Networks & telecommunications

June 16, 2015

LEARNING GOALS• Discuss networks communication models and

principles of operation• Identify the major hardware and software

components used networks.• Identify and explain the various types of

computer networks.• Identify the various types of transmission

media• Discuss LAN topology and operation

2

Networks communication models and operation

• Define how the processing takes place on the network

• Define the roles of each participating computer

• Two primary models:– Client-server– Peer-to-peer (P2P)

3

Client-server model• Computers are either clients or servers• Clients use services• Servers provide services

– File service– E-mail service– Printing service– Database service– Etc.

• Client software on client node cooperates with server software on server node– The WWW is the largest client/server network 4

Client-server model• Collaboration between Client and Server program

5

Client-server model• 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

Client Machine Server

Client ProgramServer

Program

6

Peer-to-Peer network

7

• No dedicated server• Computer are equal (peers)• Computers can all receive and provide service• Multiple P2P models over the years

– Pure P2P– P2P Viral network– P2P with index server

Pure P2P network

8

• Each computer must have the appropriate type of protocol & software for interaction with others

• Each computer must have a network connection to others• Each computer can connect to any participating computer to get service (e.g.

download files)

• What can be the major issues associated with P2P networks?

Pure P2P viral network

9

• Client connects to another client, which connects to several others, and so forth• When client first connects, it sends initiation msg to introduce itself via viral networking• Searches sent by a client are also passed to others through viral networking• When file is found, actual file downloads are done using direct (not viral) communication• Companies offering P2P viral networking service, put in place super clients that are always on with

permanent IP addresses

Client 1

Client 2 Client 3

Client 4

Client 5

P2P File download

Init or

search msg

Init or search msg

Init or search msg

Init or

search msg

Init or

search

msg

Note: Response to Init and Seach msg not shown

P2P using Index server

10

• Most common type of P2P networking used in file sharing• Introduced by Napster (now an online music store after law suits)• Relies on an Index server

Client PC

NapsterIndexServer

1.Uploads ListOf Available

FilesWhen Connects

Client PC Client PC

2.Search Query

3.Response 4.

Large P2PDownload

File List

List ofAvailable Files

From AllCurrent Clients

Advantages of Network vs. Stand-alone PCs?

– – – – – – – – – – 11

Why Networking ?• Resource sharing

– Sharing hardware (printers, processors, etc.)– Sharing software (programs, data files)

• High reliability– Can easily set automatic backups of programs and data at

different locations– Fault tolerance: can duplicate servers so that if one is down,

others can provide service. Servers have RAID so that if a disk fails, data available on other disks)

• Possible cost savings• Communication tool

– Console messages and internal email service– Remote Access service 12

Computer Network• An interconnection of computers and

computing equipment using either wires or wireless transmission media over small or large geographical distances.

“Connect to GHI”ABC

DEF GHI

JKLMNO

Once connected to the network, the computer (or another device) becomes a network node

13

Computer Network (cont.)• Based on the definition from the previous

slide, what hardware elements are needed to implement a computer network?

14

Network scope• Local area network (LAN): computer network where

the nodes are all in close proximity spanning a room, building, or campus

• Metropolitan area network (MAN): network that serves an area of 3 to 30 miles - approximately the area of a typical city.

• Wide area network (WAN): a large network that encompasses parts of states, multiple states, countries, and the world

15

Transmission Media• Physical media

– Transmission media used to physically connect nodes to the network

– Transmits electrical or optical signals– Could be copper wire or fiber optic cable

Physical

Wireless

16

Transmission Media (Continued)• Twisted PairCategory Use Signal Data rate Distance Problem

Category 1 Telephone Analog/Digital <100Kbps 3-4 miles Security, noise

Category 2 T1, ISDN Digital <2 Mbps 3-4 miles Security, noise

Category 3 LANs Digital 10 Mbps 100 m Security, noise

Category 4 LANs Digital 20 Mbps 100 m Security, noise

Category 5 LANs Digital 100 Mhz 100 m Security, noise

Category 6 LANs Digital 250 Mhz 100 m Security, noise

Category 7 LANs Digital 600 Mhz 100 m Security, noise

• Fiber optic– Thin glass fibers surrounded by coating– Uses laser or light for data transmission– Very fast (10+ Gbps, 100 miles without any repeater)– Very secure

SourcePhoto diode(LED or LD)

DestinationPhoto receptor(LED or LD)Fiber optic cable 17

18

Wireless transmission media• Infrared light

– Has many of the same characteristics as visible light

– Travels in straight lines– Cannot penetrate solid objects

• Radio waves– Travel in straight lines– Can penetrate through nonmetallic objects– Can travel long distances

19

Wireless Media issues• Use electromagnetic waves or electromagnetic radiation for data

transmission• Propagation through space, and indirectly, through solid objects• Many problems:

Laptop Comm. Tower

ShadowZone

Radio waves tend to bounce off objects. Receiver can receive 2 or more signals.

Thick objects can block the direct path. So, Receiver will be in a

Shadow zone where it cannot well receive.

