CS 268: Optical Networks Ion Stoica April 21, 2004 (Based in part on slides from Ed Bortolini...

CS 268:Optical Networks

Ion Stoica

April 21, 2004

(Based in part on slides from Ed Bortolini (Network Photonics), Ling Huang (UC Berkeley), Shivkumar Kalyanaraman (RPI),Larry McAdams (Cisco))

2

Big Picture

SONET

DataCenter SONET

SONET

SONET

DWDM DWD

M

Access

Long HaulAccess

MetroMetro

3

Overview

Optical Transmission Dense Wavelength Division Multiplexing (DWDM) Synchronous Optical Network (SONET) Generic Framing Procedure (GFP)

Optical Transmission

Waveform after 1000 kmTransmitted data waveform

5

Fiber Attenuation

Telecommunications industry uses two windows: 1310 & 1550 nm

1550 window is preferred for long-haul applications

- Less attenuation

- Wider window

- Optical amplifiers

1310window

1550window

6

Dispersion

Dispersion causes the pulse to spread as it travels along the fiber

Chromatic dispersion- Light propagation in material varies with the wavelength

- Degradation scales as (data-rate)2

(Figure from http://lw.pennnet.com/)

7

Dispersion

Modal dispersion- Only for fiber that carry multiple light rays (modes)

- Different modes travel at different speeds

- Multimodal fiber used only for short distances

8

Overview


9

DWDM

1310/1510 nm

1310/1510 nm

16 uncorrelated vawelengths

λ1λ2 λ3λ4 λ5 λ16

2.488 Gbps (1)

2.488 Gbps (16)

16*2.488 Gbps = 40 Gbps

1530-1565 nm ramge

16 stabilized, correlated vawelengts

DWDM System Design

40-80 km

Terminal

Regenerator - 3R (Reamplify, Reshape and Retime)

Terminal

120 km

TerminalTerminal

Optical Amplifiers (OA)

Terminal

OA amplifies all s

Terminal

Terminal

Terminal

Terminal

Terminal

DWDM System Design

1550

1551

1552

1553

1554

1555

1556

1557

01234567

01234567

Amplify DW

DM

Filt

er

Op

tic

al C

om

bin

er

15xx nm 1310 nmReamplifyReshapeRetime

Rx Tx1310 nm

Rx

Ex

tern

al

Mo

du

lato

r

Laser

15xx nm

12

All-Optical Switching

Natively switch s while they are still multiplexed

Eliminate redundant optical-electronic-optical conversions

DWDMFibers

inDWDMDemux

DWDMDemux

DWDMFibers

outDWDM

Mux

DWDMMux

All-optical

OXC

13

1-D MEMS

MEMS: Micro-electromechanical systems

1-Dimensional array of micro-mirrors

- 1 mirror per wavelength Digital control; no motors

14

Optical Switch

1-input 2-outoput illustration with four wavelengths

1-D MEMS with dispersive optics - Dispersive element separates the ’s from inputs

- MEMS independently switches each - Dispersive element recombines the switched ’s into outputs

1-D MEMSMicro-mirror

Array

Digital MirrorControl

Electronics1011

Wavelength Dispersive Element

Input Fiber

Output Fiber 1

Output Fiber 2

Input & Output fiber array

15

Optical Switch

2 in

4 in

5 in

7 in

N in

1 out

2 out

4 out

5 out

7 out

N out

1drop

2drop

3drop

4drop

5drop

6drop

7drop

Mdrop

1add

2add

3add

4add

5add

6add

7add

Madd

...

...

......

Tunable lasers

1 in

Wavelength-multiplexer N x M

four-portoptical matrix

switch

3 in 3 out

6 out6 in

16

Optical Add-Drop Multiplexer

Add-drop one Each is associated with a fixed add/drop port Used to implement ring topologies

... ...

...

...

...

