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Agile All-Photonic Networks and
Different Forms of Burst Switching
Gregor v. Bochmann
e-mail: [email protected]
School of Information Technology and Engineering (SITE)
University of Ottawa
Presentation given at the University of Stirling
Seminar sponsor: The Vodafone Foundation
August 8, 2003
© Gregor v. Bochmann, 2003
Agile All-Phoonic Networks and Different Forms of Burst Switching
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Abstract
In the context of a Canadian research network on agile all-photonic networks
(AAPN), we assume that very fast photonic space switches will be available
in the not-too-distant future and that the large bandwidth available over a
single optical wavelength can be shared among several traffic flows, which
means that the network performs multiplexing in the time domain and
dynamically allocates the available bandwidth to different traffic flows as
the demand varies. Our vision is a future agile all-photonic network (AAPN)
which provides transparent photonic transmission between edge nodes
that reside close to the end-user. The edge nodes perform the electicphotonic conversion and provide for agile sharing of the photonic
bandwidth among the different traffic flows. In this talk, we will give a
summary of our AAPN research program, provide some arguments for
considering a very simple network architecture based on overlaid stars,
and consider several modes of sharing the bandwidth of a single
wavelength. We consider in particular the burst switching mode and
present some new results on reducing the impact of contention losses.
© Gregor v. Bochmann, 2003
Agile All-Phoonic Networks and Different Forms of Burst Switching
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Background


Moore’s law: exponential increase of computing
speed
Similar law concerning communication


e.g. Ethernet: 10 Mbps, 100 (fast), 1Gbps, soon 10 Gbps
Optical transmission


Typically 10 Gbps per optical channel (soon 40 or 100)
Wavelength division multiplexing


Dense WDM: several hundreds of wavelengths
Data processing/switching


Electronic : opto-electronic conversion at each switch
Photonic: conversion only at edge nodes of network
© Gregor v. Bochmann, 2003
Agile All-Phoonic Networks and Different Forms of Burst Switching
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Overview






Switching principles
Protocol hierarchies and layering
User-controlled lightpath provisioning for
high-speed applications
Future “Agile All-Photonic Networks”
Some issues with burst switching
Conclusions
© Gregor v. Bochmann, 2003
Agile All-Phoonic Networks and Different Forms of Burst Switching
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Switching principles
frame
1
switch
3
2
4
Forwarding Table
Input
port, slot
Output
port, slot
1
1
3
2
1
2
4
3
2
2
3
1
© Gregor v. Bochmann, 2003
Agile All-Phoonic Networks and Different Forms of Burst Switching
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Establish long-term “connections”
(data flows)


Signaling: update forwarding tables
Routing table: given destination, find next hop
frame
1
switch
3
2
4
forwarding table entry
forwarding table entry
Forwarding Table
Input
port, slot
Output
port, slot
1
1
3
2
1
2
4
3
2
2
3
1
© Gregor v. Bochmann, 2003
forwarding table entry
forwarding table entry
Agile All-Phoonic Networks and Different Forms of Burst Switching
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Time sharing

Time division multiplexing (TDM)


each outgoing port has buffer for one frame
Asynchronous TDM = ATM


irregular arrival of data units (called “cells”)
need for header containing “channel number”


Channel number corresponds to time slot in TDM
buffers for several cells; buffer overflow leads
to data loss
© Gregor v. Bochmann, 2003
Agile All-Phoonic Networks and Different Forms of Burst Switching
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Packet switching (IP)

Advantages:



No identification of flows (no overhead for flow
establishment)
No forwarding table
Disadvantages


Header contains destination address (much longer
than channel number)
For each packet, the routing table must be consulted

Note: size of forwarding table is proportional to the switch
size – size of routing table is proportional to the network size
(various schemes have been designed to reduce the size of
the routing table: e.g. routing by prefixes)
© Gregor v. Bochmann, 2003
Agile All-Phoonic Networks and Different Forms of Burst Switching
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Learning from ATM

MPLS (Multi-protocol label switching):
establishing flows of IP packets


Optical Burst Switching



“label” plays the role of “channel number”
Burst = collection of IP packets
Burst header contains “channel number”
Networks with WDM and wavelength
conversion

wavelength plays the role of “channel number”
© Gregor v. Bochmann, 2003
Agile All-Phoonic Networks and Different Forms of Burst Switching
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Overview






Switching principles
Protocol hierarchies and layering
User-controlled lightpath provisioning for
high-speed applications
Future “Agile All-Photonic Networks”
Some issues with burst switching
Conclusions
© Gregor v. Bochmann, 2003
Agile All-Phoonic Networks and Different Forms of Burst Switching
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Protocol hierarchies
many variants
IP
many variants
© Gregor v. Bochmann, 2003
Agile All-Phoonic Networks and Different Forms of Burst Switching
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Internet infrastructure

routers/switches


IP and link (Ethernet) layers
physical links


physical layer
could be provided by






ATM over optical fiber
ATM over SONET
SONET (over optical fiber)
optical fiber
WDM over optical fiber
static or dynamic (agile – switching)
© Gregor v. Bochmann, 2003
Agile All-Phoonic Networks and Different Forms of Burst Switching
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Dynamic link establishment using
switched optical lightpaths
180.10.10.0
Optical Multiplexer
LO 5.5.5.1
1.1.1.1
LO 6.6.6.1
Router B
2.2.2.2
1.1.1.2
2.2.2.1
Router A
Router C
3.3.3.3
170.10.10.0
LO 7.7.7.1
4.4.4.4
3.3.3.4
4.4.4.3
AS 100
AS 200
190.10.10.0
AS 300
Optical switch (cross-connect)
© Gregor v. Bochmann, 2003
Agile All-Phoonic Networks and Different Forms of Burst Switching
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Optical cross-connects

