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Polycom® RealPresence Collaboration Server (RMX) 1500/2000/4000 Administrator’s Guide
4-50 Polycom, Inc.
Causes of Packet Loss
Network congestion within a LAN or WAN, faulty or incorrectly configured network
equipment or faulty cabling are among the many causes of Packet Loss.
Effects of Packet Loss on Conferences
Packet Loss affects the quality of:
• Video – frozen images, decreased frame rate, flickering, tiling, distortion, smearing,
loss of lip sync
• Audio – drop-outs, chirping, audio distortion
• Content – frozen images, blurring, distortion, slow screen refresh rate
Lost Packet Recovery
The Lost Packet Recovery (LPR) algorithm uses Forward Error Correction (FEC) to create
additional packets that contain recovery information. These additional packets are used to
reconstruct packets that are lost, for whatever reason, during transmission. Dynamic
Bandwidth Allocation (DBA) is used to allocate the bandwidth needed to transmit the
additional packets.
Lost Packet Recovery Guidelines
• If packet loss is detected in the packet transmissions of either the video or Content
streams:
— LPR is applied to both the video and Content streams.
— DBA allocates bandwidth from the video stream for the insertion of additional
packets containing recovery information.
• LPR is supported in H.323 and SIP networking environments only.
•In LPR-enabled Continuous Presence conferences:
— Both LPR-enabled and non-LPR-enabled endpoints are supported.
— The LPR process is not applied to packet transmissions from non-LPR-enabled
H.323, SIP and H.320 endpoints.
— Non-LPR-enabled endpoints can be moved to LPR-enabled conferences.
— LPR-enabled endpoints cannot be moved to non-LPR-enabled conferences.
•In LPR-enabled Video Switched conferences:
— H.323 and SIP endpoints are supported.
— When cascading between conferences running on Collaboration Server and MGC
(Polycom legacy MCU), LPR is not supported over the link between the two
conferences.
— Non-H.323 participants cannot be created, added or moved to LPR-enabled Video
Switched conferences.
• When connecting via an Entry Queue:
— A participant using an LPR-enabled endpoint can be moved to a non-LPR-enabled
conference. The participant is connected with LPR enabled.
— SIP and H.320 participants cannot be moved to LPR-enabled Video Switched
conferences.