Configuring fax in IOS

Configuring Fax for MGCP.

Below is the procedure to configure a FXS card in CME

config terminal
  ccm-manager fax protocol cisco (Select the fax protocol for MGCP in out case it is Cisco)

mgcp fax t38 ecm ( fax Configure MGCP Fax Parameters, t38 Configure MGCP Fax T.38 
Parameters, ecm Enable Error Correction Mode (ECM) )
Configure the Voice Port config (In our case the for fxs port is used which is  voice port 0/0/0)

voice-port 0/0/0 (Port where FAX Machine is connected) description FAXMachine-01
caller-id enable
 
Create a dial peer to send the call to Fax Machine

 dial-peer voice 10 pots destination-pattern 6055 (PSTN Number’s last 4 digit) port 1/0/0

Let me put some more fact on the type of Fax protocol as initially i found difficulty in remembering these ,Hence decided to record this in form of blog once i understand this ..



1. pass-through : In this the communication occurs in low  compression code like g711

2. NSE based pass-through: in this also the communiction occure in low compression codec like g711 but use a cisco propritory NSE protocol ehich help in detection of fax call aand on detection of CED tone switch from Voice to fax
  
3. Protocol based pass through : It is same as Normal passthrough only difference is switchover from Voice to fax mode is trigered by protocol message for h323 and SIP stack based on protocol , for h323 h245 messages are used to trigger the switchover

Relay Method : This method is basically demodulate the fax signal and remodulate/repack the signal as per defined protocol  there are two type T.38 (open standard) other is cisco proprietory:

Good Link from cisco on Fax : "supportforums.cisco.com/docs/DOC-1360"

Few troubleshooting commands:

For NSE Pass through
debug voip rtp session named-event  : for NSE passthrough troubleshooting check for nse messages like (192 etc)

Protocol passthrough

debug h245 asn1  : check for trigger messages for pass through
debug ccsip messages   
debug sccp messages