Communication Communication Networks Networks

Guest Instructor: Guest Instructor: YihanYihan LiLi

ECE Dept., Polytechnic UniversityECE Dept., Polytechnic University

EE3414EE3414Multimedia Communication Systems IMultimedia Communication Systems I

2

Communication Networks and Services

Communication networks: a set of equipment and facilities that provides a service to transfer information between users located at various geographical pointsServices

Radio and televisionTelephone serviceCellular telephone serviceElectronic mailWorld Wide Web (WWW)Video on demand

3

Broadcast NetworkBroadcast Communication Network do not have intermediate switching nodesEach station has a transmitter/receiver that communicates over a medium shared by other stationsTransmission from any station is received by all other stationsExample: radio and television broadcasting

Related high audio and video quality is expectedA significant amount of delay can be tolerated

4

Telephone Service

Real-time serviceConnection-oriented: a connection has to be set upUsers expect the network to be capable all the timeSecurity and privacy

5

Cellular Telephone ServiceExtends the normal telephone service to mobile usersHand off, when users move from one cell to another

6

Electronic Mail (e-mail)User provides a text message and a name/address to a mail applicationA local mail server transmits the message to a destination server across a computer networkRequires reliability, delivers without errors to the correct destinationNo need to set up connectionCan tolerate large delays

7

World Wide WebOne computer can access documents located in other computers connected to the InternetA browser is used to display the documentsUniform resource locator (URL) specifies the name of the machine and the name and location of the document

e.g., http://www.poly.edu/Delay requirement

8

Communication Network Design

Networka set of equipment and facilities transfers information between a source and a destination

Note: Network nodes do not generate informationclassified based on the way in which the nodes exchange information

Communication Networks

SwitchedCommunication Networks

BroadcastCommunication Networks

9

Broadcast Communication Networks

Broadcast Communication Network do not have intermediate switching nodes:

Each station has a transmitter/receiver that com-municates over a medium shared by other stationsTransmission from any station is received by all other stationse.g., TV networks

More like utility networks (power, water, etc.)

Packet RadioNetwork

SatelliteNetwork

Bus LocalNetwork

10

Switched Communication Networks

Consists of an interconnected collection of nodesData are transmitted from source to destination by being routed through the nodesThe switching method describes how data are processed and routed in the network

SwitchedCommunication Networks

Circuit-SwitchedNetworks

Packet-SwitchedNetworks

Datagram Network Virtual Circuit Network

11

Network Design Requirements

Cost-effectiveEasy to manageResilientHigh-speedScalable

Protocol: a set of rules that governs how two communicating parties are to interact

12

Simple SolutionConnect each pair of devices by a dedicated point-to-point linkSufficient if the number of devices is small.

13

With a large number of devices it is not practical to connect each pair of devices

Simple Solution

14

A communication network provides a general solution to the problem of connecting many devices:

Connect each device to a network nodeNetwork nodes exchange information and carry the information from a source device to a destination device

General Communication Network

CommunicationNetwork

Network Node

host

15

General ArchitectureIntermediate nodes: signal relayEnd-to-End: multi-hop transportation

3

1 5

42

Star Ring Mesh

16

Role of SwitchesA switch interconnects many links allowing for data to be switched from one link to another.

17

Communication Network Architecture

Access network is used to provide end users access to services and connectivity to other end users Backbone network interconnects access networks LAN (Local Area Network), typically deployed in offices/campus buildings WAN (Wide Area Networks), interconnects offices, buildings, homes, regions

18

Network Configuration

19

Example: vBNS Network

Source: National Science Foundation

20

Network FunctionsAddressing

Identify which network input is to be connected to which networkoutput

Traffic controlTo ensure the smooth flow of information through the networkReroute or prevent information traffic during congestion

Network managementMonitor the network performanceDetect and recover from faultsConfigure the network resources

Multiplexingconnect multiple information flows into shared connection lines

Routingdetermine the path across the network

Switching approach

21

B B

C C

A A

B

C

A

B

C

A

MUXMUX

(a) (b)Trunkgroup

Figure 4.1

Multiplexing of Signals

Multiplexers are used to multiplex data bits from different communication sessions on to one link.

Time Division Multiplexing (TDM)Frequency Division Multiplexing (FDM)Wavelength Division Multiplexing (WDM).

22

(a) Each signal transmits 1 unit every 3T seconds

(b) Combined signal transmits 1 unit every T seconds

tA1 A2

tB1 B2

tC1 C2

3T0T 6T

3T0T 6T

3T0T 6T

tB1 C1 A2 C2B2A1

0T 1T 2T 3T 4T 5T 6TFigure 4.3

Time Division Multiplexing

23A CBf

Cf

Bf

Af

W

W

W

0

0

0

(a) Individual signals occupy W Hz

(b) Combined signal fits into channel bandwidth

Figure 4.2

Frequency Division Multiplexing

24

λ1

λ2

λm

OpticalMUX

λ1

λ2

λm

OpticaldeMUX

λ1 λ2. λm

Opticalfiber

Figure 4.18

Wavelength Division Multiplexing

25

Switching ApproachesCircuit-switched (e.g., Telephone network) Packet-switched connectionless

Connectionlesspacket headers carry destination addresses and routing through the network is based on the destination address e.g., Internet - IP protocol based

Connection-orienteda "connection" is set up (i.e., a route is selected) prior to data transfer and released after data transfer.e.g., ATM: Asynchronous Transfer Mode

Switched Communication Networks

Circuit-Switched Networks Packet-Switched Networks

Datagram Networks Virtual Circuit Networks

26

In a circuit-switched network, a dedicated communication path is established between two stations through the nodes of the networkThe dedicated path is called a circuit-switched connection or circuitA circuit occupies a fixed capacity of each link for the entire lifetime of the connection. Capacity unused by the circuit cannot be used by other circuitsData is not delayed at the switches

