Optimization of Wavelength Assignment for QoS Multicast in WDM Networks

1
Optimization of Wavelength Assignment for
QoSMulticast 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.341-350
2
Outline

• Introduction
• Preliminaries
• Rerouting Algorithm
• Simulations
• Conclusion
• Further Research Problem

3
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.

4
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.

5
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.

6
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.

7
System Models

• WDM network
• Connected and undirected graph G(V, E, c, d)
• V vertex-set, Vn
• E edge-set, Em
• 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)

8
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 (si, Di, ?i)
• source si
• destination Di
• delay bound ?i
• the data transmission delay from si to any node
  in Di should be within bound ?i

9
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.
• Ti (si, Di, ?i) be the routing tree fpr request
  r i (si, Di, ?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.

10
QoS requirement

• The QoS requirement of routing tree Ti (si, Di,
  ?i) is that the delay from si to any nodes in Di
  should not exceed ?i.
• Let PTi(si, u) denote the path in Ti (si, Di,
  ?i) from si to u in Di
• Thus,
• Assume
• where PG(si, u) is the shortest path si to u in G.

11
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.

12
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.

13
Algorithm A for QoS routing
14
Algorithm A for QoS routing

• For each QoS multicast request r i (si, Di, ?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).

15
Algorithm A for QoS routing
16
Algorithm B for Wavelength Assignment
17
Algorithm B for Wavelength Assignment
18
Algorithm C Optimization through Load Balancing
19
Algorithm C Optimization through Load Balancing
20
Algorithm D Optimization through Wavelength
Reassignment
21
Algorithm D Optimization through Wavelength
Reassignment
22
Simulations

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

23
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)?exp(-p(u,v)
  /?d), where
• p(u,v) is the distance between u and v,
• d is the maximum distance between any two nodes,
• 0 lt ?, ??1
• c and d on link (u,v) are the distance between
  nodes u and v on the rectangular.

24
Simulated Model

• QoS multicast trees are generated randomly
• Delay bound is set as ?i amaxd(PG(si,u))u in
  Di
• The lower bound is defined as the maximal link
  load in the system which is obtained running
  algorithm AC (without considering wavelength
  assignment)

25

• 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.