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A Brief Introduction to Optical Networks. Gaurav Agarwal [email protected] What I hope you will learn. Why Optical? Intro to Optical Hardware Three generations of Optical Various Switching Architectures Circuit, Packet and Burst Protection and Restoration. Outline.

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Presentation Transcript
what i hope you will learn
What I hope you will learn
  • Why Optical?
  • Intro to Optical Hardware
  • Three generations of Optical
  • Various Switching Architectures
    • Circuit, Packet and Burst
  • Protection and Restoration

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outline
Outline
  • Why Optical? (Any guesses???)
  • Intro to Optical Hardware
  • Three generations of Optical
  • Various Switching Architectures
    • Circuit, Packet and Burst
  • Protection and Restoration

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bandwidth lots of it
Bandwidth: Lots of it
  • Usable band in a fiber
    • 1.30m - 1.65m  40 THz
    •  spaced at 100 GHz  400 s per fiber
  • Link Speeds upto 40 Gbps per 
    • OC-3  155Mbps
    • OC-768  40Gbps becoming available
  • Total link capacity
    • 400  * 40Gbps = 16 Tbps!
  • Do we need all this bandwidth?

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other advantages
Other advantages
  • Transparent to bit rates and modulation schemes
  • Low bit error rates
    • 10-9 as compared to 10-5 for copper wires
  • High speed transmission
  • To make this possible, we need:
    • All-Optical reconfigurable (within seconds) networks
    • Definitely a difficult task

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what a path will look like

All-Optical

Switch*

All-Optical

Switch*

All-Optical

Switch*

What a path will look like

Lasers generate the signal

Optical receivers

Optical

Amplifier

* All-optical Switch with wavelength converters and optical buffers

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outline1
Outline
  • Why Optical?
  • Intro to Optical Hardware
  • Three generations of Optical
  • Various Switching Architectures
    • Circuit, Packet and Burst
  • Protection and Restoration

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fiber lasers
Fiber & Lasers
  • Fiber
    • Larger transmission band
    • Reduced dispersion, non linearity and attenuation loss
  • Lasers
    • Up to 40Gbps
    • Tunability emerging
    • Reduced noise (both phase and intensity)
    • Made from semiconductor or fiber

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optical amplifiers
Optical Amplifiers
  • As opposed to regenerators
    • Make possible long distance transmissions
    • Transparent to bit rate and signal format
    • Have large gain bandwidths (useful in WDM systems)
    • Expensive (~$50K)

Now:

Optical Amps

Then:

Regenerators

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optical add drop multiplexers

1

1

2

OADM

2

3

’3

3

’3

Optical Add-Drop Multiplexers
  • Optical Add-Drop Multiplexer (OADM)
    • Allows transit traffic to bypass node optically
    • New traffic stream can enter without affecting the existing streams

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optical switches
Optical Switches
  • Route a channel from any I/P port to any O/P port
  • Can be fixed, rearrangable, or with  converters
  • MEMS (Micro Electro Mechanical Systems)
    • Lucent, Optical Micro Machines, Calient, Xros etc.
  • Thermo-Optic Switches
    • JDS Uniphase, Nanovation, Lucent
  • Bubble Switches
    • Agilent (HP)
  • LC (Liquid Crystal) Switches
    • Corning, Chorum Technologies
  • Non-Linear Switches (still in the labs)

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mems switches
MEMS Switches

2-D Optical Switches

  • Crossbar architecture
  • Simple Digital Control of mirrors
  • Complexity O(N²) for full non blocking architecture
  • Current port count limited to 32 x 32.

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3d mems switch architecture
3D MEMS Switch Architecture

3-D Optical Switches

  • Analog Control of Mirrors.
  • Long beam paths (~1m) require collimators.
  • Complexity O(N) (Only 2N mirrors required for a full non blocking NxN switch)
  • Lucent Lambda Router : Port

256 x 256; each channel supports up to 320 Gbps.

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

3

2

3

2

WC

No  converters

With  converters

1

New request

1 3

1

New request

1 3

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optical buffers
Optical Buffers
  • Fiber delay lines are used
  • To get a delay of 1msec:
    • Speed of Light = 3*108 m/sec
    • Length of Fiber = 3*108 *10-3 m

= 300 km

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outline2
Outline
  • Why Optical?
  • Intro to Optical Hardware
  • Three generations of Optical
  • Various Switching Architectures
    • Circuit, Packet and Burst
  • Protection and Restoration

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generation i

E-O

Switch

O-E-O

Switch

O-E

Switch

Generation I
  • Point-to-point optical links used simply as a transmission medium
  • Fiber connected by Electronic routers/switches with O-E-O conversion
  • Regenerators used for long haul

Electronic data

as the signal

Signal received

as electronic

Regenerators

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generation ii
Generation II
  • Static paths in the core of the network
  • All-Optical Switches (may not be intelligent)
  • Circuit-switched
  • Configurable (but in the order of minutes/hours)
  • Soft of here

