CSC 535 Communication Networks I Chapter 1 Introduction Dr. Cheer-Sun Yang.

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CSC 535Communication Networks I

Chapter 1Introduction

Dr. Cheer-Sun Yang

Communication and Networking

What are the differences? Communication - focuses on the transmission

of data from one end, called the source, to another end, called the destination.

Networking - focuses on the issues involved when connecting more communication hosts together and becoming a network.

CSC535- focuses on point-to-point communications

CSC581- focuses on networking including LAN and WAN

Network and ServicesA communication network connects many

hosts together to provide services. Some examples:

Radio and television networks Telephone networks Cable networks Data networks such as the Internet and SOHO

networks Transportation networks - not our focuses but

useful for understanding the services provided by a network.

Radio and TV NetworksMeans of commuinication: electrical wave

with various frequencies Services: carrying signals that encode

some entertaining programs and commercial information.

Requirements: Many programs being broadcast

simultaneously Delay in the order of seconds can be tolerated

Telephone NetworksMeans of commuinication: electrical wave with

various frequencies Services: carrying signals that encode human

conversations.Requirements:

Real-time service: delay in the order of seconds can not be accepted; acceptable delay is around 250 milliseconds

Availability requirement is higher than TV or radio. The network must be available throughout the conversations.

More “intelligent services” that users are involved.

The caller picks up the phone triggering the flow of current in wires that connect to the telephone office.

The current is detected and a dial tone is transmitted by the telephone office to indicate that it is ready to receive the destination number.

The caller sends this number by pushing the keys on the telephone set. Each key generates a pair of tones that specify a number. (In the older phone sets the user dials a number which in turn generates a corresponding number of pulses.)

The equipment in the telephone office then uses the telephone network to attempt a connection. If the destination telephone busy, then a busy tone is returned to the caller. If the destination telephone is idle, then ringing signals are sent to both the originating and destination telephones.

The ringing signals are discontinued when the destination phone is picked up and communication can then proceed.

Either of the users terminate the call by putting down a receiver.

Telephone Office

Figure 1.1

Data NetworksMeans of commuinication: electrical wave

with various frequencies Services: carrying signals that encode

information.Requirements:

connectionless (e-mail) vs. connection-oriented (ftp, telnet, www, etc.);

real-time (audio/video conferencing) vs. Non real-time (video on demand)

Figure 1.2 Retrieving e-mail

Figure 1.3 World Wide Web example

generic examples of each type of application

The user clicks on a link to indicate which document is to be retrieved.

The browser must determine the address that contains the document. It does this by sending a query to its local name server.

Once the address is known the browser establishes a connection to the specified machine, usually a TCP connection. In order for the connection to be successful, the specified machine must be ready to accept TCP connections.

The browser runs a client version of HTTP, which issues a request specifying both the name of the document and the possible document formats it can handle.

The machine that contains the requested document runs a server version of HTTP. It reacts to the HTTP request by sending an HTTP response which contains the desired document in the appropriate format.

The TCP connection is then closed and the user may view the document.

Figure 1.4

Realplayer example

Figure 1.5

Network Funcations and Some Design IssuesProvides connectivity between usersSwitching provides a saving on the number of

connectivityMultiplexing provides an efficient way to share

connectivityRouting provides a direction regarding a

destination associated with a connection Addressing identifies source and destinationsTraffic control regulates traffic flowing through a

networkNetwork management monitors network status

Network

Figure 1.6

Network

(a) A switch provides the network to a cluster of users

(b) A multiplexer connects two access networks

Access network

Figure 1.7

Metropolitan network A consists of access subnetworks a, b, c, d.

National network consists of regional subnetworks .

Metropolitan network A is part of regional subnetwork .

Metropolitan

Figure 1.8

Key Communications Tasks Transmission system utilization Interfacing Signal generation Synchronization Exchange management Error detection and correction Addressing and routing Switching and multiplexing Message formatting Security Network management

What happens “In the Cockpit”? Example: ftp

Hardware: links between source and destination

Hardware: PCs and Network Interface CardHardware: modemSoftware: TCP/IP softwareSoftware: device driverSoftware: operating system that ftp(an

application program) is running onLet’s try “ftp -d taz.cs.wcupa.edu”

[yang@coyote yang]$ ftp -d taz.cs.wcupa.eduConnected to taz.cs.wcupa.edu.220 taz.cs.wcupa.edu FTP server (Version wu-2.6.1(1) Wed Aug 9 05:54:50 EDT 2000) ready.Name (taz.cs.wcupa.edu:yang): yang---> USER yang331 Password required for yang.Password:---> PASS XXXX230 User yang logged in.---> SYST215 UNIX Type: L8Remote system type is UNIX.Using binary mode to transfer files.ftp>

ftp> cd public/socket---> CWD public/socket250 CWD command successful. ftp> get server1.clocal: server1.c remote: server1.c---> TYPE I200 Type set to I.ftp: setsockopt (ignored): Permission denied---> PASV227 Entering Passive Mode (144,26,77,43,87,139)---> RETR server1.c150 Opening BINARY mode data connection for server1.c (1639 bytes).226 Transfer complete.1639 bytes received in 0.0147 secs (1.1e+02 Kbytes/sec)

