW – MGCP – CUCM – MGCP – VG224 – Fax/Modem

     [Can do both Passthrough(NSE) and T38]

Config for both GW and VG224 doing Modem Passthrough(NSE)
no ccm-manager fax protocol cisco                             
mgcp modem passthrough voip mode nse
mgcp modem passthrough voip codec g711ulaw

Config for both GW and VG224 doing T38
no ccm-manager fax protocol cisco              
no mgcp fax t38 inhibit 
mgcp package-capability fxr-package
mgcp default-package fxr-package
no mgcp fax t38 ecm


C. Telco – FXO – GW – H323/SIP – CUCM – SCCP – VG248 – Fax/Modem

     [Can do both Passthrough(NSE) and T38(NSE). Protocol based switchover is not supported with SCCP]

Config for GW doing Modem Passthrough(NSE)
dial-peer voice <tag> voip
  modem passthrough nse codec g711ulaw
                                          OR
If there is no specific configuration on the dial-peer, then the following should be present under "voice service voip"

voice service voip
modem passthrough nse codec g711ulaw

Config for VG248 doing Modem Passthrough(NSE)
1) Configure --> Telephony --> Port specific parameters --> Choose the port to which the Fax machine is connected. Set "Fax Relay" to "disabled"

2) Configure --> Telephony --> Advanced Settings
    Set "Passthrough signaling" to IOS Mode

Config for GW doing T38(NSE)
dial-peer voice <tag> voip
  fax protocol t38 nse ls-redundancy 0 hs-redundancy 0 fallback pass-through <g711ulaw or g711alaw>
  fax-relay ecm disable
                                                OR
If there is no specific configuration on the dial-peer, then the following should be present under "voice service voip"

voice service voip
  fax protocol t38 nse ls-redundancy 0 hs-redundancy 0 fallback pass-through <g711ulaw or g711alaw>
  fax-relay ecm disable
  fax-relay sg3-to-g3

Config for VG248 doing T38(NSE)
1) Configure --> Telephony --> Port specific parameters --> Choose the port to which the Fax machine is connected
   a) Set "Fax Relay" to "T.38 peer to peer"
   b) Set "Fax relay ECM" to "disabled"
   c) Set "Fax relay NSF" to "override with 000000"

2) Configure --> Telephony --> Advanced Settings
    Set "Passthrough signaling" to IOS Mode


D. Telco – PRI – GW – MGCP – CUCM – SCCP – ATA186 – Fax/Modem [Can only do Passthrough(NSE)]

Config for GW doing Modem Passthrough(NSE)
no ccm-manager fax protocol cisco                             
mgcp modem passthrough voip mode nse
mgcp modem passthrough voip codec g711ulaw

Config for ATA186 doing Modem Passthrough(NSE)
Please refer to "Configuring and Troubleshooting the Cisco ATA 186 with Fax"


E. Telco – PRI – GW – MGCP – CUCM – SIP – ATA187 – Fax/Modem [Can do both Passthrough and T38]

Config for GW doing Modem Passthrough:
no ccm-manager fax protocol cisco                             
mgcp modem passthrough voip mode nse
mgcp modem passthrough voip codec g711ulaw

Config for GW doing T38:
no ccm-manager fax protocol cisco              
no mgcp fax t38 inhibit 
mgcp package-capability fxr-package
mgcp default-package fxr-package
no mgcp fax t38 ecm
mgcp fax t38 nsf 000000

For ATA187 please refer to "Cisco ATA 187 Analog Telephone Adaptor Administration Guide for SIP, Version 1.0"


F. Telco – PRI – GW – SIP/H323 – CUCM – SIP – Fax Server [Mostly uses T38, but need to confirm with the customer]

Config for GW doing T38
dial-peer voice <tag> voip
  fax protocol t38 nse ls-redundancy 0 hs-redundancy 0 fallback pass-through <g711ulaw or g711alaw>
  fax-relay ecm disable
                                          OR
If there is no specific configuration on the dial-peer, then the following should be present under "voice service voip"

voice service voip
  fax protocol t38 nse ls-redundancy 0 hs-redundancy 0 fallback pass-through <g711ulaw or g711alaw>
  fax-relay ecm disable
  fax-relay sg3-to-g3

G. ITSP – SIP – CUBE – SIP/H323 – CUCM – SCCP – VG224

    [VG224 needs to be an MGCP GW for this setup to work. NSE  switchover is only specific to Cisco devices and providers do not  support NSE based switchovers]

Config for CUBE doing T38:
dial-peer voice <tag> voip
  fax protocol t38 nse ls-redundancy 0 hs-redundancy 0 fallback pass-through <g711ulaw or g711alaw>
  fax-relay ecm disable
                                          OR
If there is no specific configuration on the dial-peer, then the following should be present under "voice service voip"

voice service voip
  fax protocol t38 nse ls-redundancy 0 hs-redundancy 0 fallback pass-through <g711ulaw or g711alaw>
  fax-relay ecm disable
  fax-relay sg3-to-g3

Config for VG224 doing T38:
no ccm-manager fax protocol cisco              
no mgcp fax t38 inhibit 
mgcp package-capability fxr-package
mgcp default-package fxr-package
no mgcp fax t38 ecm


H. ATA186 – SCCP – CUCM – SIP – ATA187

    [ATA187 needs to run firmware 9.2.3 to support NSE based passthrough, otherwise integration is not possible]

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Comments

kc (not verified) Fri, 07/20/2012 - 07:55

Fantastic document - one of the best ever posted here.

Matt Amagi (not verified) Wed, 01/23/2013 - 13:22
mgcp package-capability fxr-package
mgcp default-package fxr-package

What exactly do these commands do? Some sites show examples with those packages removed, while you suggest adding them. Can't seem to find a clear explanation for these commands.

Tim C (not verified) Tue, 03/26/2013 - 13:21

Is it possible to use method D. without an ATA present?

Tim W (not verified) Wed, 04/10/2013 - 05:35

Any notes on the following call flow?

ITSP - SIP - CUBE - SIP - CUCM - SIP -  VG224 - FAX (& modems)

sergio (not verified) Sat, 05/04/2013 - 10:36

About ITSP - FXO - GW - MGCP - CUCM8.6 - SIP - ATA187 - FAX

j.reinbold Sat, 09/28/2013 - 02:54

Very nice compendium !

I suggest to make a similar document for isdn digital data transmission over Voip, with RFC 4040 clearmode.

In this case we could have the following scenarios:

BRI Modem - digital third party gateway Like Patton Smartnode 4661 - SIP/RFC4040 - Cisco H323 Gwy - PRI PSTN

this ist the peer to peer scenario for small integrations

BRI Modem - digital third party gateway Like Patton Smartnode 4661 - SIP/RFC4040 - CUCM -

SIP/RFC4040 - Cisco H323 Gwy - PRI PSTN

this is the scenario for greater campus integrations in a Campus (for example in european countries) to have more managed control through  the CUCM SIP trunk implementation.  This is preventing a peer to peer "jungle" deployement with scenario 1.

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Posted June 20, 2012 at 3:28 AM
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