Switching Architectures for Optical Networks by m4S53q8c

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									Switching Architectures
 for Optical Networks

         CSIT560 by M. Hamdi   1
                             Internet Reality


                               M                          DWD


         Access                        Long Haul            Metro       Access

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Hierarchies of Networks: IP / ATM /
          SONET / WDM

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                    Why Optical?
• Enormous bandwidth made available
   – DWDM makes ~160 channels/ possible in a fiber
   – Each wavelength “potentially” carries about 40 Gbps
   – Hence Tbps speeds become a reality
• Low bit error rates
   – 10-9 as compared to 10-5 for copper wires
• Very large distance transmissions with very little

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    Dense Wave Division Multiplexing

                                 Long-haul fiber
  Output fibers

Multiple wavelength bands on each fiber
   Transmit by combining multiple lasers @ different

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              Anatomy of a DWDM System

     Terminal A                                              Terminal B

Transponder   M                                                E    Interfaces
              U                                                M
              X                                                U
                  Post-         Line Amplifiers       Pre-     X
                  Amp                                 Amp

  Direct                                                             Direct
Connections                                                        Connections

                          Basic building blocks
                           • Optical amplifiers
                           • Optical multiplexers
                           • Stable optical sources

                               CSIT560 by M. Hamdi
       User Services & Core Transport

                EDGE                              CORE

Frame Relay              Frame    OC-3

                         Relay    OC-3
               Router             OC-12
      ATM                Switch
                         Sonet    STS-1
Lease Lines                       STS-1
                TDM      ADM

Users         Service Provider            Transport Provider
Services      Networks                    Networks

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• Provisioned           Core Transport Services
SONET circuits.

• Aggregated into     Circuit

• Carried over
Fiber optic cables.

             OC-3                                     Circuit
             OC-3                                     Destination


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              WDM Network: Wavelength View

                               WDM link

                                                     Edge Router

( e.g.,   PoS, Gigabit                                   Interfaces
  Ethernet, IP/ATM)


                                    Optical Switch

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              Relationship of IP and Optical
• Optical brings
     –Bandwidth multiplication
     –Network simplicity (removal of
     redundant layers)
• IP brings
     –Scalable, mature control plane
     –Universal OS and application
     –Global Internet
• Collectively IP and Optical
  (IP+Optical) introduces a set of
  service-enabling technologies

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                  Typical Super POP

                                            Core    SONET
     Core        Large
       IP     Multi-service    Voice        ATM
     router   Aggregation      Switch      Switch

                              OXC                     Coupler
DWDM                                                    &
 Metro   +                                            Opt.amp
 Ring ADM
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    Typical POP


W    OXC                             D

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     What are the Challenges with Optical
• Processing: Needs to be done with electronics
   – Network configuration and management
   – Packet processing and scheduling
   – Resource allocation, etc.
• Traffic Buffering
   – Optics still not mature for this (use Delay Fiber Lines)
   – 1 pkt = 12 kbits @ 10 Gbps requires 1.2 s of delay => 360
     m of fiber)
• Switch configuration
   – Relatively slow

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                      Optical Hardware
• Optical Add-Drop Multiplexer (OADM)
   – Allows transit traffic to bypass node optically

             1                                        1
             2                  OADM                  2
             3                                        ’3

                                  3   ’3

          Add and Drop


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                      Wavelength Converters
• Improve utilization of available wavelengths on links
• All-optical WCs being developed
• Greatly reduce blocking probabilities
        2                  3                                      3


                 No  converters                        With  converters

    1   New request                       1   New request
          1 3                                  1 3

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                    Late 90s: Backbone Nodes





                                       Digital Crossconnect

Multiplexer & Demultiplexer     IP                             ATM
                              Router                          Switch

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• About 80% traffic through each node is “pass-
   – No need to electronically process such traffic

• 80-channel DWDM requires 80 ADMs

• Speed upgrade requires replacing all the ADMs in
  the node

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          Today: Optical Cross Connect (OXC)



