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MGCP and H.323 with SRST Gateway Configuration

Vaijanath Sonvane
VIP Advocate VIP Advocate
VIP Advocate

Hi Support,

I have below queries regarding the configuration of MGCP and H323 protocol with SRST on IOS gateway:

1. Can we configure the MGCP and H323 on same gateway. If yes, then which scenerio this is aplicable and how?

2. If I have MGCP with SRST configured on gateway. In this case is it neccessary/valid to configure  H323 on same gateway?

Thanks & Regards,


Please rate helpful posts and if applicable mark "Accept as a Solution".
Thanks, Vaijanath S.

5 Replies 5

Abu Hadee

Hi Vaijanath

SRST is sepearate component or feature on IOS GW than H323/SIP/MGCP.

No matter what protocol you run, you may or may not have SRST.

When the phone do not have any call manager to connect to, it will try to register to SRST GW no matter whether it is MGCP, SIP or H323 Gateway.

But based on the protocol you run to connect to CUCM, you need some other configuration.

Like if it MGCP, when phones are registered to SRST GW, you need to terminate the ISDN msg local to the gateway. So you need to configure

ccm-manager fallback-mgcp

This command will remove the isdn l3-bind command from the serial interface when no call manager is available. So PRI can be used locally.

If it is MGCP analog lines, you need to configure

call application alternate default

for the same purpose

If it is H323, the PRI and analog ports are always termincate locally. But then dial-peer selection could cause problem. Like when the phones are registered in callmanager, you want to send the call to callmanager. But if you have CME as SRST, you'll also have ephone-dn created with more specific. So Gateway will try to send the call to ephone-dn where phones aren't register. So call may fail.

In that case, you need to modify preference and routing rule on the gateway. Smae goes for SIP

Regarding the MGCP and H323 on same gateway. You can have it. But you can not share a PRI with MGCP and H323 at the same time.

Analog ports can be shared by both H323 and MGCP at the sametime but only for outgoing. Incoming call will trigger MGCP application. So H323 will not be able to use it.

Hope this clarifies your doubts

Thank you

- abu


1. Yes, the two protocols can co-exist. The most common application would be MGCP fallback into H323 for SRST purposes. You'll need:

! Fallback to H323 if MGCP fails:



  service alternate default


ccm-manager fallback-mgcp


! Bind H323 to the correct interface:

inter lo1

h323-gateway voip interface

h323-gateway voip bind scraddr x.x.x.x


!Create SRST Dial-Peers

dial-peer voice 10 pots
translation-profile incoming PSTN-Inbound
incoming called-number .
port 0/1/0:15
dial-peer voice 101 pots
description 0/1/0:15 - Outbound calling
translation-profile outgoing PSTN-Outbound
preference 1
destination-pattern 0T
port 0/1/0:15



2. Yes. SRST relies on H323.


with the configuration you post, you just "Backup" the PRI line.

If you want your devices, phones in this case, to use that configuration it's a most to configure SRST, in other way, they never register against the router and will be unable to dial.

I'm I right?

To answer your question, yes, SRST config is neccessary for the phones to register with the gateway router. Also phones must know their SRST reference in order to register.



* If you find this post helpful, please rate


I have to configure an FXO on our MGCP gateway. This FXO will be used for the local site emergency calls to 999.

I have local dial-peers and the gateway turn to use them when its in the SRST mode but when the site is online

those dial-peers get ignored.

can you please give some example of how to configure so that everthing in MGCP but only that FXO uses H323 for 999 calls.



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