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Cisco Bug: CSCtf17820 - Poor video quality behind Cisco 871 VPN Router

Last Modified

May 08, 2010

Products (1)

  • Cisco UC Integration(TM) for Microsoft Office Communicator

Known Affected Releases

8.0(1) 8.1(1)

Description (partial)

Symptom:
Periodic, but frequent poor video quality, exhibited by smearing, ghosting, and blockiness.  The problem is not always 2-way, but often only exhibited on one side of the video call.  Video Statistics shows a large number of lost packets under RTCP Stats, Cumulative Lost on the side of the call where the video looks poor.

Conditions:
This problem occurs when one user is behind a CIsco 871 ECT router (the "at home" user.)  The poor video is normally seen by the user on the other side of the call, typically on the LAN.

This problem occurs due to IP packet fragmentation which is caused by video packets being too large for the MTU of the PC's NIC or the 871's interface.  The 871 seems to be treating the large amount of fragmentation as an fragment attack and begins to drop the packets.  The large amount of packet loss causes poor video quality.
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