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Additional Conferencing Information
Polycom®, Inc. 195
Packet Loss Compensation - LPR and DBA
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.
LPR and DBA are applicable for AVC conferencing only.