Optimization of Wavelength Assignment for QoS Multicast in WDM Networks Xiao-Hua Jia, Ding-Zhu Du, Xiao-Dong Hu, Man-Kei Lee, and Jun Gu, IEEE TRANSACTIONS ON COMMUNICATIONS, VOL. 49, NO. 2, FEBRUARY 2001 pp

Outline Introduction Preliminaries Rerouting Algorithm Simulations Conclusion Further Research Problem

Introduction There are two types of architectures of WDM optical networks: single-hop systems and multihop systems [2]. –Single-hop system a communication channel should use the same wavelength throughout the route of the channel –Multihop system a channel can consist of multiple lightpaths and wavelength conversion is allowed at the joint nodes of two lightpaths in the channel. In this paper, we consider single-hop systems, since all-optical wavelength conversion is still an immature and expensive technology.

Introduction Multicast is a point to multipoint communication, by which a source node sends messages to multiple destination nodes. A light-tree, as a point to multipoint extension of a lightpath, is a tree in the physical topology and occupies the same avelength in all fiber links in the tree.

Introduction Each fork node of the tree is a multicast- capable optical switch, where a power splitter [4] is used to split an input optical signal into multiple signals which are then forwarded to output ports without electrical conversions. End-to-end delay is an important quality-of- service (QoS) parameter in data communications. QoS multicast requires that the delay of messages from the source to any destination be within a bound.

Introduction The problem is formalized as follows: given a set of QoS multicast requests in a WDM network system, compute a set of QoS routing trees and assign wavelengths to them. The objective is to minimize the number of distinct wavelengths to be used under the following constraints on each routing tree: – the delay from the source to any destination along the tree does not exceed a given bound; –the total cost of the tree is suboptimal.

System Models WDM network –Connected and undirected graph G(V, E, c, d) –V: vertex-set, |V|=n –E: edge-set, |E|=m –Each edge e in E is associated with two weight functions c(e): communication cost d(e): the delay of e ( include switch and propagation delays)

System Models Cost of path P(u,v): Delay of path P(u,v): k bidirectional QoS multicast requests in the system are given, denoted by multicast request r i (s i, D i, ∆ i ) –source s i –destination: D i –delay bound ∆ i –the data transmission delay from s i to any node in D i should be within bound ∆ i

System Models This paper assumes an optical signal can be split into an arbitrary number of optical signals at a switch. Thus, there is no restriction on node degree in a routing tree. T i (s i, D i, ∆ i ) be the routing tree fpr request r i (s i, D i, ∆ i ) The light signal is split at si and forwarded to the output ports leading to its children, which then transmit the signal to their children until all nodes in the tree receive it.

QoS requirement The QoS requirement of routing tree T i (s i, D i, ∆ i ) is that the delay from si to any nodes in Di should not exceed ∆ i. Let P Ti (s i, u) denote the path in T i (s i, D i, ∆ i ) from s i to u in D i Thus, Assume: where P G (s i, u) is the shortest path s i to u in G.

Objective The cost of the tree One objective of the multicast routing is to construct a routing tree which has the minimal cost. The problem is regarded as the minimum Steiner tree problem, which was proved to be NP-hard. Another objective is to minimize the number of wavelengths used in the system. In a single-hop WDM system, two channels must use different wavelengths if their routes share a common link, which is the wavelength conflict rule.

Rerouting Algorithms Four algorithms –A: QoS routing algorithm –B: wavelength assignment problem –C and D aiming at minimizing the number of wavelengths over the results produced by algorithms A and B. C: reroutes some of the routing trees to reduce the maximal link load by avoiding use of the links whose load is the maximum. D: reroutes the trees whose wavelengths are the least used, which tries to free out the least used wavelengths.

Algorithm A for QoS routing

For each QoS multicast request r i (s i, D i, ∆ i ), algorithm A constructs a suboptimal QoS routing tree. Generate a low cost routing tree by applying a heuristic for the Steiner tree problem. Modifies this tree into the one which meets the QoS requirements (delay requirement).

Algorithm A for QoS routing

Algorithm B for Wavelength Assignment

Algorithm C: Optimization through Load Balancing

Algorithm D: Optimization through Wavelength Reassignment

Simulations Four different combinations of algorithms A, B, C, D nonoptimization AB, load balancing optimization ACB, wavelength assignment optimization ABD, combined optimization ACBD

Simulation Model Network topology: random generated 100 nodes are distributed randomly over a rectangular coordinate A link between two nodes u and v is added by using the probability function P(u,v)=λexp(-p(u,v)/γδ), where –p(u,v) is the distance between u and v, –δ is the maximum distance between any two nodes, –0 < λ, γ ≦ 1 c and d on link (u,v) are the distance between nodes u and v on the rectangular.

Simulated Model QoS multicast trees are generated randomly Delay bound is set as: Δ i = αmax{d(P G (s i,u))|u in D i } The lower bound is defined as the maximal link load in the system which is obtained running algorithm AC (without considering wavelength assignment)

We assume an optical signal can be split into an arbi-trary number of optical signals at a switch. Thus, there is no restriction on node degree in a routing tree. the root to any node is at most a constant times the shortest-path distance in the graph and the total cost of the tree is at most thewavelength-division multiplexing (WDM) [1] is basically fre-quency- division multiplexing in the optical frequency domain, where on a single optical fiber there are multiple communica-tion channels at different wavelengths. There are two types of architectures of WDM optical networks: single-hop systems and multihop systems [2]. In single-hop systems, a communi-cation channel should use the same wavelength throughout the The problem is formalized as follows: given a set of QoS multicast requests in a WDMnetwork system, com-pute a set of QoS routing trees and assign wavelengths to them. The objective is to minimize the number of distinct wavelengths to be used under the following constraints on each routing tree: the delay from the source to any destination along the tree does not exceed a given bound; the total cost of the tree is suboptimal. as-signment, WDM network. I. INTRODUCTION End-to-end delay is an important quality-of-service (QoS) pa-rameter in data communications. QoS multicast requires that the delay of messages from the source to any destination be within a bound.the number of wavelengths through reducing the maximal link load in the system; while the other does it by trying to free out the least used wavelengths. Simulation results demonstrate that the proposed algorithms can produce suboptimal QoS routing trees Each fork node of the tree is a multicast-capable optical switch, where a power splitter [4] is used to split an input optical signal into multiple signals which are then forwarded to output ports without electrical conversions. multicast routing, but also the optimal wavelength assignment. Multicast is a point to multipoint communication, by which a source node sends messages to multiple destination nodes. In this paper, we propose a new optimization method, which integrates routing and wavelength assignment in optimization of wavelengths. Two optimization algorithms are also proposed in minimizing the number of wavelengths. One algorithm minimizes A light-tree, as a point to multipoint extension of a lightpath, is a tree in the physical topology and occupies the same wavelength in all fiber links in the tree.