                                ATM           Digital        Terabit
                              Backbone        Cross            IP
                               Switch        Connect         Router

Multiplexer & Demultiplexer
                                           IP        ATM
                                         Router     Switch

                                                                       Source: JPMS
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    Wavelength Cross-Connects (WXCs)
• A WDM network consists of wavelength cross-connects (WXCs) (OXC)
  interconnected by fiber links.
• 2 Types of WXCs
   – Wavelength selective cross-connect (WSXC)
       • Route a message arriving at an incoming fiber on some
         wavelength to an outgoing fiber on the same wavelength.
       • Wavelength continuity constraint
   – Wavelength interchanging cross-connect (WIXC)
       • Wavelength conversion employed
       • Yield better performance
       • Expensive

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                      Wavelength Router
                                                       Wavelength Router

 Control Plane:
Wavelength Routing

   Data Plane:
  Optical Cross
  Connect Matrix

          DWDM Links to                                   Unidirectional
         other Wavelength                                DWDM Links to
                             Single Channel Links to    other Wavelength
                             IP Routers, SDH Muxes,         Routers
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                  Optical Network Architecture

                        Mesh Optical Network
              UNI                                  UNI
IP Network                                               IP Network

      IP Router
                         OXC Control unit           Control Path

      Optical Cross                                 Data Path
     Connect (OXC)

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                OXC Control Unit
• Each OXC has a control unit
• Responsible for switch configuration
• Communicates with adjacent OXCs or the client
  network through single-hop light paths
   – These are Control light paths
   – Use standard signaling protocol like GMPLS for
     control functions
• Data light paths carry the data flow
   – Originate and terminate at client networks/edge routers
     and transparently traverse the core

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         Optical Cross-connects (No wavelength
                           2                          4

All Optical Cross-connect (OXC)
Also known as Photonic
Cross-connect (PXC)



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    Optical Cross-Connect with Full Wavelength
                                1                             2
          1,2, ... ,n                                                     1,2, ... ,n
                                2                            1
      1                                                                                       1
                                n                            n

                                1                            1
          1,2, ... ,n                                                     1,2, ... ,n
                                2                            2
      2                                                                                       2
                                n                            n
                           .                                             .
                           .                                             .
                           .                                             .
                                1                            n
          1,2, ... ,n                                                     1,2, ... ,n
                                2                            1
                                n                            2                              M

                   Wavelength        Optical CrossBar                Wavelength
                    Demux                 Switch                       Mux

• M demultiplexers at incoming side
• M multiplexers at outgoing side
• Mn x Mn optical switch has wavelength converters at switch
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        Wavelength Router with O/E and E/O

  Incoming Interface                          Outgoing Interface
Incoming Wavelength                          Outgoing Wavelength



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      O-E-O Crossconnect Switch (OXC)

Incoming                                               Outgoing
                     Individual wavelengths             fibers
        Demux          O              O             Mux
                       O/E     E      E/O
 1                     O/E            E/O                      1
                        O/E                  E/O
                        O/E                  E/O                    2
 2                      O/E                  E/O
     WDM                O/E                  E/O
     (many λs)

 N                      O/E                  E/O                    N
                        O/E                  E/O
                        O/E                  E/O

Switches information signal on a particular wavelength on an
incoming fiber to (another) wavelength on an outgoing fiber.
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   Optical core network
   Opaque (O-E-O) and transparent (O-O) sections
                                                       optical island
Client             E/O        O/E
                               O             O     O            O
           E                          E                   O

          to other nodes
                           from other nodes
                         O     O            O      O            O
               E                       E                  O

               Opaque opticalCSIT560 by M. Hamdi                  27
                OEO vs. All-Optical Switches
           OEO                                         All-Optical

• Capable of status monitoring          • Unable to monitor the contents of
• Optical signal regenerated –            the data stream
  improve signal-to-noise ratio         • Only optical amplification – signal-
• Traffic grooming at various levels      to-noise ratio degraded with distance
                                        • No traffic grooming in sub-
                                          wavelength level
• Less aggregated throughput
• More expensive                        • Higher aggregated throughput
• More power consumption                • ~10X cost saving
                                        • ~10X power saving

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        Large customers buy “lightpaths”
A lightpath is a series of wavelength links from end to end.


