TANDBERG MPS 800, MPS 200 manual 159, Other Features, Flow Control DownspeedingTF

Features

Other Features (1:2)

TANDBERG MPS ADMINISTRATOR GUIDE

IP Adaptive Bandwidth Management	Asymmetrical Encoders and Decoders	LipSync	Latency and Jitter
IP Adaptive Bandwidth Management	Asymmetrical Encoders and Decoders	Lip Sync	Latency & Jitter

The MCU never produces more traffic than need- ed, for better utilization of network resources. Most of the data sent in a videoconference is video data. Thus, by incorporating smart video algorithms, the codec sends no more video data than necessary. Little movement in the picture gives low bit rate; while a lot of movement gives higher bit rate.

The MCU regulates outgoing and incoming me- dia bit rates by means of flow control signal- ling.

An example of this is automatic adjustment of total bandwidth used when DuoVideoTF is opened.

Realizing there are many different types of vid- eoconferencing units in the world that do not support the same video and audio algorithms, TANDBERG has implemented asymmetrical en- coders and decoders.

This feature allows different systems with dif- ferent video and audio algorithms to communi- cate with the TANDBERG MPS without having to settle on the best common protocols.

The asymmetrical nature of the TANDBERG MPS allows the MCU to accept any of its sup- ported algorithms in any combination from any site and will always transmit the highest pos- sible quality video and audio to the far end.

By this, the TANDBERG MPS can send H.263 and receive H.264 at the same time.

IP is an asynchronous network that sends au- dio and video separately. It is easy to see that these two streams may not arrive at their desti- nation at the same time. Lip sync problems are a certainty if precautions are not taken in the implementation of the codec.

TANDBERG MPS supports sequencing of the video and audio IP packets and the reassembly and reordering of these packets at the destina- tion if they are received out of order. If the vid- eo stream is received before the audio stream, the TANDBERG MPS will buffer this data until the necessary audio is received and reassem- ble the data that the destination codec will use to reproduce a clear image with exceptional sound quality and lip sync.

Latency is defined as the time between a node sending a message and receipt of the message by another node.

TANDBERG MPS can handle any value of latency however, the higher the latency, the longer the delay in video and audio. This may lead to con- ferences with undesirable delays causing partici- pants to interrupt and speak simultaneously.

Jitter is defined as the difference in latency. Where constant latency simply produces delays in audio and video, jitter can have a more ad- verse effect. Jitter causes packets to arrive out of order or at the wrong times, which again leads to packet loss.

TANDBERG MPS can manage packets with jit- ter up to 200ms. If excessive packet loss is detected, the TANDBERG MPS will downspeed the connection until acceptable packet loss is achieved.

Flow Control (DownspeedingTF)

Flow Control (DownspeedingTF)

The TANDBERG MPS uses Flow Control to control the amount of information being received from each endpoint. If the TANDBERG MPS requires bandwidth to be changed, the TANDBERG MPS will use Flow Control to request the other endpoint to drop the bandwidth.

If the ISDN networks drops channels during a call, the conference will not shut down but adjust to the remaining number of available channels. This ability is called “Downspeeding” and is in accor- dance to the BONDING Mode 1 standard.

ISDN Downspeeding will be started when one of the following actions occurs:

1.Fallback to 2xH221 call when no BONDING framing is found

2.Non-matching number of channels (N) during BONDING setup (e.g. N=4 on site A, N=6 on site B)

3.Downspeeding during call setup caused by a channel that will not connect

4.Disconnect and downspeed if a channel will not sync

5.Downspeeding when detecting B-channels that are looped

6.Downspeeding if a channel drops during the

call

The TANDBERG system will also start the BOND- ING synchronization procedure if there is a long fatal failure situation:

7.Extended loss of H221 framing

8.Continuous BCH framing error in the video stream. If then a channel fails to sync, it will be disconnected (as mentioned in 4.)

Packet Loss

This feature comes also in handy when using H.323 over networks with poor QoS such as the Internet.

If TANDBERG MPS detects excessive packet loss,

it will use Flow Control to downspeed the far end to overcome the packet loss problem.

Packet loss can occur when routers become over- loaded and discard packets or when the receiving video system cannot keep up with the transmit- ting video system.

Downspeeding on IP

The TANDBERG system follows a multilevel in- telligent adaptive algorithm based on measured packet loss when downspeeding on IP.

Different from the ISDN downspeeding, the sys- tem will not change Audio and Video algorithms during the downspeeding of an IP call.

Main	Table of	Introduction	Installation	Quick	Using	System	System	Gateway	MCU	Technical	Appendices
	Contents			Setup	the MPS	Status	Configuration	Configuration	Configuration	Descriptions
D 13373.08					159						MPS
NOVEMBER 2007