DE

MU

X

MU

X

17

Overview


18

SONET

Encode bit streams into optical signals propagated over optical fiber

Uses Time Division Multiplexing (TDM) for carrying many signals of different capacities

- A bit-way implementation providing end-to-end transport of bit streams

- All clocks in the network are locked to a common master clock

- Multiplexing done by byte interleaving

19

Synchronous Transport Signal (STS)

First two bytes of each frame contain a special bit pattern that allows to determine where the frame starts

Receiver looks for the special bit pattern every 810 bytes

- Size of frame = 9x90 = 810 bytes

90 columns

9 ro

ws

Data (payload)overhead

SONET STS-1 Frame

Synchronous Payload Envelope (SPE)

20

Encoding

Overhead bytes are encoded using Non-Return to Zero- high signal 1; low signal 0

To avoid long sequences of 0’s or 1’s the payload is XOR-ed with a special 127-bit patter with many transitions from 1 to 0

- Duration of a frame is 125 µsec (51.84 Mbps for STS-1)

21

SONET Overhead Processing

Three layers of overhead- Path overhead (POH): end-to-end transport

- Line overhead (LOH): mux-to-mux transport

- Section overhead (SOH): adjacent network element

MU

X

IntermediateMultiplexer(ADM or DCS)

Regenerator Regenerator

Section Section Section Section

Line Line

Path

DE

MU

X

22

STS-1 Frame Format

Two-dimensional: 9*80 = 810 bytes Time Frame: 125 µsec Rate: 810*8 bit/125 µsec = 51.84 Mbps For STS-3 only the number of columns changes

(3*80 = 270)

90 Bytes90 BytesOr “Columns”Or “Columns”

99RowsRows

Small Rectangle =1 Byte

23

STS-1 Headers

90 Bytes90 BytesOr “Columns”Or “Columns”

99RowsRows

Section Overhead (SOH)

Line Overhead (LOH)Path Overhead (POH): Floating; can begin anywhere

24

Section Overhead (SOH)

First 3 lines in the header Main functions

- Framing (A1, A2)

- Monitor performance

- Local orderwire (E1): select repeater/terminal within communication complex

- Proprietary OAM (Operation, Administration, and Maintenance) (F1)

SOH

3 B 87 B

A1=0xF6

A2A2=0x28=0x28

J0/Z0J0/Z0STS-IDSTS-ID

B1B1BIP-8BIP-8

E1E1OrderwireOrderwire

F1F1UserUser

D1D1Data ComData Com



25

Line Overhead (LOH)

Last 3 lines in the header Main functions

- Locating payload (SPE) in the frame (H1, H2)

- Muxing and concatenating signals

- Performance monitoring

- Automatic protection switch (K1, K2)

• Switchover in case of failure

- Line maintenanceLOH

3 B 87 B

H1H1PointerPointer

H2H2PointerPointer

H3H3Pointer ActPointer Act

B2B2BIP-8BIP-8

K1K1APSAPS

K2K2APSAPS










S1S1SyncSync

M0M0REIREI

E1E1OrderwireOrderwire

26

Path Overhead (POH)

1st column in SPE Main functions

- Info about SPE content

- Performance monitoring

- Path status

- Path trace SPE can start anywhere in

the current frame and span the next one

- Avoids buffer management complexity & artificial delays 1st STS-1

2nd STS-1

POH

9 rows

J1J1TraceTrace

B3B3BIP-8BIP-8

C2C2Sig LabelSig Label

G1G1Path StatPath Stat

F2F2UserUser

H4H4IndicatorIndicator

Z3Z3GrowthGrowth

Z4Z4GrowthGrowth

Z5Z5TandemTandem

SPE

27

STS-N Frame Format

Composite Frames:Composite Frames:• Byte InterleavedByte Interleaved STS-1’s STS-1’s• Clock RateClock Rate = Nx51.84 Mbps = Nx51.84 Mbps• 9 colns overhead9 colns overhead

90xN Bytes90xN BytesOr “Columns”Or “Columns”

