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

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

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

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.

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.

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

Introduction

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

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

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.

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.

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

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 

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.

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

OBS JET Offset Time Delayed Reservation (DR)

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

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

Without FDLs t01 > l0

With FDLs

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

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

Performance Issues

Performance Issues

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

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