SIT
9
1
SIT



Today, there is a general consensus that in
near future wide area networks (WAN)(such
as, a nation wide backbone network) will be
based on Wavelength Division Multiplexed
(WDM) optical networks.
WDM comes under 3rd generation of network.
The concept of light tree is introduced in a
wavelength routed optical network, which
employs wavelength -division multiplexing
(WDM).
2
SIT


A lightpath is a point-to-point all-optical
wavelength channel connecting a transmitter
at a source node to a receiver at a destination
node.
A light-tree is a point-to-multipoint
generalization of a lightpath.
3
SIT




A light path is an all-optical channel, which
may be used to carry circuit switched traffic,
and it may span multiple fiber links.
It assign a particular wavelength to fiber link .
A light path can create logical (or virtual)
neighbors .
Light path communication employs equal no
of transmitters and receivers .
4
SIT


It extends the light path concept by
incorporating optical multicasting capability .
Light tree enables single-hop communication
between a source node and a set of
destination nodes.
5
SIT
6
SIT
7
SIT
Transceivers
Light path solution
4
6
8
4
1.59
1.58
1.58
5
1.48
1.38
1.38
6
1.42
1.32
1.30
Transceivers
Light tree solution
Wavelengths
4
5
6
Wavelengths
4
6
8
1.23
1.13
1.08
1.21
1.12
1.07
1.19
1.09
1.07
8
SIT


Multicast –capable wavelength routing
switches (MWRS) .
More optical amplifiers in the network to
maintain the optical signal power above a
certain threshold .
9
SIT

Po1=(1-α1)(1-α3) Pi1+(1-α2) α3Pi2 and
Po2=α1 (1-α4) Pi1+α1α4Pi2
10
SIT


A physical topology for light tree can be given
as ::
Gp=(V,Ep)
Gp: A weighted undirected graph
V: Set of network nodes
Ep: Set of links connecting nodes
The number of wavelength channels carried
by each fiber =W.
11
SIT


An NxN traffic matrix, where N is the number
of network nodes and the (i, j) th element is
the average rate of traffic flow from node i to
node j.
The number of wavelength tunable lasers (Ti)
and wavelength tunable filters (Ri) at each
node.
12
SIT

A virtual topology Gp=(V, Ep) as another
graph the out-degree of a node is the
number of transmitters at the node the nodes
of the virtual topology. In the virtual topology
correspond to the nodes in the virtual
topology, a link between nodes i, and j
corresponds to a light tree rooted at node i
with node j as one of the leaves on the light
Tree.
13
SIT


Optimization criterion –
Minimize one of the two objective functions:
1:Average packet hop distance
2:Total number of transceivers
required in the network
Constraints –
1:Constraints arising from limited number of
transceivers per node.
2:Constraints arising from limited number of
wavelengths.
3:Constraints arising from the limited
bandwidth of light tree.
14
SIT



Enables single-hop communication between a
source node and a set of destination nodes.
A light tree based virtual topology can
significantly reduce the hop distance, thereby
increasing the network throughput.
Enormous bandwidth of an optical fiber (up
to 50 terabits bits per second) because of
WDM
15
SIT


Light trees is capable of supporting
broadcasting and multicasting over a WAN by
employing a minimum number of
opto-electronic devices
Preliminary results show that if we employ a
set of light trees, then significant savings can
be achieved in terms of the number of optoelectronic devices that are required in the
network.
16
SIT





www.ieng.com/univercd/cc/td/doc/product/
softwares
www.seminartopics1.blogspot.com/2007/06
/light-tree.html
www.ieeexplore.ieee.org/iel5/8585/27205
www.springerlink.com/index
www.dspace.cusat.ac.in/dspace/bitstream
17
SIT
18
19