Infocom 2005, March 13-17, Miami
On Survivable Routing of Mesh
Topologies in
IP-over-WDM Networks
Maciej Kurant, Patrick Thiran
EPFL, Switzerland
Mapping
• Logical topology GL - mesh of IP links
GL
M
• Physical topology GΦ - mesh of
physical links (fibers)
• Each logical link is mapped on the
physical topology as a physical path
called a lightpath.
• We assume infinite capacities of fibers
GΦ
• Mapping M - a set of lightpaths
associated with a set of logical links
2
Survivability
GL
How to deal with failures?
M
There are several methods
• Protection vs restoration
• WDM layer vs IP layer
GΦ
We use only the IP restoration approach:
(The failures are detected at the IP layer,
and a new route is found dynamically.)
3
Link-survivability example
GL
GΦ
GL
GΦ
GL
GΦ
The logical topology remains conneceted after any single physical link failure
The mapping is link-survivable
4
Node-survivability example
Connected
GL
GΦ
Not connected!!
Connected
GL
GΦ
v*
v*
GL
GΦ
The failure of node v* disconnects the remaining logical topology GL\{v*}
The mapping is not node-survivable
5
The problem of finding a survivable
mapping is not new…
J. Armitage, O. Crochat, and J. Y. Le Boudec,
Design of a Survivable WDM Photonic Network,
Proceedings of IEEE INFOCOM 97, April 1997.
E. Modiano and A. Narula-Tam,
Survivable lightpath routing: a new approach to the design of WDM-based
networks, IEEE Journal on Selected Areas in Communications, vol. 20, no. 4, 2002
F. Giroire, A. Nucci, T. Taft, and C. Diot,
Increasing the Robustness of IP Backbones in the Absence of Optical Level
Protection, Proc. of IEEE INFOCOM 2003.
L-W. Chen and E. Modiano,
Efficient Routing and Wavelength Assignment for Recongurable WDM Networks
with Wavelength Converters, Proc. of IEEE INFOCOM’03.
…
6
Our solution
Contraction
GC=G C
G
e
b
f
c
a
d
g
e
g
f
h
Contraction of
C={a, b, c}
d
h
8
The SMART algorithm (link-survivability example)
GC
b
g
e
d
h
e
d
h
d
a
d
g
e
b
a
GΦ
GL
g
d
e
b
f
c
h
A single node!
GL
f
c
e
f
GL
b
GC
g
f
c
a
GC
e
f
c
a
h
GΦ
g
d
h
GΦ
Iteration
1
Iteration
2 GC converges
Iteration
Theorem
1: If the contracted
logical
topology
to 3
a single node,
9
then the mapping is (link/node)-survivable.
Verification of mapping existence
GC
g
e
d
a
g
h
d
h
d
GL
e
b
a
GL
g
d
e
b
f
c
e
f
f
c
GC
a
A node-survivable mapping
of the logical topology GL
on GΦ does not exist.
GΦ
g
d
e
b
f
c
h
GL
f
c
a
h
g
d
h
A node-survivable mapping
of the contracted topology
GC={e,d} does not exist.
GΦ
GΦ
Iteration
1
Iteration
2
3 iff any 10
Theorem
2: A (link/node)-survivable
mapping
of GLIteration
on GΦ exists
contracted topology GC can be mapped on GΦ in a (link/node)-survivable way.
Sequence of cycles does not matter!
b
GC
e
Application 1
SMART applied to the verification
of the existence of a link/nodesurvivable mapping
11
Verification of mapping existence (2)
SMART
- physical topology
- logical topology
SMART
converges
SMART does
not converge
Survivable
mapping found
Survivable
mapping
Exhaustive
search for GC
Contracted logical
topology GC
Survivable
mapping not found
Survivable mapping
not possible (proof)
12
Random graph on NSFNET
(a) Random graph on NSFNET
10
14
13
11
1
8
12
7
4
5
2
9
6
3
Random graph (2-node-connected)
10
14
13
11
1
8
12
7
4
5
Fraction of mapped topologies
1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
2
Unknown
0.1
3
6
NSFNET
9
0
2.3
2.5
2.7
2.9
3.1
3.3
3.5
Average node degree of random graph
13
Application 2
SMART applied to the fixing a
vulnerable topology (enabling
link/node-survivable mapping)
14
Where to introduce a new link?
GC
e
i
d
i
A new logical link which is a
self-loop in the contracted
topology GC will never help.
GL
e
b
g
Only a new logical link between
two different nodes in GC might
help.
f
a
i
d
h
i
In simulations (up to 64 nodes):
GΦ
• New logical link introduced at random
rarely helped (<10%)
• New logical link between two different
nodes in GC helped in more than 80%
of cases.
15
Applications of SMART (summary)
• The formal verification of the existence of a
link/node-survivable mapping,
• a tool tracing and repairing the vulnerable
areas in network,
• a fast heuristic.
16
Thank you!
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