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gen ii ip over optical

IP Router Network

IP Router Network

IP Router Network

NNI

UNI

Light Path

Optical

Subnet

Optical

Subnet

Optical

Subnet

End-to-end path

Gen II: IP-over-Optical

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peer model
Peer Model
  • IP and optical networks are treated as a single integrated network
  • OXCs are treated as IP routers with assigned IP addresses
  • No distinction between UNI and NNI
  • Single routing protocol instance runs over both domains
  • Topology and link state info maintained by both IP and optical routers is identical

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overlay model
Overlay Model
  • IP network routing and signaling protocols are independent of the corresponding optical networking protocols
  • IP  Client & Optical network  Server
  • Static/Signaled overlay versions
  • Similar to IP-over-ATM

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integrated model
Integrated Model
  • Leverages “best-of-both-worlds” by inter-domain separation while still reusing MPLS framework
  • Separate routing instances in IP and ON domains
  • Information from one routing instance can be passed through the other routing instance
  • BGP may be adapted for this information exchange

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generation iii
Generation III
  • An All-Optical network
  • Optical switches reconfigurable in milli-seconds
  • Intelligent and dynamic wavelength assignment, path calculation, protection built into the network
  • Possibly packet-switched
  • Dream of the Optical World

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generation iii contd
Generation III (contd.)
  • Optical “routers” perform L3 routing
  • No differentiation between optical and electrical IP domains
  • Routing decision for each packet made at each hop
  • Statistical sharing of link bandwidth
  • Complete utilization of link resources

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outline3
Outline
  • Why Optical?
  • Intro to Optical Hardware
  • Three generations of Optical
  • Various Switching Architectures
    • Circuit, Packet and Burst
  • Protection and Restoration

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state of the world today

Electronic

Network

Electronic

Network

Electronic

Network

Electronic

Network

State of the World Today

O/E/O

E/O

E/O

O/E/O

O/E/O

O/E/O

O/E/O

O/E/O

E/O

E/O

Optical Core

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view of a e o node
View of a E/O node

Input Port 1

Input Port 1

O P 1

Optical Link 1

Electrical

Optical

Input Port 2

Input Port 2

O P 2

Optical Link 2

Input Port 3

O P 3

Input Port 3

O P 4

Optical Link 3

Input Port 4

Input Port 4

O P N-1

O P N

Physical View

Logical View

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optical circuit switching

Electronic

Network

Electronic

Network

Electronic

Network

Electronic

Network

O/E/O

O/E/O

O/E/O

O/E/O

O/E/O

O/E/O

Optical Circuit Switching

OS

O/E/O

E/O

E/O

O/E/O

OS

OS

O/E/O

OS

O/E/O

O/E/O

OS

O/E/O

OS

E/O

E/O

Optical Core

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optical circuit switching1

Electronic

Network

Electronic

Network

Electronic

Network

Electronic

Network

Optical Circuit Switching

O/E/O

OS

E/O

E/O

OS

O/E/O

O/E/O

OS

O/E/O

OS

OS

O/E/O

OS

WC

O/E/O

E/O

E/O

Optical Core

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optical circuit switching2
Optical Circuit Switching
  • A circuit or ‘lightpath’ is set up through a network of optical switches
  • Path setup takes at least one RTT
  • Need not do O/E/O conversion at every node
  • No optical buffers since path is pre-set
  • Need to choose path
  • Need to assign wavelengths to paths
  • Hope for easy and efficient reconfiguration

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problems
Problems
  • Need to set up lightpath from source to destination
  • Data transmission initiated after reception of acknowledgement (two way reservation)
  • Poor utilization if subsequent transmission has small duration relative to set-up time. (Not suited for bursty traffic)
  • Protection / fault recovery cannot be done efficiently

Example : Network with N switches, D setup time per switch,

T interhop delay.

Circuit Setup time = 2.(N-1).T + N.D

If N = 10, T = 10ms, D = 5ms, setup time = 230 ms.

At 20 Gbps, equivalent to 575 MB (1 CD) worth of data !

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optical packet switching
Optical Packet Switching
  • Internet works with packets
  • Data transmitted as packets (fixed/variable length)
  • Routing decision for each packet made at each hop by the router/switch
  • Statistical sharing of link bandwidth leads to better link utilization
  • Traffic grooming at the edges? Optical header?

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problems1
Problems
  • Requires intelligence in the optical layer
  • Or O/E/O conversion of header at each hop
  • Packets are small  Fast switching (nsec)
  • Need store-and-forward at nodes or Deflection Routing. Also store packet during header processing
  • Buffers are extremely hard to implement 
  • Fiber delay lines
    • 1 pkt = 12 kbits @ 10 Gbps requires 1.2 s of delay => 360 m of fiber)
    • Delay is quantized
  • How about QoS?

