1. Optical Burst Switching
CSIT 560 Internet Infrastructure: Switches and Router
Prepared By Eric Lo
Date: 6 Dec 2005

2. Agenda Introduction OBS Concept Other research Basic Motivation
Burst Assembly
Just Enough Time (JET)
Scheduling
Content Resolution
QoS
Potential problem
Other research
R&D activities in Japan
Dual header OBS
Synchronized OBS
Layered Architecture

3. Introduction Circuit Switching Packet Switching
Bandwidth inefficient of bursty data (internet traffic).
Frequent long circuit setup
Waste bandwidth during off/low-traffic periods
Packet Switching
A packet contains a header (e.g., addresses) and the payload (variable or fixed length).
Each node needs to buffer, process the header, and send it to the next hop.
Statistic sharing of link BW among packets with different source/destination (Statistical multiplexing)

4. Introduction (Bursty traffic)
Left:
Poisson traffic (voice)
smooth at large time scales and mux degrees
Right:
data (IP) traffic, bursty at all time scales and large mux degrees
circuit-switching not efficient (max >> avg)

5. Motivation Problems: Solution:
Explosive traffic growth and bursty Traffic pattern
Lack of optical buffer (RAM) for packet switching.
Fiber delay lines (FDLs) are bulky and provide only limited & deterministic delays
Need fast processing power of header and payload
Solution:
Find a method between circuit switching and packet switching.
To increase the Bandwidth efficiency.
That’s Optical Burst Switching comes into the picture.
Data traffic growth still doubling every year

6. Agenda Introduction OBS Concept Other research Basic Motivation
Burst Assembly
Just Enough Time (JET)
Scheduling
Content Resolution
QoS
Potential problem
Other research
R&D activities in Japan
Dual header OBS
Synchronized OBS
Layered Architecture

7. OBS Concept Burst Assembly (and Disassembly) at Edge
client data (e.g., IP packets) assembled into bursts
Burst Switching/Reservation Protocol
Control packet (CP) sent an offset time t ahead of burst
Dedicated control channel (out-of-band signaling) for CP
No fiber delay lines (FDLs) nor O/E/O conversions for burst at any intermediate (core) nodes
Photonic Burst Switching Fabric inside Core
Leverages the best of optics (for burst switching) and electronics (for CP processing and fabric control)

8. Packet (a) and OBS(b) switching

9. Optical Burst Switching Node
Multiple data channels share one control channel. Data bursts remain in optical domain while CPs go through O/E/O conversions

10. Burst Assembly – Step 1 Control channel Data channel
Time or length
threshold is reached
Control channel
Assembly queues
for different egress
nodes
Data channel
Burst Assembly Node
ATM Cell
SONET Frame
IP Packet

11. Burst Assembly – Step 2 Control channel Data channel
A CP is generated and sent out
Control channel
Assembly queues
for different egress
nodes
Data channel
Burst Assembly Node
ATM Cell
SONET Frame
IP Packet

12. Burst Assembly – Step 3 Control channel Data channel
Assembly queues
for different egress
nodes
Data channel
Burst Assembly Node
ATM Cell
SONET Frame
IP Packet

13. Just-Enough-Time (JET)
An offset time between Control packet(CP) and burst
No fiber delay line (FDL) required to delay the burst when CP is processed and switch fabric is configured.
CP carries the burst length information
Facilitates delayed reservation (DR) for intelligent, efficient allocation of BW and FDL (if any), including look-ahead scheduling.

14. JET – Step 1 OOO OOO OEO OEO CP arrives the OEO node at time t1
Offset = T
OOO
OEO
OOO
OEO

15. JET – Step 2 OOO OOO OEO OEO CP goes through O/E
conversion and configure
switch fabric
OOO
OEO
OEO
OOO

16. JET – Step 3 OOO OOO OEO OEO CP goes through E/O conversion and leaves
O/E/O node at time t1+
OOO
OEO
OOO
OEO

17. JET – Step 4 OOO OOO OEO OEO
When burst arrives at the intermediate node, the switch fabric is already configured

18. JET – Step 5 OOO OOO OEO OEO Offset = T- 
Without any delay, the burst goes through the optical switch fabric

19. JET – Offset time
Control packet can leave right after d = D – s (s is the switch setting time)

20. Delayed Reservation (DR)
DR leads to efficient allocation of BW and any available FDLs (though not shown). Without DR, 2nd burst will be dropped in both cases (and FDLs will be wasted in Case 2).

21. Burst Scheduling
In general approach, it is to schedule incoming bursts in the order of the CP arrivals. It leaves several free time intervals between the scheduled reservations called void.
Without void filling (only use open interval such as LAUC).
With void filling (Can minimize starting and ending void such as LAUC-VF)

22. Burst Scheduling

23. Burst Scheduling – New approach
Ordered Scheduling is to schedule bursts in the order of the burst arrivals instead of header arrivals.
It places incoming reservations in a buffer and defers the scheduling until just before the actual burst arrives.
Able to remove the negative effect of header arrival dynamics.

24. Ordered Scheduling

25. Content Resolution (1)
When multiple bursts compete for the same output channel, how to avoid/reduce burst loss?
Three major strategies
Deflection in space, time and wavelength
Preemption of an existing reservation
Segmentation of a burst into smaller pieces

26. Content Resolution (2) Deflection Segmentation
Space domain: applying deflection routing
Wavelength domain: use a different wavelength via wavelength conversion
Time domain: wait using a fiber delay line
Segmentation
Drops, deflects or preempts one or more segments instead of an entire burst

27. QoS
Different offset time is assigned to different service classes over JET OBS networks so as to provide differentiated services in terms of burst loss probability for classes of different priorities.
Difficult to maintain the same offset time in all routers.
May starve lower priority bursts because higher priority bursts always have more opportunities to make wavelength reservation
It may be unfair to long bursts of low priority because it is hard to find a long gap to serve a long burst of low priority in an almost full schedule table.

28. QoS – New approach (PWRP)
Preemptive Wavelength Reservation Protocol (PWRP)
Each class is associated with a predefined usage limit. Each switch maintains a usage profile for a class per output link and monitors the current usage of each class.

29. QoS - PWRP

30. Potential Problem Tends to have a high blocking probability
May require an uneconomically large increase in network transmission capacity.

31. Agenda Introduction OBS Concept Other research Basic Motivation
Burst Assembly
Just Enough Time (JET)
Scheduling
Content Resolution
QoS
Potential problem
Other research
R&D activities in Japan
Dual header OBS
Synchronized OBS
Layered Architecture

32. Other Research
R&D activities in Japan

33. Other Research
Dual header optical burst switching (DOBS)

34. Other Research
Synchronous Optical Burst Switching (SOBS)

35. Other Research
A Layered Architecture for Supporting Optical Burst Switching

36. References OBS Forum tutorial slides by Chunming Qiao
R. Parthiban, C. Leckie, A.Zalesky, AV.Tran*, Does Optical Burst Switching have a role in Core Network ?
Farid, Vinod, Joel, A Layered Architecture for Supporting Optical Burst Switching
Sami Sheeshia, Chun Qiao, Synchronous Optical Burst Switching
Neil Barakat and Edward H Sargent, Dual Header Optical Burst Switching: A New Architecture for WDM Burst-Switched Networks
Ken, etal., Photonic Network R&D Activities in Japan
Wanjiun Liao, Chi-Hong Loi, Providing Service Differentiation for Optical-Burst-Switched Networks

37. Thank you!