238 Journal of Optical Communications 26 (2005) 5 Summary The concept of wavelength router optical burst switch- ing (WR-OBS) aims to allow the access of the band- width without using wavelength for routing, instead, it provides guaranteed delivery of optical data bursts to the destination. However, there are some inherent “wast- ing” times at edge router which influence negatively on some delay sensitive applications. This paper presents a comprehensive analytical study for all significant latency aspects. It can be considered as a guide line to network designer to make the required optimization. The main latency sources are investigated through two different network sizes. 1 Introduction Next generation all-optical networks require protocol, bit-rate, and efficient network design for format trans- parency to achieve efficient routing of data packets to their appropriate destination. Recently, optical burst switching (OBS) networks bas emerged as a promising paradigm to deal with the exponential growth rate of Internet Protocol (IP) traffic volume [1, 2]. However, there are still several issues remained to be overcome, such as high burst loss rates at high traffic loads, and quality of services (QoS) mechanisms [3]. To overcome these problems, a wavelength-router OBS (WR-OBS) was emerged [4]. In WR-OBS, the wavelengths are not used for routing, instead they are used to provide point- to-point connections. The highlight features of WR-OBS are the acknowledged wavelength reservation with guar- anteed latencies. However, reserving a free channel and waiting to receive an acknowledgment need some time because the packets must stay at edge router. Waiting for “long” time may be not accepted by some delay- sensitive applications like video conference services, for example. As a result, this paper is aimed to study influ- ence of delay sources on the performance of WR-OBS. We analyze the main characteristics of latency through investigating two different network sizes. We give an analysis to the most significant time parameters through illustrating two methods to aggregate the bursts. Delay at edge router is the key parameter for design any edge router, so it has received much attention in this paper. The remainder of this paper is organized as follows: Section II includes a description for WR-OBS model, and then we turn to focus on the two methods of burst aggregation process in Sec. III, where the analysis is separated into two parts. The first studies the Limited- Size Bursts (LS-Bs) method. The second part describes the not Limited-Size Bursts (NS-Bs) methods. A detailed analysis for burst blocking probability with delay at edge router is given in Sec. IV. Section V presents our simula- tion results and discussions, and finally a summarization is drawn in Sec. VI. 2 The model 2.1 Network edge router architecture Figure 1 shows schematically the edge router set up which is considered in this work. Packets received from several sources are firstly presorted according to their destina- tion and class of services (CoS) and sorted in separate queues. Each type of these sorted packets is then aggre- gated to form a burst. Length of these bursts is specified in one of the two designable methods [5]: Limited-Size Burst (LS-Bs) or not Limited-Size Bursts (NS-Bs). A wavelength request is sent to a control node after a time- out signal indicates that packets have to be transmitted to meet application specific latency requirements. Then, control node sends an acknowledgment and the bursts are dynamically assigned to free wavelength. In case of no free wavelength channel available, the packets do not discarded and, instead, are stored in the buffers of edge router. However, store in buffer could be subject to ad- ditional delay. A uniform destination address distribution is assumed throughout this paper. Therefore, the electronic switch provides statistical multiplexing. Unlike the conventional IP router architecture, packets are forwarded to buffer queues within the edge router. Recently, random access Time Delay Analysis in Wavelength Router Optical Burst Switching (WR-OBS) Networks Haider M. AlSabbagh, Jianping Chen, Guiling Wu, Xinwan Li Address of authors: Shanghai Jiao Tong University The State Key Laboratory on Fiber-Optic Local Area Network and Advanced Optical Communication Systems Shanghai 200030, P. R. China Email: haidermaw@yahoo.com Received 9 February 2005 J. Opt. Commun. 26 (2005) 5, 238–243 © by Fachverlag Schiele & Schön 2005