Circuit Switching

27

Circuit-switched communication involves three phases:

1. Circuit Establishment2. Data Transfer3. Circuit Termination

“Busy Signal” if capacity for a circuit not available.Most important circuit-switching networks

Telephone networksISDN (Integrated Services Digital Networks)

Circuit Switching

28

Telephone Network

Signal

Source

Signal

Release

Signal

Destination

GoAhead Message

Telephone call setup

29

Making a Phone Call

30

Circuit Switching

A node in a circuit-switching network:

Configured according to request

31

Circuit Switching

circuit 2

circuit 1

32

Packet SwitchingExample: Internet

Operates much like the postal system, where an envelope is sent in the mail with a destination addressEach intermediate post office determines the next hop post office based on this addressIntermediate post offices are comparable to IP routers

Data are sent as formatted bit-sequences, so-called packetsHeader and Trailer carry control informationEach packet is passed through the network from node to node along some path (Routing)At each node the entire packet is received, stored briefly, and then forwarded to the next node (Store-and-Forward Networks)No capacity is allocated for packets

Header Data Trailer

33

Packet Switching

2

3

1

3

34

Datagram Packet SwitchingPackets are called datagramsThe network nodes process each packet independently

If Host A sends two packets back-to-back to Host B over a datagram packet network, the network cannot tell that the packets belong together. In fact, the two packets can take different routes.

Implications of processing packets independentlyA sequence of packets can be received in a different order than it was sentEach packet header must contain the full address of the destination

35

Datagram Packet Switching

A.3

A.2

C.2 A.1

C.1

A.3A.2A.1

C.1C.2

A.3 A.2 A.1

C.1C.2

A.3

A.2

C.2 A.1

C.1

A.3 A.2 A.1

C.1C.2

A.2

A.3

A.1

A.2A.2A.2

C.2

A.2

A.3

A.1A.2A.3A.2A.1

36

Virtual-Circuit Packet Switching

Virtual-circuit packet switching is a hybrid of circuit switching and packet switchingAll data is transmitted as packetsAll packets from one packet stream are sent along a pre-established path (virtual circuit)Guarantees in-sequence delivery of packetsHowever, packets from different virtual circuits may be interleavedExamples

X.25, since the 1970s, used in many public packet switching networksATM (Asynchronous Transfer Mode), developed in the 1980s, for transmission of voice, video, and data in a single network

37

Virtual-Circuit Packet Switching

A.3A.2A.1

VC 2

VC 1

C.1C.2

C.1C.2

A.3 A.2 A.1A.3 A.2 A.1

C.1C.2

A.3 A.2 A.1A.3 A.2 A.1

A.3 A.2 C.2 A.1 C.1

A.3 A.2 C.2 A.1 C.1

C.1

A.3

A.1

C.2 A.3

A.1A.2A.3A.2A.1

C.1

A.3

A.1

C.2 A.3

A.1A.2A.3A.2A.1

38

Comparison

Dedicated transmission pathContinuous transmission Path stays fixed for entire connectionCall setup delayNegligible transmission delayNo queueing delayBusy signal overloaded networkFixed bandwidth for each circuit No overhead after call setup

Circuit SwitchingNo dedicated transmission pathTransmission of packetsRoute of each packet is independentNo setup delayTransmission delay for each packetQueueing delays at switchesDelays increase in overloaded networksBandwidth is shared by all packetsOverhead in each packet

Datagram Packet Switching

No dedicated transmission path Transmission of packetsPath stays fixed for entire connectionCall setup delayTransmission delay for each packetQueueing delays at switchesDelays increase in overloaded networksBandwidth is shared by all packetsOverhead in each packet

VC Packet Switching

39

QoS Requirements of Real-Time Applications

Constraints on delay and jitter For telephony traffic, one-way delay requirement is 25ms if there are no echo cancellers on the path, 150ms with an echo canceller for excellent quality voice, and 400ms with an echo canceller for acceptable quality voice. Delay in transmitting a voice packet on a packet-switched network consists of packetization delay (time to fill the packet), emission delay on the links (packet size divided by transmission rate), propagation delay on the links (length of the link divided by the speed of light in the link medium), queueing delays, and playout delays at the receiver. Voice codec rates vary; PCM codecs generate data at 64kbps, Good speech codecs at 16 kbps or below.

40

Matching of applications needs/traffic to networking modes

Bursty traffic: best served by packet-switched networksContinuous traffic: best served by circuit-switched networksDelay-sensitive traffic: best served by connection-oriented networksShort delay-insensitive transfers: best served by connectionless networksConclusions:

Interactive, streaming and recording applications best served by packet-switched connection-oriented networks;Short non-real-time transfers: best served by (packet-switched) connectionless networksLarge non-real-time transfers: best served by circuit-switched networks

41

Key Factors in Communication Network Evolution

Success new telecommunication service

Technology must be available to implementGovernment regulationsmuch permit the service to be offeredMarket for the service existStandards, to move away from single providers

42

StandardsStandards are agreements, with industrywide, national and possibly international scope, that allow equipment manufactured by different vendors to be interoperable

Standards on interfaces, allow interconnecting equipmentStandards on data communications, allow computers ‘talking to one another’

Result from a consultative process (on a national and possibly international basis

e.g., International Telecommunications Union (ITU)Enable smaller companies to enter large marketsAllows network operators to choose equipment from multiple suppliers

43

References

A. Leon-Garcia and I. Widjaja, Communication networks, Chapter 1