A brief introduction to optical networks
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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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A brief introduction to optical networks

A Brief Introduction to Optical Networks

Gaurav Agarwal

[email protected]


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

EECS - UC Berkeley


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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