ITU Kaleidoscope 2013
Building Sustainable Communities
PROPOSAL OF A SUB-λ SWITHING
NETWORK AND ITS TIME-SLOT
ASSIGNMENT ALGORITHM FOR
NETWORK WITH ASYNCHRONOUS
TIME-SLOT PHASE
Keisuke Okamoto
Kyoto University
okamoto@cube.kuee.kyoto-u.ac.jp
Kyoto, Japan
22-24 April 2013
A label of contents
 Sub-λ
switching network
 Multi-time-slot bonding
 Global-time-based scheduling
 Simulation analysis
Kyoto, Japan, 22-24 April 2013
ITU Kaleidoscope 2013 – Building Sustainable Communities
1/11
Sub-λ switching network architecture


All nodes are operated synchronously under a certain timecontrol mechanism
The scheduler creates a schedule table, which controls the
timing of optical time-slot switching
Merit
・Low power consumption
・fine granularity
・headerless
Kyoto, Japan, 22-24 April 2013
ITU Kaleidoscope 2013 – Building Sustainable Communities
2/11
Time-slot flow
in sub-λ switching network

Time-slot arrive at the optical switch with a certain propagation
delay
Kyoto, Japan, 22-24 April 2013
ITU Kaleidoscope 2013 – Building Sustainable Communities
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Operation technique
multi time-slot bonding

Multiple optical bursts to the same destination are allocated
in the successive time slots without guard-time
single
3
Multi
Time-slot
Frame length
3
3
3
3
2
condense
3 3 3 3 3
Kyoto, Japan, 22-24 April 2013
ITU Kaleidoscope 2013 – Building Sustainable Communities
2
2
1
Gurad-time
2 2 2
1
Time
4/11
Problem
time-slot assignment

We have to add fiber cable for one time-slot duration at
worst case to adjust transmission delay
(ex:around 2km fiber for a 10 μs time-slot)
objective

Reducing unused time
approach


Scheduling algorithm
under 1 time-slot length
Delay shift packing
algorithm
5/11
Approach
global-time-based scheduling


Reference node is selected in the network
We shift the time-slot-search start point by the value of
propagation delay
Reference node
1
2
3
node
2→3
time
Time
Propagation
delay
node
1→2
FirstFit
time
Time-slot-based optical burst allocation is efficient when empty
time-slots are successive
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Shift decision
Shift：time-slot position in frame


We preselect reference node in the network
We calculate shift volume from propagation delay between
node i and reference node
node
3→7
φ3+φ5
5
φ3
2
6
0
3
1
4
Reference node
φ3+φ7
7
8
φ3
Time
node
3→5
φ3
Time
node
1→3
FirstFit
Time
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Shift lag

We cannot calculate shift volume specifically in complicated
network
upstream
downstream
3
D32
D23
1
D12
D21
－(D21+D32)
0
D24
2
4
D42
Reference node 2
3
D21
2
1
0
－(D21+D32)
or
D12－D32
4
D12
D12+D24
Reference node 1
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Simulation setup

Performance metric(increase ratio of minimum time-slot)=
 T:required number of time-slots determined using the timeslot assignment algorithm
 Tmax:required number of time-slots to accommodate all data
on the most heavy link determined by routing
Simulation model



Toplogy:NSFNET(the number on the link is propagation delay [ms])
Traffic:1～995 Mbps at random
routing:shortest path(metric is hop count)
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Result

Global time based scheduling improve the effective time of
network capacity
(local-time based scheduling: time-slot-search start point=0)
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Conclusion

We proposed a sub-λ switching network, which is
all-optical, achieving finer granularity than a λ
switching network

We also proposed a multi-time-slot bonding
technique and delay shift packing

We simulated time-slot scheduling in NSFNET and
demonstrated the efficiency of these algorithm
Kyoto, Japan, 22-24 April 2013
ITU Kaleidoscope 2013 – Building Sustainable Communities
11/11