Light Reading

All-Optical Switching Tutorial, Part 1

Light Reading

This is the first of a pair of technology tutorials on all-optical switching by Geoff Bennett, vice president of technology advocacy at Marconi PLC (Nasdaq/London: MONI).

This tutorial covers the all-optical switches themselves – the various types, how they differ from electronic switches, where they sit in networks, what functions they perform, how they're controlled, and what they can and can't do.

The second tutorial covers optical switching fabric. In particular, it shows how different sizes and types of switch require different methods of routing light through their cores.

Both of these tutorials are based on a presentation given by Bennett at Opticon 2001, Light Reading's annual conference held in San Jose, Calif., in August of this year. Bennett would like to acknowledge the help of Peter Duthie, senior technical specialist, Marconi Optical Components, in preparing this presentation.

As a rule, Light Reading doesn't accept editorial contributions from manufacturers, but Bennett's tutorials provide valuable vendor-neutral insight into issues that have often been muddied by marketing hype.

In Bennett's view, the key to understanding all-optical switches is to consider the following issues in order:

Applications Identifying the purpose of an all-optical switch pinpoints key requirements in terms of scale, functions, and performance.

Techniques This covers how traffic is directed through the switch (the control plane) and the way in which it's handled (on its own dedicated wavelength or multiplexed with other traffic).

Technologies Dealt with in the second tutorial, this covers the fabric that routes optical pulses from input ports to output ports.

Here's a hyperlinked summary of this report:

Page 2: Basics

  • How optical and electronic switches work
  • Optical > analog > strange Page 3: OEO vs OOO

  • Why OEO is nothing new
  • How some optical cores have OEO add-ons Page 4: GMPLS Context

  • New taxonomy
  • Latest MPLS lingo Page 5: Applications

  • What switch goes where
  • Lambda, burst, and packet switching Page 6: Really Difficult Things

  • Reading at extreme speeds
  • Buffering optical packets Page 7: Lambda Switching

  • Manual versus automatic
  • Why "dynamic" is different Page 8: Optical Burst Switching

  • How it works
  • Lambda versus burst switching Page 9: Optical Packet Switching

  • An impossible dream?
  • Researchers push the limits Introduction by Peter Heywood, Founding Editor, Light Reading Next Page: Basics

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    User Rank: Light Beer
    12/5/2012 | 4:24:40 PM
    re: All-Optical Switching Tutorial, Part 1


    Is it possible to put the images in the tutorials by Geoff Bennett in "Light Readings" annual conference held in San Jose 2001.

    It is kind of difficult to learn without the images.

    It would be great help

    Thank you


    User Rank: Light Beer
    12/5/2012 | 1:20:38 AM
    re: All-Optical Switching Tutorial, Part 1
    Dear all,

    One problem in OBS is that it is very hard to do traffic engineering. I am very curious about the routing issues in OBS. Will it provide a single path for each source destination pair and update the routing table periodically, or provide multiple path candidates in the routing table?

    Other comments on OBS and wavelength routing are as follows:

    1. OBS is said to be better than the wavelength routing because it is able to multiplexing the data, thus more efficiently utilising the bandwidth. However, OBS is very bad at dealling with the blocking, whilst wavelength routing can provide guaranteed service upto a certain level.

    2. Therefore, it is very hard to say which is better actually. Current network status shows that there are far more sufficient network resources in the backbone. So it seems that bandwidth efficiency is not the biggest concern. From this point of view, dynamic wavelength routing seems more adoptable.

    User Rank: Light Beer
    12/5/2012 | 1:03:24 AM
    re: All-Optical Switching Tutorial, Part 1
    Dear Sir/Madam,

    Can we practically, think about an Optical Hybrid Switch which may contain "OBS" for short lived traffic or called best effort traffic and "OCS" for long-lived traffic or video conferencing etc.

    If we give strict priority to OCS traffic and equal priority to OCS traffic what could be possible discussions?

    User Rank: Light Beer
    12/4/2012 | 11:39:40 PM
    re: All-Optical Switching Tutorial, Part 1
    All-optical swtiching really can break the bottlenecks of the speed of transmission, but I would like to know how the header can be processed optcally. (Through optical Logic gate with syncronization processes?) - I just start working on this topic, and would like to learn more - thank you
    User Rank: Light Beer
    12/4/2012 | 11:38:20 PM
    re: All-Optical Switching Tutorial, Part 1
    Really hope that, someone would help~

    I am wonder that the header is still processed in the electronic domain. And so the processing time is still slow. Also OE-conversion is still needed in this processing.

    So, does OPS need OE-conversion?
    or my concept is not correct?

    Thank you very much
    User Rank: Light Beer
    12/4/2012 | 11:29:12 PM
    re: All-Optical Switching Tutorial, Part 1

    I want to know about current optical switching methods and MEMS method of optical switching.

    Please E mail the details of it.

    User Rank: Light Beer
    12/4/2012 | 11:06:28 PM
    re: All-Optical Switching Tutorial, Part 1

    As far as I know its really a research topic atm.

    The technique is quite new (1997), so there's still a lot of work to be done at the basis.

    Currently I only know of one 1 research project, which just started, that may apply obs to run over a fully optical router.

    For a starting point you might try :

    Can you tell me what work alcatel is doing on the topic (if any ?)

    happy new year,

    User Rank: Light Beer
    12/4/2012 | 11:04:14 PM
    re: All-Optical Switching Tutorial, Part 1
    At one time Alcatel were working on an SOA-based, broadcast & select switch.

    SOAs are quite a fast way to gate a B&S design, probably fast enough for OPS.

    There are some interesting drawbacks to using SOAs, however. These include both a significant noise component, and the fact that you introduce a polarisation dependency (which adds a few network design challenges).

    I'm planning an update to the article now and will include a more detailed description of broadcast and select (or gate), with both SOA and EDFA gating described.

    User Rank: Light Beer
    12/4/2012 | 10:21:18 PM
    re: All-Optical Switching Tutorial, Part 1
    KEOPS is undoubtedly the fore father in optical packet switch research and tonnes of research papers published after it. But with ATM diminishing and IP become the dominant player, there is really no point talking about KEOPS, WASPNET, ... what we need is an optical packet switch for IP packets.

    The problem with switching IP packets is that the packet size distribution is highly dynamic at any instant of time. TO buffer these packets, you will need the same dynamic mechanism in the buffers. And this is exactly the weak point of optics, the buffers are build up of dumb static optical delay line where the next buffer is fixed step increase of the previous buffer. In short we have a highly random packet size distribution at the input and a dumb buffer.

    What we need is what we don't have, repeating the facts stated in previous posted messages,there are no intelligence and no dynamic buffers. Unlesss there is breakthrough in this area, there's no ground breaking solution.
    User Rank: Light Beer
    12/4/2012 | 7:40:27 PM
    re: All-Optical Switching Tutorial, Part 1
    A1: For a connectionless OPS network, we send the packet header in-band with the data, but at a lower bit rate than the data.

    Is this concept similar to TDM rob-bit signaling?
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