Research Issues on Routing and Wavelength Assignment for Wavelength Routed WDM Networks Hsu-Chen, Cheng PhD. Student Department of Information Management

Research Issues on Routing and Wavelength Research Issues on Routing and Wavelength Assignment for Wavelength Routed WDM NetworksAssignment for Wavelength Routed WDM Networks

Hsu-Chen, Cheng

PhD. Student

Department of Information Management

National Taiwan University

10/27/2003

Qualifying ExamQualifying Exam

2

OutlineOutline

Introduction of Optical Networks WDM Technology Optical Network Control Plane IP/WDM Traffic Engineering

Optical Network Design and Engineering Routing and Wavelength Assignment (RWA) Heuristics

Optical Multicasting Multi-granularity Architecture of Optical Network Future Research Direction

3

The Trend of Network TechnologyThe Trend of Network Technology

Circuit Switch Packet Switch

E

M

S

DWDM

SONET

ATM

IP

E

M

S DWDM

SONET

IP /MPLS E

M

S DWDM OXC

Thin SONET

IP GMPLS

E

M

S

DWDM OXC

IP GMPLS

Time

Introduction of Optical Networks

4

Optical NetworksOptical Networks

First Generation: FDDI Gigabit Ethernet

Second Generation: WDM Local Area Network

Passive Star Network Single-Hop WDM Network

WDM Wide Area Network Wavelength routed Network OBS OPS

Wavelength-routed optical networks are the most promising candidates for backbone high-speed WAN.


5

Optical Network TechnologiesOptical Network Technologies

WDM Technology Fixed Point-to-Point Wavelength routed 300 λ x 40Gbps

Optical Components OADM (Optical add/drop multiplexer) OXC (Optical cross-connect) Tunable Laser Amplifier Wavelength Converter Wavelength Splitter


6

The Architecture of Wavelength RouterThe Architecture of Wavelength Router


7

Physical Topology and Logical TopologyPhysical Topology and Logical Topology

A physical topology is a graph representing the physical interconnection of the wavelength routing nodes by means of fiber-optic cables.

A logical topology is a directed graph that results when the lightpaths are setup by suitably configuring the wavelength routing nodes.

Optical Network Design and Engineering

8

The Architecture of Wavelength-routed Optical The Architecture of Wavelength-routed Optical NetworkNetwork


9

Optical Network Control PlaneOptical Network Control Plane

Apparatus IETF (Internet Engineering Task Force) ODSI (Optical Domain Service Interconnection) OIF (Optical Internetworking Forum)

Issues Signaling Mechanism (UNI) Signaling and control protocol for dynamic lightpath

establishment and traffic engineering


10

Optical Network Control Plane (cont’d)Optical Network Control Plane (cont’d)


RouteComputation

LightpathManagement

TrafficEngineeringDatabase

Topology andResourceDiscovery

Signaling Protocol RWA algorithms/traffic engineering

Routeinformation

Topology and resourceinformation

Updates

•Neighbor discovery

•Link Monitoring

•State distribution

•LMP [J. P. Lang 2001]

•RSVP-TE

•CR-LDP

Link-state routing protocol (OSPF)

11

IP/WDM Traffic EngineeringIP/WDM Traffic Engineering

Overlay Model Closer to classical IP and ARP over ATM scheme The IP and optical network are independent of each other Edge IP router interacts with its ingress OXC over a well-

defined UNI Peer Model

The IP and optical network are treated together as a single network

Augmented Model IP and optical networks use separate routing protocol, but

information from one routing protocol is passed through the other routing protocol


G. N. Rouskas and H. G. Perros, A Tutorial on Optical Networks, Networking 2002 Tutorials, vol. 2497, 2002, pp. 155-193.

12

TE ModelTE Model

WDM Traffic Engineering Model Minimum average packet delay Maximize scale up capability

MPLS Traffic Engineering Model Overlay model Virtual topology (LSPs)

IP over WDM Traffic Engineering Model Virtual topology design Routing and wavelength assignment


13

RWA constraintsRWA constraints

Wavelength continuity constraint Distinct wavelength constraint


14

Wavelength ConversionWavelength Conversion

1λ

2λ

3λ

1λ

2λ

3λ

1λ

2λ

3λ

1λ

2λ

3λ

1λ

2λ

3λ

1λ

2λ

3λ

1λ

2λ

3λ

1λ

2λ

3λ

(a) No conversion (b) Fixed conversion

(c) Limited conversion (d) Full conversion


Wavelength converters translate wavelength fi to fk. They may be used as components of the wavelength routin

g nodes.