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multiprotocol lambda switching
Multiprotocol Lambda Switching
  • D. Awduche et. al., “Requirements for Traffic Engineering Over MPLS,” RFC 2702
  • Problem decomposition by decoupling the Control plane from the Data plane
    • Exploit recent advances in MPLS traffic engineering control plane
    • All optical data plane
    • Use  as a “label”
    • The  on incoming port determines the output port and outgoing 

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oxcs and lsrs
OXCs and LSRs
  • Electrical Network – Label Switched Routers (LSR)
  • Optical Network – Optical Cross Connects
  • Both electrical and optical nodes are IP addressable
  • Distinctions
    • No  merging
    • No  push and pop
    • No packet-level processing in data plane

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optical burst switching
Optical Burst Switching
  • Lies in-between Circuit and Packet Switching
  • One-way notification of burst (not reservation) – can have collisions and lost packets
  • Header (control packet) is transmitted on a wavelength different from that of the payload
  • The control packet is processed at each node electronically for resource allocation
  • Variable length packets (bursts) do not undergo O/E/O conversions
  • The burst is not buffered within the ON

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various obss
Various OBSs
  • The schemes differ in the way bandwidth release is triggered.
  • In-band-terminator (IBT) – header carries the routing information, then the payload followed by silence (needs to be done optically).
  • Tell-and-go (TAG) – a control packet is sent out to reserve resources and then the burst is sent without waiting for acknowledgement. Refresh packets are sent to keep the path alive.

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offset time schemes
Offset-time schemes
  • Reserve-a-fixed-duration (RFD)
  • Just Enough Time (JET)
  • Bandwidth is reserved for a fixed duration (specified by the control packet) at each switch
  • Control packet asks for a delayed reservation that is activated at the time of burst arrival
  • OBS can provide a convenient way for QoS by providing extra offset time

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qos using offset times

ta2(= ts2)

ta2(= ts2)

to1

ta1

ts1

ts1+ l1

QoS using Offset-Times

Assume two classes of service

Class 1 has higher priority

Class 2 has zero offset time

to1

i

Time

ta1

ts1

ts1+ l1

i

Time

ta2(= ts2)

ts2+ l2

tai = arrival time for class i request

tsi = service time for class i request

toi = offset time for class i request

li = burst length for class i request

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comparison
Comparison

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hierarchical optical network

Optical MAN

Optical MAN

Optical MAN

Optical MAN

Hierarchical Optical Network

E/O

E/O

E/O

E/O

E/O

OS

All O

All O

OS

E/O

E/O

E/O

OS

OS

OS

WC

E/O

E/O

E/O

E/O

All O

All O

Optical Core

E/O

E/O

E/O

E/O

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hierarchical optical network1
Hierarchical Optical Network
  • Optical MAN may be
    • Packet Switched (feasible since lower speeds)
    • Burst Switched
    • Sub- circuit switching by wavelength merging
  • Interfaces boxes are All-Optical and merge multiple MAN streams into destination-specific core stream
  • Relatively static Optical Core
  • Control distributed to intelligent edge boxes

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outline4
Outline
  • Why Optical?
  • Intro to Optical Hardware
  • Three generations of Optical
  • Various Switching Architectures
    • Circuit, Packet and Burst
  • Protection and Restoration

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link vs path protection
Link vs Path Protection
  • For failure times, need to keep available s on backup path
  • Link: Need to engineer network to provide backup
  • Path: need to do end-to-end choice of backup path

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types of protection
Path protection

Dedicated (1+1) – send traffic on both paths

Dedicated (1:1) – use backup only at failure

Shared (N:1) – many normal paths share common backup

Link Protection

Dedicated (each  is also reserved on backup link)

Shared (a  on backup link is shared between many)

Types of Protection

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restoration
Restoration
  • Do not calculate protection path ahead of time
  • Upon failure, use signalling protocol to generate new backup path
  • Time of failover is more
  • But much more efficient usage of s
  • Need also to worry about steps to take when the fault is restored

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protection and restoration
Protection and Restoration
  • Time of action
    • Path calculation (before or after failure ?)
    • Channel Assignments (before or after failure ?)
    • OXC Reconfiguration
  • AT&T proposal
    • Calculate Path before failure
    • Try channel assignment after failure
    • Simulations show 50% gain over channel allocation before failure

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protection algorithms
Protection Algorithms
  • Various flavors
    • Shortest path type
    • Flow type
    • ILP (centralized)
    • Genetic programming
  • In general, centralized algos are too inefficient
  • Need distributed algos, and quick signalling
  • Have seen few algos that take into account the different node types (LWC/FWC)

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conclusion
Conclusion
  • Optical is here to stay
  • Enormous gains in going optical
  • O/E/O will soon be the bottleneck
  • Looking for ingenious solutions
    • Optical Packet Switching
    • Flavors of Circuit Switching

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collective references
Collective References
  • “Optical Networks: A practical perspective” by Rajiv Ramaswami and Kumar Sivarajan, Morgan Kaufman.
  • IEEE JSAC
    • September 1998 issue
    • October 2000 issue
  • IEEE Communications Magazine
    • March 2000 issue
    • September 2000 issue
    • February 2001 issue
    • March 2001 issue
  • INFOCOM 2001
    • ‘Optical Networking’ Session
    • ‘WDM and Survivable Routing’ Session
  • INFOCOM 200
    • ‘Optical Networks I’ Session
    • ‘Optical Networks II’ Session
  • RFC 2702 for MPS
  • www.cs.buffalo.edu/pub/WWW/faculty/qiao/
  • www.lightreading.com

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