Research On The Key Technologies Of AAL2

Driven by economics, people are interested in developing an integrated service network to carry both data and voice service. Compared with traditional circuit-switched mode, packet-switched mode can carry more voice calls when the transmission links are of the same bandwidth. Besides voice, packet-switched networks can also support data and video, and provide more services support for the end user. All these contribute to the rapid development of carrying voice over packet-switched networks. ATM has in principle several intrinsicadvantages over other networking technologies when it comes to voice. Among all the ATM adaptation layers, AAL2 can efficiently support low-bite-rate and delay-sensitive variable bit rate services, which is the most suitable technique for delivering voice over ATM. Delivering voice using AAL2 has received wide acceptance and much research interests.Based on the AAL2 specifications and the previous academic research, this dissertation investigates the following subjects. These subjects include the models for the AAL2 packet voice multiplexer, the bandwidth allocation algorithm suitable to the AAL2 packet voice multiplexer, the AAL2 voice packet buffer queue and the bit dropping thresholds, the ATM cell assembly delay, and the implementation of AAL2. This dissertation consists of the following seven chapters.Chapter one introduces the basic concepts of AAL2 and the current research status. Then it overviews the research contents carried out and the main achievements.Chapter two analyzes the models for the AAL2 packet voice multiplexer. A set of computation formulae for some parameters are presented, which use the UAS model to accurately predict the packet loss ratio of the AAL2 packet multiplexer without bit dropping. Then an M'/D/l/K model is built on the AAL2 packet voice multiplexer with bit dropping at the input port. Its performance is also analyzed. Simulation results show that the M'/D/l/K model works well with the AAL2 packet voice multiplexer with bit dropping at the input port.I.Chapter three discusses the bandwidth allocation algorithm suitable to the AAL2 packetvoice multiplexer. A conclusion is drawn that bandwidth assignment on average rate can basically meet the quality of service requirements of AAL2 packet voice multiplexer without bit dropping if the ATM VC bandwidth is high. If the ATM VC bandwidth utilization is suitably reduced, we can further improve voice quality. Based on the above conclusion, a bandwidth allocation algorithm suitable to the AAL2 packet voice multiplexer is proposed. The algorithm can easily control the number of voice calls that can be multiplexed into the AAL2 packet voice multiplexer when the ATM VC bandwidth is given, or determine the ATM VC bandwidth if the voice calls multiplexed are known. As far as the AAL2 packetivvoice multiplexer with bit dropping is concerned, bandwidth assignment on average rate can well meet the quality of service requirements of packet voice and can result in good voice quality.Chapter four investigates how to determine the AAL2 packet buffer size and the bit dropping thresholds. A conclusion is drawn that for the AAL2 packet voice multiplexer with bit dropping, the buffer size which corresponds to a delay budget of 9 ms is suffice to meet the quality, of service requirements of AAL2 packet voice if bandwidth assignment on average rate is applied. In addition, the author proposes to use the number of packets to represent the bit dropping thresholds with relevant computation formulae presented.In chapter five, the simulation algorithm of voice packet generator for the on-off voice source model is given. The algorithm uses one dimension matrix to represent the arriving time of voice packets which are produced by multiple voice sources. Then the issues related to the cell assembly delay introduced by filling AAL2 packets from different users into the payloads of ATM cells are investigated. A conclusion is drawn that the cell assembly delay is affected by the voi...