Cannot call to some external site

[Abzal]

Hello gents,

We are having some problems with calling to external sites. The phone call to that site goes through Voice Gateway in Italy. We've checked IP routing, Call Manager configurations.  Also we've checked that VG configurations it all seem ok. Nothing is blocking voice packets or UDP traffic. Last thing we've done is port span where our Cisco IP Phone (7941G) is connected with Wireshark and you did not see any voice packets coming out of that port but coming in voice packets there is no problem.

The problem is we (where call is originated) can hear other side but they cannot hear us. Call registration establishment is ok.

Call manager version is 4.3.

Please, help me out.

I will provide you with additional information if you need.

[Chris Deren]

One way routing is 99.999% result of IP routing issues or firewal blocking the RTP ports.

Is there a firewall or ACL in between?

Have you tried ping and trace route between the voice subnets?

Chris

[Abzal]

Hi Chris,

Yes, I've checked ACL on all interfaces between switches and routers it's all ok. Call goes through WAN connection no firewalls are involved. Nothing is blocking RTP packets. Yes, I thought that there might be routing problem but connection between phone and registration server goes normal problem only with converation.

[brmeade]

Abzal,

Call registration messages are sent to your registration server whereas RTP traffic is usually directly between the end devices.  You will want to verify your IP routing between the 2 phones or the remote gateway if it is going out to the PSTN via a digital/analog line.

Brian

[Abzal]

Brian,

Yes, I know that, let me explain network topology. IP phone located on our network and second end device is some cell phone of foreign country. When someone calls it goes from our local network to WAN router then to Voice gateway located in Italy. I did trace of route of packets it ok, but when end devices get connected one side calling side cannot hear anything. I've done some tests and result is RTP packets did not reach even WAN router after connection is established. There is no any ACL between them.

I'm a little bit confused with situation.

[brmeade]

Which side cannot hear the other side?  Can you ping from the IP phones subnet to the media IP address of the voice gateway in Italy?  If you are losing RTP packets somewhere, you can narrow it down to a certain hop using packet captures.  That way you can narrow it down to which router is not routing the RTP packets properly.

[Gregory Garrian]

Also, are you using MTPs?  If so make sure both end devices have connectivity to the MTP.

[Abzal]

Gregory,

That details I really do not know. How can I check it?

[Abzal]

Brian,

If I call for example, I can hear voice of second side but second cannot hear me. Per us investigation RTP packets comes to LAN from external site, but our packets do not reach them.

[Abzal]

Could be the problem some codec issue or some mismatch of some settings of registration server or voice gateway? Because even Cisco IP Phone do not send RTP packets. I've checked it with port spanning with Wireshark.

[brmeade]

Can you attach the Wireshark trace for a call?  The phone should be sending RTP packets unless it doesn't have a route to the destination network.  Does the phone have a defaqult gateway configured or assigned via DHCP?

[Abzal]

Brian,

I actually already have done it. IP phones get their IP by DHCP. All other calls are ok. And default gateway configured properly. The problem is after call is established our phones do not send RTP only receives them.

[Brian Meade]

Can you attach the Wireshark file so I can take a look at it?

[Abzal]

There is file. IP phone addr. is 10.156.28.48 def. gateway is 10.156.28.1 and 10.129.2.166 is addr. of voice gateway or server I really do not know it is on different location. 10.156.20.84 is addr. of our Call manager.

[brmeade]

I'm having problems playing both audio streams from both directions.  It looks like there's a little bit of buzzing and clicking, but that's it.  Are these phones using SRTP or anything like that?