Cisco Remote location IP phones not able to make/receive outside calls (works when calling internal lines)

[benacquis]

We are currently having issues with  all of our Cisco IP phones, that are located outside of our office/firewall. For some reason, all our 3 external Cisco IP phones are not able to make calls to any external users, nor are able to receive incoming calls from external callers correctly.

The 3 external phones can make/receive the actual call (rings on their lines) fine. However there seems to only be dead air on the line itself. The calls never actually "connect' completely and neither party is able to hear each other at all.

All internal calls via direct extension do work however. So, if we dial any of the 3 external IP phones via their internal extension, the calls work fine. However, the problem lies with making and receiving calls from outside/external sources that don't seem to work. This was working fine for us for a long time; however just started noticing that all 3 external IP phones no longer work correctly. All 3 external IP phones are connected to our CUCM fine and listed / registered to CUCM successfully, so not sure what's causing the issue.

All 3 phones are connected to our CUCM 7.1.3 via WAN (users use basic home firewalls, internet connections). We manually entered the TFTP into the remote Cisco IP phones and they connected fine to our CUCM.  All 3 phone models are 7962G and we have 2 nodes in the cluster (publisher and subscriber).  Also, during an external call text and after I hit "?" on the IP Phone; I see that the Receive Packets are at 0, bu Sender Packets is populated. 

Any help will be appreciated as Cisco TAC has been working on this with me as well, for several days now without a definitive fix.  Thanks in advance

[yahsiel2004]

Verify that you're PRI and or ITSP gateways IP address, is allowed to communicate with the external phones IP addresses. This is more than likely your issue and you should verify the firewall and or ACLs.

HTH

Yosh

[benacquis]

thanks for the response yahsiel2004.

Unfortunately, I'm not to well versed with the Cisco ASA here.  What should I verify in our Firewall exactly? Should I verify the external IP addresse(s) from our ISP that point to our Call Manager system via TFTP server (66.x.x.x)?

Is there any other particular config I need to do besides ensuring that specific port(s) is open?  The only gateway IP I know of is for our gateway device, that has an internal IP (192.x.x.x).

thanks again

[yahsiel2004]

I would reach out to your security team and have them verify the connection. Your external IP phones have different IP addresses and you may have an ACL blocking that network, from communicating with the ISP gateways network. Whenever you have one-way or no-way audio, its a routing a issue. It would be kinda hard for us to help you troubleshoot. The best that I can do is mention devices and configurations to check. You can also view the call statistics on your phones, to see if you're sending and receiving traffic (hit the "?" twice on your phones, while on the call to see the statistics. For newer phones you will need to drill down through the menus, to locate the call statistics)

1 - Firewall - Make sure that the external phones have access to the internal address, using the SCCP and RTP ports.

2 - Verify on your Core or router, that is in between the external and the GWs, for any ACLs which may be blocking the RTP traffic.

HTH

Yosh

[benacquis]

Thanks again.  Cisco and I definitely think it's firewall / routing related; however not sure what the culprit may be.  We didnt make any changes to the firewall at all and the issue just started happening over this past weekend.  But something is clearly wrong and hope to resolve it.  Unfortunately, since our company is fairly small (50 people), i'm the only one in IT and rely on Cisco's TAC help and here to hopefully resolve the issue.

I did in fact make another test call from one of the external phones and pressed "?" during an external test call from one of the remote phones and noticed the Received Statistics said 0

In response to #1:  the external phones connect fine to the cucm and can make internal calls to anyone in the main office fine using their extensions.  So the remote themselves are connecting fine to internal addressess

In regards to #2:  this is most likely where the issue resides.  The single ASA router we have does in fact lie inbetween one of the GW's and external PSTN device.  I'm not sure what/how to open ports up for RTP here however.  CAn you please confirm how to check to see if the RTP ports are open?  I believe I opened up a UDP range that corresponds with RTP; however not sure if configured correctly since it's still not working.  But according to Cisco and my assumptions, it looks like there's definitely a firewall/routing mis-configuration somewhere.

Thanks again in advance

[Bradley Pelletier]

I was wondering if you ever got this issue fixed. I have one vpn phone it is a cordless non cisco phone that was working fine. Then after an update it started having the same problem. If I call internally but if I call outside numbers you can not hear a dial tone or any audio at all. If connect the phone at our main site it works fine. I connected a Cisco 6945 over the vpn and it works fine so I am not sure why the 3rd party sip phone does not work over the vpn. Very frustrating.

[kelvinffhan]

Hi Bradley, Have you got your case resolved?

[Bradley Pelletier]

Yes. It was the phone that I was having issues with.  I had the enable codecs in the wrong order.  I went in after and now only G729 is enabled on that phone.

[kelvinffhan]

I see, meaning this will be the codec related issue. :) Thanks.

[pedram]

Hello ,

I am having same issue but only for one phone which can not be called from outside. Is there any firewall related issue? The phone can called internally but not externally.

Any thought?

[kelvinffhan]

I configure MTP Required on the phone itself which stream directly from the voice gateway to resolve the issue.

[pedram]

Thanks .

I am trying first to see we hit the GW or not by making test call and run debug ISDN q931.

If the call is hitting the GW then I am wondering how I can configure your suggestion? Can you provide any reference or documents?