basic concepts and principles chapter 1 copyright 2001 panko

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Basic Concepts and Principles Chapter 1 Copyright 2001 Panko

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Page 1: Basic Concepts and Principles Chapter 1 Copyright 2001 Panko

Basic Concepts and Principles

Chapter 1

Copyright 2001 Panko

Page 2: Basic Concepts and Principles Chapter 1 Copyright 2001 Panko

2

Network

Network

A Network is an Any-to-Any Communication System– Can connect any station to any other

Page 3: Basic Concepts and Principles Chapter 1 Copyright 2001 Panko

3

“Connect to GHI”

Network

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

ABC

DEF GHI

JKLMNO

Page 4: Basic Concepts and Principles Chapter 1 Copyright 2001 Panko

4Data 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

Page 5: Basic Concepts and Principles Chapter 1 Copyright 2001 Panko

5Voice 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

CustomerPremises

Page 6: Basic Concepts and Principles Chapter 1 Copyright 2001 Panko

6Voice and Video Networks

Hierarchy of switches Trunk lines connect switches

Switch

Trunk Line

Page 7: Basic Concepts and Principles Chapter 1 Copyright 2001 Panko

7Voice and Video Networks

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

capacity during call

CircuitCircuit

Page 8: Basic Concepts and Principles Chapter 1 Copyright 2001 Panko

8Voice and Video Networks

Reserved Circuit Capacity is Expensive– 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 average of 60 seconds between brief downloads

– Capacity is wasted between bursts; still must pay of capacity

Page 9: Basic Concepts and Principles Chapter 1 Copyright 2001 Panko

9Packet-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

Page 10: Basic Concepts and Principles Chapter 1 Copyright 2001 Panko

10Packet-Switched Data Networks

Packet 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 packet switch

B?

D?

C?

Switch A

B

C

DPacket

Page 11: Basic Concepts and Principles Chapter 1 Copyright 2001 Panko

11Packet Switched Data Networks

Multiplexing– Packets from many conversations are mixed

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

Multiplexing onTrunk Line

Page 12: Basic Concepts and Principles Chapter 1 Copyright 2001 Panko

12Analog Transmission

In analog transmission, rising and falling smoothly in intensity among an infinite number of states– State may be voltage, frequency or other line signal

characteristic

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

Line is in one state (voltage level, etc.) during each clock cycle; at end of cycle, stays same or changes abruptly.

TimeStrength

Clock Cycle Time

State 1 Stays Same

Abrupt Change

State 2

Page 13: Basic Concepts and Principles Chapter 1 Copyright 2001 Panko

13Digital 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

Modem

AnalogSignal

Page 14: Basic Concepts and Principles Chapter 1 Copyright 2001 Panko

14LANs 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

Page 15: Basic Concepts and Principles Chapter 1 Copyright 2001 Panko

15Elements of a Simple LAN

Hub or Switch

Wiring

Hub or Switch connects all stations housing NIC

Wiring is standardbusiness telephone wiring

(4 pairs in a bundle)

Page 16: Basic Concepts and Principles Chapter 1 Copyright 2001 Panko

16Terminal-Host Systems

Created in the 1960s– Central host computer does all the processing– Terminal is dumb--only a remote screen and keyboard– Largest hosts are mainframes (file storage & retrieval)

– Legacy systems--systems created by your predecessors

– Would not use the same platform today if built new; however, too expensive to rewrite all legacy applications at once

Terminals Host

Page 17: Basic Concepts and Principles Chapter 1 Copyright 2001 Panko

17PC Networks

The Most Common Platform in Organizations– Allows PCs to share resources

File Servers– Store files (data files and programs)

Programs are downloaded to client PC for execution, not on file server– The most common type of server in PC networks– Almost all file servers are themselves PCs

Network

ClientPC

ClientPC

PC Server

PC Server

Page 18: Basic Concepts and Principles Chapter 1 Copyright 2001 Panko

18Client/Server Processing

Client and Server Machines– Neither has to be a PC (Although the client usually is)

Platform independence: not limited to PC server– Two programs: client and server programs

Example: browser and webserver application program

Servers usually Workstation Servers– Look like PCs but…

More powerful (and expensive) than PCs

Do not use standard Intel PC microprocessors

Usually run the UNIX operating system

Client Machine ServerClient

ProgramServer

Program

Request

Response

Page 19: Basic Concepts and Principles Chapter 1 Copyright 2001 Panko

19Program 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

Page 20: Basic Concepts and Principles Chapter 1 Copyright 2001 Panko

20Platform 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

Page 21: Basic Concepts and Principles Chapter 1 Copyright 2001 Panko

21Scalability

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

Page 22: Basic Concepts and Principles Chapter 1 Copyright 2001 Panko

22User 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

Page 23: Basic Concepts and Principles Chapter 1 Copyright 2001 Panko

23Response 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

Page 24: Basic Concepts and Principles Chapter 1 Copyright 2001 Panko

24The Internet

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

– Individual networks on the Internet are called subnets

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

(message)Routers

RouteHost

Host

Page 25: Basic Concepts and Principles Chapter 1 Copyright 2001 Panko

25The Internet

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

IP addresses (computer friendly) Host names (user-friendly)

Host IP addresses (required)– 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

127.18.47.145 127.47.17.47

Page 26: Basic Concepts and Principles Chapter 1 Copyright 2001 Panko

26The 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 But “octet” is used in networking

