business data communications and networking raymond r. panko copyright 2001 prentice hall revision...

Business Data Communications and Networking

Revision 1: August 2000

Modified by Nancy Smithfield 2002

Basic Concepts and Principles

Chapter 1

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Part A:Business Data Communications and Networking

What’s in a Title?

6Business

For IS (information systems) students in business schools

– Computer science and electrical engineering students are trained to work in hardware, software, and networking vendor firms, such as Microsoft, IBM, Oracle, and Cisco Systems

– IS graduates are trained to work in end user organizations, such as banks, government agencies, and manufacturing firms--organizations that use IT (information technology) to get their work done

7Business

The IS Job: Full life cycle support

– To help firms understand how networking will help them work better

– To do needs analysis

– To plan and develop new networks

– To manage new networks after they are developed

Network

A Network is an Any-to-Any Communication System– Can connect any station to any other– Stations are called nodes on a network

“Connect to GHI”

Network

Each Station has a Unique Network Address– To connect, only need to know the receiver’s address– Like telephone number

DEF GHI

JKLMNO

10Data Communications

Originally, There was a Sharp Distinction:– Voice and Video Communication versus

– Data Communications, in which one or both parties is a computer

Database Electronic mail World Wide Web

– Distinction is fading because voice and video communication are increasingly computer-based

11Voice and Video Networks

Telephone Network– Customer premises (home or office)– Local loop (access line) connects customer premises to

first switching office

Connection

Switching OfficeLocal Loop

(Access Line)

CustomerPremises

Telephone Network– Local loop - each telephone has a pair of wires that

goes directly to a telephone company’s nearest office– if a customer (subscriber) attached to a particular office

calls another subscriber attached to the same office, the switching equipment sets up a direct electrical connection between the 2 local loops.

Connection

Switching OfficeLocal Loop(Access Line)

CustomerPremises Customer

Premises

Telephone Network– The connection remains intact for the duration of

the call. The call has a “reserved circuit capacity”.

Connection

Switching OfficeLocal Loop(Access Line)

CustomerPremises Customer

Premises

If the called telephone is attached to another end office, the the connection will be made through a trunk line. There is a hierarchy of switches

Trunk lines connect switches

Switch

Trunk Line

Circuit– End-to-End Connection between Phones– May pass through multiple switches– And trunk lines

CircuitCircuit

Reserved Capacity– Circuit capacity is reserved during duration of

each call– At each switch– On each trunk line

Circuit

ReservedCapacity

Reserved Capacity– Another name for this type of circuit is circuit

switching– Circuit Switching Characteristics

a connection is established before 2 stations begin transmitting

bandwidth (range of frequencies) is dedicated to the connection until the connection is terminated

Reserved Circuit Capacity Guarantees Throughput– Never get less than reserved capacity– Nothing like congestion on the Internet

Reserved Circuit Capacity is Expensive– Pay for it whether you use it or not– Good for voice, because conversations are fairly

constant– Bad for data, because most data transmission is bursty;

e.g., in World Wide Web, download, then stare at screen for a long time until next download

19Packet-Switched Data Networks

Packet Switching– Circuit switching is expensive due to reserved capacity – Packet switching breaks transmissions into messages

– Messages are short (averaging a few hundred bytes) because switches handle short messages efficiently

– Messages are called packets (sometimes, frames or other names)

Message Packets

Packet Switching– packets can travel any path to a destination– packets contain destination address and sequencing

information (puts packets back in proper order)– example

class (message) send you to Ruby Tuesday’s in Mall won’t tell you mode of transportation or route how can this be done?

Message Packets

Packet Switching– example

class (message) send you to Ruby Tuesday’s in Mall won’t tell you mode of transportation or route use a car, bus or walk (different network

technologies) go towards Ft. Campbell and then down 101st or out

college street? Which door of mall will you enter?

22Circuit-Switched Data Networks

Circuit Switching– example

class (message) send you to Ruby Tuesday’s in Mall reserved 3 busses that will arrive at end of class

– make the reservation ahead of time (establish a circuit)

– pay for 36 seats (12 per bus) - if only 2/3 of the class is here, I have wasted capacity

Switching Decision– When a packet arrives at a switch, the switch must

decide which of several ports (connections) to use to send the packet back out

– Complex– Made at each switch

Switch A

DPacket

24Packet Switched Data Networks

Multiplexing– Packets from many conversations are mixed

(multiplexed) over each trunk line– Only pay for the capacity used– Dramatic trunk line cost savings– The reason for packet switching

