Advanced Centralized RWA Protocol for WDM Networks

Sandeep Kumar Konda, T.K.Ramesh, and P. R Vaya

Department of E.C.E, AMRITA School of Engineering AMRITA Vishwa Vidyapeetham

Bangalore, India kondasandeepkumar@gmail.com

Abstract— In this paper we present the design of an Advanced Centralized RWA Protocol (ACRP) in which the cost of a lightpath is computed based on its number of available free wavelengths and number of wavelength conversions. Centralized Management System (CMS I) assigns optimal primary and backup lightpaths. CMS II updates the optimal primary and backup lightpaths as and when the number of free wavelengths of primary lightpath reaches the threshold value ‘N≤ 4’ . In case of failure the data will be rerouted through the backup lightpath and very next lightpath with best cost is assigned as backup lightpath. The advantage of this protocol is that the tasks are shared using two CMS which improves the computation bottleneck and also if one fails the other will take over the entire process. By simulation results, we showed that our proposed protocol has minimal request rejection and set-up time.

Keywords - CMS; grooming; request rejection; setup time

I. INTRODUCTION Wavelength Division Multiplexing (WDM) and routing are

rapidly becoming the technologies-of-choice in network communication to meet the remarkably increasing bandwidth demand. WDM is a data transmission mechanism in which many wavelength bands can share a single mode optical fiber and it is generally employed to increase the network bandwidth [1]. In WDM network a connection is realized by a lightpath. Without wavelength conversion capability, the establishment of a lightpath requires the same wavelength to be used along entire route of the lightpath, which is referred to the Wavelength Continuity Constraint (WCC) [2]. The WCC constraint increases the request rejection and degrades network performance. Protocol used for selecting routes and wavelengths to establish lightpaths is known as Routing and Wavelength Assignment (RWA) protocol. Many problems in wavelength routed WDM networks have RWA as sub problem and also the RWA problem is NP-complete [3]. Therefore, it is mandatory to use a good RWA protocol to establish lightpaths in an efficient manner so has to increase the network performance [4].

Lightpath establishment in WDM networks can use either distributed or centralized control. In the case of distributed control, no central controller is used. Up-to-date knowledge of the network state is not known to any node. In the case of centralized control, a central controller is assumed to be

available. It keeps track of the state of the network. It is responsible for selecting routes and wavelengths for the request and sending control signals to appropriate nodes for establishing and releasing lightpaths [5].

As each lightpath is expected to operate at a rate of several gigabytes per second, a failure can lead to a severe data loss. Therefore, it is very important to have networks that are capable of preventing such failures; these are known as survivable networks [6]. In survivable WDM networks, the lightpath known as primary lightpath carries traffic during normal operations. In case a primary lightpath fails, the traffic is rerouted over a new lightpath known as the backup lightpath [7].

II. RELATED WORK Lu Ruan et al. [8] have presented a distributed dynamic

routing algorithm for restorable connections that uses load balancing heuristics in both primary and backup path computations to achieve low demand blocking. The key idea was to assign costs to links so that heavily loaded links will be avoided in the routing of the primary and backup paths and links with a high chance of including a sharable backup channel will be included in the backup path. Simulation results showed that the algorithm performs significantly better than a simple distributed algorithm and achieves comparable performance as a centralized algorithm.

Alvaro L.Barradas and Maria do Carmo R. Medeiros [9]

have presented a traffic engineering approach for path selection with the objective of minimizing contention using only topological information. The main idea was to balance the traffic across the network to reduce congestion without incurring link state dissemination protocol penalties. This protocol also does not consider the dynamic traffic load into consideration and hence not adaptive.

S. Dharma Rao et. al. [10], proposed distributed dynamic

routing algorithms for QoS constrained routing and survivable routing based on preferred link routing approach. For QoS constrained routing they provided a common framework for routing connections with constraints on different types of metrics such as bandwidth, delay, bit-error-rate and reliability. A distributed routing algorithm for fault-tolerant connections

was also proposed and described how dedicated and shared protection can be provided in case of single link failures and studied the performance of fault-tolerant routing in terms of call acceptance ratio, cost of the path, hop length, call setup time and compared the results with that of an existing approach.

