Performance Optimization And Improvement On H.232 Protocol Stack Software

Along with fast development of VoIP technology, the application of VoIP telephone has come out from lab to normal Internet users. In recent years, the commercial application of VoIP has grown from enterprise-class users to telecommunication-class users and the latter provides voice service to broadband users. Such application requires H.323 gateway be able to process concurrent calls in high performance. H.323 call processing is normally accomplished by software running on general computer platform, which requires call processing software be able to process concurrent calls in high performance, too. Call processing part of H.323 protocol is transferred on top of TCP. There are two TCP connections during whole lifecycle of each call. Therefore, H.323 call processing software shall not only be able to setup, use and close TCP connections at high speed, but also be able to keep such capability under large number of concurrent connections. To process large number of concurrent connections at high speed, some kind of concurrency mode is needed.This thesis describes results of the study on concurrency, event dispatching and scalability of high performance TCP connection processing. It provides dynamic balanced load thread pool mode as a solution for large number of concurrent connection processing.The thesis is organized as below. Firstly, it gives a brief introduction on history of VoIP, H.323 protocol and performance requirement of H.323 gateway. Then the problems to be solved in this thesis are raised. Related studies are also introduced in this part.Secondly, this thesis discusses the single process, multithread and thread poll concurrency modes to meet the certain performance requirement of different call traffics. Based on that, it provides an improved concurrency mode: dynamic thread pool.Dynamic thread pool mode keeps high performance of thread pool mode and solves the problem of thread shortage during high call load due to creating threads in advance. Event dispatching mechanism is an important part of concurrency mode. This thesis discusses two kind of event dispatching means: synchronous event dispatching and contest event dispatching. Their performance is compared there.Thirdly, this thesis discusses the issues during large number of concurrent TCP connections. The concurrency mode described in the second part is improved to a new solution: balanced load thread pool. In this part the problem is discussed that system calls, select( ) and pool( ) for I/O multiplexing, have scalable issue. A solution to use /dev/poll is provided to solve this problem.At last, the thesis concludes results of the study, and points out the existing problems of concurrency modes in the current practice. A new direction is raised to try asynchronous concurrency mode for further practice.