15

RWA ProblemRWA Problem

Static RWA Topology Subproblem Lightpath routing subproblem Wavelength assignment subproblem Traffic routing subproblem

Dynamic RWA Route Computation Wavelength Assignment


16

Physical Topology DesignPhysical Topology Design

This step includes – Sizing the links (no. of wavelength channel, capability of eac

h channel) Sizing the OXCs Placement of resources (Amplifiers, Converters, Splitters) Dealing with link or OXC failures

Placement of converters [J. Iness, 1999] Sparse location of wavelength converters Sharing of converters (Nodal Design) Limited-range wavelength conversion [R. Ramaswami and G.

H. Sasaki, 1998]

Static RWA

17

Virtual Topology DesignVirtual Topology Design

A solution to the static RWA problem consists of a set of long-lived ligthpaths which create a logical topology among the edges node.

It is not possible to implement fully connected virtual topologies.

N(N-1) lightpaths Objective

Minimize the maximum congestion level Minimize the average weighted number of hops Minimize the average packet delay

Static RWA

18

Wavelength AssignmentWavelength Assignment

1

23

4

5

6

7

8

Static RWA

1

3

4

56

7

8

2

1λ

1λ

1λ

0λ

0λ

0λ

2λ 2λ

Graph-coloring problem

NP-complete

Sequential graph-coloring algorithms

19

Route ComputationRoute Computation

Static algorithm and adaptive algorithm Lightpath routing

Constraint algorithm Fixed routing algorithm Fixed alternative algorithm

Adaptive unconstrained routing (AUR) Hybrid routing

Least to most congested

AUR has better improvement on call blocking probability[A. Mokhtar and Murat Azizoğlu, 1998]

Dynamic RWA

20

Candidate PathsCandidate Paths

The candidate paths for a request are considered in increasing order of path length (or path cost).

Path length is defined as the sum of the weights assigned to each physical link along the path.

K-minimum hop paths K-minimum distance paths

K-shortest path Pair-wise link disjoint Dijkstra algorithm

Physical constraints (attenuation, dispersion et al.) Constraint-based shortest path first algorithm [B. Davie, 2000]

Dynamic RWA

21

Wavelength AssignmentWavelength Assignment

[H. Zanf et al., 2000] Random Wavelength Assignment (R) First-Fit (FF) Least-Used (LU) Most-Used (MU) Min-Product (MP) Least-Loaded (LL) MAX-SUM (MΣ) Relative Capacity Loss (RCL) Wavelength Reservation (Rsv) Protecting Threshold (Thr)

Dynamic RWA

Multi-fiber

Single-fiber

22

General Model of Virtual Topology DesignGeneral Model of Virtual Topology Design

Mixed Integer Linear Programming [B. Mukherjee et al., 1994] [B. Mukherjee et al., 1996] [R.Ramaswami and K. N. Sivarajan, 1996] [R. Krishnaswamy and K. N. Sivarajan, 1998] [R. Krishnaswamy and K. N. Sivarajan, 2001]

Objective

General Model

)min( max

23

CongestionCongestion

Congestion may be viewed as a function of the various parameters of the network such as

the traffic matrix, number of wavelengths the fiber can support, resources at each node (number of transmitters and

receivers), the hop lengths of the logical links, the multiplicity restrictions on the logical topology, the multiplicity restrictions on the physical topology, symmetry/asymmetry restrictions, the propagation delay.

General Model

24

ObjectiveObjective

The motivation for choosing this objective is that the electronic processing (switching speed) requirement is proportional to the congestion.

If the switching speeds at the nodes are limited, then minimizing congestion would be appropriate as it would enable the traffic carried per wavelength to increase.

If there is heavy traffic between some source–destination pair, then there is a logical link between them; this is a desirable property.

This happens because of the objective function, i.e., if there is heavy traffic between node i and node j then because of the objective there would tend to be an edge in the logical topology.

)min( max

General Model

25

NotationsNotations

s,d source and destination of a packet, when used as superscripts;

i,j originating and terminating node of a logical link (lightpath);

l,m endpoints of a physical link;

k wavelength number, when used as a superscript.

