Agile All-Phoonic Networks and Different Forms of Burst Switching 1 © Gregor v. Bochmann, 2003 Agile All-Photonic Networks and Different Forms of Burst Switching Gregor v. Bochmann 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

Agile All-Phoonic Networks and Different Forms of Burst Switching 2 © Gregor v. Bochmann, 2003 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.

Agile All-Phoonic Networks and Different Forms of Burst Switching 3 © Gregor v. Bochmann, 2003 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

Agile All-Phoonic Networks and Different Forms of Burst Switching 4 © Gregor v. Bochmann, 2003 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

Agile All-Phoonic Networks and Different Forms of Burst Switching 5 © Gregor v. Bochmann, 2003 Switching principles Forwarding Table Input port, slot Output frame switch

Agile All-Phoonic Networks and Different Forms of Burst Switching 6 © Gregor v. Bochmann, 2003 Establish long-term “connections” (data flows) Signaling: update forwarding tables Routing table: given destination, find next hop Forwarding Table Input port, slot Output frame switch forwarding table entry

Agile All-Phoonic Networks and Different Forms of Burst Switching 7 © Gregor v. Bochmann, 2003 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

Agile All-Phoonic Networks and Different Forms of Burst Switching 8 © Gregor v. Bochmann, 2003 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)

Agile All-Phoonic Networks and Different Forms of Burst Switching 9 © Gregor v. Bochmann, 2003 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”

Agile All-Phoonic Networks and Different Forms of Burst Switching 10 © Gregor v. Bochmann, 2003 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

Agile All-Phoonic Networks and Different Forms of Burst Switching 11 © Gregor v. Bochmann, 2003 Protocol hierarchies many variants IP

Agile All-Phoonic Networks and Different Forms of Burst Switching 12 © Gregor v. Bochmann, 2003 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)

Agile All-Phoonic Networks and Different Forms of Burst Switching 13 © Gregor v. Bochmann, 2003 Dynamic link establishment using switched optical lightpaths Router A Router B Router C AS 300 AS 200 AS LO LO LO Optical Multiplexer Optical switch (cross-connect)

Agile All-Phoonic Networks and Different Forms of Burst Switching 14 © Gregor v. Bochmann, 2003 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

Agile All-Phoonic Networks and Different Forms of Burst Switching 15 © Gregor v. Bochmann, 2003 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

Agile All-Phoonic Networks and Different Forms of Burst Switching 16 © Gregor v. Bochmann, 2003 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

Agile All-Phoonic Networks and Different Forms of Burst Switching 17 © Gregor v. Bochmann, 2003 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. fixed allocation over lifetime of each flow : like TDM 2. 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)

Agile All-Phoonic Networks and Different Forms of Burst Switching 18 © Gregor v. Bochmann, 2003 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 frame switch Slotted operation of switch (fixed data block sizes, like ATM, requiring synchronized sources) or variable length bursts

Agile All-Phoonic Networks and Different Forms of Burst Switching 19 © Gregor v. Bochmann, 2003 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

Agile All-Phoonic Networks and Different Forms of Burst Switching 20 © Gregor v. Bochmann, 2003 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)

Agile All-Phoonic Networks and Different Forms of Burst Switching 21 © Gregor v. Bochmann, 2003 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)

Agile All-Phoonic Networks and Different Forms of Burst Switching 22 © Gregor v. Bochmann, 2003 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

Agile All-Phoonic Networks and Different Forms of Burst Switching 23 © Gregor v. Bochmann, 2003 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

Agile All-Phoonic Networks and Different Forms of Burst Switching 24 © Gregor v. Bochmann, 2003 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