ftp> put server1.clocal: server1.c remote: server1.cftp: setsockopt (ignored): Permission denied---> PASV227 Entering Passive Mode (144,26,77,43,180,246)---> STOR server1.c150 Opening BINARY mode data connection for server1.c.226 Transfer complete.1639 bytes sent in 0.000157 secs (1e+04 Kbytes/sec)ftp>

ftp> quit---> QUIT221-You have transferred 3278 bytes in 2 files.221-Total traffic for this session was 5858 bytes in 5 transfers.221-Thank you for using the FTP service on taz.cs.wcupa.edu.221 Goodbye.

PS = packet switch

C = computer

Figure 2.7

G = gateway/router

Figure 2.8

Net Interface

Ethernet PPP

Router

router

(1,3) r

Ethernet

Server PC

Figure 2.13

User Interface

User PI

User DTP

PI = Protocol interpreter

DTP = Data transfer process

User FTP

Server PI

Server DTP

Server FTP

Control

Connection

Figure 2.19

Communication ProtocolsA set of rules that is used for “governing” how a

source and a destination communicates. Must speak the same languageEntities

User applications e-mail facilities terminals

Systems Computer Terminal Remote sensor

Key Elements of a ProtocolSyntax

Data formats Signal levels

Semantics Control information Error handling

Timing Speed matching Sequencing

Examples of ProtocolsApplications:

HTTP(p.45) SMTP(p. 48) FTP(p.82)

Transportation: TCPNetworking: IPmany others....almost too many (skip sections 1.2.2, 1.2.3, 1.2.4,1.2.5,

1.2.6, 1.3.1)

TCP/IP Protocol ArchitectureDeveloped by the US Defense Advanced

Research Project Agency (DARPA) for its packet switched network (ARPANET)

Used by the global InternetNo official model but a working one.

Application layer Host to host or transport layer Internet layer Network access layer Physical layer

TCP/IP Protocol Architecture Model

Protocol Data Units (PDU)At each layer, protocols are used to

communicateControl information is added to user data at

each layerTransport layer may fragment user dataEach fragment has a transport header added

Destination SAP Sequence number Error detection code

This gives a transport protocol data unit

ApplicationLayer

PresentationLayer

SessionLayer

TransportLayer

NetworkLayer

Data LinkLayer

PhysicalLayer

ApplicationLayer

PresentationLayer

SessionLayer

TransportLayer

NetworkLayer

Data LinkLayer

PhysicalLayer

Application A Application Bdata

Figure 2.9

Physical LayerPhysical interface between data

transmission device (e.g. computer) and transmission medium or network

Characteristics of transmission mediumSignal levelsData ratesetc.

Network Access LayerExchange of data between end system

and networkDestination address provisionInvoking services like priority

Internet Layer (IP)Systems may be attached to different

networksRouting functions across multiple

networksImplemented in end systems and routers

Transport Layer (TCP)Reliable delivery of dataOrdering of delivery

Application LayerSupport for user applicationse.g. http, SMPT

OSI ModelOpen Systems InterconnectionDeveloped by the International

Organization for Standardization (ISO)Seven layersA theoretical system delivered too late!TCP/IP is the de facto standard

ApplicationLayer

PresentationLayer

SessionLayer

TransportLayer

NetworkLayer

Data LinkLayer

PhysicalLayer

ApplicationLayer

PresentationLayer

SessionLayer

TransportLayer

NetworkLayer

Data LinkLayer

PhysicalLayer

NetworkLayer

Electrical and/or Optical Signals

Application A Application B

Data LinkLayer

PhysicalLayer

NetworkLayer

Data LinkLayer

PhysicalLayer

Communication Network

Figure 2.6

OSI LayersApplicationPresentationSessionTransportNetworkData LinkPhysical

OSI v TCP/IP

StandardsRequired to allow for interoperability

between equipmentAdvantages

Ensures a large market for equipment and software

Allows products from different vendors to communicate

Disadvantages Freeze technology May be multiple standards for the same thing

Who defines standards? International: The International Standards

Organization(ISO)The American National Standards Institute(ANSI)The International Telecommunications Union-

Telecommunication Standards Sector (ITU-T, formally the CCITT)

The Institute of Electrical and Electronics Engineers (IEEE)

Internet Society (ISOC) and Internet Engineering Task Force (IETF)

ATM Forum

What have they defined?

ISO: Open Systems Interconnection(OSI)ANSI: represents USA in ISO ITU-T: X.25, X.400, X.500; e-mail; ISDN IEEE: IEEE 802.2, 802.3, 802.4, 802.5,

802.11 ISOC and IETF: TCP/IP, SNMP, routing

protocols (RIP, OSPF, BGP) IETF: maintains Request for

Comments(RFCs)ATM: ATM related standards

CSC 535 Communication Networks I Chapter 1 Introduction Dr. Cheer-Sun Yang.

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