Download Optical Burst Switching

Optical Burst Switching
CSIT 560 Internet Infrastructure: Switches and Router
Prepared By Eric Lo
Date: 6 Dec 2005
Agenda

Introduction
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
OBS Concept
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–
–
–
–
–

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
Introduction

Circuit Switching
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–
–

Bandwidth inefficient of bursty data (internet traffic).
Frequent long circuit setup
Waste bandwidth during off/low-traffic periods
Packet Switching
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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)
Introduction (Bursty traffic)

Left:
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Poisson traffic (voice)
smooth at large time scales
and mux degrees

Right:
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data (IP) traffic, bursty at all
time scales and large mux
degrees
circuit-switching not efficient
(max >> avg)
Motivation

Problems:
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–
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
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:
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Find a method between circuit switching and packet switching.
To increase the Bandwidth efficiency.
That’s Optical Burst Switching comes into the picture.
Agenda

Introduction
–
–

OBS Concept
–
–
–
–
–
–

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
OBS Concept

Burst Assembly (and Disassembly) at Edge
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
Burst Switching/Reservation Protocol
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
client data (e.g., IP packets) assembled into bursts
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)
Packet (a) and OBS(b) switching
Header recognition,
processing, and generation
Payload
C
Header
A
Setup
Synchronizer
1
2
A
New
headers
(a)
Control
wavelengths
Control
packets
D
C
2
2
O/E/O
1
Control packet processing
(setup/bandwidth reservation)
Offset time
2
B
2
FDL’s
1
Data
wavelengths
1
2
Fixed-length
(but unaligned)
B
Switch
1
Incoming
fibers
2
Switch
1
1
Data bursts
(b)
D
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
Burst Assembly – Step 1
Time or length
threshold is reached
Control channel
Assembly queues
for different egress
nodes
ATM Cell
IP Packet
SONET Frame
Data channel
Burst Assembly Node
Burst Assembly – Step 2
A CP is generated
and sent out
Control channel
Assembly queues
for different egress
nodes
ATM Cell
IP Packet
SONET Frame
Data channel
Burst Assembly Node
Burst Assembly – Step 3
Control channel
Assembly queues
for different egress
nodes
ATM Cell
IP Packet
SONET Frame
Data channel
Burst Assembly Node
Just-Enough-Time (JET)

An offset time between Control packet(CP) and
burst
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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.
JET – Step 1
Offset = T
CP arrives the OEO
node at time t1
OEO
OEO
OOO
OOO
JET – Step 2
CP goes through O/E
conversion and configure
switch fabric
OEO
OEO
OOO
OOO
JET – Step 3
CP goes through E/O
conversion and leaves
O/E/O node at time t1+
OEO
OEO
OOO
OOO
JET – Step 4
When burst arrives at
the intermediate node,
the switch fabric is
already configured
OEO
OEO
OOO
OOO
JET – Step 5
Offset = T- 
OEO
OEO
OOO
OOO
Without any delay, the
burst goes through the
optical switch fabric
JET – Offset time

Control packet can leave right after  = D  s (s
is the switch setting time)
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).
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.
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Without void filling (only use open interval such as
LAUC).
With void filling (Can minimize starting and ending
void such as LAUC-VF)
Burst Scheduling
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.
Ordered Scheduling
Content Resolution (1)


When multiple bursts compete for the same
output channel, how to avoid/reduce burst loss?
Three major strategies
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Deflection in space, time and wavelength
Preemption of an existing reservation
Segmentation of a burst into smaller pieces
Content Resolution (2)
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Deflection
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Space domain: applying deflection routing
Wavelength domain: use a different wavelength via
wavelength conversion
Time domain: wait using a fiber delay line
Segmentation
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Drops, deflects or preempts one or more segments
instead of an entire burst
QoS
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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.
QoS – New approach (PWRP)

Preemptive Wavelength Reservation Protocol
(PWRP)
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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.
QoS - PWRP
Potential Problem


Tends to have a high blocking probability
May require an uneconomically large increase
in network transmission capacity.
Agenda

Introduction
–
–

OBS Concept
–
–
–
–
–
–

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
Other Research

R&D activities in Japan
Other Research

Dual header optical burst switching (DOBS)
Other Research

Synchronous Optical Burst Switching (SOBS)
Other Research

A Layered Architecture for Supporting Optical
Burst Switching
References
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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
Thank you!