Insecure: Easier to

“intercept” messages

ElectromagneticInterference (EMI) from

Other stations,Microwave ovens, etc

MultipathInterference

Computing Equipment• Network interface card (NIC): Device that

– provides a computer with unique address– Converts data into signal for transmission

• Hub / Switch: Central collection point for transmission media that interconnect computers

• Modem– Converts digital data into analog signal and back again

• Router – special hardware that determines optimal routing path for data

packets – Usually used to connect a LAN to a WAN

• Bridge– Forwards messages between LANs 20

Small Network illustrated

Hub or Switch

Media

Router

Wide Area Network

21

1.Station A transmits

to the Hub

2.Hub broadcasts

to all stations

Station C must wait,or its signal willcollide with Station A'ssignal

StationA

StationB

StationC

StationA

StationB

StationC

Hub operation

Hubs split available bandwidth among computers, i.e. with a 100 Mbps hub, the network speed will be 100 Mbps / n (where n is the number of computers)Active hubs include repeater capabilities for regenerating signals.Passive hubs don't regenerate signals. Limited to a 30meter distance apart from computers.

(Except sending station)

Switch operation

StationC

StationD

Switch

StationB

Station ATransmits

to Station C

Switch SendsSignal out aSingle Port

1 62 3 4 5

StationA

Station BTransmits

Simultaneouslyto Station D

Switches send out a single port: destination port.Most switches can efficiently handle simultaneous transmissionsSwitches provide a full bandwidth to all connected computers.

Switching tableMAC Address PortA1-44-D55-1F-AA-4C 1 (Station A)B2-CD-13-5B-E4-65 2 (Station B)C3-2D-55-3B-A9-4F 5 (Station C) ; ;

Network Software• Network operating system

– Used on servers– Used by network admins for managing network

resources– Examples: Novell NetWare, Windows Server 2008

• Workstation operating system– Used on client PCs– Used to manage local resources & access network

resources• Network monitoring software

– Packet sniffers – allow seeing data as it moves over network

– Keystroke monitors – allow seeing what users are typing

24

Protocols• An agreed upon set of rules that govern

communication in a network• All computers on a network must use same protocol

for effective communication• Example of protocols:

• Ethernet (for communication in a LAN)• Token Ring (for communication in a LAN)• TCP/IP suite (for communication in a LAN and the Internet)

Computer 1

Rules for Task 1

Rules for Task 2

Rules for Task 3

Rules for Task 4

Rules for Task 5

Computer 2

Rules for Task 1

Rules for Task 2

Rules for Task 3

Rules for Task 4

Rules for Task 5

LAN network Topologies

• The configurations of network components– How physically the network looks like– How logically data is transferred on the network

• Types of network topologies:– Bus– Star– Ring

26

Bus topology• Most simple network topology• All devices connected to a common central

cable called a “bus”• Inexpensive• If cable fails, the entire network will shut down

27

Star topology

• Centered around central device called a hub or a switch

• All network nodes connect to the hub/switch

• Easy to install and update

• If hub fails, network fails

28

Ring topology

• Node connected to a logical ring in a central device called MAU

• More reliable than bus or star– Only one node sends at a

time (no collisions)

• Expensive and limited speed

29

Summary QuestionsBook Notes

1) Name categories of computer networks based on their scope; i.e. their range of operation

2) Name one example of: (a) WAN, (b) LAN

3) Name physical and wireless media used in networking

4) What is the role of (a) a modem, (b) a router, (c) a bridge?

5) What is the difference between a Network operating system and a workstation operating system?

6) What is a network topology?

7) Distinguish between network topologies

8) Distinguish between Client-server and P2P networks

30

Summary Questions (cont.)

• What category of network is illustrated here?

Summary Questions (cont.)

• What category of network is illustrated here?

Problem

• Four students share a dorm. They would like to set up a network in order to share programs and data files. Three of the students own PCs and the fourth student has a laptop computer.

Question: What computing equipments they need to buy in order to set up the network with a star topology?

33

Telecommunications

Voice vs. Data Communication• Originally, There was a Sharp Distinction:

– Voice Communication

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

• Database• Electronic mail• World Wide Web

• Distinction is fading because voice communication is increasingly computer-based

35

Circuit Switching and Reserved Capacity

– Circuit switching is traditionally used in telecommunications

– Circuit capacity is reserved during duration of each call

– At each switch– On each trunk line

Circuit

ReservedCapacity

ReservedCapacity

36

Pros and cons of Reserved Capacity

• Nothing like the congestion on the Internet• Reserved Circuit Capacity is Expensive

– Have to 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

37

Packet-Switching Data Networks

• Packet Switching– Large messages are broken into small pieces called

packets (or frames)

– Packets are short (averaging a few hundred bytes) because networking devices handle short messages more efficiently

Message Packets

38

Packet-Switching Data Networks

• Multiplexing– Packets from many conversations are mixed

(multiplexed) over each trunk line

Multiplexing onTransmission LinePacket Switching

39