Preserving Survivability During
Logical Topology Reconfiguration
in WDM Ring Networks
Hwajung Lee, Hongsik Choi,
Suresh Subramaniam,
and Hyeong-Ah Choi
The George Washington University
Supported in part by
DARPA under grant #N66001-00-18949
(Co-funded by NSA)
DISA under NSA-LUCITE Contract
NSF under grant ANI-9973098
Outline
Introduction – Network Survivability
Motivation
Problem Formulation
Problem Complexity
Simple Reconfiguration Approach
& its Limitation
MinCostReconfiguration Algorithm
Concluding Remarks
Introduction
Network Survivability
 To guarantee for users
to use the network
service without any
interruption.
 Each layer has its own
fault recovery functions.
 Fault propagation
IP
ATM
IP
IP
SONET/
SDH
SONET/
SDH
ATM
WDM Optical Network
Physical Fiber Plant
IP
Introduction
Survivable Logical Topology
Logical topology (Upper Layer) is called
survivable if it remains connected in the
presence of a single optical link failure.
 Faulty Model : Single optical link failure.
Introduction
Survivable Logical Topology
1 Optical Layer
0
0
= Physical Topo.
Survivable
Upper Layer
= Logical Topology
1
2
5
3
4
3
4
2
Desirable! 5
1
Not Survivable 0
Map each connection request
to an optical lightpath.
2
5
Electronic layer is connected
even when a single optical link fails
4
3
Introduction
Survivable Logical Topology
 Sometimes, there is no way to have a Survivable
Logical Topology Embedding
on a Physical Topology.
Optical Layer
= Physical Topo.
Electronic Layer
= Logical Topology
c
e2
b
…
…
a
e1
2-Edge Connected
d
a
c
d
b
Introduction
Survivable Logical Topology Design
Problem (SLTDP)
 Given
 a physical topology, and
 a logical topology = a set of connection requests.
 Objectives
 Find a route of lightpath for each connection
request, such that the logical topology remains
connected after a single link failure if possible.
 Otherwise, determine and embed the minimum
number of additional lightpaths to make the
logical topology survivable.
Introduction
H. Lee, H. Choi, S. Subramaniam, and H.-A. Choi,
“Survivable Logical Topology Design in WDM Optical
Ring Networks,” The 39th Annual Allerton Conference,
October 2001, Invited Paper
 Survivable LT design possible
 Completely connected (i.e., (n-1)-edge connected)
 NO survivable LT design when logical topology G is
 2-edge connected
 3-edge connected
 4-edged connected
 Degree Constraints
2n
 Survivable LT design possible when min. degree >= 3
n
 No survivable LT design for min. degree <= ( 2 -1)
 Experimental Results – Near Optimal
Motivation
Reconfiguration of Survivable
Logical Topologies
Survivable Logical Topology = G1
Survivable Logical Topology = G2
What if # of Wavelength < 3 or # of Ports < 3
0
1
0
1
3
2
3
2
# of Ports = 3
Physical Topology = Gp
0
3
# of Wavelength = 3
1
2
Delete G1\G2
Add G2\G1
to form G1  G2
Problem
Formulation
Reconfiguration of Survivable
Logical Topologies
 Given
Two Survivable Logical Topology G1 and G2
on a physical topology Gp
 Constraints
the number of port p, the number of wavelength W
 Objectives
During the entire period of reconfiguration,
(1) The logical topology remains survivable
(2) The port p and wavelength W constraints are
satisfied.
Problem
Complexity
Problem Complexity
 If no p or W constraint exists,
In General, the problem can be solved by
 Add G2\G1 to form G1  G2.
 Delete G1\G2.
 Except CASE 1 in the next slide.
 If the port and/or wavelength constraints exist(s),
more Complicated.
 CASE 2 and CASE 3.
Problem
Complexity
CASE 1
Need to change the directions of some lightpaths in G1  G2.
Logical topologies
Physical topology
1
6
6
6
1
5
1
5
2
4
2
4
5
2
4
3
3
3
Survivable
isolated
1
Survivable
1
6
2
5
3
4
6
2
5
3
4
Problem
Complexity
CASE
CASE 32
Need
and re-establish
some

Need to
to temporarily
temporarilydelete
add some
lightpaths not
in Glightpaths
1  G2
intoGguarantee
to survivability
Wavelength and
Constraints.
1  G2 duethe
delete later.
1
1
6
Physical
topology 2
6
5
6
1
5
Logical
topologies
5
4
3
2
3
4
2
4
3
?!
1
2
6
2
5
3
No !!
Yes
(W = 4)
3)
1
6
5
3
4
W = 3, p = 4
4
.
Reconfiguration Algorithm
Simple Reconfiguration Approach
If the current lightpath setup uses W-1 wavelength
in each optical link and upto p-2 ports at each node,
 add a lightpath btw
each pair of
adjacent nodes,
 delete all lightpaths
in G1 except the
above, and
 establish all
lightpaths in G2
based on its
survivable
embedding.
W = 4, p = 6
1
6
2
5
3
4
Reconfiguration Algorithm
Limitation
of Simple Reconfiguration Approach
n-k+2
n-k+1
n-k
1
2
3
4
...
n
...
...
W=k+1
Reconfiguration Algorithm
Algorithm
MinCostReconfiguration
Cost = # of add * UnitCostadd + # of delete * UnitCostdelete
 Given Input : M1, M2, Gp
 Output : Wadd,
Wadd = Wreconfig – max{WM1, WM2}
 Constraints
the number of port p, the number of wavelength W
 Objectives
(1) To minimize Wreconfig while reconfiguration cost is
preserved minimum.
