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FXO with MGCP vs. H323


In my test lab, CM4.1.2 with 2821 (12.4.3) running MGCP fallback to H323 with FXO loopstart

In MGCP, outbound calls intermittently work so tried H323 by failing to SRST and found that after pressing 9 and waiting for 2nd dialtone, all calls go through but if I do not wait for 2nd dial tone but press the full DN quickly, I also have intermittent outbound failures.

How do I fix this on the MGCP side as I am not too worry with the H323 side as I'll tell users to wait for 2nd dialtone before dialing.

Cisco Employee

Re: FXO with MGCP vs. H323


On the MGCP side, you said you have intermittant failures.. Can you please qualify that statement? what actually happens? can the users dial the full DN? if so, does the call go thru? do you have no way audio? or do you get fast busy? Does the terminting end hear a ring at all?

Then, send us a debug mgcp packet and debug vpm signal for a good and bad scenario.

For the SRST issue, can you give us a debug vtsp dialpeer all, debug vpm signal and debug voice ccapi inout.


Cisco Employee

Re: FXO with MGCP vs. H323

please send us configs from the router as well


Re: FXO with MGCP vs. H323


Callflow (if successful, is normal 2 way audio, there is no problems with one way audio)

IP Phone 1801 calls 9-273-6261 (CCM or SRST strips 9)


a. if I dial 9, then wait for 2nd dialtone, then 273-6261, all calls successfully go through

b. If I dial 92736261 quickly or hit redial, sometimes it works and if not, I get fast busy

MGCP (BTW, doesn't matter if "overlap sending" is on or off. Although I prefer it off ):

a. If I dial 92736261 or hit redial, sometimes it works and if not, I get fast busy

The 1st debug is "deb vpm all"

The 2nd debug is "deb voip hpi all"

The last debu is "deb mgcp packet"


Cisco Employee

Re: FXO with MGCP vs. H323


For the H323 case, Can you please change this:

dial-peer voice 10 pots

destination-pattern 9

port 0/1/0



dial-peer voice 10 pots

destination-pattern 9[2-7]......

forward-digits 7

port 0/1/0

dial-peer voice 11 pots

destination-pattern 91[2-7]..[2-7]......

forward-digits 11

port 0/1/0

dial-peer voice 12 pots

destination-pattern 911

forward-digits all

port 0/1/0


secondary-dialtone 9


For the MGCP case, the problem is this:

*Sep 15 23:06:03.445: MGCP Packet sent to>

502 258 Active connection exists


You just have to wait long enought to make the next call.. Give it a few seconds...Come on, be nice to the router :)