General Model

26

ParametersParameters

General Model

Physical Topology: ),( PP EVG

Link Indicator: lmP

Virtual Degree: n

Traffic Matrix: ][ )(sd

Allowed Physical Hop: ][ ijhH

27

VariablesVariables

Lightpath Indicator: ijb

Lightpath wavelength Indicator: )(k

ijc

Link-lightpath Wavelength Indicator: ),()( mlc kij

Traffic intensity variables: )(sdij

General Model

28

Constraints- Degree ConstraintsConstraints- Degree Constraints

The above constraint ensures that the number of logical links originating (out-degree) and terminating (in-degree) at node is less than or equal to the number of transmitters and receivers at that node.

.1,...2,1,0 and 1,0 Nibij

General Model

ib lj

ij ,

ib lj

ji ,

29

Constraints- Traffic ConstraintsConstraints- Traffic Constraints

Traffic routing constraints

Flow Conservation

The above first two equations ensure that the load on any logical link is no greater than the maximum load, which is being minimized.

),( ,max jiij

),( ,)( jisd

sdijij

),(),,( ,)()( dsjib sdij

sdij

),(

if

, if

if

,0

,)(

)(

)()( ds

ii and d s

id

issd

sd

j

sdji

j

sdij

General Model

30

Constraints- Wavelength Continuity ConstraintsConstraints- Wavelength Continuity Constraints

Unique wavelength constraints:

This ensures that if logical link exists, then only one wavelength is assigned to it, among the possible choices.

This equation ensures that only those could be nonzero for which the corresponding variables are nonzero.

),()(. mlC kml

),()( jiC k

1

0

)( ,W

kij

kij (i,j)bc

kmljicmlc kij

kij ),,(),,( ,),( )()(

General Model

31

Constraints- Wavelength Continuity ConstraintsConstraints- Wavelength Continuity Constraints

Wavelength clash constraints

Conservation of wavelength constraints

Let logical link bij use wavelength k. Then by conservation of wavelength constraints there is a path in the physical topology from node i to node j with wavelength assigned to it.

kmlmlcij

kij ),,( ,1),()(

mj)(i

jmim

im

jm

b

b

PlmCPmlC ij

ijF

k llm

kij

W

k llm

kij ,,

. and if

, if

if

,0

,

,

),(),(1

0,

)(1

0

)(

General Model

32

Constraints- Hop Bound ConstraintsConstraints- Hop Bound Constraints

Hop bound Constraints

,ki,jhmlC ijlm

kij )( ,),()(

General Model

33

HeuristicsHeuristics

Subproblems: Topology Subproblem: bij

Lightpath routing subproblem: Wavelength assignment subproblem: Traffic routing subproblem:

Some of above subproblem are NP-hard. Solving the subproblems in sequence and combining

the solutions may not result in the optimal solution for the full integrated problem.

RWA Heuristics

),()( mlc kij

)(kijc

)(sdij

34

Lower Bound on CongestionLower Bound on Congestion

Physical topology independent bound (p.43)

Minimum flow tree bound (MFT) (p.43)

Iterative LP-relaxation bound (p.43) Aggregate formulation Cutting Plane

Independent topologies bound (p.43) Uniform traffic: 5% - 10% tighter than the bound obtained fro

m MFT Nonuniform traffic: up to 50% higher than MFT bound

ij

lijl EHrE /)/1(max

lEHr /minmax

RWA Heuristics

35

Lower Bound on the Number of WavelengthLower Bound on the Number of Wavelength

Physical topology degree bound (p.45) Derived from the Simple consideration that he node with the

minimum physical degree.

Physical topology link bound (p.46) Assuming that each node sources lightpaths to exactly those

node it can be reach with the minimum number of hops.

Lagrangian relaxation bound 顏宏旭 (2001)

RWA Heuristics

p

l

i

lip lE )()2/1(

36

Regular TopologiesRegular Topologies

Regular topologies such as hypercube have several advantages as virtual topologies.

They are well understood, and results regarding bounds and averages are comparatively easier to derive.

Two subproblem Node Mapping Subproblem Path Mapping Subproblem

RWA Heuristics

37

Pre-specified TopologiesPre-specified Topologies

The topology in terms of a list of lightpaths with their source and destination nodes is supposed to be given for each instance of problem.

The lightpath routing and wavelength assignment subproblems can be viewd as having goals defined purely in terms of lightpaths.

