1. A Survey of Optical Burst Switching in the Next-Generation Optical Internet

2. Outline Introduction Switching Techniques Optical Burst Switching
QoS Support in All-Optical Networks
Performance Issues
Conclusions 

3. Introduction Introduction IP runs over all-optical WDM layer
Challenging issues
How to support QoS?

4. Introduction
New optical switches/routers (hardware) are being built for the next-generation optical Internet.
The huge bandwidth of fiber optic networks
Due to DWDM (dense wavelength-division multiplexing ) technique
Data transmitted optically has to be slowed down at each node if it is to be switched electronically.

5. Introduction IP over WDM No optical form of RAM available today
Transport IP packets directly over the optical layer without any O/E/O conversion.
No optical form of RAM available today
Novel protocols (software) running on top of optical switches/routers are needed.

6. Introduction Challenging issues
The current lack of optical random access memory
The requirement for synchronization
How to provide basic QoS support?

7. Introduction

8. Switching Techniques Switching Technique Wavelength routing
Optical packet switching
Optical burst switching

9. Switching Techniques Wavelength routing Advantages: Limitations:
Two-way reservation is needed to setup lightpaths
Advantages:
No optical buffer or O/E/O conversion of data is needed.
Limitations:
Low bandwidth utilization
There are not enough wavelengths in the fiber to enable full mesh connectivity
Setting up and tearing down a lightpath would take at least several tens of milliseconds

10. Switching Techniques Optical packet/cell switching
The payload(data) is sent along with its header without setting up a path
Each packet needs to be buffered
Due to the tight coupling in time between the payload and header, store-and-forward nature
The size of the payload is too small given the high channel bandwidth of optical networks, resulting in relatively high control overhead.

11. Switching Techniques Optical burst switching
Combines the best of circuit and packet switching while avoiding their shortcomings.
One-way reservation. (a data burst follows a corresponding control packet without waiting for an acknowledgment)
Control can be performed electronically, but data can be switched optically.
A burst will cut through intermediate nodes without being buffered.

13. Switching Techniques Low High Medium Optical switching paradigm
Bandwidth utilization
Latency (including setup)
Implementation difficulty
Adaptivity (to traffic and fault)
Wavelength
Low
High
Packet/cell
OBS
Medium

14. OBS Optical Burst Switching
Open-ended
TAG ( tell-and-go )
IBT ( in-band-terminator )
Close-ended
JET ( just-enough-time )
Differ mainly in the way that bandwidth release is triggered 

15. OBS TAG (tell-and-go) IBT (in-band-terminator)
The source node sends a release packet
IBT (in-band-terminator)
A burst contains an IBT (e.g., silence in a voice circuit), and bandwidth is released as soon as the IBT is detected.

16. OBS
JET (just-enough-time)
T(i) = T - Σδ(h)

17. OBS
JET
Offset Time
Delayed Reservation (DR)

18. QoS Support QoS Support in All-Optical Networks Without FDLs With FDLs
( FDL : fiber delay line )

19. QoS Support
QoS scheme
Critical data can be transported at the WDM layer more reliably than noncritical data.
Intraclass contentions and interclass contentions

20. Without FDLs
t01 > l0

21. With FDLs

22. Multiple Classes
tdiff : the difference in the offset times assigned to class i and class (i-1)
R : The lower bound of the isolation degree

23. Performance Issues Performance Issues Blocking probability
Queuing delay and end-to-end latency

24. Performance Issues

25. Performance Issues

26. Performance Issues
The impact of the extra offset time, depends on the number of classes, and the offset time difference (tdiff)used.
The mean burst size : 15 kbytes
10 Gb/s => L = 12 μs
Service classes (n) : 4
tdiff = 3L (at least 95% class isolation)
Maximum additional delay = 108 μs (n -1) * tdiff

27. Conclusions The integration of IP and WDM
Overview of Optical Burst Switching
Achieving a balance between wavelength routing and optical packet switching
Without requiring buffering at the WDM layer
Support QoS in optical networks
An OBS protocol : JET
The use of offset time and DR