Remote use of Cisco IP Phones

[djohnson28]

I am currently evaluting Cisco Call Manager Express and have a question regarding the options for home users. I currently have my CME router directly on the Internet at the main office and I am testing a 7912 IP phone from home. I have tried the phone behind two different Linksys broadband routers and a sonicwall. I am successfull at registering the phone, getting dial tone, placing and receiving calls but no audio in any of these situations. Broadband connection is SBC DSL. Does anyone have any insight on why this problem is occuring?

 

[jerake75]

Not too familiar with CME, but no audio could possibly be a codec mismatch somewhere...you using G.729 or G711? No firewalls blocking RTP traffic?

Here's some threads that might help you:

http://www.tek-tips.com/viewthread.cfm?qid=1169997

Troubleshooting One-Way Voice Issues:

http://www.cisco.com/en/US/tech/tk652/tk698/technologies_tech_note09186a008009484b.shtml

TMH

 

[pndscm]

Since call setup signaling is done thru the CME but audio is phone to phone, can the 2 phones ping each other? Sounds like a codec or routing issue.

 

[djohnson28]

I have narrowed it down to the Linksys devices being the problem. I tried out a DLink DI-604 broadband router and everything works like a charm. There is one special settings on the DLink which needs to be set or else only one way audio will work. It is a DMZ setting, you put the IP phone in a DMZ on the router. I did find another post suggesting to port forward all ports (0-65535) on the linksys to the IP phone but that did not work in my case. Seems like these low cost routers are really hit or miss.

 

[jgiacobbe]

This is definitly a routing issue. To successfully connect, several things need to happen.

1. Both phones must be able to talk to CME. Sounds like you have this down.
2. Traffic from phone A needs to be able to get to Phone B.
3. Traffic from Phone B needs to be able to get to Phone A.

If all three of these conditions are met you will be able to get phone calls between phones. As it stands you are getting no adio because 2 and 3 are not successful. Mostly these are firewall/Nat issues and they can be somewhat hard to overcome as most home firewalls are not RTP aware and most likely both your phones do not have public IP addresses.

The easiest solution may be to get a VPN configured. I regularly use IP communicator over a VPN. If you can set up a VPN between your office and your home router this may be the best solution for using an IP phone at home but opens your network up to threats from the home users network.

Bottom Line: Lots of firewall configuration and lots of security concerns.


Jeremy Giacobbe
MCSE, CCNA