                             One fiber

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  Hierarchical switching: Node with switches
            of different granularities
A. Entire fibers            O          O              O
                   Fibers                         Fibers

B. Wavelength                           O             O     trains”

C. Individual               O           E             O
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               Wide Area Network (WAN)

Up to 200-500 wavelengths
40-160 Gbit/s/
wavebands (> 10 )               OXC: Optical Wavelength/Waveband Cross
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                          Packet (a) vs. Burst (b) Switching
                                                                                      Header recognition,
        Payload                                                                    processing, and generation
                                                           Synchronizer                                 Setup

                  1                                                                            Switch
Incoming                                                                      1                                     1
                                                                              2                                     2
              (but unaligned)                          FDL’s
    B                                                                                                        New            D
                                                                     (a)                                    headers
        A         Control                                                                                                   C
                                                   2                                                            2
                                                               1   O/E/O                                                1
                                                                            Control packet processing
                      packets                Offset time                    (setup/bandwidth reservation)
                                2                                                         2
   Data                                                            Switch
                                1                                                                1

        B                            Data bursts
                                                                      (b)                                                   D

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            MAN (Country / Region)

                   CSIT560 by M. Hamdi   33
           Optical Switching Technologies
       •   MEMs – MicroElectroMechanical
       •   Liquid Crystal
       •   Opto-Mechanical
       •   Bubble Technology
       •   Thermo-optic (Silica, Polymer)
       •   Electro-optic (LiNb03, SOA, InP)
       •   Acousto-optic
       •   Others…
Maturity of technology, Switching speed, Scalability, Cost,
Relaiability (moving components or not), etc.

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  MEMS Switches for Optical Cross-Connect
                                         Moveable Micromirror

Proven technology, switching time (10 to 25 msec), moving mirrors is a
reliability problem.

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WDM “transparent” transmission system
         (O-O nodes)

Wavelengths     Wavelengths
disaggregator   aggregator
    O           O         O           O                O
Fibers                        multiple

                Optical switching fabric (MEMS devices, etc.)

                               Tiny mirrors
         Incoming fiber

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             Outgoing fibers
            Upcoming Optical Technologies
• WDM routing is circuit switched
   – Resources are wasted if enough data is not sent
   – Wastage more prominent in optical networks
• Techniques for eliminating resource wastage
   – Burst Switching
   – Packet Switching
• Optical burst switching (OBS) is a new method to transmit data
• A burst has an intermediate characteristics compared to the basic
  switching units in circuit and packet switching, which are a
  session and a packet, respectively

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        Optical Burst Switching (OBS)
• Group of packets a grouped in to ‘bursts’, which is
  the transmission unit
• Before the transmission, a control packet is sent out
   – The control packet contains the information of burst
     arrival time, burst duration, and destination address
• Resources are reserved for this burst along the
  switches along the way
• The burst is then transmitted
• Reservations are torn down after the burst

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Optical Burst Switching (OBS)

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              Optical Packet Switching
• Fully utilizes the advantages of statistical
• Optical switching and buffering
• Packet has Header + Payload
   – Separated at an optical switch
• Header sent to the electronic control unit, which
  configures the switch for packet forwarding
• Payload remains in optical domain, and is re-
  combined with the header at output interface

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               Optical Packet Switch
• Has
   – Input interface, Switching fabric, Output interface and
     control unit
• Input interface separates payload and header
• Control unit operates in electronic domain and
  configures the switch fabric
• Output interface regenerates optical signals and inserts
  packet headers
• Issues in optical packet switches
   – Synchronization
   – Contention resolution
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• Main operation in a switch:
   –   The header and the payload are separated.
   –   Header is processed electronically.
   –   Payload remains as an optical signal throughout the switch.
   –   Payload and header are re-combined at the output interface.

