Problem with Nortel 1535 handset not sending video


Asterisk v13.0.1
FreePBX v12.0.64
Ubuntu 14.0.4
Handset - 2 x Nortel 1535 desk phones with Video
Softphone - 2 x Bria 4 Windows clients
Asterisk server, handsets and laptops running softclients are all connected to same network switch.
The Nortel handsets and the Bria clients are all registered against my FreePBX install.
Voice calls work fine with bidirectional audio between all registered clients.
Video calls between the 2 Bria softphones show bidirectional video stream.

Video calls between the 1535’s and Bria4 show Video being received from the 1535 (into Bria4) but no Video being received on the 1535 from the softphone.
Video calls between the 2 1535 desk phones show an outgoing stream but no incoming video on either unit.

The 1535’s use H.263 as the video codec.
The Bria clients are set to use H.263, H.263+, VP8.

If it was a codec issue then calls between the 2 1535 units should work (as they are setup identically apart from extension number) so I’m guessing it’s not that.

The Asterisk log files show no errors.
My firewall shows no dropped or blocked packets during a call.

Short of looking for a firmware upgrade for the 1535’s I’m not sure what else to try…

Any ideas?

Many thanks