One way voice - CUCM to PSTN

[carl_townshend]

Hi All

Can anyone help

we are in the middle of a cucm deployment.

Basically we have a clustered cucm between 3 sites with PSTN breakout on each using local route groups.

If we register the phones in site 1 with cucm 1 going out of the local gateway, all is OK.

However if we switch of the subscriber in site 1 so the phones register to the subscriber in site 2 we get one way voice.

How would this be, the local phone is still using the local gateway, so what would cause this?

when I do a >show voip rtp connections on the phone, I do not see the phones IP address as the remote endpoint, I see local IP as the Gateway and remote IP as our firewall IP for some reason, Am I right in saying you should be seeing the phones IP address?

Any ideas what is happening guys?

cheers

[@Syed]

Do you have MTP configured on this pstn router? if yes, check SUB 2 is added as secondary call manager

[carl_townshend]

Hi

The engineer did configure transcoding on router and conf resources, but he did not enable it so guess it will use the built in software one on CUCM? The router resources are not registered in CUCM.

How should the RTP flow between the phone and the local Gateway, why does it not work using backup CUCM?

I thought the RTP should go direct from phone to Gateway?

cheers

[R0g22]

If no media resources on the CUCM are getting invoked ( i mean UCM software), RTP should flow b/w the phone and the gateway. Do you have any logs to check for a audio issue call ? Are the IP addresses negotiated correctly ? What do you see on the gateway if you do a "show voip rtp connections" ? What is the remote IP address ? Is it reachable from the router ?

[carl_townshend]

Hi

we have noticed that when the phone goes to the local on site subscriber the calls flows too and from the Gateway fine, when we switch this sub off and it registers with the sub on the other site, the RTP seems to go towards our firewall, its like the RTP is not going direct between the gateway and phone like it supposed to.

why would this be ?

[Jerome BERTHIER]

Hi


One way voice is quite often a firewall filtering problem.

It is possible that RTP traffic (negociated UDP ports during call sig) is broken on the path between the phone and the voice gateway.

In your setup (except if CUCM2 are providing MTP), the phone will try to reach the gateway in front of PSTN network and the gateway has to be able to answer.

So, you should check if :

- any firewall is doing SIP / MGCP / SCCP inspection and if this is working

- any filter is missing for call traffic between phones and cucm / cucm and voice gateway / voice gateway and phones


You might try to disable firewall inspection SIP / MGCP / SCCP and to setup fully bidirectionnal firewall filter to open call sig and RTP between all pieces of your solution.


Regards


Jérôme

[carl_townshend]

Hi

Please see my comment before

The phone is one hop away from the Gateway and no firewall in between.

However there is a Firewall between the sites, but with open access.

I am not sure why moving the phone to another CUCM breaks the voice as surely the RTP stream should go direct from phone to Gateway.

In what circumstance would this not happen? The RTP never goes via CUCM does it?

[jonathan.salter · Accepted solution]

99.9% of the time it's either a firewall issue or a network routing issue.

The only other time I have see was a SIP trunk profile setting.