                                    hdr             CPU

                 payload      hdr                                 payload   hdr

                                                                    Wavelength i
  Wavelength i      packet                                          output port j
  input port j
                                                 Optical switch

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              Output port contention
• Assuming a non-blocking switching matrix, more than one
  packet may arrive at the same output port at the same time.

            Input ports     Optical Switch      Output ports

                                payload hdr         .
               .                   .                .
               .                   .                .
               .                payloadhdr

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    OPS Architecture: Synchronization
Occurs in electronic switches – solved by input buffering

                Slotted networks
 •Fixed packet size
 •Synchronization stages required

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  OPS Architecture: Synchronization

           Slotted networks
•Fixed packet size
•Synchronization stages required

                      CSIT560 by M. Hamdi   45
 OPS Architecture: Synchronization

           Slotted networks
•Fixed packet size
•Synchronization stages required

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 OPS Architecture: Synchronization

           Slotted networks
•Fixed packet size
•Synchronization stages required

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 OPS Architecture: Synchronization

           Slotted networks
•Fixed packet size
•Synchronization stages required

                      CSIT560 by M. Hamdi   48
OPS Architecture: Synchronization


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            OPS: Contention Resolution
• More than one packet trying to go out of the same
  output port at the same time
   – Occurs in electronic switches too and is resolved by
     buffering the packets at the output
   – Optical buffering ?
• Solutions for contention
   – Optical Buffering
   – Wavelength multiplexing
   – Deflection routing

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           OPS Architecture
Contention Resolutions

 1                                      1

 2                                      2

 3                                      3

 4                                      4

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          OPS: Contention Resolution

• Optical Buffering
   – Should hold an optical signal
      • How? By delaying it using Optical Delay Lines (ODL)
   – ODLs are acceptable in prototypes, but not commercially
   – Can convert the signal to electronic domain, store, and re-
     convert the signal back to optical domain
      • Electronic memories too slow for optical networks

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              OPS Architecture
Contention Resolutions
  •Optical buffering

          1                                    1

          2          1                         2

          3      1                             3

          4                                    4

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              OPS Architecture
Contention Resolutions
  •Optical buffering

          1                                  1

          2                                  2

          3                                  3

          4                                  4

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              OPS Architecture
Contention Resolutions
  •Optical buffering

          1                                  1   1

          2                                      2

          3                                      3

          4                                      4


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         OPS: Contention Resolution
• Wavelength multiplexing
  – Resolve contention by transmitting on different
  – Requires wavelength converters - $$$

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                    OPS Architecture
Contention Resolutions
     •Wavelength conversion

 1                                             1

 2                                             2

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               OPS Architecture
Contention Resolutions
     •Wavelength conversion

 1                                          1

 2                                          2

                     CSIT560 by M. Hamdi   58
               OPS Architecture
Contention Resolutions
     •Wavelength conversion

 1                                          1

 2                                          2

                     CSIT560 by M. Hamdi   59
               OPS Architecture
Contention Resolutions
     •Wavelength conversion

 1                                          1

 2                                          2

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               OPS Architecture
Contention Resolutions
     •Wavelength conversion

 1                                                  1

 2                                                  2

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                   Deflection routing

• When there is a conflict between two optical packets, one will
  be routed to the correct output port, and the other will be
  routed to any other available output port.
• A deflected optical packet may follow a longer path to its
  destination. In view of this:
   – The end-to-end delay for an optical packet may be
     unacceptably high.
   – Optical packets may have to be re-ordered at the destination

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Electronic Switches Using
    Optical Crossbars

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 Scalable Multi-Rack Switch Architecture
                                       Optical links

