M.Sc Thesis

M.Sc StudentSenderov Yuri
SubjectAdaptive Playout Scheduling Algorithms in Real-time
DepartmentDepartment of Electrical and Computer Engineering
Supervisor PROFESSOR EMERITUS Moshe Sidi


The quality of service limitation of the Internet is a major problem for real-time voice communications. Excessive delay, packet loss and high delay jitter all impair the communication quality. To compensate for the variation in network delay playout buffer is employed at the receiver. Using this technique, packets are not played out immediately after reception but held in the buffer until their scheduled playout time arrives. There is a tradeoff between the average time that packets spent in the buffer and the number of packets that have to be dropped because they arrive too late. The main challenge of playout scheduling algorithms is to reduce average packet delay while keeping loss percentage low. Many algorithms were introduced to overcome this problem. There are two main techniques to absorb the delay variation. The first is per packet approach and the second is per talkspurt approach. In this work we concentrated on algorithms that advocate per talkspurt approach. We examined current existing algorithms under various network conditions and made conclusions about their performance. We found that in order to obtain satisfactory quality of the voice conversation under conditions of high jitter and high network delay, the playout adjustment algorithm should adapt its behavior according to the current delay characteristics.