Multiplexing onTrunk Line

Part B:More Basic Concepts

Analog and Digital Communication

Modems

LANs and WANs

26Analog Transmission

In analog transmission, the state of the line can vary continuously, rising and falling smoothly in intensity among an infinite number of states– State may be voltage, frequency or another line signal

characteristic– The human voice is like this– When we speak into a telephone, we generate

analogous (similar) electrical signals, hence the name

Strength

27Digital Transmission

In digital transmission, time is divided into periods of fixed length called clock cycles

The line is kept constant (in one state) during each clock cycle so that the receiver can sample it anywhere during the cycle and get the same result

Clock CycleTime

Strength

The line is kept in one of only a few possible states (conditions) during each clock cycle– 2, 4, 8, 16, 32, rarely more– There are fairly large differences between states– If a signal is near one state but a bit off, the receiver

will still read it correctly as being at that state

Clock CycleTime

Strength

At the end of each clock cycle, the line may change abruptly to another of these few states – Can also stay the same

Strength

AbruptChange

Stays Same

Clock Cycle

30Digital Versus Binary Transmission

Digital transmission: a few states (2, 4, 8, 16, etc.)

Binary transmission: exactly two states– One state represents 1, the other 0

Digital Binary

Two StatesFew States

31Digital Communication

Modems– Computers have digital output

– Telephone network assumes analog input

– Modem translates between digital device and analog line for data transmission over the phone system

DigitalSignal

AnalogSignal

32LANs and WANs

Networks Have Different Geographical Scopes

Local Area Networks (LANs)– Small Office– Office Building– Industrial Park / University Campus

Wide Area Networks (WANs)– Connect corporate sites or– Connect corporate sites with sites of customers and

suppliers

33Elements of a Simple LAN

Hub or Switch

Wiring

Hub or Switch connects all stations

Wiring is standardbusiness telephone wiring

(4 pairs in a bundle)

Server

Client PC

Server

Client PCs are used byordinary managers and

professionals; receive service

Servers provide servicesto client PCs

Server

Client PC– Begin with stand-alone PC

– Add a network interface card (NIC) todeal with the network

– Networks have many client PCs

Server– Most PC nets have multiple servers

Part C:Distributed Processing

Terminal-Host Systems

File Server Program Access

Client Server Processing

37What is distributed?

Data Storage - Where and in what type of structure is the data stored (DB or files)

Data Access Logic - Process required to get the correct data

Application Logic - Processing required before and after data is retrieved

Presentation Logic - User Interface, System Commands, Data Entry

38Terminal-Host Systems

Created in the 1960s– Central host computer does all the processing– Terminal is dumb--only a remote screen and keyboard– Created in the 1960s, when microprocessors for

terminal intelligence did not exist

Terminals Host

– Mainframes are the largest business hosts Optimized for business uses--file access speed is

more crucial than mathematical processing

Many Mainframe Applications Were Created in the 1960s through 1980s– Legacy systems--systems created by your predecessors

– Would not use the same platform today if built new

– But too expensive to rewrite all legacy applications at once

– Must live with many host legacy applications for now

– Older networks can be legacy systems as well; “legacy system” is not just limited to mainframe applications

41PC Networks

The Most Common Platform in Organizations– Allows PCs to share resources– Both Wintel (Windows/Intel) PCs and Macintoshes

Network

42PC Network Components

File Servers– Store files (data files and programs)– The most common type of server in PC networks– Almost all file servers are themselves PCs

File Server

43File Server Program Access

File Server Program Access is the Most Common Way to Execute Programs in PC Networks– Program files are stored on the file server before

execution

File ServerClient PC

Storedon the

FileServer

File Server Program Access– Program and data files are downloaded (copied) to the

Client PC– Executed on the client PC, not on the file server– File server merely stores programs and data files

Downloaded toClient PC,Executed There

PC Processing Power Limits FSPA Programs– Client PCs do not get very large– Only programs small enough to operate on limited

client PCs can be used

Data Storage is the only thing done on server

Executed on theClient PC

46Client/Server Processing

Client and Server Machines– Neither has to be a PC– Platform independent

Client Machine Server

47C/S Servers often are Workstation Servers

Workstations– Are computers more powerful (and expensive)

than PCs

– Do not use standard Intel PC microprocessors

– Usually run the UNIX operating system

– Client and server workstations

– Confusingly, Windows NT client operating system is called Windows NT Workstation, where workstation is synonymous with “client”

Two Programs– Client program on client machine– Server program on server machine– Work together to do the required processing

