Growing popularity of new network services including distributed computing, cloud computing, content delivery networks enforces implementation of new data ...
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Dynamic Routing of Many-to-Many Traffic in WDM Networks Damian Bulira, Student Member, IEEE, and Krzysztof Walkowiak, Member, IEEE Department of Systems and Computer Networks, Wrocław University of Technology, Wrocław, 50-370 Poland, Wybrzeże Wyspiańskiego 27 Tel: (4871) 320 3539, Fax: (4871) 320 2902, e-mail: {damian.bulira, krzysztof.walkowiak}@pwr.edu.pl ABSTRACT Growing popularity of new network services including distributed computing, cloud computing, content delivery networks enforces implementation of new data delivery paradigms that can provide improvement in network performance. Therefore, in this paper we focus on many-to-many (m2m) traffic, that can be applied in computer networks to minimize resource consumption in group communication. We consider bandwidth demanding m2m applications, therefore we assume that the traffic is provisioned in optical layer using Wavelength Division Multiplexing (WDM) technology. We tackle dynamic Routing and Wavelength Assignment (RWA) problem with m2m traffic by designing effective algorithms. Moreover, we provide results of simulations showing performance of the proposed approach in terms of m2m session blocking probability. Keywords: many-to-many networking, WDM networks, dynamic routing, routing and wavelength assignment. 1. INTRODUCTION Constant growth of the Internet traffic and a need for higher transmission bandwidth follows evolution of computer networks and various distributed appliances. Transmission paradigms are adapting towards bandwidth saving, multiuser data exchange and communication reliability. In this paper, we focus on many-to-many transmission that is the next step in the evolution of communication paradigms. This type of data exchange follows unicast (one-to-one), multicast (one-to-many), broadcast (one-to-all) and anycast (one-to-one of many) transmissions. We propose dynamic routing algorithms for m2m transmission in WDM networks, where replica (rendezvous) servers are used, thus the notion of anycasting is implemented in proposed m2m algorithms. We implement m2m routing algorithms on the top of WDM networks, due to their leading position among backbone networks. Furthermore, the distributed computing requires exchange of significant amount of traffic and WDM provides bandwidth up to 100 Gb/s per channel with even broader perspective in the future [1]. In this paper, we define dynamic routing algorithms for m2m transmission as a 2 step procedure. The former is a Client-Server Assignment (CSA), where clients are assigned to the predefined replica servers using Lowest Total Distance (LTD) and Closest Replica (CR) algorithms. The latter is a Routing and Wavelength Assignment problem in WDM network, that is to assign lightpaths between clients and replicas. We propose two RWA algorithms that reserve lightpaths in Shortest Path First (SPF) and Lowest Wavelength First (LWF) approach. The main contribution of this paper are aforementioned dedicated algorithms solving RWA problem in WDM networks for m2m traffic and numerical experiments presenting dependencies of different network scenarios serving m2m traffic. To the best of our knowledge, this work is the first one that addresses dynamic routing algorithms in WDM optical networks with many-to-many transmissions. The remainder of the paper is organized as follow. In Section 2, we are presenting related works in the topic of dynamic RWA in WDM networks and m2m transmissions. Section 3 addresses m2m communication scheme and underlying WDM network. In Section 4, we present proposed algorithms and Section 5 shows results of the numerical experiments on the aforementioned procedures. Finally, we conclude our work in Section 6. 2. RELATED WORKS Dynamic Routing and Wavelength Assignment problem is addressed in numerous publications. Comprehensive survey on RWA problem in WDM networks can be found in [2]. In [3], the authors prove that general RWA problem is NP-Complete. In [4], the author presents dynamic approach to the RWA problem and highlights the effects of different resource allocation strategies in WDM networks. Heuristic approaches solving dynamic RWA problem are addressed in [5]. The authors of [6] propose genetic algorithms solving RWA in WDM networks. Dynamic RWA in multicast optical networks is the main topic of [7], and work on anycast routing connected to the same topic is addressed in [8]. Many-to-many transmission problem in WDM network is presented in the context of traffic grooming in [9]. In [10], ILP models of m2m communication in replicated multimedia environment are presented. The author of [11] proposes and evaluates several algorithms for dynamic routing of anycast traffic provisioned by replica servers. 3. NETWORK ARCHITECTURE The network architecture consists of 2 layers. Many-to-many group are established in the upper overlay layer, whereas lower optical layer is responsible for setting up the communication with specific node pairs in the optical domain.
