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Walkthrough Wednesdays

MGCP FXO/FXS Best practices

I am trying to find what is the best way to implement FXO ports in CUCM/MGCP environment.

I have a 2801 voice router setup as MGCP on CUCM 8.0 and i also have FXS and FXO ports on this router. FXS ports will provide analog endpoints and FXO will be used for SRST to route local 911 calls during emergency.

Question: If i setup them as MGCP endpoints, will they fallback to SRST when CUCM is offline, specially FXO does it behaves.

another question specifically for FXO is caller iD, i know they dont support sending caller id in MGCP mode, would it be a good idea to setup them in h323 endpoints in same router and maybe add same gateway as h323 in another instace, will this confilct with other mgcp config ?

Hall of Fame Master

For FXO, the best choice is H.323 or SIP.

For FXS, the best choice is SCCP.

Avoid MGCP if possible at all.


Hi Paolo, how are you?

I know this is an old tread, but I got a little curios reading your statement. "Avoid MGCP if possible at all".

My company is planning the deploy of some gateways and we are considering using MGCP in Cisco 881 routers, to use FXS and FXO ports.

Could please explain your opinion why you preferer other protocols than MGCP?

Thank you very much.



IMO there are two or three use cases where using MGCP is at least a defendable choice:

  • You have a single site with CUCM and the gateway coresident, no need for SRST/MGCP fallback and this won't change in the future. The router just needs to be a dumb media gateway.
  • You need QSIG functionality. This is now possible over SIP as well so this reason is shaky at best.
  • Your day two admin wants to manage FXS ports from within CUCM and you have a third-party fax server so SCCP isn't possible. This is also shaky since you still need to manually add the destination-pattern command to the MGCP-generated POTS dial-peer for it to receive calls during MGCP fallback (i.e. it doesn't totally alleviate you from IOS commands).

Outside of those scenarios, MGCP is a choice made by lazy/ignorant voice engineers who don't understand IOS dial-peers. Cisco is no longer investing in MGCP or H.323 from a development perspective; it's all about SIP now.

Please remember to rate helpful responses and identify helpful or correct answers.


Thanks for your words Jonathan.

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