 Line card
    rack                      Switch Core
• Number of linecards is limited in a single rack
   – Limited power supplement, i.e. 10KW
   – Physical consideration, i.e. temperature, humidity
• Scaling to multiple racks
   – Fiber links and central fabrics

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            Logical Architecture of Multi-rack Switches

                  Line Card                                                              Line Card

                        Local                                                                  Local
Fiber I/O                        Laser   Laser                           Laser   Laser                           Fiber I/O
             Framer    Buffers                                                                Buffers   Framer

                  Line Card                                                              Line Card

                        Local                                                                 Local
                                 Laser   Laser                           Laser   Laser                           Fiber I/O
Fiber I/O    Framer    Buffers                                                               Buffers    Framer

                                                  Switch Fabric System

      • Optical I/O interfaces connected to WDM fibers
      • Electronic packet processing and buffering
            – Optical buffering, i.e. fiber delay lines, is costly and not mature
      • Optical interconnect
            – Higher bandwidth, lower latency and extended link length than copper
              twisted lines
      • Switch fabric: electronic? Optical?
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                                  Optical Switch Fabric
                   Line Card                                                             Line Card

                         Local                                                                 Local
Fiber I/O                         Laser   Laser                          Laser   Laser                           Fiber I/O
              Framer    Buffers                                                               Buffers   Framer

                   Line Card                                                             Line Card

                         Local                                                                Local
                                  Laser   Laser                          Laser   Laser                           Fiber I/O
Fiber I/O     Framer    Buffers                                                              Buffers    Framer

                                                  Switch Fabric System

     • Less optical-to-electrical conversion inside switch
            – Cheaper, physically smaller
     • Compare to electronic fabric, optical fabric brings advantages in
            – Low power requirement, Scalability, Port density, High capacity
     • Technologies that can be used
            – 2D/3D MEMS, liquid crystal, bubbles, thermo-optic, etc.
     • Hybrid architecture takes advantage of the strengths of both
                               CSIT560 by M. Hamdi                                                               66
       electronics and optics
             Electronic Vs. Optical Fabric


              Trans. Buffer Inter-                    Inter- Buffer Trans.
               Line        connection               connection       Line
                                         Fabric                              Optical


                                                                             E/O or O/E

              Trans. Buffer Inter-                    Inter- Buffer Trans.
               Line        connection               connection       Line

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Multi-rack Hybrid Packet Switch


   Buf f er    E/O                         O/E   Buf f er

   Buf f er    E/O                         O/E   Buf f er

                 Optical Optical     Optical
                  Fiber Crossbar      Fiber

   Buf f er    E/O                        O/E    Buf f er

   Buf f er    E/O                        O/E    Buf f er

                       Switch Core

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            Features of Optical Fabric
• Less E/O or O/E conversion
• High capacity
• Low power consumption
• Less cost

• Reconfiguration overhead (50-100ns)
   – Tuning of lasers (20-30ns)
   – System clock synchronization (10-20ns or higher)

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  Scheduling Under Reconfiguration Overhead

• Traditional slot-by-slot approach


                                 Schedule Reconfigure Transfer

                                                                 Time Line

• Low bandwidth usage

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                                     Reduced Rate Scheduling
                       Fabric setup (reconfigure)
                        Traffic transfer
                              Time slot

        Slot-by-slot Scheduling, zero fabric setup time           Slot-by-slot Scheduling with reconfigure delay

                                  Reduced rate Scheduling, each schedule is held for some time

•       Challenge: fabric reconfiguration delay
    –         Traditional slot-by-slot scheduling brings lots of overhead
•       Solution: slow down the scheduling frequency to compensate
    –         Each schedule will be held for some time
•       Scheduling task
    1.        Find out the matching
    2.        Determine the holding time
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    Scheduling Under Reconfiguration

• Reduce the scheduling rate
   – Bandwidth Usage = Transfer/(Reconfigure+Transfer)

• Approaches
   – Batch scheduling: TSA-based
   – Single scheduling: Schedule + Hold

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                Single Scheduling
• Schedule + Hold
  – One schedule is generated each time
  – Each schedule is held for some time (holding time)
  – Holding time can be fixed or variable
  – Example: LQF+Hold

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Routing and

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                 Optical Circuit Switching
• An optical path established between two nodes
• Created by allocation of a wavelength throughout the path.
• Provides a ‘circuit switched’ interconnection between two
   – Path setup takes at least one RTT
   – No optical buffers since path is pre-set

Desirable to establish light paths between every pair of nodes.

