Optical Slot Switching Architecture based on dynamic path setup using ultra-high speed PLZT optical switch Teruo Kasahara, Masahiro Hayashitani, Daisuke Ishii and Naoaki Yamanaka Dept. of Information and Computer Science, Faculty of Science and Technology, Keio University, Yokohama, 223-8522, Japan Email:
[email protected]
Abstract— We propose the Optical Slot Switching(OSS) Architecture, that dynamically establishes the path without considering the current condition of the wavelength. This architecture provides a new wavelength reservation method and shows greater link utilization.
I. I NTRODUCTION In WDM network, it is important to use the bandwidth of the optical fiber efficiently and to distribute the load of the wavelength allocation[1]. The wavelength reservation method in WDM network includes one-way reservation and two-way reservation[3]. In this reserch, we examine the two-way backward wavelength reservation to guarantee a clear bandwidth and transmit a bulk data and streaming delivery efficiently. In two-way backward reservation method, there are some problems. First, delay time, which includes propagation delay and switching delay, reduces bandwidth efficiency since data transmission is not done till wavelength reservation have succeeded. Especially, switching time of conventional switch with order of several msec or more µ sec deteriorates a bandwidth use efficiency. Second, the brocking probability of many-hops request will rise to compare with that of short-hops since souce node sends a connection request any time. That is to say, fair QoS between source and destination nodes are not enabled. II. T WO - WAY BACKWARD RESERVATION METHOD Figure1 shows a example of bandwidth waste because of conventional reservation method. In conventional twoway backward reservation method, other path setup using λ0 is not available during data transfer using λ0 , so we must setup a new path after finishing the path release. Signaling must need a propagation delay, electrical processing of routing or header modifing and switching delay. So the singnaling period causes the bandwidth wasting, which we call Death Period. In addition, since source node sends a PATH signal
Fig. 1. method.
A example of wasted time by signaling in conventional
as connection request arrives and begins wavelength reservation, there is a problem of causing unfairness the blocking probability by the number of hops from a source node to a desitination node. Concretely, the long hop request is often blocked for the short hop request. III. P ROPOSED METHOD : OSS In this research, we propose Optical Slot Switching(OSS) architecture based on dynamic path setup using ultra-high speed PLZT optical switch. In proposed method, we take a synchronization of all nodes in the network, and all nodes divide time into slots with same timing. Death Period is decreased sharply by using the PLZT optical switch that can be switched at 10ns for the switching[2]. A source node which has a connection request sends the PATH signal to a destination node to reserve wavelength in the next slot by two-way reservation method, and data transfer is done in one slot as shown in fig.2. The user can establish the path without considering the current condition of the bandwidth use and transmit a data in the reserved slot transparetly. In proposed method, we control the timing of sending PATH signal in a slot to reduce the unfairness by the
Conventional Proposed1 (without considering hops) Proposed2 (considering hops) 0.6
Link Utilization Efficiency
0.5
0.4
0.3
0.2
Fig. 2.
A example of signaling in proposal method. 0.1 0
number of hops from a source node to a destination node. A PATH signal transmitted early in a signaling slot reserve a data slot easier than later PATH signal. IV. P ERFORMANCE E VALUATION In this chapter, evaluation of characteristics of the link use efficiency in the proposed method by the number of hops is done by the computer simulation. We assume the one-directinal ring network which consist of number of nodes is 8. The input traffic follows the Poisson process of the arrival rate ρ, and destination node is decided at random. Arrival rate ρ is assumed to be a number of generation of requests for each 1msec here. The slot period is set to 4.25msec. Figure3 shows the comparison of link utilization in all methods. In this paper, it is assumed that link utilization is the ratio of the link used to all links in the network. This simulation shows that proposed two methods achieve higher link utilization than conventinal method. This is because that proposed two methods can reserve a bandwidth during other data transfer, and it decrease the Death Period, which conventional method.This is because that in conventional method wavelength reservation can not be done during the data trasfer and Death Period increases. On the other hand, proposed two methods can reserve a bandwidth during other data transfer and Death Period decrease. In addition, it is understood to show the performance whose the proposed method with considering the number of hops than that without considering the number of hops. This is because that long hop request preferentially suceeds wavelength reservation in the proposed method with considering the number of hops, and a lot of links are used efficiently. Especially the difference of three methods is great at high load situation. This is because that connection request increases with rising of load and wavelength reservation of long hops is often given priority. V. C ONCLUSION In this research, we propose the Optical Slot Switching (OSS) Architecture, that dynamically establishes the
Fig. 3.
0.1
0.2 0.3 Load ρ (call/msec)
0.4
0.5
Comparison of link utilization in all methods.
path by using ultra-high speed optical switch. In our proposed scheme, all node divide time into slots with same timing. In our scheme, a source node which has a connection request sends the PATH signal to destination node to reserve wavelength in the next slot by twoway reservation scheme. And, a node can establish the path without considering the current condition of the wavelength. Changing time of sending PATH message with considering hops between source node and destination node improves fairness of blocking probability about hops. According to computer simulation, it is shown that the link utilization is improved . And with controling the timing of sending a PATH signal, we can support fair blocking performance. Therefore, our proposed method can achive the higher performance compared with conventional method. ACKNOWLEDGMENT This work is partly supported by Keio University 21 century COE program on “Optical and Electronic Device for Access Network” and Japan Socity for the Promotion of Science(JSPS). R EFERENCES [1] H.Zang, J.P.Jue and B.Mukherjee, “Review of routing and wavelength assignment approaches for wavelength-routed optical WDM networks，” Optical networks, vol. 1, no.1,pp.47-60, Jan. 2000. [2] Keiichi Nashimoto，Nobuyuki Tanaka，Mitchell LaBuda， Dwight Ritums，Madhan Raj，Jeffrey Dawley，David Kudzuma，Tuan Vo and Jane Fang，“1×N ultra high speed optical switching sub-systems using PLZT waveguide devices，” The Institute of Electronics, Information and Communication Engineers，Vol.105，pp13-18，Oct．2005. [3] X. Yuan, R. Melhem, R. Gupta, Y. Mei, and C. Qiao, “Distributed Control protocols for wavelength reservation and their performance evaluation,” photonic Network Commun., Vol.1 no.3, pp.207-218, Nov. 1999.
