====== Fax Relay ======
Cisco Fax Relay is a proprietary fax relay implementation that uses Real-time Transport Protocol (RTP) to transport fax data. It is the default fax relay type on Cisco voice gateways and the only supported fax option for Cisco Unified CME 4.0(3) and later versions.

This feature enable Skinny Client Control Protocol (SCCP) Fax Relay for analog foreign exchange service (FXS) ports under the control of Cisco Unified CME. 

If your voice gateway is a separate router than the Cisco Unified CME router, an IP voice image of Cisco IOS Release 12.4(11)T or later is required. 

[[ccme-stcapp|SCCP Telephony Control Application]] is enabled. 

===== Configuration =====

==== STCAPP ====
  * Enable [[ccme-stcapp|SCCP Telephony Control Application]]

==== Voice Service Fax Relay ====
  * Enable Fax Relay
<code>
voice service voip
  fax protocol cisco
</code>

==== (Optional) Voice Service SG3 to G3 ====
  * Add support for Cisco Fax Relay and Super Group 3 (SG3) to G3 fax relay. 
  * This feature allows the fax stream between two SG3 fax machines to negotiate down to G3 speeds (less than 14.4 kbps) allowing SG3 fax machines to interoperate over fax relay with G3 fax machines. 
<code>
voice service voip
  fax-relay sg3-to-g3 
</code>

===== Debug =====
  * **show voice call summary** — Displays fax relay voice port settings. 
  * **show voice dsp** — Displays fax relay digital signal processor (DSP) channel status. 
  * **debug voip application stcapp all** — Displays SCCP telephony control (STC) application fax relay information. 
  * **debug voip dsm all** — Displays fax relay DSP stream manager (DSM) messages. 
  * **debug voip dsmp all** — Displays fax relay distributed stream media processor (DSMP) messages. 
  * **debug voip hpi all** — Displays gateway DSP fax relay information on RTP packet events. 
  * **debug voip vtsp all** — Displays gateway voice telephony service provider (VTSP) debugging information for fax calls