© Gregor v. Bochmann, 2003Agile All-Phoonic Networks and Different Forms of Burst Switching

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Agile All-Photonic Networks andDifferent Forms of Burst

Switching

Gregor v. Bochmann

e-mail: bochmann@site.uottawa.ca

School of Information Technology and Engineering (SITE)

University of Ottawa

Presentation given at the University of StirlingSeminar sponsor: The Vodafone Foundation

August 8, 2003

© Gregor v. Bochmann, 2003Agile 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 electic-photonic 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, 2003Agile 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, 2003Agile 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, 2003Agile All-Phoonic Networks and Different Forms of Burst Switching

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Switching principles

1

2

3

4

Forwarding TableInputport, slot port, slot

Output

1 1 3 2

1 2 4 3

2 2 3 1

frame

switch

© Gregor v. Bochmann, 2003Agile 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

1

2

3

4

Forwarding TableInputport, slot port, slot

Output

1 1 3 2

1 2 4 3

2 2 3 1

frame

switch

forwarding table entry

forwarding table entry

forwarding table entry

forwarding table entry

© Gregor v. Bochmann, 2003Agile 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, 2003Agile 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, 2003Agile 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 “label” plays the role of “channel number”

Optical Burst Switching 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, 2003Agile 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, 2003Agile All-Phoonic Networks and Different Forms of Burst Switching

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Protocol hierarchies

many variants

many variants

IP

© Gregor v. Bochmann, 2003Agile 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, 2003Agile All-Phoonic Networks and Different Forms of Burst Switching

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Dynamic link establishment using switched optical lightpaths

Router A

Router B

Router C

AS 300AS 200

AS 100

2.2.2.2

2.2.2.1

1.1.1.1

1.1.1.2

170.10.10.0

180.10.10.0

190.10.10.0

3.3.3.34.4.4.4

3.3.3.4 4.4.4.3

LO 5.5.5.1

LO 6.6.6.1 LO 7.7.7.1

Optical Multiplexer

Optical switch (cross-connect)

© Gregor v. Bochmann, 2003Agile All-Phoonic Networks and Different Forms of Burst Switching

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Optical cross-connects

Based on electronic switching and opto-electronic conversion Switching time: fast Complex - expensive

MEM switches (small mirrors) Switching time: typically some milli-

seconds Other photonic switches (e.g. change of

diffraction index) Switching time: in the nano-seconds

© Gregor v. Bochmann, 2003Agile 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, 2003Agile 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, 2003Agile 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 cases1. fixed allocation over lifetime of each flow : like TDM2. Individually reserved slots (reservation requires round-trip

delay between edge node and switch) 3. 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, 2003Agile All-Phoonic Networks and Different Forms of Burst Switching

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Photonic vs. electronic switching

Photonic TDM Switch positions

change after each time slot

Time slot in output is the same as in input

However, buffers may be introduced in the form of fiber delay lines

1

2

3

4

frame

switch

Slotted operation of switch (fixed data block sizes, like ATM, requiring synchronized sources)or variable length bursts

© Gregor v. Bochmann, 2003Agile 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, 2003Agile 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, 2003Agile 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, 2003Agile All-Phoonic Networks and Different Forms of Burst Switching

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How to reduce contention ? Increase N

Install many fibers Introduce wavelength conversion

Reduce traffic load [Maach 03] How low is reasonable (efficiency ??)

Introduce segmented bursts [Maach 02] 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, 2003Agile 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 time-

shared use of each wavelength channel Simple, regular network architecture (e.g.

overlaid stars) simplifies network control

© Gregor v. Bochmann, 2003Agile 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