Optical Communications and Networking

Lecture 1: Introduction 朱祖勍1

Optical Communications and Networking

朱祖勍

Sept. 6, 2021

Lecture 1: Introduction 朱祖勍2

Outline

Basic Course Information

Review of Basic Concepts

Optical Communications

Lecture 1: Introduction 朱祖勍3

Basic Course InformationLecture Schedule:

09/06/2021 – 01/03/2022, 16 Lectures + Final10/04 is a national holiday (No Lecture)Monday, 15:55 – 17:55 pm

Experiment Schedule:Starting from 11/08/2021, 5 experimentsDetailed schedule will be announced latter

Scoring SystemIn-Class Quiz, 25% (two, random time)Final on 01/03, 62.5% (open-book exam)Experiments, 12.5%

Lecture 1: Introduction 朱祖勍4

Basic Course InformationTextbook:

《光网络－光纤通信技术与系统》上卷（《OpticalNetworks: A Practical Perspective, SecondEdition》） , by Rajiv Ramaswami and Kumar N.Sivarajan, 中译本，机械工业出版社， ISBN 7-111-14228-4

Lecture Notes: http://www.zuqingzhu.info/OCN.html

Lecture 1: Introduction 朱祖勍5

Basic Course InformationRelated Courses:

《现代通信光电子学》（Recommend to Take）

《通信网络理论基础》（Recommend to Take）

《光波导技术基础》（Can Take as Reference）

My Email: [email protected]

李 上 宾 老 师 主 讲 12/06-12/27 的 四 次 课 ，

[email protected]

Lecture 1: Introduction 朱祖勍6

Outline

Basic Course Information

Review of Basic Concepts

Optical Communications

Lecture 1: Introduction 朱祖勍7

What is Digital Communication?

TX RX

Communication: Exchange of Information

Four Key Elements:Transmitter, 信源

Receiver, 信宿

Channel, 信道

Carrier, 载波

Lecture 1: Introduction 朱祖勍8

How to Perform Digital Communication?

TX RX

Encoding, 编码（信息 => 比特流）:Source Coding: 数据压缩, 降低冗余度, 例如：霍夫曼编码

Channel Coding : 差错纠正, 增加冗余度, 例如：汉明编码

Encoding + Modulation Demodulation + Decoding

平均码长: 1.85 bits/symbol 4 bits => 7 bits, 一位纠错

Lecture 1: Introduction 朱祖勍9

How to Perform Digital Communication?

TX RX

Modulation, 调制（比特流 => 波形）:Amplitude Modulation: ASK

Phase Modulation: PSK, DPSK, QPSK

Frequency Modulation: FSK

Combinational Modulation: 16QAM, 64QAM, …

Carriers, 载波（声、光、电）

Encoding + Modulation Demodulation + Decoding

星座图: 8-PSK

Lecture 1: Introduction 朱祖勍10

Communication Channels

Open Channel: Atmosphere, Deep SpaceAgile, Cheap, Insecure, Unreliable, lots of interference

Lecture 1: Introduction 朱祖勍11

Communication Channels

Guided Channel: Optical Fiber, Coaxial Cable, …Secure, reliable, less interference, expensive

Lecture 1: Introduction 朱祖勍12

Multiple Access: Multiplexing

Lecture 1: Introduction 朱祖勍13

Multiple Access: Multiplexing

TX RX

Multiplexing, 共享信道:Time Division Multiplexing (TDM)

Frequency Division Multiplexing (FDM)

Wavelength Division Multiplexing (WDM)

Code Division Multiplexing (CDM)

TX RX

TDM

FDM

Lecture 1: Introduction 朱祖勍14

Wavelength Division Multiplexing (WDM)

WDM is FDMWavelength/Frequency => Color

Lecture 1: Introduction 朱祖勍15

Wavelength Division Multiplexing (WDM)

Lecture 1: Introduction 朱祖勍16

What is a Telecommunication Network?

Definition: a collection of terminal nodes, links and anyintermediate nodes that are connected so as to enabletelecommunication between the terminals.

Mathematically: G(V, E), V is the set of nodes, E is the set oflinks

1

3

4

5

6

2

Lecture 1: Introduction 朱祖勍17

Telecommunication Networks

In terms of clients:Private: Enterprise Networks …

Public: Campus Networks …

In terms of geographic coverage:Long-haul: Core Networks

Wide-area: Metro Networks

Local-area: Access Networks

Lecture 1: Introduction 朱祖勍18

Telecom Network Infrastructure

Core Network

Metro Networks

Access Networks

Lecture 1: Introduction 朱祖勍19

Telecom Network Infrastructure

Core NetworksCoverage: Several hundred to thousands ofkilometersTopology: MeshSpeed and Reliability are important

Metro NetworksCoverage: A few hundred kilometersTopology: Ring or MeshSpeed is important

Lecture 1: Introduction 朱祖勍20

Access NetworksCoverage: Tens of kilometersTopology: Ring or StarCost is important

Telecom Network Infrastructure

Lecture 1: Introduction 朱祖勍21

Fiber-Optic Networks

An Optical Fiber Junction Box

Lecture 1: Introduction 朱祖勍22

Fiber-Optic NetworksMultiple Planes

Control Plane: carrying control information, i.e., signaling

Management Plane: carrying the operations andadministration traffic for network management