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3.1 Many-to-many communication Many-to-many communication is a data transmission paradigm where network nodes are exchanging the information across many-to-many group [12]. Every group member receives information from the rest of the hosts involved in the transmission. Therefore, at the end of the transmission every host in the group has the same set of information. Within the notion of network demands, m2m group members are equal to the clients belonging to the particular demand. In this paper, we introduce a concept of replica servers, that are rendezvous points of the m2m transmission. Each client transmits data to the replica, that is responsible for aggregating, processing and forwarding it further to the rest of m2m group members. In this paper, we are establishing the m2m flows in the multi-layer approach, taking under consideration underlying network structure. 3.2 WDM Networks In the wavelength-division multiplexing approach the optical signals are multiplexed into a single optical fiber by using separate wavelengths. At the transmitter side a multiplexer is used to introduce multiple optical signals into one fiber, at the receiver the signal is split back by a demultiplexer. WDM carries multiple optical signals in the fiber using separated frequency bands [13]. This technology allows to multiply bandwidth transmitted in one fiber and is one of the core solutions in modern backbone networks. 4. ALGORITHMS The algorithms investigated in this paper can be divided into two groups - Client-Server Assignment (CSA) and Routing and Wavelength Assignment. CSA stage takes place before RWA and is aware of the static network architecture only (distance between network nodes). After all clients are assigned to the replica servers, routing in the optical domain is calculated. Here, we use the concept of pre-calculated candidate paths between all network nodes. Furthermore, routing is dynamic, hence in each step the current state of occupied wavelengths is considered. 4.1 Client-Server Assignment For CSA problem we compared two approaches – Closest Replica (CR) and Lowest Total Distance (LTD). In the former case, clients are assigned to the closest replicas, basing on the number of hops between them. Other clients in the m2m group that are taking part in the m2m demand are not considered in this CSA metric. In LTD, the metric is calculated using the distance between client and the server (data upload) and between server and other clients that are included in the m2m demand (data replication). We assume that each transmission consumes one wavelength, therefore metric is calculated from hop distance, rather than required bandwidth. Hence, in LTD all clients in the demand are using the same replica server. 4.2 Routing and Wavelength Assignment RWA algorithms at the input receive the products of CSA stage – clients of the m2m group (demand) and their assignment to the replica servers. Here, we compare two approaches of assigning lightpaths in the optical domain – Shortest Path First (SPF) and Lowest Wavelength First (LWF). In SPF, the algorithm firstly places lightpaths in the shortest path and then find and unoccupied wavelength within this path. Whereas in LWF, lightpaths at first are fitted in the lowest available wavelength followed by shortest path assignment. 5. RESULTS The aim of our experiments is to compare proposed algorithms for dynamic routing in m2m networks. We performed numerical experiments for all of the algorithms proposed in the previous Section. Therefore, we combined all of the proposed algorithms of CSA and RWA, that resulted in experiments on CR-SPF, CR-LWF, LTD-SPF and LTD-LWF methods. The problem studied in this paper is dynamic, what means that the algorithm is fed with demands (m2m sessions) on-line. Furthermore, demands are time-varying and reserved resources are released after the expiration time. We control the number of m2m sessions using average lifetime of the demand. The experiments are performed using a European Nobel-EU network topology, that is built with 28 nodes and 82 links. Replica servers location is predefined in the topology and different scenario consist of 3 – 11 rendezvous points. Therefore, location of the replica servers is not addressed in this work. For purposes of particular experiment we adjusted number of wavelengths in the network to 80, 40, 16, 8 or 4. In our experiments, we use 30 predefined candidate paths that provide distance-sorted shortest routes between all nodes in the network. We assume that the streaming rates of the m2m sessions fit into bandwidth of single wavelength. Session Blocking Probability (SPB) is used as the main performance metric. It is the ratio between accepted demands and all requested demands. It is essential, that the session is considered as blocked if just one of the underlying path between client and replica cannot be allocated. All results are averaged from 10 randomly generated demand sets for the particular demand and network parameters. In each scenario the number of demands is 1,000, however we assume, that during the first 100 requests the network is not in a steady state, hence those demands are not taken to the final evaluation.
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In the first experiment, we compared all four proposed algorithms using demands pattern of 5 clients in the m2m group and a network of 80 wavelengths in the fiber and 3 replica servers, similar setup will be used in the further experiments, unless otherwise stated. The results of this experiments are depicted in Fig. 1. We can see that LTD methods of CSA provides much lower blocking probability than CR algorithms. Furthermore, LWF spectrum assignment results in slightly better results compared to SPF. Due to that fact, we will use LTD-LWF algorithm in the rest of our simulations.
Figure 1. Session Blocking Probability for different m2m routing algorithms. The next objective of our experiments is to compare various number of replica servers in the network. In Fig. 2, we report SBP for 3, 5, 7, 9 and 11 replicas. We can see that with the number of the servers blocking probability is decreasing. This follows from the fact that using servers situated closer to the clients, the lightpaths are shorter and the network can fit more demands. In the investigated scenarios the biggest performance gaps are between 5 – 7 servers and 7 – 9 replicas. That can be explained by the fact that location of the servers was predefined and given as an input.