Paramjeet Singh et. al. [11], considered RWA problem on

wavelength division multiplexing networks without wavelength conversion. Also, they presented efficient RWA strategies which were used to minimize the blocking probability.

Osama Awwad et. al. [12], considered the RWA problem with traffic grooming for mesh networks under static and dynamic lightpath connection requests. They proposed an Integer Linear Programming (ILP) model that accurately depicted the Grooming Routing and Wavelength Assignment problem (GRWA). The problem of grooming routing and wavelength assignment was solved by proposing two novel heuristics. The strength of these proposed heuristics stems from their simplicity, efficiency and applicability to large-scale networks.

P.Rajalakshmi and Ashok Jhunjhunwala [13] have proposed two heuristic reassignment algorithms using centralized method namely, minimum overlapped to least congested (MOLC) and random techniques and have studied their performance. Simulation results show that the reassignment algorithm can mostly remove the blocking due to the WCC. But as the reassignment is done link by link, the latency for data transmission will increase and also throughput is less because of disturbance of a live call during the reassignment process. Furthermore, as it uses single central controller it is vulnerable due to its single point of failure and as the traffic load increases, the control traffic to and from the controller increases substantially and the central controller requires sufficient buffer and processing power to handle the requests i.e. the central controller is a computation bottleneck for large-scale networks. To overcome this in our protocol we are using two CMS which will share the work and also if one fails the other one will takeover the entire process.

The WCC, CMS failure and computation bottleneck for

large-scale networks have overcome in our proposed protocol ACRP by using wavelength convertors to overcome WCC and two Central Management Systems CMS I and CMS II which will overcome single point failure and computation bottleneck. One of the drawbacks of using wavelength convertors is its conversion time which we have reduced by selecting a lightpath with minimum number of wavelength conversions. To further reduce request rejection and for better utilization of bandwidth we use the concept of traffic grooming for ACRP called Advanced Centralized Grooming RWA Protocol (ACGRP).

III. ADVANCED CENTRALIZED RWA PROTOCOL (ACRP)

A. Calculation of Number of Free Wavelengths and Wavelength Conversions

The CMS I and CMS II are used to establish optimal primary and backup lightpaths on the basis of number of free wavelengths and number of wavelength conversions.

i. Number of free available wavelength on lightpath ‘j’, Wj, free = Min (Wi1, free, Wi2, free, ..….., Wim, free) 0 < j ≤ n; 0 < i ≤ m, where Wi1, free is the number of free wavelength in link 1 on lightpath ‘j’ ‘j’ is the lightpath number ‘n’ is the total number of available lightpaths ‘i’ is the link number ‘m’ is the maximum number of links

ii. Minimum conversion lightpath MCL = Min (Cj); 0 < j ≤ n), where

‘j’ is the minimum conversion lightpath ‘n’is the maximum number of available lightpaths

B. Traffic Grooming Traffic grooming concept is used to improve the bandwidth utilization, i.e. we can send more than one request in a single wavelength at the same time. There by efficiently utilizing the bandwidth.

C. Algorithm Step1: CMS I wait for the requests. Step2: CMS I calculates the number of free wavelengths and wavelength conversions on all the possible lightpaths. Step3: CMS I selects the lightpath which is having more number of free wavelengths and minimum number of wavelength conversions as primary lightpath and very next lightpath as backup lightpath as follows:. • LP = [ 1 2 3 4] • FW = [ 30 20 31 10] • WC = [ 2 5 6 1 ] • LPDFW = [ 3 1 2 4 ] • LPIWC = [ 4 1 2 3 ] o Primary lightpath = Lightpath number 1 o Backup lightpath is selected by repeating step3 excluding primary lightpath, Where LP is the lightpath number. FW is the number of free wavelengths in the order of lightpath number. WC is the number of wavelength conversions in the order of lightpath number. LPDFW is the lightpath number in the decremental order of number of free wavelengths.

