【 Weak current College 】 enterprise-level video conference system five top technical details (1)

According to the market advisory company WinterGreenResearch forecast, the unified communications market development cycle is about to step into the healthy growth and rapid application of the stage. In 2008, the market may achieve 15% growth in 2009 will grow by 30%. And video in the enterprise-class unified communications deployments will be uncompromising black horse.
Traditional enterprise video technologies include: MCU, H. 323, frame relay, and IP network-based video application, would bring more rich functionality to the user. But to successfully use these features, the user needs to some new hot technology to give more attention.
A LPR: get stable video stream
Unified communications enterprise voice, video and data synchronization hosting over IP networks to transfer the video data packets, which inevitably encounter network packet question. Packet loss will result in video image mosaic; image local deformation, frequent refresh or flashing screen; video and audio are not synchronized; frame rate drops and the still image. In unified communications, video, voice and data flow is synchronous transmission, packet loss will result in overall audio distortion, continuous or intermittent noise, as well as the quality of the content of the presentation, such as fuzzy distortion of slide or page slower, etc. These issues will significantly impact the consumer experience of application. If the network packet loss rate is too large or too frequently, will cause the excessive delay for video communication, or even result in loss of communication.
Packet loss is congestion by internal or external network priority flow caused by the conflict, etc. To avoid loss, it is first necessary to determine the host network packet loss rate, packet loss distribution over time, as well as a video call in various terminals and equipment performance.
LPR (packet loss recovery) is the current resolution of video transmission packet loss of one of the most effective method, the technology is based on Polycom company developed a new algorithm, with the aim of protecting IP video call from the effects of network packet. In fact, LPR is a use of forward error correction (FEC) method to override the implementation of lost packets. By the sending system to issue a data stream to add redundant data so that the receiving system can detect and correct the error without having to request the sending system to transfer the missing information. This is not required to wait for the network will have the ability to correct, make the FEC is ideal for real-time communications, such as television broadcasting, IP telephony and IP video conferencing.
LPR works through video Terminal control all ongoing calls inbound packet information. Once detected, packet loss, the terminal will take three means to guarantee call quality: lost packet recovery (LPR), the dynamic bandwidth allocation (DBA), and does not support LPR, using the traditional video error yinxiao (PVEC) technology.
Unlike most mistakes avoidance algorithm only yinxiao or intervene in receiving packet loss information system, LPR will intervene to video call in all levels of the system, part by temporarily assigned to a call bandwidth data channel, which is used to send FEC data to the receiving system to play a role. In the network packet loss occurs, a loop through the above process, LPR will increase or decrease the size of the FEC data channel until you find must be assigned to the FEC data channel minimum bandwidth, allowing the receiving system to be able to recover all lost packets.
When the FEC data channel is larger than the standard value, the system will detect whether you can reduce over FEC data channel size for audio, video and content data provide more bandwidth available on the phone. Since LPR only detect packet loss will only be occupied bandwidth, this feature makes the LPR is great for random or unexpected packet environment.
Against packet loss rate relatively fixed network environment, the dynamic bandwidth allocation (DBA) function in conjunction with LPR. DBA is also a kind of algorithm, you can video call process automatically and dynamically adjust the video bitrate, to eliminate or avoid packet loss. For example, in a video call 384kbps detected a stable at 10 percent packet loss rate, the DBA will decrease by about 10% of the video bit rate to minimize by 320kbps 288kbps left and right, and resampling signals, to see if there are packet loss. If necessary, the DBA can further reduce the video bit rate, until a few seconds until it no longer appears lost packets.
At lower bit rates, if measurement of packet loss for the DBA temporary phenomenon, the DBA will gradually increase the video bit-rate. Conversely, if the DBA continues to detect packet loss, it will no longer resize video bit rate, but will continue the call. Therefore DBA applies to Internet overuse or throughput problems caused by packet loss environment.
The parties involved in communication systems do not support LPR, you can use video error yinxiao (PVEC) feature. PVEC is an IP video quality of service (QoS) algorithm, it can by packet loss effects caused by the compensation. It is through the use of neighboring macroblock, front frame and the rear frame to estimate the current contents of the video frame. And LPR recover lost packets and DBA avoid packet technology, the role of the obscure PVEC packet loss.
On this basis, the LPR that users can BER higher IP networks (DSL, cable, satellite, high conflict and LAN/WAN, etc) for high quality video calls without having to endure the consequences of lost packets. Through the ongoing call rate for temporary adjustment, LPR can protect a video call from short-time network problems. Once the network problem solving, LPR will initiate the call rate or current bandwidth availability, automatic bit rate back to the highest level. This makes network bandwidth can be fully utilized to achieve the recovery of lost packets and transmission of real-time reconstruction so that the audio and video data stream patency, exclude waiting, intermittent, noise or information clutter, more capable of reducing the dynamic jitter buffer space and the associated delay.
But makeUse LPR FEC channel bandwidth is generated, use the video call itself reduce the available bandwidth. In the low connection speeds, can cause temporary reduced frame rate or resolution.