Client ProgramServer

Program

Division of Labor– Client program handles lighter work, such as user

interface chores and light processing chores

– Server program handles heavy work, such as database retrieval

Program

Cooperation Through Message Exchange– Client program sends Request message, such as a

database retrieval request

– Server program sends a Response message to deliver the requested information or an explanation for failure

Program

Request

Response

Widely Used on the Internet

For instance, webservice– Client program (browser) sends an HTTP request

asking for a webserver file

– Server program (webserver application program) sends an HTTP response message with the requested webpage

HTTP Request Message

HTTP Response Message

On the Internet, a Single Client Program--the Browser (also known as the client suite)--Works with Many Kinds of C/S server applications– WWW, some E-mail, etc.

Browser

Webserver

E-mailServer

53Program Functionality (Size)

High program functionality requires large program size

File Server Program Access– Poor: client PCs are small, can only execute small

programs

Client/Server Processing– Good: not limited to client PC processing power– Heavy work can be done on the server machine

Terminal-Host Systems– Good: Hosts can be very large

54Platform Independence

File Server Program Access– Poor: Only works with PC clients and PC file servers

Client/Server Processing– Excellent: use any server you want, also any client

Terminal-Host Systems– Poor: Hosts require terminals and only work with a few

terminal types

55Scalability

Ability to grow as demand grows

File Server Program Access– Poor: client PCs do not get very large

Client/Server Processing– Very good: Platform independence allows servers to be

larger than PCs– To grow, leave client machine the same, increase the

size of the server machine

Terminal-Host Systems– Excellent: have an enormous range of processing power

56User Interface

File Server Program Access– Very good: uses local PC processing power

Client/Server Processing– Very good: uses local PC processing power for user

interface

Terminal-Host System– Poor: Relies on distant hosts; user interface quality

limited by high long-distance transmission costs– Monochrome, text-only screen; no animation

57Response Time (When User Hits a Key)

File Server Program Access– Very good: uses local PC processing power

Client/Server Processing– Very good: local PC processing power for user interface– But retrievals from the server can cause delays

Terminal-Host System– Poor: Relies on distant hosts; long delays if overloaded

Part D:Accessing the World Wide Web from Home

Many students access the World Wide Web from home

Here is how it works, in terms of standards

59Accessing the WWW from Home

A Common and Important Situation– Must be understood

– Good way of introducing networking concepts

60The Internet

The Internet is a Worldwide Group of Networks– Not a single network

– Individual networks on the Internet are called subnets

61The Internet

Messages are Broken into Small Packets for Transmission, as Noted Earlier– More efficient than sending long messages

Message Packets

62The Internet

Routers– Connect the Internet’s individual networks (subnets)– Cooperate to give an end-to-end route for each packet

Routers

63The Internet

Hosts– Any computer attached to the Internet is a host– Webservers are host– Desktop and notebook PCs are hosts too

64The Internet

Network deliver messages based on network addresses– The Internet has two addressing systems for hosts

IP addresses Host names

65The Internet

Host IP addresses– Strings of 32 ones and zeros– Usually represented by four number segments

separated by dots: dotted decimal notation– For example, 128.171.17.13– Official addresses for hosts

127.18.47.145127.47.17.47

66The Internet

Dotted Decimal Notation

– IP addresses are really strings of 32 bits (1s and 0s) 10000000101010100001000100001101

– To convert this to dotted decimal notation, first, divide them into four bytes (also called octets)

10000000 10101010 00010001 00001101

– Both octets and bytes are collections of eight bits

67The Internet

Dotted Decimal Notation

– Convert each binary (Base 2) octet into decimal (Base 10)

10000000 is 128 10101011 is 171 00010001 is 17 00001101 is 13

The Internet

Value(2N) Bit Decimal

128 1 128

64 0 0

32 1 32

16 0 0

Position(N)

Binary10100011

=Decimal

Note: Starts with 0

Position7

Position0

69The Internet

Why dotted decimal notation?

– Strings of 32 bits are very difficult to memorize

– Dotted decimal representations of IP addresses are (somewhat) easier to remember

– So dotted decimal notation is merely a mnemonic device for representing IP addresses

70The Internet

Host Names– The other network addressing system on the Internet

– Easy to remember www.microsoft.com voyager.cba.hawaii.edu Two or more text “labels” separated by dots No relationship between segments and labels

CNN.COM

71The Internet

Host Names– Like nicknames

Not official addresses Each host must have an IP address But only some hosts have host names If you give it a host name, your browser must look

up IP address of host (Chapter 2 discusses how)

CNN.COM

72The Internet

Internet Service Providers (ISPs)– You must have an account with an ISP– Connects you to the Internet– May provide other services (e-mail account, etc.)

