Polycom 1500/1800/2000/4000 manual Packet Loss Compensation LPR and DBA, Lost Packet Recovery

Additional Conferencing Information

Packet Loss Compensation - LPR and DBA

LPR and DBA are applicable for AVC conferencing only.

Lost Packet Recovery (LPR) and Dynamic Bandwidth Allocation (DBA) help minimize media quality degradation that can result from packet loss in the network. Packet loss Compensation is available in AVC CP Conferencing Mode only and is not supported in SVC Conferencing Mode or CP and SVC Conferencing Mode.

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.

●Due to the LPR increasing the required bandwidth, content rate might be reduced (to no less than 64K) to preserve it.

When this reduction is insufficient, either the video rate or the LPR strength are reduced as well, depending on the value of the system flag LPR_CONTENT_RATE_ADJUST_WEAK_LPR. For more information on that flag see LPR_CONTENT_RATE_ADJUST_WEAK_LPR.

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