(2) During the entire period of reconfiguration,
(1) The logical topology remains survivable
(2) The port p and wavelength W constraints are satisfied.
From
Wreconfig = max{ML1, ML2}
= 4 (= Winitial )
0
1
2
0
6
ML1 = 4
5
4
7
1
7
3
To
2
6
ML2 = 3
3
5
4
Wreconfig = 4
0
1
7
6
2
3
5
4
Wreconfig = 4
0
1
7
6
2
3
5
4
Wreconfig = 4
0
1
7
6
2
3
5
4
Wreconfig = 4
0
1
7
6
2
3
5
4
Wreconfig = 5
0
1
7
6
2
3
5
4
Wreconfig = 5
0
1
7
6
2
3
5
4
Wreconfig = 5
Wadd = Wreconfig - Winitial
=5–4=1
0
7
1
6
2
3
5
4
Results
Numerical Results
# of Simulations per each case = 500
n=8
10%
20%
30%
40%
50%
60%
70%
80%
90%
<W ADD >
<W M1>
<W M2>
Max Min Avg
Max Min Avg
Max Min Avg
1
0 0.008
8
4 5.784
8
3 5.464
2
0 0.068
8
3 5.770
7
3 5.388
2
0 0.100
8
3 5.692
8
3 5.380
2
0 0.122
8
4 5.806
8
3 5.282
2
0 0.076
8
4 5.800
8
3 5.368
2
0 0.062
8
3 5.796
8
3 5.180
2
0 0.092
8
3 5.772
7
3 5.086
2
0 0.064
8
3 5.772
8
3 4.850
1
0 0.066
8
4 5.750
7
3 4.736
Average
8 3.4 5.771 7.7
3 5.193
# o f Diff Co nn Req. Expected # o f Diff Co nn
(fro m Simulatio n) Req.(Calculated)
1.091
2.375
3.762
5.420
6.710
8.212
9.433
10.869
12.099
1.400
2.800
4.200
5.600
7.000
8.400
9.800
11.200
12.600
Results
Numerical Results
# of Simulations per each case = 500
n = 16
10%
20%
30%
40%
50%
60%
70%
80%
90%
<W ADD >
Max Min Avg
3
0 0.034
1
0 0.008
2
0 0.012
4
0 0.064
5
0 0.076
3
0 0.046
2
0 0.020
1
0 0.008
1
0 0.008
Average
<W M1>
<W M2>
Max Min Avg
Max Min Avg
21 10 14.588 19
8 13.360
20 11 14.668 20
7 13.026
21
9 14.698 20
7 14.330
22 10 14.726 19
9 14.586
20 10 14.528 19
9 14.536
21 10 14.610 20
9 14.426
21 10 14.624 19
6 14.182
22 10 14.594 19
7 13.158
21 10 14.506 20
9 13.332
21 10.0 14.616 19.4 7.9 13.882
# o f Diff Co nn Req. Expected # o f Diff Co nn
(fro m Simulatio n) Req.(Calculated)
5.971
12.155
17.790
24.118
29.923
35.977
42.221
47.889
54.062
6.000
12.000
18.000
24.000
30.000
36.000
42.000
48.000
54.000
Results
Numerical Results
# of Simulations per each case = 500
n = 32
10%
20%
30%
40%
50%
60%
70%
80%
90%
<W ADD >
Max Min Avg
3
0 0.104
3
0 0.114
4
0 0.140
2
0 0.074
3
0 0.094
4
0 0.086
3
0 0.084
3
0 0.046
7
0 0.056
Average
<W M1>
Max Min Avg
Max
52 34 42.742 52
52 33 42.988 54
54 35 43.100 52
52 34 43.020 52
53 34 42.896 56
52 34 42.714 52
52 35 42.710 56
53 34 42.834 53
54 34 42.824 53
53 34.1 42.870 53.3
<W M2>
Min Avg
34 42.802
32 42.716
35 42.916
34 42.802
34 42.896
36 42.634
34 42.468
34 42.614
33 42.822
34 42.741
# o f Diff Co nn Req. Expected # o f Diff Co nn
(fro m Simulatio n) Req.(Calculated)
24.904
49.400
74.557
98.931
124.731
148.447
173.743
198.260
223.142
24.800
49.600
74.400
99.200
124.000
148.800
173.600
198.400
223.200
Results
Numerical Results
DiffFactor = 2(|E(G1)-E(G2)|+|E(G2)-E(G1)|)/n(n-1)
500 Simulations for Each Case
0.160
Avg (n=8)
Avg (n=16)
# of Additional Wavelengths
0.140
0.140
Avg (n=32)
0.122
0.120
0.114
0.100
0.104
0.100
0.094
0.080
0.092
0.086 0.084
0.074 0.076
0.068
0.064
0.060
0.062
0.064 0.066
0.056
0.046
0.046
0.040
0.034
0.020
0.020
0.008 0.008
0.012
0.008 0.008
0.000
10%
20%
30%
40%
50%
60%
Difference Factor
70%
80%
90%
Concluding Remarks
Concluding Remarks
Develop Algorithms
 to guarantee min # of Wavelength
 to find a proper compromising point of
reconfiguration cost and the best number of
wavelength under the reconfiguration cost
constraint and the number of wavelength
constraint.