Carrier Access Line– Usually provided by local telephone carrier– Connects you to the ISP– You pay for this separately from your ISP charges

ISPCarrier Access Line

73The Internet

The Internet is Not Free– You pay your ISP around $20 per month, sometimes

more– Part of this pays for ISP expenses– Part of this pays the Internet backbone to carry your

messages

You Usually Also Pay the Telephone Carrier Separately for the Carrier Access Line

74The Internet

Some ISPs are “free”– More correctly, they are advertiser supported– You must see advertisements every time you use a free

75The Internet

Internet Backbone– Itself consists of many competing but interconnected backbone

carriers

– Sometimes, backbone carriers are also ISPs

– Most are competing carriers called network service providers (NSP)

Internet Backbone

Carriers

ISPISP

76Brief History of the Internet

1957 - USSR launches Sputnik, USA forms Advanced Research Projects Agency (ARPA)

1969 - DoD supports ARPAnet as a research into networks (4 nodes - UCLA, Stanford, UCSB, Univ. of Utah)

1973 - First international nodes in England and Norway

1982 - TCP/IP established as Internet Protocol

77Internet History Continued

1986 - NSF Net established 5 connected supercomputer sites

1988 - NSF Net upgraded to T1(1.54Mbps) with international connections

1991 - Backbone upgraded to T3 (45 Mbps)

1992 - WWW introduced by CERN

1995 - Original NSF retired and replaced with NSP Tier 1, 2, 3, 4

78The Internet

ISPs and NSPs– Began in the United States

– Is being copied and adopted by other countries

– However, not universal

Part E:Standards

Layered Standards Architectures

TCP, IP, and TCP/IP

Other Architectures

80Standards

Standards are rules of operation that most or all vendors follow

Open standards are created and owned by public standards organizations– No single vendor controls these standards

81Standards Are Layered

For Internet Access to a Webserver, standards are set at five layers– Application– Transport– Internet– Data Link– Physical

Together, these standards provide all that is needed for application programs on different hosts on different networks to work together

82Internet Standards

Messages are Exchanged at Multiple Layers

AppApp

TransTrans

IntInt

PhyPhy

User PC

IntInt

PhyPhy

Router

AppApp

TransTrans

IntInt

PhyPhy

Webserver

Application Layer Standards– Standards at the application layer specify how two

application programs communicate – For example, browser on user PC and webserver

application program on webserver

Browser

WebserverApplication

Program

HTTP (HyperText Transfer Protocol)– World Wide Web standard for browser-webserver

application program exchanges– Other applications (E-mail, etc.) have different

application standards

Browser

WebserverApplication

Program

Transport Layer Protocols– Standards at the transport layer specify how two host

computers will work together, even if they are of different platform types (PCs, workstations, mainframes, and so forth)

– For instance, PC and non-PC webserver

PCPC or

Other Computer

The Transport Layer Gives Platform Independence– Two computers do not have to be of the same platform

A PC user does not even know what kind of computer the webserver is

HTTP Requires the Use of the TCP Transport Standard– Transmission Control Protocol– TCP messages are called TCP segments

Internet Layer Protocols– Standards at the internet layer specify how hosts and

routers will act to route packets end to end, from the source host to the destination host, across many single networks (subnets) connected by routers

Single Network(Subnet)Host

The Internet Protocol (IP) is the Main Protocol for Routing Packets Across the Internet– The IP in “TCP/IP”– IP messages are called packets– All internet layer messages are called packets

Packet

Subnets– Single networks (LANs, WANs, point-to-point link) on

the Internet– A packet will pass through several subnets along its

route across the Internet

Subnet

Different Subnets Can Have Different Subnet Protocols– IP at the internet layer routes across different protocols

at the subnet layer

Point-to-Point SubnetProtocol 1

WAN SubnetProtocol 2

LAN Subnet Protocol 3

92Subnets Standards

Subnets are Single Networks on the Internet

Subnet Standards Divided into Two Layers

– Physical layer standards govern the transmission of individual bits within a subnet

– Data Link layer standards govern the transmission of messages within a subnet

Organize individual bits into structured messages

Data Link Layer Standards– Standards at the data link layer specify how to transmit

messages within a single network– Messages at the data link layer are called frames

10010001001

Data Link

Data Link Layer Standards– For accessing the Internet from home ...

