报文分流最优策略研究

Study on Optimal Packet Dispersion Strategy

在向下一代互联网络演进的过程中,一个重要的趋势是IP网络将成为语音、视频等应用的主要承载.VoIP是一个重要的语音应用.然而,IP网络的丢包造成了VoIP的服务质量不能得到保证,并且对于VoIP而言,连续丢包对其服务质量的影响要远大于分散丢包.报文分流是近年来学术界讨论的一种提高VoIP服务质量的方法,其基本思想是把1个VoIP会话的报文分散到多个网络链路传输,从而把连续丢包转化为分散丢包,缓解丢包对VoIP服务质量的影响.然而,目前的研究只局限于用一种特定的分流策略(平均分流)说明报文分流的潜力.报文分流的理论基础,比如报文分流能在多大程度上提高VoIP的服务质量,什么是最优的分流策略等,并不明了.对报文分流的理论基础进行了研究,首次给出了分流策略与VoIP服务质量的定量关系描述,给出并证明了Bernoulli网络丢包模型下的最优分流策略.同时,以ns-2仿真实验验证了该最优分流策略在Gilbert网络丢包模型下的有效性.

During the migration to next generation network, an important trend is that IP-based network will become the main vehicle for carrying audio and video applications. VoIP is a representative of such applications. However, packet loss is a main factor that degrades QoS of VoIP, and bursty loss jeopardizes QoS of VolP much more than scattered loss. Packet dispersion is a mechanism that disperses packets between paralllel paths following some dispersion strategies. It transforms hursty packet loss to scattered packet loss so as to improve QoS of VoIP. Although there are researches focusing on the use of packet dispersion in VoIP transmitting, the theoretic foundation of packet dispersion, such as to which extent packet dispersion can improve QoS and what is the optimal dispersion strategy, is unknown. In this work, concentrating on these problems, the quantitative relation between QoS of VoIP and the packet dispersion strategy is formulated as constrained optimization problems under Bernoulli packet loss model. Based on the closed form solution of the optimization problem, an algorithm is presented to find the optimal packet dispersion strategy. The proposed optimal dispersion strategy is verified under Gilbert packet loss model with ns- 2 simulation.