Packet Loss; Causes Of Packet Loss; Effects Of Packet Loss On Conferences; Lost Packet Recovery - Polycom 1500 Administrator's Manual

RealPresence Collaboration Server (RMX) 1500/1800/2000/4000 Administrator's Guide

Packet Loss

Packet Loss refers to the failure of data packets, transmitted over an IP network, to arrive at their
destination. Packet Loss is described as a percentage of the total packets transmitted.

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 IP (H.323 and
SIP) and ISDN (Collaboration Server 1500/2000/4000) 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 (Collaboration Server 1500/2000/4000):
 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.
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