Figure 2. Session Blocking Probability for LTD-LWF and different number of replica servers. Figure 3 reports SBP for different numbers of available wavelengths in the WDM network. This not only can simulate available WDM solution but also remaining spectrum for dynamic demands, assuming that the network is fitted with other (static) demands. With the broader available spectrum, blocking events start with significantly higher amount of m2m sessions.
Figure 3. Session Blocking Probability for LTD-LWF and different number of available wavelengths. Finally, Fig 4. presents relationship between SBP and number of m2m session in the network. The network operates more efficient if the same amount of clients is divided into smaller m2m groups. This comes from the fact that less clients connected to the particular server results in lower spectrum congestion and shorter lightpaths needed for particular demand.
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Figure 4. Session Blocking Probability for LTD-LWF and different number of clients in m2m group. 6. CONCLUSIONS In this paper, we addressed the problem of dynamic routing of many-to-many flows using replica servers in WDM networks. We proposed several algorithms for Client-Server Assignment and Routing and Wavelength Assignment. As a result, we conclude that LTD-LWF outperforms other algorithms. Moreover, we performed experiments introducing different number of replica servers, clients in the m2m group or available wavelengths. In the future work, we plan to introduce different transmission strategies within many-to-many concept. The aim is also to develop dynamic joint CSA-RWA algorithms, where client-server assignment is done according to the current lightpaths allocation in the network. Finally, we want to move forward to the recently proposed elastic optical networks, where the flexibility of adjusting spectrum to the needs of particular demand is much higher. ACKNOWLEDGEMENTS The work was supported by statutory funds of the Department of Systems and Computer Networks, Wroclaw University of Technology. REFERENCES [1] M. Eiselt, B. Teipen, K. Grobe, and J.P. Elbers: WDM transport towards Terabits/s line rates – What will be gained?, in Proc. 12th ITG Symposium on Photonic Networks, pp. 1-6, 2-3 May 2011. [2] H. Zang, J. Jue, and B. Mukherjee: A review of routing and wavelength assignment approaches for wavelength-routed optical WDM networks, Optical Networks Magazine, vol. 1, no. 1, pp. 47-60, 2000. [3] R. Ramaswami and K. Sivarajan: Routing and wavelength assignment in all-optical networks, IEEE/ACM Trans. Netw., vol. 3, no. 5, pp. 489-500, Oct. 1995. [4] J. Späth: Dynamic routing and resource allocation in WDM transport networks, Computer Networks 32, no. 5, pp. 519-538, 2000. [5] G. Shen, S.K. Bose, T.H. Cheng, C. Lu, and T.Y. Chai: Efficient heuristic algorithms for light-path routing and wavelength assignment in WDM networks under dynamically varying loads, Computer Communications 24(3), pp. 364-373, 2001. [6] V. T. Le, S. H. Ngo, X. Jiang, S. Horiguchi, and M. Guo: A genetic algorithm for dynamic routing and wavelength assignment in WDM networks, in Parallel and Distributed Processing and Applications (pp. 893-902), Springer Berlin Heidelberg, 2005. [7] J. He, S.H. Chan, and D.H. Tsang: Routing and wavelength assignment for WDM multicast networks, in Proc. Global Telecommunications Conference, GLOBECOM'01, vol. 3, 2001. [8] K. Bhaskaran, J. Triay, and V.M. Vokkarane: Dynamic anycast routing and wavelength assignment in WDM networks using ant colony optimization (ACO), in Proc. 2011 IEEE International Conference on Communications (ICC), pp. 1-6, 5-9 Jun. 2011. [9] M.A. Saleh and A.E. Kamal: Many-to-many traffic grooming in WDM networks, Journal of Optical Communications and Networking , pp. 376-391, 2009. [10] K. Walkowiak, D. Bulira, and D. Careglio: ILP modeling of many-to-many replicated multimedia communication, Journal of Telecommunications and Information Technology (JTIT) 3/2013, pp. 56-65. [11] K. Walkowiak: QoS dynamic routing in content delivery network, Lecture Notes in Computer Science, vol. 3462, pp. 1120-1132, Springer Verlag, 2005. [12] C. Diot, W. Dabbous, and J. Crowcroft: Multipoint communication: A survey of protocols, functions, and mechanisms, IEEE Journal on Selected Areas in Communications, vol. 15, no. 3, pp. 277-290, Apr. 1997. [13] B. Mukherjee: Optical WDM Networks, Springer-Verlag New York, Secaucus, NJ, USA, 2006.
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