Investigating the Performance of Audio/Video Service Architecture I: Single Broker Ahmet Uyar & Geoffrey Fox Tuesday, May 17th, 2005 The 2005 International Symposium on Collaborative Technologies and Systems (CTS 2005) Saint Louis, Missouri, USA

Outline Introduction Design Principles GlobalMMCS Overview Characteristics of Audio and Video Streams Quality Assessment of Media Delivery Performance Tests for One Broker Conclusion

Introduction The network bandwidth and computing power are increasing rapidly. In addition to homes and small offices, even cell phones will have broadband Internet access in the near future. There are excellent quality audio and video add-ons (video cameras and microphones) for computers. Scalable videoconferencing systems are needed to support high number of users. Universally accessible videoconferencing systems are needed to support diverse set of users.

Design Principles Developing videoconferencing systems over Internet is a challenging task, since the distribution of real-time audio/video streams requires high bandwidth and low latency. the processing of audio and video streams is computing intensive. Scalable media distribution middleware and scalable media processing unit are needed. It is also essential to separate media distribution and media processing units completely to provide scalability. Diverse clients and firewalls require flexible transport mechanisms. New protocols should be added easily. Diverse clients require customized audio and video streams. Scalable server side media processing components are needed.

GlobalMMCS Overview-I A videoconferencing system based on a publish/subscribe event brokering network. Three main components: Media and content distribution middleware Media processing unit Meeting management unit

GlobalMMCS Overview-II NB provides a scalable unified messaging middleware for all collaboration applications including media and data with distributed broker architecture. This reduces overall system complexity significantly. Media processing unit provides a scalable media processing framework. New media processors can be added easily. Since media processors do not handle media delivery, high number of clients can be supported. Media processors can be located anywhere in wide area network. Users and media processors are not directly connected. Currently the media processing unit provides three types of services: audio mixing, video mixing and image grabbing. NB provides a flexible transport framework. Supports many transport protocols (TCP, UDP, HTTP, etc) and makes it easy to add new ones. Can go through firewalls, NATs and proxies.

Characteristics of Audio and Video Streams Audio streams are composed of fixed size packages with regular intervals. We chose 64 kbps ULAW audio stream to be used in the tests: One audio package is sent every 30ms. Each audio package is 252 bytes. There are 4100 packages in total, during 2 min. Video codecs also encode frames periodically. However, each frame may have multiple video packages. Full picture update frames have much more packages. We chose H.263 video format, average bandwidth 280kbps, for 2 min: 15 frames are encoded every second. One frame every 66ms frames and 5610 packages in total. On avrg. 3.1 packages per frame. One full picture update every 60 frames or 4 seconds.

Quality Assessment of Media Delivery There are three important factors: latency, jitter and package loss ITU recommends that the mouth-to-ear latency of audio should be Less than 400ms for acceptable quality Less than 300ms for good quality Less than 150ms for excellent quality. The total latency is the combination of: Processing at sender and receiver Transmission latency Routing latency by the broker network We limit the routing latency to 100ms at most. The packages that take more than 100ms are labeled as late arrivals. We limit the jitter caused by routing to 10ms We limit the loss rate to 1.0%

Performance Tests for Audio/Video Distribution with One Broker Single Meeting Tests Single audio meeting tests Single video meeting tests Audio + Video meeting tests Multiple Meeting Tests Multiple audio meeting tests Multiple video meeting tests Multiple Audio + Video meeting tests

Single Meeting Tests One transmitter and 12 measuring receivers. Other receivers are passive. Tests are conducted in a Linux cluster with 8 identical nodes. Each node had Double Intel Xeon 2.4GHz CPUs, 2GB of memory with Linux kernel. All programs are written in Java. The nodes are connected with gigabit connection.

Single Audio Meeting Tests Number Of Clients L(1) (ms) L(N) (ms) L(av) (ms) J(av) (ms) LA(av) (%)

Single Video Meeting Tests-I Number Of Clients L(1) (ms) L(N) (ms) L(av) (ms) J(av) (ms) LA(N) (%)

Single Video Meeting Tests-II Below graph shows latency values for the last receiver in single video meeting with 400 participants. Peaks correspond to full picture update frames. One broker can support at most 400 participants because of late arriving packages. Although the broker is saturated when there are 1000 participants.

Audio+Video Meeting Tests We gave priority to audio routing at the broker, since the impact of video meeting on the performance of an audio meeting was significant. Two queues at the broker: audio and non-audio. when an audio package arrives, it is routed as long as the routing of the currently routed package is over. The broker supports almost the same number of participants as in the case of single video meetings. The broker resources are utilized better with two concurrent meetings.

Multiple Video Meeting Tests Total users # of Meet ings L(av) (ms) J(av) (ms)LA(av) % % % 98

Summary of The Tests 1500 participants are supported in one audio meeting 400 participants are supported in one video meeting Up to 400 audio participants and 400 video participants are supported in audio + video meetings. 700 participants can be supported in 35 video meetings each having 20 participants 1300 participants can be supported in 65 audio meetings each having 20 participants 20 audio and 20 video meetings can be supported each having 20 participants.

Conclusion A NaradaBrokering broker can provide audio and video conferencing services to a few hundred users with very good quality. A small or middle size organization can deploy GlobalMMCS videoconferencing system to provide videoconferencing services. Larger organizations need to deploy distributed brokers to support higher number of users in geographically distant locations.

Resources Global Multimedia Collaboration System Project website: We have a booth for demonstration. Tutorial at Tuesday 3:30pm.