Voip Phone has one way commnication

hi, i'll give a quick run down of kit:
Panasonic KXNT-321 VOIP phone
HP procurve switches (various)
Panasonic KXTDE-200

We currently have 2 VLANs set up. STD traffic and VOIP traffic.  The TDE and the phone are both sat on the VOIP VLAN.
VLAN has a static IP which is defined on the TDE and the phone. The phone has a static IP and the subnets are both the same. Both are untagged in the VLAN. The phone is registered on the TDE and can communicate with it. The issue is voice doesn't return from the phone to another user. They can hear the user but can't talk back.
I have tested the phone on the same switch the TDE is plugged in to see if we have a rogue config on a switch and it still doesn't work.
Any help would be appreciated.
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David AtkinTechnical DirectorCommented:
In my experience one way voice is normally due to SIP ALG being configured on a network switch or router.
Alex BaharCommented:
It doesn't seem like a network/firewall/ALG issue because the problem exists even in the same VLAN.

One way speech path is usually an issue related to ANSWER supervision. In a scenario, A calls B. The audio path from B to A is established with the call set-up message (SETUP, INVITE, CTI answer etc). The audio path from A to B is established when B goes off-hook (answer supervision). On a hybrid PBX, the analog line goes off-hook, then this should be converted to the corresponding ANSWER message (CONNECT, 200 OK, etc) on the VoIP side. KXNT-321 uses a proprietary VoIP CTI Protocol. I suggest that you contact the vendor about this issue. My feeling is that, there is a problem with the analog phone side. Try different answer supervision settings to see if it will make any difference.

I hope this helps.
Alex BaharCommented:
Basically, if the answer/off-hook is not properly propagated, then you get one way speech issue.

winterhillschoolAuthor Commented:
hi all,
we ended up getting the telephone company installed. The issue is currently on going but they have found the cause. it is to do with the card that translates VOIP in our pbx. I didn't know this but our pbx isn't fully VOIP enabled. When it was installed, they fitted a card that passes it from the network into the pbx. This is faulty and works after a reboot every couple of days.

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winterhillschoolAuthor Commented:
self resolved
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