– Point-to-Point Protocol (PPP) dominates

– Only used between home and ISP!

– Other subnets connecting routers are likely to use different subnet protocols!

ISPPPP ?

Physical Layer Standards– While the data link layer is concerned with the

organization and transmission of organized messages, standards at the physical layer specify how to transmit single bits one at a time

– Work bit by bit; no frame organization

Physical Layer Standards in Internet Access from Home– Telephone jack (RJ11)– Telephone wire– Serial port connection to external modem– Modem

SerialPort

External Modem TelephoneWire Wall Jack

Subnet Versus Internet Layer Standards– Internet layer provides routing across multiple subnets– Subnet layer standards (data link and physical) provide

for transmission within a single network

InternetLayer

Subnet Layer

Analogy for Subnet versus Internet– Take a vacation– Route from beginning to end (like internet layer)– For different parts, may travel by car, airplane, or boat

(like subnet layer)

InternetLayer

Subnet Layer

99Standards Organizations and Architectures

Architecture is a Design for Standards Creation

– Specifies what types of standards are needed (application, transport, etc.)

– After architecture is designed, individual standards of each type are created

– Analogy: architecture of house specifies what rooms will be needed and their relationships.

– After architecture is settled, individual rooms are designed

TCP/IP Standards– Created by the Internet Engineering Task Force (IETF)– Named after its two most widely known standards, TCP

and IP TCP/IP is the architecture, while TCP and IP are

individual standards However, these are not its only standards, even at

the transport and internet layers– IETF standards dominate in corporations at the

application, transport, and internet layers However, application, transport, and internet

standards from other architectures are still used

OSI Standards– Reference Model of Open Systems Interconnection

– Created by the International Telecommunications Union-Telecommunications Standards Sector (ITU-T)

– And the International Organization for Standardization (ISO)

– OSI standards dominate the data link and physical layers

Other architectures specify the use of OSI standards at these layers

5-Layer Hybrid TCP/IP-OSI Architecture– Most widely used architecture in organizations today– Used on the Internet

Application TCP/IP

Transport TCP/IP

Internet TCP/IP

Data Link OSI

Physical OSI

Recap: Accessing the WWW from Home

AppApp

TransTrans

IntInt

PhyPhy

User PC

IntInt

PhyPhy

Router

AppApp

TransTrans

IntInt

PhyPhy

Webserver

104TCP/IP versus OSI

Lowest Four Layers are Comparable in Functionality

TCP/IP OSI

Application ApplicationPresentationSession

Transport TransportInternet NetworkData Link (use OSI) Data LinkPhysical (use OSI) Physical

105OSI Divides the Application Layer

OSI Session Layer– Sets up a connection between two application programs

on different machines– Manage streams of transactions (session); if there is a

break, can resume at the last roll-back point

Transactions

OSI Presentation Layer– Handles presentation differences between the two

machines (how data are stored and represented)

– Two presentation layer processes select and use a common format for exchanging data

Application DataExchange in

Common Format

OSI Application Layer

– Governs application-to-application communication freed from concerns about presentation format and transaction management

F.Tomorrow

Quality of Service (QoS)

Security

109Quality of Service (QoS)

Throughput Problems and Guarantees

Congestion– When too many transmissions are on a network, traffic

will slow down; this is congestion

Latency– Latency is the amount of time that packets or frames

are delayed because of congestion. Measured in milliseconds (ms),

– Want guarantees of worst-case latency

Throughput– Throughput is the guaranteed speed in bits per second

110Quality of Service (QoS)

Reliability Measures

Availability– Availability is the percentage of time the network is

available to users.– Telephone system has 99.999% availability

Error Rate– Error rate is the percentage of bits or messages that

contain errors – 3% - 6% of all packets are lost on the Internet

111Security

A Growing Problem Encryption for Confidentiality

– Sender encrypts messages before sending them so that anyone intercepting them en route cannot read them

– Receiver can decrypt encrypted messages and read them

– Have confidentiality (unreadability by interceptors)

47 Encryption 101101 Decryption 47

112Security

Authentication– Sender of a message must prove their identity– To thwart impostors who impersonate people

Access Control– Prohibits or authorizes access to various resources

(files, programs, etc.)

– Needs authentication but also more

– Access control lists for resources specify what resources the authorized person may use and how they may use them

business data communications and networking raymond r. panko copyright 2001 prentice hall revision...

video networksif

business data communications

telephone companys

end office

work donebusinessthe

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information systems

customer subscriber

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