LPIWC is the lightpath number in the incremental order of number of wavelength conversions. Step4: CMS I checks for the possibility of grooming if the arrived request is equal to or less than 5Gbps else no. Step5: If a primary lightpath fails CMS II inform it to repair processor and backup lightpath is chosen as primary lightpath and very next lightpath as backup lightpath.

Step6:CMS II repeats the steps from 2 to 3 if the number of free wavelengths on primary lightpath reaches the threshold value ‘N ≤ 4’ accordingly CMS-I assigns new primary and backup lightpaths.

IV. SIMMULATION RESULTS In this section, we examine the performance of our ACRP and ACGRP protocol with MOLC protocol [13] with an extensive

simulation study based upon the MATLAB 7.10.0(R2010a) simulator. We used west part of ARPANET (Figure II) of 10 nodes 13 links for the analysis. Various simulation parameters considered are as given in table1.

TABLE I: SIMULATION PARAMETER

Figure I. Number of Request Arrived V/S Number of Request Rejected

TABLE II: COMPARISON OF ACGRP, ACRP AND MOLC

Source Node

Destination Node

Optimal Lightpath Number of Requests Arrived

Number of Requests Rejected

ACRP / ACGRP MOLC MOLC ACRP ACGRP

4 1 4-3-6-7-1 4-3-6-7-1 50 35 24 19 3 9 3-2-1-8-9 3-2-7- 1-8-9 55 51 32 7 4 1 4-3-2-1 4-3-6-7-1 60 52 43 32 4 10 4-3-2-1-8-9-10 4-3-6-7-1-8-9-10 65 48 38 31 3 1 3-2-1 3-2 -7-6 -5-4-10-9-8-1 70 52 47 34 1 6 1-7-6 1-2-7-6 75 71 51 50 5 8 5-4-3-6-7-2-1-8 5 -4-3-6-7 -1-8 80 78 61 47 5 7 5-6-3-2-7 5 -4-3 -6 -7 85 84 72 60 4 2 4-3-6-7-1-2 4 -3 -6-7-2 90 86 74 60 1 6 1-7-2-3-6 1 -2-7 -6 95 84 77 63

Number of Nodes 10 Number of Links 13 Number of Wavelengths 40 Wavelength conversion factor 1 Wavelength conversion time 10ms Wavelength reassignment time 20ms Control signaling time 5ms

FIGURE II: WEST PART OF ARPANET WITH 10 NODES 13 LINKS

Table II shows the simulation result comparison of our protocol ACRP and ACGRP with MOLC in terms of optimal lightpath selection and number of request rejection. Figure I shows the Request Rejection obtained with our ADRP and ADGRP compared with MOLC scheme [13] as per the simulation results recorded in table 2. It shows that Request Rejection is significantly less than the MOLC. This is because, in MOLC, the number of requests that can be processed depends on the number of free continuous wavelengths available i.e. the number of free wavelengths satisfying the WCC, whereas in our ADRP we have considered the number of free wavelengths and minimum number of wavelength conversions and to further improve we have considered grooming in ADGRP which increases the bandwidth utilization of the network.

TABLE III: SETUP TIME

Table 3 gives the setup time required for ACRP/ACGRP and MOLC for the first lightpath setup tabulated in table 2; source node 4 and destination node 1. Setup time for ACGRP = Control signaling time + Conversion time (2 conversions) 5*10-3 + 2*10*10-3 = 25 ms Setup time for MOLC = Control signaling time + Reassignment time (Wavelength reassignment in 3 links) 5 *10-3 + 3*15*10-3 = 50 ms

V. CONCLUSION In this paper we proposed Advanced Centralized RWA protocol (ACRP) for WDM networks which gives better performance compared to the wavelength reassignment method used in WDM networks. In our approach the tasks are shared among two CMS which enhances the Quality of Service to a great extend. As opposed to the reactive protocols, our proposed protocol is proactive in the sense it automatically adapts to the traffic load variation across the network. By simulation results, we have shown that our proposed protocol has low request rejection and setup time with high bandwidth utilization.

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ACRP / ACGRP MOLC

25 ms 50 ms