Unified Communication QoS

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Unified Communication enables video applications, voice, and data of enterprises to be synchronously hosted on an IP network and transmitted as video data packets, which inevitably leads to network packet loss. Packet loss may cause video mosaic, partial image deformation, frequent screen refreshes or flashes, non-sync of audio and video, decreased frame rate, and static images. In a unified communication environment, because video, voice, and data streams are transmitted synchronously, packet loss can also cause overall Audio Distortion, interruption, or intermittent noise, and the reduction of content demonstration quality, such as blurred slides or slow pages. These problems will greatly affect users' application experience. If the packet loss rate is too large or too frequent, the video communication may be excessively delayed or even cause communication interruption.

 

Packet loss is caused by internal network congestion or external network priority traffic conflict. To avoid packet loss, first determine the packet loss rate of the bearer network, the distribution of packet loss over time, and the performance of various terminals and devices in video calls.

 

LPR (packet loss recovery) technology is currently one of the most effective methods to solve packet loss in video transmission. This technology is based on a new algorithm developed by Polaroid, the objective is to protect IP video calls from network packet loss. In fact, LPR is a mechanism that uses the forward correction (FEC) method to overwrite lost data packets. The sender System adds redundant data for the sent data streams so that the receiver system can detect and correct errors without requesting the sender system to re-transmit the lost information. This capability enables error correction without waiting for network transmission, making FEC very suitable for real-time communication, such as television broadcasting, IP phone calls, and IP video conferencing.

 

LPR is used to monitor packet loss information of all ongoing calls through video terminals. Once packet loss is detected, the terminal uses three methods to ensure the quality of the call: packet loss recovery (LPR), dynamic bandwidth allocation (DBA), and without LPR support, traditional video error concealment (PVEC) technology is used.

 

Unlike most error concealment or avoidance algorithms, LPR only applies to systems that receive packet loss information, A part of the call bandwidth is temporarily allocated to a data channel for sending FEC data to the receiving system. When packet loss occurs during network transmission, LPR increases or decreases the size of the FEC data channel through the preceding cyclic processing until the minimum bandwidth that must be allocated to the FEC data channel is found, this allows the receiving system to recover all lost data packets.

 

When the FEC Data Channel size exceeds the standard value, the system repeatedly checks whether the FEC Data Channel size can be reduced to provide more available call bandwidth for audio, video, and content data. Because LPR only occupies bandwidth when packet loss is detected, this feature makes LPR very suitable for random or sudden packet loss environments.

 

In a network environment with a relatively fixed packet loss rate, the dynamic bandwidth allocation (DBA) function can work with LPR. DBA is also an algorithm that automatically and dynamically adjusts the video bit rate during video calls to eliminate or avoid packet loss. For example, if a packet loss rate of 10% is detected in a 10% kbps video call, DBA will reduce the video bit rate by about, from Kbps to about kbps, and then re-sample the signal, check whether packet loss still exists. If necessary, DBA can further reduce the video bit rate until packet loss does not occur in a few seconds.

 

After the bit rate is reduced, if the DBA determines that packet loss is temporary, the DBA will gradually increase the video bit rate. On the contrary, if DBA continuously detects packet loss, it will not adjust the video bit rate, but will continue the call. Therefore, DBA is suitable for packet loss environments caused by network overuse or throughput problems.

 

When the systems of all parties involved in the call do not support LPR, you can use the video error concealment (PVEC) function. PVEC is an algorithm used for IP video quality of service (QoS). It can compensate for the impact caused by packet loss. It uses adjacent macro blocks, front frames, and back frames to estimate the content of the current video frame. Unlike the LPR packet loss recovery technique, PVEC is used to mask the impact of packet loss.

 

On this basis, LPR enables users to make high-quality video calls on IP networks with high error rates (DSL, wired, satellite, and high-conflict LAN/WAN, the impact of packet loss does not have to be tolerated. By temporarily adjusting the bit rate of ongoing calls, LPR can protect video calls from short-term network problems. Once the network problem is solved, LPR automatically calls back the bit rate to the highest level based on the call rate or the current bandwidth availability. This enables full use of network bandwidth, recovery of lost data packets and real-time reconstruction of transmission, smooth audio and video data streams, and elimination of waiting, intermittent, noisy, or information disorder, it can reduce the buffer space and latency of dynamic jitter.

 

However, using LPR generates FEC channel bandwidth, which reduces the available bandwidth of video calls. When the connection speed is low, the temporary frame rate or resolution may decrease.