A Brief Introduction to Optical Networks EE 122, UC Berkeley April 27 & 30, 2001 Gaurav Agarwal...

A Brief Introduction to Optical Networks

EE 122, UC BerkeleyApril 27 & 30, 2001

Gaurav [email protected]

4/27/2001 EE122, UC Berkeley 2

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 Why Optical? (Any guesses???) Intro to Optical Hardware Three generations of Optical Various Switching Architectures



Bandwidth: Lots of it Usable band in a fiber

1.30m - 1.65m 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?


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


What a path will look like

* All-optical Switch with wavelength converters and optical buffers

All-OpticalSwitch*

All-OpticalSwitch*

All-OpticalSwitch*

Optical Amplifier

Lasers generate the signal Optical receivers


Outline Why Optical? Intro to Optical Hardware Three generations of Optical Various Switching Architectures



Fiber & Lasers Fiber

Larger transmission band Reduced dispersion, non linearity and

attenuation loss Lasers

Upto 40Gbps Tunability emerging Reduced noise (both phase and intensity) Made from semiconductor or fiber


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)

Then:Regenerators

Now:Optical Amps

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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

OADM

1

2

3

1

2

’3

’33

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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

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

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 upto 320 Gbps.

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Wavelength Converters Improve utilization of available wavelengths on

links All-optical WCs being developed Greatly reduce blocking probabilities

No converters

1

2 3

New request 1 3

1

2 3

New request 1 3

With converters

WC

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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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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

E-OSwitch

O-E-OSwitch

O-ESwitch

Regenerators

Electronic data as the signal

Signal receivedas electronic

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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

Optical Subnet

Optical Subnet

Optical Subnet

UNI

NNI

Light Path

End-to-end path

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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

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 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

4/27/2001 EE122, UC Berkeley 23

Generation III An All-Optical network Optical switches reconfigurable in milli-

seconds Intelligent and dynamic wavelength

asignment, path calculation, protection built into the network

Possibly packet-switched Dream of the Optical World

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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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State of the World Today

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 Core

E/O

E/O E/O

E/O

4/27/2001 EE122, UC Berkeley 27

View of a E/O node

Electrical Optical

Input Port 1

Input Port 4

Input Port 3

Input Port 2

Optical Link 1

Optical Link 2

Optical Link 3

Input Port 1

Input Port 4

Input Port 3

Input Port 2

O P 1

O P 2

O P 3

O P 4

O P N-1

O P NPhysical View

Logical View

4/27/2001 EE122, UC Berkeley 28

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 Core

E/O

E/O E/O

E/OOS

OS

OS

OS

OS

OS

O/E/O

O/E/O

O/E/O

O/E/O

O/E/O

O/E/O

4/27/2001 EE122, UC Berkeley 29

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 Core

E/O

E/O E/O

E/OOS

OS

OS

OS

OS

OS

WC

4/27/2001 EE122, UC Berkeley 30

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 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 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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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 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 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 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 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.

4/27/2001 EE122, UC Berkeley 38

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

4/27/2001 EE122, UC Berkeley 39

QoS using Offset-TimesAssume two classes of serviceClass 1 has higher priorityClass 2 has zero offset time

i Time

tai = arrival time for class i

requestts

i = service time for class i request

toi = offset time for class i request

li = burst length for class i request

ta1 ts

1

to1

ts1+ l1ta

2(= ts2)ta

2(= ts2)

i Time

ta1

to1

ta2(= ts

2) ts1 ts

1+ l1ts2+ l2

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Comparison

4/27/2001 EE122, UC Berkeley 41

Hierarchical Optical Network

Optical MAN

Optical MANOptical MAN

Optical MAN

Optical Core

All O

All O All O

All O

E/O

E/O

E/O

E/O

E/O

E/OE/O

E/O

E/O

E/O

E/O

E/O

E/O

E/O

E/O E/O

OS

OS

OS

OS

OS

WC

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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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4/27/2001 EE122, UC Berkeley 44

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

NormalPath

BackupPath

LinkProtection

NormalPath

BackupPath

PathProtection

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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)

4/27/2001 EE122, UC Berkeley 46

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

4/27/2001 EE122, UC Berkeley 47

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 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 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

“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 MPS www.cs.buffalo.edu/pub/

WWW/faculty/qiao/ www.lightreading.com

A Brief Introduction to Optical Networks EE 122, UC Berkeley April 27 & 30, 2001 Gaurav Agarwal...

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