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I get audio clipping due to packet loss on outbound traffic when holding a IP video conference

Posted on 2008-10-20
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Last Modified: 2013-11-16
I have 2 sites connected by an internet VPN. One site has a 2mb SDSL to the internet, the other a leased line 2mb also to the internet. There are very few users on either side (no more than 10-15 in all) and I am trying to set up a Video Conference between the two using some specialist LifeSize equipmment. For data, the link is very good, ping response times are no more than 40ms on average over a 24 hour period, with very little ICMP packet loss. When I try an run a Video conference however, one of the sites experiences bad audio clipping due to packet loss when transmitting. Receiving is absolutely fine. Even if this site is video linked to a remote ADSL mini web cam, the incoming audio is good but the ADSL user has problems hearing what is is being said from the SDSL LifeSIze end. I have tried reducing the bandwidth to 256k on all sites but it makes no difference. Also, my Firebox routers are configured to use QoS so that voice/video has priority over data. Other than moving to ISDN or implementing an expensive MPLS network I am absolutely stuck!

I have contacted LifeSize but they are not much use in helping other than that we have packet loss.


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Question by:trevor87
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by:pgerard
ID: 22761027
I would think that the packet loss is the issue.  When you say that you are getting very little packet loss, are you saying 1 in every 4 packets or 1 in every 100 packet or somewhere in between?
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Expert Comment

by:SysExpert
ID: 22761292
Don't forget that you are using an Inetrnet connection and depending on the routing, you can have all sorts of issues. Not much you can do, and some days it may work perfectly and others, not.

Unless you can implement end to end QOS or similar, or buy more expensive equipment that knows how to rebuild bad or out of sequence packets, I do not see an easy solution.

Maybe someone else has better knowledge.


I hope this helps !
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Author Comment

by:trevor87
ID: 22761445
In terms of packet loss, it is about 1 in 500 when running a ping.

What I am trying to understand is why the audio clipping affects one site only (always the remote end) and not both in the video link. Would there not be a problem at both ends?
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Expert Comment

by:pgerard
ID: 22762447
Is this being run on a PC?  I'm just wondering if you have AV software that may be scanning the incoming packets and causing the clipping?
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Author Comment

by:trevor87
ID: 22762604
There are no PC's involved in the configuration except for the Ping test and home pc.  Site 'A' Has a Lifesize Team VC system + Lifesize Phone. It also has a 10:1 contention SDSL line The firewall is a Watchguard Firebox X700 with full H323 support. Qos is enabled. Site 'B' is the same except for a smaller Firebox and a 2mb leased line to the internet. Site 'C' is a home computer with 8mb ADSL, polycom PVX software and a Netgear switch Site 'A' always receives perfect audio - regardless of who it is connected to. The other sites get clipped audio most times (but not always).
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dpk_wal earned 250 total points
ID: 22764300
As I understand you have configured BOVPN [in WG terms] between the site A and B; and site C is a RUVPN or MUVPN.

First I would like to know which policies have you configured to allow traffic between site A and B; by default if you are using ver 10.x of WFS and have used VPN wizard then ANY policiy is created by default. Or have you implemented specific H323 proxy service for QoS puposes; if it H323; I would suggest you to use ANY service instead and check if there is any difference. Sometime, proxy services might be the concern; although in this case there is no NAT/PAT involved but still proxy would do L7 packet inspections.

Other thing which I am thinking is, what is the upload rate at site A; what are the results about video quality. If you use audio/video conferencing between site B and C are the results any different. Assumption is we would normally have ANY service allowing traffic from remote users and would not have a proxy maintained.

As you mentioned about QoS; other than WG, which device you have which implements QoS; and how have you configured QoS on WG.

Please provide details.

Thank you.
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Author Closing Comment

by:trevor87
ID: 31507949
The big thing you mentioned that wasn't set on my WG was the H323 proxy service as we normally don't use them. Once set, I was able to hold a 3 way video confernence which was very successfull! Thanks for your help.
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