• Limitations in WDM routing networks,
   – Number of wavelengths is limited.
   – Physical constraints:
      • limited number of optical transceivers limit the number of channels.

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   Routing and Wavelength Assignment (RWA)

• Light path establishment involves
   – Selecting a physical path between source and destination
     edge nodes
   – Assigning a wavelength for the light path
• RWA is more complex than normal routing
   – Wavelength continuity constraint
      • A light path must have same wavelength along all the links in
        the path
   – Distinct Wavelength Constraint
      • Light paths using the same link must have different wavelengths

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               No Wavelength Converters


Access Fiber
                         Wavelength 1

                         Wavelength 2

                        Wavelength 3
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         With Wavelength Converters


                            Wavelength 1
Access Fiber

                    Wavelength 2

                   Wavelength 3
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                 Routing and Wavelength
                   Assignment (RWA)
• RWA algorithms based on traffic assumptions:
• Static Traffic
   – Set of connections for source and destination pairs are given
• Dynamic Traffic
   – Connection requests arrive to and depart from network one by
     one in a random manner.
   – Performance metrics used fall under one of the following
     three categories:
       • Number of wavelengths required
       • Connection blocking probability: Ratio between number of blocked
         connections and total number of connections arrived

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             Static and Dynamic RWA
• Static RWA
  – Light path assignment when traffic is known well in
  – Arises in capacity planning and design of optical networks

• Dynamic RWA
  – Light path assignment to be done when requests arrive in
    random fashion
  – Encountered during real-time network operation

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                   Static RWA

• RWA is usually solved as an optimization problem
  with Integer Programming (IP) formulations
• Objective functions
   – Minimize average weighted number of hops
   – Minimize average packet delay
   – Minimize the maximum congestion level
   – Minimize number of Wavelenghts

                     CSIT560 by M. Hamdi        81
                    Static RWA

• Methodologies for solving Static RWA
  – Heuristics for solving the overall ILP sub-optimally
  – Algorithms that decompose the static RWA problem into
                                           RWA problem into
    a set of individual sub-problems, and solve a sub-set

  – http://www.tct.hut.fi/~esa/java/wdm/

                     CSIT560 by M. Hamdi                82
              Solving Dynamic RWA
• During network operation, requests for new light-
  paths come randomly
• These requests will have to be serviced based on the
  network state at that instant
• As the problem is in real-time, dynamic RWA
  algorithms should be simple
• The problem is broken down into two sub-problems
   – Routing problem
   – Wavelength assignment problem

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Optical Circuit Switching
all the Way: End-to-End
Why might this be possible:
   • Huge CS bandwidth (large # of wavelength) – BW
   efficiency is not very crucial
   • Circuit switches have a much higher capacity than
   Packet switches, and QoS is trivial
   • Optical Technology is suited for CS
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        How the Internet Looks Like Today
The core of the Internet is already “predominantly” CS.
Even a “large” portion of the access networks use CS (Modem, DSLs)

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How the Internet Really Looks Like Today


               CSIT560 by M. Hamdi     86
How the Internet Really Looks Like Today

              Modems, DSL

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Why Is the Internet Packet Switched in the First

• PS is bandwidth     “Circuit switching is rarely used
  efficient           for data networks, ... because of
  “Statistical        very inefficient use of the links”

                      ”For high reliability, ... [the
• PS networks are     Internet] was to be a datagram
  robust              subnet, so if some lines and
                      [routers] were destroyed,
                      messages could be ... rerouted”
                      CSIT560 by M. Hamdi            88
    Are These Assumptions Valid Today?
                          •    10-15% average link
                               utilization in the
• PS is bandwidth              backbone today.
  efficient               •    Similar story for
                               access networks

                             Routers/Switches are
• PS networks are
                              designed for <5s down-time
                              per year.
                             They take >1min to recover
                              when they do (circuit
                              switches must recover in
                    CSIT560 by M. Hamdi              89
How Can Circuit Switching Help the Internet?

