International Journal of Computer Science Trends and Technology (IJCST) – Volume 2 Issue 4, Jul-Aug 2014 ISSN: 2347-8578 www.ijcstjournal.org Page 153 Path Computation Algorithm Using Delay & Bandwidth Constraint Shalley Tyagi 1 , Rakesh Kumar Singh 2 Research Scholar 1 , Associate Professor 2 Department of Computer Science and Engineering Kamla Nehru Institute of Technology (KNIT) Sultanpur-India ABSTRACT MPLS is a fast forwarding mechanism which provides support for traffic engineering. In the MPLS network constraint based routing computes routes, it not only considers the topology of the network but also another parameters such as bandwidth, delay etc. It may find a longer but lightly loaded path which is better than heavily loaded shortest path. This paper deals with modification of Wang-Crow croft algorithm based on best fit approach in the computation of label switch path resulting increases the quality of service. Both algorithms have been implemented in NS-2 and compared on the basis of throughput. Keywords:- MPLS, NS-2, LSP, Wang Crow croft I. INTRODUCTION MPLS [4] is a forwarding mechanism which forward the data packet based on labels rather than long network address, avoiding complex lookups in routing table. It makes use of labels to create virtual link for data transmission between data nodes. The structure of MPLS consists of various routers that support MPLS and are known as Label Switching Routers LSRs. The LSRs which are in the periphery of the MPLS Network are called Edge LSRs or Label Edge Routers (LERs) and must be capable of accepting packets from all types of networks. The end-to-end virtual path that is set up with the use of labels is known as LSP (Label switched path). An LSP starts at the ingress node and terminates at the egress node passing through several intermediate routers. Ingress LSR receives a packet that is not labeled yet, it insert a label in front of the packet and send it on link. Egress LSR receives labeled packets, remove the label and send them on link [3]. The basic function of a PCE [8] is to find a network path that satisfies multiple constraints (as QoS Bandwidth Constraint) [4]. A PCE can be realized according to two models- 1. Centralized computation Model. 2. Distributed computation model. Centralized Model-In this model all the paths are computed by a single, centralized PCE .This may be a dedicated server or a designated router. In this model off- line path computation algorithm is used. A centralized PCE can take into account global information on network resources and existing connection paths to implement optimal computation procedures. Off-line path computation algorithms have the knowledge of the entire set of demands and make more efficient use of network capacity. Figure 1: Structure of MPLS Network Distributed Model-This model include multiple PCEs and where the computation of paths is shared among the PCEs. A given path may in turn be computed by a single PCE or by multiple PCEs, but often the computation of an individual path is entirely performed by a single PCE. Distributed PCEs usually adopt on line path computation algorithms. II. QOS METRICES Routing metrics are links features used to represent a network. Given the metric d(i, j), associated to the link(i, j), and the path p= (i, j, k, … , l, m), the metric d is:  additive if d(p)= d(i, j)+ d(j, k)+ … +d(l, m)  multiplicative if d(p)= d(i ,j)*d(j, k)* … *d(l, m)  concave if d(p)= min[d(i, j);d(j, k); … ;d(l, m)] Routing protocols usually characterize a network through a single metric (the cost of the link). In the case of QoS routing protocols and constrained-based path computation RESEARCH ARTICLE OPEN ACCESS