N Individual STS-1 FramesN Individual STS-1 Frames

ExamplesExamples STS-1STS-1 51.84 Mbps 51.84 Mbps

STS-3STS-3 155.520 Mbps 155.520 MbpsSTS-12STS-12 622.080 Mbps 622.080 MbpsSTS-48STS-48 2.48832 Gbps 2.48832 GbpsSTS-192 9.95323 GbpsSTS-192 9.95323 Gbps

Multiple frame streams, w/ independent payload pointersNote: header columns also interleaved

28

STS-N: Generic Frame Format

STS-1 STS-N

29

STS-Nc Frame Format

Concatenated mode:Concatenated mode:• Same header structure and data rates as Same header structure and data rates as STS-NSTS-N• Not all header bytes usedNot all header bytes used• First H1, H2 Point To POHFirst H1, H2 Point To POH• Single PayloadSingle Payload In Rest Of SPE In Rest Of SPE

90xN Bytes90xN BytesOr “Columns”Or “Columns”

Transport Overhead: Transport Overhead: SOH+LOHSOH+LOH

Current IP over SONET technologies use concatenated mode: OC-3c (155 Mbps) to OC-192c (10 Gbps) ratesa.k.a “super-rate” payloads

30

Practical SONET Architecture

ADM – Add-Drop MultiplexerDCS – Digital Crossconnect

31

Protection Technique Classification

Restoration techniques can protect the network against:- Link failures

• Fiber-cables cuts and line devices failures (amplifers)

- Equipment failures

• OXCs, ADMs, electro-optical interface. Protection can be implemented

- In the optical channel sublayer (path protection)

- In the optical multiplex sublayer (line protection) Different protection techniques are used for

- Ring networks

- Mesh networks

32

1+1 Protection

Traffic is sent over two parallel paths, and the destination selects a better one

In case of failure, the destination switch onto the other path Pros: simple for implementation and fast restoration Cons: waste of bandwidth

33

1:1 Protection

During normal operation, no traffic or low priority traffic is sent across the backup path

In case failure both the source and destination switch onto the protection path

Pros: better network utilization Cons: required signaling overhead, slower restoration

34

1:1 Ring Protection

Each channel on one ring is protected by one channel on the other ring

When faults loop around

ADM

ADM

ADM ADM

ADM

ADM

ADM ADM

35

Protection in Ring Network

1+1 Path Protection

Used in access rings for traffic aggregation

into central office

1:1 Line Protection

Used for interoffice rings

1:1 Span and Line Protection

Used in metropolitan or long- haul rings

(Unidirectional Path Switched Ring)

(Bidirectional Line Switched Ring)

36

Protection in Mesh Networks

Working Path

Backup Path

Network planning and survivability design - Disjoint path idea: service working route and its backup route are

topologically diverse.

- Lightpaths of a logical topology can withstand physical link failures.

37

Path Switching: restoration is handled by the source and the destination.

Normal Operation

Line Switching: restoration is handled by the nodes adjacent to the failure. Span Protection: if additional fiber is available.

Line Switching: restoration is handled by the nodes adjacent to the failure.

Line Protection.

Path Protection / Line Protection

38

Shared Protection

1:N Protection

Backup fibers are used for protection of multiple links Assume independent failure and handle single failure. The capacity reserved for protection is greatly reduced.

Normal Operation

In Case of Failure

39

Overview


40

Generic Framing Procedure (GFP)

GFP provides a generic mechanism to adapt traffic from higher-layer client signals over an octet synchronous transport network (e.g., SONET)

GFP – Common Aspects (Payload Independent)

GFP – Client Specific Aspects (Payload Dependent)

Ethernet IP/PPP Other Client Signals

SONET/SDH VC-n Path

OTN ODUk Path

Other octet-synchronous

paths

41

Generic Framing Procedure (GFP)

Frame-mapped- Need to know the client protocol

- Associate a length to each higher level frame

- Efficient: eliminate the need for byte stuffing or for block encoding (e.g., 8B/10B)

Transparent- No need to know the client protocol

- Less efficient; can transmit signal even when the client is idle

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CS 268: Optical Networks Ion Stoica April 21, 2004 (Based in part on slides from Ed Bortolini...

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