Based on electronic switching and optoelectronic conversion



MEM switches (small mirrors)


Switching time: fast
Complex - expensive
Switching time: typically some milli-seconds
Other photonic switches
diffraction index)

(e.g. change of
Switching time: in the nano-seconds
© Gregor v. Bochmann, 2003
Agile All-Phoonic Networks and Different Forms of Burst Switching
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Overview






Switching principles
Protocol hierarchies and layering
User-controlled lightpath
provisioning for high-speed
applications
Future “Agile All-Photonic Networks”
Some issues with burst switching
Conclusions
© Gregor v. Bochmann, 2003
Agile All-Phoonic Networks and Different Forms of Burst Switching
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Network Design Parameters

Transmission
Bandwidth per wavelength : 10 Gbps
 Propagation delay for 1000km : 5 msec


Packetized data :
IP packet : 50 (PCM speech) to 64 koctets, average
10 kbits
 Burst : average 10 packets (100 kbits)

–> 10 μ sec transmission time



Over 1000km : 500 bursts in transit
If kept in buffer until confirmation of absense of collision : 1000
bursts (100 Mbits)
Switching time : lower than 1 μ sec
Note: this includes time for the synchronization of the
receiving clock
© Gregor v. Bochmann, 2003

Agile All-Phoonic Networks and Different Forms of Burst Switching
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Different types of bandwidth
sharing


The bandwidth of a single wavelength may be shared by
different data flow
Slotted (slot corresponds to fixed burst size):


Needs protocol to synchronize edge nodes with central switch
Three cases
1.
2.
3.
fixed allocation over lifetime of each flow : like TDM
Individually reserved slots (reservation requires round-trip delay
between edge node and switch)
Statistical multiplexing without reservation with contention for the
outgoing link
1.

There are different approaches to alleviate the contention problem (see later)
Unslotted

(variable sized bursts):
Several cases as above (but case 1 does not work)
© Gregor v. Bochmann, 2003
Agile All-Phoonic Networks and Different Forms of Burst Switching
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
Photonic vs. electronic switching
frame
Photonic TDM


Switch positions
change after each
time slot
Time slot in output
is the same as in
input

1
2
switch
3
4
Slotted operation of switch
(fixed data block sizes, like ATM,
However, buffers
requiring synchronized sources)
may be introduced in
or variable length bursts
the form of fiber
delay lines
© Gregor v. Bochmann, 2003
Agile All-Phoonic Networks and Different Forms of Burst Switching
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Overview

Switching principles
Protocol hierarchies and layering
User-controlled lightpath provisioning for
high-speed applications
Future “Agile All-Photonic Networks”

Some issues with burst switching

Conclusions



© Gregor v. Bochmann, 2003
Agile All-Phoonic Networks and Different Forms of Burst Switching
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Burst switching principle

Like ATM, but


header is sent over a separate fixed
wavelength channel that is converted into the
electrical domain and processed in order to
control the switch.
The switch forwards the data burst to an
appropriate output port (with updated header
sent over separate channel)
© Gregor v. Bochmann, 2003
Agile All-Phoonic Networks and Different Forms of Burst Switching
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Contention in burst switching



There are N outgoing ports for each neighbour
switch
For a given incoming burst, if there is no free
port to the next-hop neighbour found in the
forwarding table, there is contention
Possible actions in case of contention:



Drop the burst
Sent it to an different neighbour (deflection routing)
Store it in a buffer (like packet switching)
© Gregor v. Bochmann, 2003
Agile All-Phoonic Networks and Different Forms of Burst Switching
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How to reduce contention ?

Increase N



Reduce traffic load [Maach 03]


How low is reasonable (efficiency ??)
Introduce segmented bursts [Maach 02]



Install many fibers
Introduce wavelength conversion
Give earlier segments higher priority
Only part of the segments will be dropped
Prior reservation on a per burst basis



Control overhead
Additional reservation delay, especially for long-distance
networks
Further delay in case of contention
© Gregor v. Bochmann, 2003
Agile All-Phoonic Networks and Different Forms of Burst Switching
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Conclusions





Current economic low in the field of optical
networking
Up-turn expected in a few years: in the
meantime, new technical developments
Like CPU-power, bandwidth will be cheap
Fast switching is possible, allowing timeshared use of each wavelength channel
Simple, regular network architecture (e.g.
overlaid stars) simplifies network control
© Gregor v. Bochmann, 2003
Agile All-Phoonic Networks and Different Forms of Burst Switching
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Ongoing research projects




Improvements to burst switching
Synchronization issues in agile photonic
networks (star and other architectures)
Allocation of wavelength paths through
optical networks for inter-domain IP traffic
Protocols for routing and resource
management in photonic networks
© Gregor v. Bochmann, 2003
Agile All-Phoonic Networks and Different Forms of Burst Switching
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