Static Lightpath Establishment problem [I. Chlamtac, 1995]

Maximize wavelength utilization [C. Chen, 1995] Randomized rounding and graph coloring [D. Banerje

e 1996]

RWA Heuristics

38

Arbitrary TopologiesArbitrary Topologies

[R. Ramaswami, 1996] HLDA (Heuristic topology design algorithm) MLDA (Minimum-delay logical topology design algorithm) TILDA (Traffic Independent logical topology design algorith

m) LPLDA (LP-relaxation logical topology design algorithm) RLDA (Random logical topology design algorithm)

[D. Banerjee, 2000] Maximizing Single-Hop Traffic Maximizing Multihop Traffic

RWA Heuristics

39

Optical MulticastingOptical Multicasting

Multicasting at IP layer

Optical Multicasting

40


Multicasting by Lightpaths


41


Multicasting at WDM Layer (Light Tree Architecture)


42

Light Tree ArchitectureLight Tree Architecture

Application Optical multicast Enhanced virtual connectivity Traffic grooming

Steiner Tree Problem Shortest path-based heuristic (SPH) Spanning tree-based heuristic (STH) Metaheuristics


43

WDM Multicast ModeWDM Multicast Mode

[Y. Yang et al., 2000] Multicast with same wavelength

(MSW) Multicast with same destination

wavelength model (MSDW) Multicast with any wavelength

model (MAW)


44

MC-RWAMC-RWA

MC-RWA bears many similarities to the RWA problem.

The tight coupling routing and wavelength assignment remains and becomes stronger.

Physical topology design problem Resources placement [M. Ali and J. Deogun, 2000]

Virtual topology design problem Minimize call blocking probability Minimize the number of transceiver needed Minimize average packet hop distance


45

MC-RWA Researches (1/2)MC-RWA Researches (1/2)

[L. H. Sahasrabuddhe, 1999] An optimum light tree-based virtual topology has a lower valu

e of average packet hop distance than that of an optimum lightpath-based virtual topology

An optimum light tree-based virtual topology requires fewer opto-electronic components

Light forest [X. Zhang et al., 2000] Reroute-to-Source Reroute-to-Any Member-First Member-Only


46

MC-RWA Researches (2/2)MC-RWA Researches (2/2)

[Y. Sun et al., 2001] The USCH1 algorithm gives the worst network throughput

The wavelength continuity constraint limits the performance of the MSCH1 algorithm

The best approach is the MSCH2 if the wavelength converters are not available


47

Super-Lightpath RWASuper-Lightpath RWA

WDM + OTDM


48

Tree Shared MulticastTree Shared Multicast

[D. N. Yang and W. Liao, 2003] A light tree can carry data of multiple multicast streams, and

data of a multicast stream may traverse multiple light-trees to reach a receiver.

Multicast routing and wavelength assignment of light-trees Design of light-tree based logical topology for multicast strea

ms [郭至鈞，民國 92]

Multicasting group aggregation and MC-RWA Source-based tree aggregation Maximize the total revenue Lagrangian relaxation


49

Tree-Sharing StrategiesTree-Sharing Strategies

Given the set Mi at edge router i, we consider a strategy to decompose Mi into a number of MSCs (Multicast Sharing Class)

Perfect Overlap (PO), Super Overlap (SO), and Arbitrary Overlap (AO)


50

Optical Waveband SwitchOptical Waveband Switch

WBS has attracted attention for its practical importance in reducing port count, associates control complexity, and cost of photonic cross-connect.

In WBS networks, several wavelengths are grouped together as a band and switch as single entity using single port.

MG-OXC not only switch traffic at multiple granularities such as fiber, band, and wavelength, but also add and drop traffic at multiple granularities .

Multi-granularity Optical Networks

51

Multilayer MG-OXCMultilayer MG-OXC


Waveband Cross-connect(BXC)

Fiber Cross-connect(FXC)

Wavelength Cross-connect(WXC)

TX/RX block

BTFMux

BTWDemux

WTBMux

FTBDemux

FXClayer

BXClayer

WXClayer

FaddBdrop Wadd

Wdrop BaddFdrop

1

n

1

n

52

Single Layer MG-OXCSingle Layer MG-OXC


n

TX/RX block

FaddBdropWadd

WdropFdropBadd

FXC

BXC

WXC

1

2

1

2

n

m

53

Lightpath Grouping StrategyLightpath Grouping Strategy

End-to-end grouping: Grouping the traffic (lightpaths) with same source-destination

only One-end grouping:

Grouping the traffic between the same source (or destination) nodes and different destination (or source) nodes

Subpath grouping: Grouping traffic with common subpath (from any source to a

ny destination)


54

WRN vs. WBSWRN vs. WBS

WRN Minimum the number of wavelengths Minimum wavelength hops

WBS Minimum the number of ports

Waveband conversion


1λ

2λ

3λ

0λ

1λ

2λ

3λ

0λ

1λ

2λ

3λ

0λ

1λ

2λ

3λ

0λ

0b

1b

0b

1b

55

WBS Failure RecoveryWBS Failure Recovery

Band Merging

Band Swapping


1λ

2λ

3λ

5λ4λ

0λ

0b

1b

1λ

2λ

3λ

5λ4λ

0λ

0b

1b

56

Hierarchical Routing ModelHierarchical Routing Model

Network node architecture Sequence of routing and waveband aggregation Route Computation


Integrated routing

Separate routing

Offlinerouting

Onlinerouting

57

Researches of M. Lee et al. Researches of M. Lee et al.

Multi-Layer MG-OXC The waveband is formed by grouping lights with the same dest

ination in a network ILP formulation Maximize the reduction gain of crossconnect size with the mini

mum number of wavelengths Results

The introduction of waveband leads to a very large reduction in crossconnect requirements for large-scale networks.

A large reduction of crossconnect requirements can still be expected even at nonoptimal wavelength granularity.

The reduction depends on network topology, traffic demand and traffic pattern.


Integrated routing

Separate routing

Homog

eneo

us

netw

ork

Heter

ogen

eous

netw

ork

Offlinerouting

Onlinerouting

58

Researches of Y.Suemura et al. Researches of Y.Suemura et al.

Propose and analyze two heuristic routing and

aggregation algorithms (online and offline) to be used for homogeneous networks in separate routing framework.

Minimum the routing cost Assume that all the ports (OEO and optical ones) have the same

cost. The cost of routing is the total number of used ports.

The simulations demonstrate a significant cost reduction by employing hierarchical routing (from 33% in online algorithm to almost 60% in offline one)


Integrated routing

Separate routing

Homog

eneo

us

netw

ork

Heter

ogen

eous

netw

ork

Offlinerouting

Onlinerouting

59

Researches of X. Cao et al. Researches of X. Cao et al.

This research show that WBS is different from traditional wavelength, and thus techniques developed for wavelength-routed networks cannot be directly applied to effectively WBS-related problem.

The objective is to route lightpaths and assign appropriate wavelength to them so as the minimum the total number of prots required by the MG-OXCs.

Static offline problem (Network Planning) Balanced Path Routing with Heavy Traffic (BPHT)

Dynamic real-time problem (Network Servicing) Maximum Overlap Ratio (MOR)

Results BPHT: 50% fewer total ports than using ordinary OXCs MOR: 35 % saving in the number of ports


Integrated routing

Separate routing

Homog

eneo

us

netw

ork

Heter

ogen

eous

netw

ork

Offlinerouting

Onlinerouting

60

Researches of P. Ho et al. Researches of P. Ho et al.

Dynamic tunnel allocation (DTA) Use fixed alternative routing with k-shortest paths to inspect netwo

rks along each alternative path for dynamically setting up lightpaths.

Capacity-balanced static tunnel allocation (CB-STA) Fiber and waveband tunnels are allocated into networks at the pla

nning stage according to weighted network link-state.

Simulation Results DTA is outperformed by CB-STA in the same network environment

duo to a well-disciplined approach for allocating tunnels with CB-STA.

The mix of the two approaches yields the best performance given the same network environment apparatus.

Integrated routing

Separate routing

Homog

eneo

us

netw

ork

Heter

ogen

eous

netw

ork

Offlinerouting

Onlinerouting


61

Future Research TopicsFuture Research Topics

New optical component application Optical Multicasting

QoS Multicasting Tree Aggregation Problem Call Admission Control

WBS Converter and Splitter Placement Waveband Multicasting Heterogeneous WBS Network Survivability

Optical Packet Switch and Optical Burst Switch Passive Optical Network- EPON and GPON After the Optical Bubble?

Q & AQ & A

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Research Issues on Routing and Wavelength Assignment for Wavelength Routed WDM Networks Hsu-Chen, Cheng PhD. Student Department of Information Management