Lecture: 4 WDM Networks Design

1
Lecture 4 WDM Networks Design Operation
Ajmal Muhammad, Robert Forchheimer Information
Coding Group ISY Department
2
Outline

• Key Terminology in WDM Optical Network
• Different Core Network Topologies
• Designing Network Nodes
• Categorizations of WDM Networks
• Wavelength-routed and broadcast-and-select
• Static and dynamic
• Routing and Wavelength Assignment (RWA)
• Static, dynamic
• Grooming

3
Optical core Networks
4
Key Terminology in WDM Optical Networks

• Optical node/cross-connect/switch/router
• Optical node has a number of input (output)
  fibers, each carrying one or more incoming
  (outgoing) optical signals
• The purpose of which is to direct each incoming
  optical signal to an appropriate outgoing fiber
• End nodes all possible sources or destinations
  of data
• Physical topology graph showing the major
  physical components (i.e., fibers, nodes) of the
  network

5
Key Terminology.

• Lightpath optical connection from one end node
  to another, used to carry data in the form of
  encoded optical signals
• Logical/Virtual topology graph whose nodes
  indicate the end nodes and edges as lightpaths

From E1 to E3 From E2 to E4 From E1 to E2 From E3
to E4 From E4 to E1
Physical topology of WDM network with four end
nodes E1,..,E4, and four optical routers R1,..,R4
Lightpaths on physical topology
6
Logical/Virtual Topology
From E1 to E3 From E2 to E4 From E1 to E2 From E3
to E4 From E4 to E1
Corresponding logical topology
Lightpaths on physical topology
7
Topologies for core Networks
National scientific foundation (NSF) network
Optical cross-connect
8
Topologies for core Networks
14 nodes, 21 bidirectional links
European optical network topology
German network topology
9
Designing Network NodeExample

• 4 input and output fibers
• 32 wavelengths on each fiber
• Design the node such that
• 4 signals can be dropped/added
• Wavelengths are added/dropped through tunable
  transponders

14 nodes, 21 bidirectional links
10
Designing Network Node

• 4 Nos. of 1x32 DMUX
• 4 Nos. of 32x1 MUX
• 32 Nos. of 8x8 optical switch
• 1 144x144 optical switch
• 16 Nos. of transponder

14 nodes, 21 bidirectional links
11
Constructing a Large Switch from Smaller Switches
4 wavelength channels in fiber
Optical add-drop multiplexer (OADM)constructed
from MUX, DEMUX, a 6x6 optical switch, and 2
tunable transponders
How to construct an OADM with the same
functionality by using 4x4 switches ?
12
First Method
Constructing an OADM using 4x4 switches
4 wavelength channels in fiber
13
Second Method
Constructing an OADM using 4x4 switches
4 wavelength channels in fiber
14
Categorizations of WDM Networks

• Wavelength-routed and Broadcast-and-select
  networks
• Wavelength-routed optical signal is sent along
  a specified path and not broadcast to all nodes
  in the network
• Broadcast-and-select source end node selects an
  appropriate wavelength and broadcasts the data to
  be transmitted to all end nodes in the network
• Static and Dynamic lightpath allocation
• Static once the lightpaths are set-up between
  the ordered pairs of the end nodes, they will
  continue to exist for a relatively long period of
  time (months or years)
• Dynamic set-up on demand and, when the
  communication is over, the corresponding
  lightpath is taken down (i.e., no longer remain
  operational)

15
Categorizations of WDM.

• Single-hop and Multi-hop WDM networks
• Single-hop all data communication involves a
  path length of one logical edge, i.e., one
  lightpath is involved in each communication
• Single-hop networks are also called
  all-optical networks
• Multi-hop some data communication involves more
  than one lightpath

Multi-hop network
Single-hop network
16
Static Routing and Wavelength Assignment (RWA)

• Assumption The amount of traffic for each
  source-destination pair is in wavelength units
• Traffic Model Set of lightpaths to be
  established in the network is known in advance
• Constraint Any two lightpaths sharing the same
  physical link are assigned different wavelengths
• Objective Establish a set of lightpaths in such
  away to minimize the number of wavelengths used
  in the network
• Application Static RWA problem arises naturally
  in the design and capacity planning of an optical
  network

17
Static RWA

• Decompose into two sub-problems
• Routing
• Fixed routing
• Alternate routing
• Adaptive routing
• Wavelength assignment (WA)
• Random WA
• First-fit
• Least-used/SPREAD
• Most-used/PACK

18
WA Graph Coloring Problem

• Problem can be reduced to graph coloring
• Construct a graph G where nodes represents
  lightpaths, an edge exists between two nodes if
  the corresponding lightpaths pass through a
  common physical link
• Color the nodes in G such that no two adjacent
  nodes have the same color

2
3
1
4
5
6
Network with eight routed-lightpaths
Auxiliary graph for the lightpaths in the network
19
Static RWA a Layered Graph Approach

• Route and assign wavelength to each connection
  one by one
• Use layered graph to deal with wavelength
  continuity constraint
• Create W copies of the network graph, W number
  of wavelengths in a fiber
• RWA is solved by finding a path in one copy of
  the network graph
• Limited/fixed conversion add links between layers

20
Static RWA with Wavelength Conversion

• If each node has full wavelength conversion
  capability
• Only need solve routing problem
• Minimizing the maximum flow will minimize the
  number of wavelengths used

21
Dynamic RWA

• Traffic Model Service requests arrive to and
  depart from the network dynamically in a random
  manner
• Constraint Any two lightpaths sharing the same
  physical link are assigned different wavelengths
• Objective Route and assign wavelengths in such a
  way as to minimize the blocking probability of
  the network
• Application Dynamic RWA problem is encountered
  during the real-time network operational
  performance of the optical networks

22
Dynamic RWA Assumptions

• Each service request or call needs one wavelength
  units of transmission rate
• Service requests arrivals for source-destination
  pair form a Poisson process
• Source-destination pairs are uniformly
  distributed among all network nodes
• Each service request has the holding-time that is
  exponentially distributed
• Blocked calls are lost from the network there is
  no reattempt

23
RWA In General
24
Sub-wavelength Traffic Traffic Grooming

• So far we assume that each source-destination
  (s-d) pair has its traffic demand equal to an
  integer multiple of wavelength unit
• What if the traffic of an s-d equal to 0.3
  wavelength unit ?
• In this scenario, a single lightpath may carry
  multiple traffic streams from different s-d pairs
  
• Traffic grooming multiplexing several traffic
  streams onto a common lightpath
• Necessary for efficient wavelength channel
  usages

25
Traffic Grooming Strategies

• Aim Minimize electronic costs by reducing the
  number of add-drop multiplexers (ADMs) and make
  efficient use of wavelengths
• Each ADM can multiplex several lower rate streams
  to form a higher rate stream OR demultiplex a
  higher rate stream to several lower rate ones
• Employs O-E-O conversion
• Works at a particular wavelength
• ADM works on a single wavelength, if there are W
  wavelengths, every node would need NW ADMs

26
Example
Network Topology
a) Physical Network
b) Traffic on the Network
t1
0
1
0
1
t5
t6
fiber
t2
t4
2
3
3
2
t3
27
Traffic Grooming Approach1 (Random)
Total number of ADMs needed 8
28
Traffic Grooming Approach 2
Total number of ADMs needed 7
29
(No Transcript)