Page 27: Basic Concepts and Principles Chapter 1 Copyright 2001 Panko

27

Binary to Decimal Conversion

Value(2N) Bit Decimal

128 1 128

64 0 0

32 1 32

16 0 0

8 0 0

4 0 0

2 1 2

1 1 1

163

Position(N)

7

6

5

4

3

2

1

0

Binary10100011

=Decimal

163

Note: Starts with 0

Position7

Position0

Page 28: Basic Concepts and Principles Chapter 1 Copyright 2001 Panko

28The Internet

Host Names (otional)– Two or more text “labels” separated by dots

www.microsoft.com Mtsu.edu No relationship between segments and labels Usually, only servers have host names

Page 29: Basic Concepts and Principles Chapter 1 Copyright 2001 Panko

29The Internet

Internet Service Providers (ISPs)– Connects you to the Internet, via Carrier Access Line

May provide other services (e-mail account, etc.)– Costs

ISP = Approx. $20 per month, sometimes more– % for ISP expenses

– % for Internet backbone to carry your messages

Carrier Access Line fee separate from ISP

ISPCarrier

Access Line Internet Backbone

ISP

Carriers

Page 30: Basic Concepts and Principles Chapter 1 Copyright 2001 Panko

30Standards

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

Page 31: Basic Concepts and Principles Chapter 1 Copyright 2001 Panko

31Standards 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

Page 32: Basic Concepts and Principles Chapter 1 Copyright 2001 Panko

32Internet Standards

Messages are Exchanged at Multiple Layers

AppApp

TransTrans

IntInt

DLDL

PhyPhy

User PC

IntInt

DLDL

PhyPhy

Router

AppApp

TransTrans

IntInt

DLDL

PhyPhy

Webserver

HTTP

TCP

IP

PPP

Modem

IP

?

?

Page 33: Basic Concepts and Principles Chapter 1 Copyright 2001 Panko

33Internet Standards

Application Layer Standards– specify how two application programs communicate – Example: browser on user PC and webserver application program

on webserver Webservice = HyperText Transfer Protocol (HTTP)

Transport Layer Standards

– specify how two host computers will work together,regardless of platform types (PCs, workstations, mainframes)

– Gives platform independence HTTP Requires the Use Transmission Control Protocol

(TCP)

Page 34: Basic Concepts and Principles Chapter 1 Copyright 2001 Panko

34Internet Standards

Internet Layer Standards– specify how hosts and routers will act to route packets from source host to destination host, across many

single networks (subnets) connected by routers Internet Protocol (IP) The IP in “TCP/IP”

– All internet layer messages are called packets– Subnets

single networks (LANs, WANs, point-to-point link) on Internet Packets pass through several subnets in route across Internet Different Subnets Can Have Different Subnet Protocols

RouteSingle Network

(Subnet)Host

Host

Page 35: Basic Concepts and Principles Chapter 1 Copyright 2001 Panko

35Subnets Standards

Subnet Standards Divided into Two Layers– Physical layer standards govern the transmission of

individual bits within a subnet

Interpretation of bits is left to data link layer

SerialPort

External Modem TelephoneWire Wall Jack

Page 36: Basic Concepts and Principles Chapter 1 Copyright 2001 Panko

36Subnets Standards

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

Organize individual bits into structured messages or frames

Controls timing of message transmission Point-to-Point Protocol (PPP) when accessing

Internet from home via telephone modem Only used between home and ISP! Other subnets connecting routers are likely to use

different subnet protocols!

Page 37: Basic Concepts and Principles Chapter 1 Copyright 2001 Panko

37Standards Organizations and Architectures

Architecture – a Design or framework 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

Page 38: Basic Concepts and Principles Chapter 1 Copyright 2001 Panko

38Standards Organizations and Architectures

TCP/IP Architecture– Under the Internet Engineering Task Force (IETF)– TCP/IP is the architecture, while TCP and IP are individual standards

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

OSI Standards (Reference Model of Open Systems Interconnection)– 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 (subnet)

Other architectures specify the use of OSI standards at these layers

Page 39: Basic Concepts and Principles Chapter 1 Copyright 2001 Panko

39Internet Standards

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

Page 40: Basic Concepts and Principles Chapter 1 Copyright 2001 Panko

40TCP/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

Page 41: Basic Concepts and Principles Chapter 1 Copyright 2001 Panko

41Quality of Service (QoS)

Congestion & Speed– Latency: amount of time packets are delayed due to

congestion. Measured in milliseconds (ms), Desired Latency = 50 ms maximum

– Throughput: transmission speed. Measured in bits per second (bps)

Desired Throughput = 1 Million bps

Page 42: Basic Concepts and Principles Chapter 1 Copyright 2001 Panko

42Quality of Service (QoS)

Reliability – Availability: percentage of time network is available.

Desired Availability = 99.999%– Error Rate: percentage of bits or messages with errors

1999 average = 3% - 6% of all packets Desire much lower average

Page 43: Basic Concepts and Principles Chapter 1 Copyright 2001 Panko

43Security

Encryption for Confidentiality– Sender encrypts (scrambles) messages before transmission– Receiver decrypt messages to original form

Access Control– Prohibits or authorizes access to various resources (files, programs)

– Access control lists specify what & how a person may use a resource

Authentication– Sender of a message must prove their identity