 •       Simple switches/routers:
     •     No buffering                            Higher
     •     No per-packet processing (just          capacity
           per connection processing)
     •     Possible all-optical data path

 •       Peak allocation of BW
                                                   Simple but
     •     No delay jitter
                                                   strict QoS
                             CSIT560 by M. Hamdi              90
     Myth: Packet switching is simpler
• A typical Internet router contains over 500M
  gates, 32 CPUs and 10Gbytes of memory.

• A circuit switch of the same generation could run
  ten times faster with 1/10th the gates and no

                    CSIT560 by M. Hamdi           91
                                 Packet Switch Capacity
Instructions per arriving byte

                                                     What we’d like: (more features)
                                                     QoS, Multicast, Security, …

                                                 What will happen: (fewer features)
                                                 Or perhaps we’re doing something wrong?

                                       CSIT560 by M. Hamdi                        92
  What Is the Performance of Circuit Switching?
                                                   File = 10Mbit
         100 clients
                                             1 server
                          1 Gb/s
                                                             x 100

              Circuit sw Packet sw                      99% of
    Flow BW 1 Gb/s       10 Mb/s                        Circuits
  Avg latency 0.505 s    1s                              Finish
Worst latency 1 s            1s                         Earlier
                       CSIT560 by M. Hamdi                   93
What Is the Performance of Circuit Switching?
                                         File = 10Gbit/10Mbit
          100 clients
                                              1 server
                           1 Gb/s
                                                            x 99

               Circuit sw Packet sw                   A big file
     Flow BW 1 Gb/s       10Mb/s+1Gb/s               can kill CS
  Avg latency 10.495 s     1.099 sec                 if it blocks
 Worst latency 10.990 s 10.990 sec                     the link
                        CSIT560 by M. Hamdi                 94
What Is the Performance of Circuit Switching?
                                         File = 10Gbit/10Mbit
          100 clients
                                              1 server
                           1 Gb/s
                                                           x 99
             1 Mb/s

               Circuit sw Packet sw
     Flow BW 1 Mb/s       1 Mb/s
  Avg latency     109.9s     109.9sec
                                                     CS and PS
 Worst latency 10,000 s 10,000 sec
                                                       in core
                        CSIT560 by M. Hamdi                95
       Possible Implementation

            • Create a separate circuit for each
            • IP controls circuits
            • Optimize for the most common
Switching     case
               – TCP (85-95% of traffic)
               – Data (8-9 out of 10 pkts)

               CSIT560 by M. Hamdi            96
TCP Switching Exposes Circuits to IP

                                   IP routers

            TCP Switches

             CSIT560 by M. Hamdi                97
           TCP “Creates” a Connection

Source      Router    Router          Router   Destina-



    Packets     Packets      Packets       Packets
                     CSIT560 by M. Hamdi             98
        State Management Feasibility
• Amount of state
   – Minimum circuit = 64 kb/s.
   – 156,000 circuits for OC-192.
• Update rate
   – About 50,000 new entries per sec for OC-192.
• Readily implemented in hardware or software.

                       CSIT560 by M. Hamdi          99
      Software Implementation Results

TCP Switching boundary router:
• Kernel module in Linux 2.4 1GHz PC
• Forwarding latency
   – Forward one packet: 21s.
   – Compare to: 17s for IP.
   – Compare to: 95s for IP + QoS.
• Time to create new circuit: 57s.

                      CSIT560 by M. Hamdi   100

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