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New Member

one way audio

I have a VG200 connected to a CCM3.0 which is connected to a Unity2.4. When I call from VG200 to Unity, I get one way audio (I can hear Unity, but Unity can't hear me).<br><br>


Re: one way audio

From the support library:


Unity 2.4.6 w/Call Manager 2.x and 3.0(8). Users Can Hear Prompts, But Can't Record
Resolution -
First, check the NT event log for wave record errors. If you have any,
Then it's a Unity wave problem. Contact Support with the event log
Messages. If not, then it could be a network and/or firewall
Configuration problem.
In Call Manager-land, audio streams across RTP (which is different from
The skinny messages used for call setup, etc.) Thus, the routers /
Firewalls / etc must allow RTP streams to go in both directions. These
RTP streams typically use UDP ports 16384 and above, so the network must
Allow traffic on these UDP ports to go *both* ways.
While trying to record, push the "info" button twice on the IP phone.
This will bring up a bunch of things, one of which is a "Tx packet
Count" If that is not increasing as you speak, then you know that no
RTP data is being sent. Sometimes, though, the firewalls will silently
Drop packets and so just because the audio gets sent from the phone
Doesn't always mean it'll make it to Unity. Which brings us to a more
Definitive test:
Place a phone on the same hub / switch / whatever as the Unity box and
See if audio makes it both ways between that phone and the other phones.
If not, then something in the middle is blocking that traffic. Also,
While you're at it, see if you can record messages from that phone to
Unity. (You should be able to, because this takes away all the Intermediary firewalls, etc.)

Jeff Lindborg
Unity Product Architect/Answer Monkey
Cisco Systems (new page for Unity support tools and scripts)


Re: one way audio

I have the same or similar problem. I am using a 2600 with an FXO port in it. I am using mgcp and I have the above mentioned command in the router. I have a def route and IP routing is turned on. If I dial into the FXO port from the PSTN I can get to voicemail and it will response to touch tones from the phone, but it does not hear me. I can dial an extension and the 7960 IP phone can receive the call. I can hear the person on the IP phone but they cannot hear me. Everything is on the same subnet, so there are no routers or firewall that I have to go through, so that is not the issue. Any ideas?

New Member

Re: one way audio

I had a similar problem with vg200's and 3620's. Here's what corrected ours: First of all, we changed the IOS versions to the newest 12.1.5T release (ie. 12.1.5T4 for 3620's and 12.1.5T7 for vg200's at the time). Then under the ethernet config we added:

h323-gateway voip bind srcaddr "ethernet ip-address"
(we're obviously using h323)

then under general config term:

voice rtp send-recv

These commands along with the IOS change fixed our one-way voice.

Hope this helps,

Tom Parker


Re: one way audio

How many NICs do you have in the Unity box?


Keith Chambers
Customer Support Engineer
Cisco Systems


Re: one way audio

Make sure you have your default gateway set on the VG200 (ie: ip route the 172 address being the IP address of your default gateway on that segment.


New Member

Re: one way audio

How are you connecting to the VG200(H.323, MGCP)? What version of IOS are you running?

Also, check the configuration of the VG200, if you see "no ip routing", then this is your problem. Although the VG200 is not really 'routing' anything, 'ip routing' needs to be enabled so that the RTP stream can be fast-switched. If it is disabled, one-way audio will result.

If you are using MGCP, ensure you have command below configured:

mgcp dtmf-relay codec all mode out-of-band

If you are using H.323, configure (under dial-peer voice xx voip):

dtmf-relay h245-alphanumeric