Data Plane: carrying the networker’s users traffic

Layered Structure

Lecture 1: Introduction 朱祖勍23

Optical Network Topology –Bus

Single-Hop Network

Broadcast and Select

Access Networks

Simple, Low cost, Scalable

Not Reliable

Lecture 1: Introduction 朱祖勍24

Optical Network Topology –Star

Central Hub Acts as a Repeater

Access Networks

Simple, Low cost, Scalable

Not Reliable

Lecture 1: Introduction 朱祖勍25

Optical Network Topology –Ring

Multi-Hop Network

Bi-directional Routing

Metro/Access Networks

Simple, Scalable

Can be Restored from Single-Link/Node Failure

Lecture 1: Introduction 朱祖勍26

Optical Network Topology –Tree

Multi-Hop Network

Metro/Access Networks

Simple, Scalable

Not Reliable

Lecture 1: Introduction 朱祖勍27

Multi-Hop Network

Matrix Routing

Core Networks

Complicated, Reliable, Not Scalable1

14

6

75 9

3

842

13

12

11

10

11

1414

66

7755 99

33

884422

1313

1212

1111

1010

Optical Network Topology –Mesh

Fully Connected

Partially Connected

Lecture 1: Introduction 朱祖勍28

Communication in a Telecom Network

Routing:Find a proper route between the source anddestination nodes

Forwarding:Send data to the destination following a pre-determined route

Switching:Setup a communication session.

Lecture 1: Introduction 朱祖勍29

Communication in a Telecom Network

Setup an end-to-end communicationsession.

Establish communication channelbetween the transmitter and receiver.

Adjust the working status of eachintermediate node if there is any.

Switching: Circuit Switching, Packet Switching

Lecture 1: Introduction 朱祖勍30

Switching in NetworksCircuit Switching

End-to-end communication is carried by circuits

Reserve bandwidth b on each link along therouting path p

Data is forwarded along in the circuit pipeline

Packet SwitchingEnd-to-end communication is carried by packets

Each packet is labeled with its destination address

Each packet is forwarded based on its destinationaddress

Lecture 1: Introduction 朱祖勍31

Circuit Switching

SwitchFabricDeMux Mux

Crossconnect

Lecture 1: Introduction 朱祖勍32

Circuit Switching

Connection-Oriented Services

Resource Reservation

FDM, TDM, …

Guaranteed Quality-of-Service (QoS)

Expensive but Reliable

Examples: Telephone Networks

Lecture 1: Introduction 朱祖勍33

Packet Switching

Router

Lecture 1: Introduction 朱祖勍34

Packet SwitchingConnectionless Services

Resource Allocation

Statistical Time-Division Multiplexing

Best-Effort

Cheap but Unreliable

Examples: IP Data Networks

Lecture 1: Introduction 朱祖勍35

Routing in a NetworkSingle-path Routing:

Request is carried with a single routing path fromthe source to the destination.

Shortest path routing: Dijkstra Algorithm

Weighted routing

Multi-path Routing:Request is carried with multiple routing paths fromthe source to the destination.

K-shortest path search algorithm

Lecture 1: Introduction 朱祖勍36

1

3

4

5

6

2

1 6

Original TopologyPath 1: 1 → 2 → 4 → 6

1

2

3

4

6

5

Topology after 1st IterationPath 1: 1 → 2 → 4 → 6Path 2: 1 → 3 → 5 → 6

Topology after 2nd IterationPath 1: 1 → 2 → 4 → 6Path 2: 1 → 3 → 5 → 6

3

4

5

2

Lecture 1: Introduction 朱祖勍37

Outline

Basic Course Information

Review of Basic Concepts

Optical Communications

Lecture 1: Introduction 朱祖勍38

History of Optical Communications

Time: 1000 B.C.

Data-rate: 1 bit / 24 hours

Manually operated

Free-space transmission

Applications:Defense

Entertainment（烽火戏诸侯）

Earliest Optical Communications

烽火台

Lecture 1: Introduction 朱祖勍39

History of Optical Communications

Time: 2010 A.D.

Data-rate: 322 Tb/s (1 Tb = 1012 bits)

Electrically powered

Guided transmission in Fibers

Wavelength-Division Multiplexing

Applications:Telecommunication Core Router

Modern Optical Communications

Cisco CRS-3 Router

Lecture 1: Introduction 朱祖勍40

What is Optical Communication?

TX RX

TransmitterElectrical-to-Optical (E/O) ConverterLight Sources: Laser, LED, …E/O Modulator: Direct Modulators, External Modulators, …

Light Source

E/O Modulator

Lecture 1: Introduction 朱祖勍41

What is Optical Communication?

TX RX

ChannelOpen Channels (Wireless Optical Communications):Atmosphere, free-space …Guided Channel (Fiber Optical Communications): Optical Fiber

Or

Lecture 1: Introduction 朱祖勍42

What is Optical Communication?

TX RX

ReceiverOptical-to-Electrical (O/E) ConverterE/O Converter: Photo-detector, …

O/E Converter

Lecture 1: Introduction 朱祖勍43

What is Optical Communication?

TX RX

CarrierOptical Waves/PhotonsSpectrum Range: ~1012 Hz (Infrared) - ~1016 Hz(Ultraviolet)Wavelength Range: ~10-8 m - ~10-5 mRelationship between Frequency and Wavelength:

cf

Lecture 1: Introduction 朱祖勍44