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richard Beck

Cisco SX20 calling Polycom - lots of packet loss | PolyCom to Polycom works fine


I have a weird situation that i cannot figure out. I have a Polycom endpoint calling an outside party (to another HDX8000) which works fine. Some packet loss but video and audio are great. When I call the SAME unit from a Cisco SX20 the packet loss is so bad they can not continue the call.

They are connecting to the same endpoint, same bandwidth etc. The only difference I see is that the PolyCom negotiates the H.264-HP codec and the Cisco negotiates just the H.264 codec.

Any ideas on how to resolve? 

Patrick McCarthy
Cisco Employee

Consistent packet loss is often caused by a duplex mismatch. What do you have the SX20 set for vs the switch it's plugged into? You need to make sure they are the same - if one is auto, make the other auto, or if one is fixed - say 100/full, the other needs to be the same also. If you have them set differently, you will end up with a duplex mismatch. For example, if the switch is set to auto negotiate, but the SX20 is set to 100/full, the switch will not be able to auto negotiate with the codec, will see the 100 mb speed, and default to half duplex - and you will have packet loss galore. 

Note this problem can be anywhere in the path that the traffic is flowing too - so if the Polycom that works fine is in a different location and going through a different path check the switches/routers. 

Just wanted to  update this thread.

It seems that its a combo problem. The video protocol that is used and the bandwidth the other side has. The polycoms would use the H264 High Profile protocol while the cisco would use straigh H264. This caused the endpoint to use more bandwidth which they couldnt handle.

Wayne DeNardi
VIP Advisor

If you could give us a bit more information about your setup and the calls, that could be helpful in working out what is happening.

Are the calls H.323 or SIP?  What bandwidth are the calls being made at?  What other traffic is over the links at the same time?  Do you have QoS configured within your network in case there is congenstion on the links?  Are the endpoints configured to appropriately mark the traffic with the right markings?  Are the devices registered to a call control (VCS, CUCM, etc.) or are they Standalone?  Are all the required firewall ports configured on any firewalls in the call path?

Note: Your question would be better placed in the TelePresence section of the forums where these devices are more actively discussed than in the Video Over IP section you've posted in - I'd suggest that you move your discussion over there, you can do this by editing your original discussion post.

Please remember to rate responses and to mark your question as answered if appropriate.

Please remember to rate responses and to mark your question as answered if appropriate.


Moved the topic. Thanks

  • H323
  • 512k
  • On our end? some calls but we have a 1gb connection to the internet.
  • QoS is configured correctly.

Any idea as to why the Cisco Codec doesn't use the H.264 HP video protocol like the PolyCom?

H.264 HP is not a widely adopted codec, and implementations can differ depending on the manufacturer - so this is likely something that is supported only on your Polycom, and not the Cisco - which will do H.264 nicely, as there is generally no real benefit of H.264HP over H.264 (see this White Paper for some discussion: Great Codec Debate White Paper).

One thing that I would recommend would be that you make sure that both the Cisco and the Polycom devices are running up to date software - I've seen many issues with devices on older software versions.  For your SX20, upgrade to TC7.3.6 (or CE8.2.0 if you can - depending on what remote or touch controller you have).  The Polycom HDX devices should be on Release 3.1.x, or if it's an older VSX, on at least version 9.0.6.x.

Another thing you could possibly check and easily replace is the network cable from the SX to your switch - a poor quality cable can be the source of many packet loss issues.

Please remember to rate responses and to mark your question as answered if appropriate.

Please remember to rate responses and to mark your question as answered if appropriate.
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