Computer Networks

Networking

Computer networkA collection of computing devices connected in order to communicate and share resources

Connections between computing devices can be physical using wires or cables or wireless using radio waves or infrared signals

Networking…

Node

Any device on a network

Data transfer rate (bandwidth)

The speed with which data is moved from one place to another on a network

Basic Components

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Basic Components…

Terminals: end user work station

Telecommunications Channels & Media: Media over which data are transmitted – coaxial cables, fiber optics etc.

Computer: carry out their information processing assignments. Mainframe host computer/server.

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Basic Components…

Telecommunication Software: controls the telecommunication activities

Telecommunication Processors: to enhance data communication b/w two points – modems, message switchers, multiplexers, front end processors

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Basic Components…

Modems: most common type; convert analog signals to digital and vice versa.

Message Switchers: device that receives data messages from terminals, determine their destination and routes them one by one to the CPU.

Advantages – reduce long distance transmission costs since only single line is required

Multiplexers : collects messages from many senders, puts them in order & transmits them thru a broadband; allows simultaneous transmission

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Basic Components…

Concentrator : a smart multiplexer, can be programmed, more processing capability (used for load balancing)

Controller : link groups (clusters) of terminals to a communication channel

Front-end processors: located near the host computer, relieves the host computer of some of the communications tasks, so that it can process other applications requests.

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Communications Media

Channel:

means by which data is transmitted b/w sending and receiving devices.

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Types of Networks

Local-area network (LAN)

A network that connects a relatively small number of machines in a relatively close geographical area

Ring topology connects all nodes in a closed loop on which messages travel in one direction

Star topology centers around one node to which all others are connected and through which all messages are sent

Bus topology nodes are connected to a single communication line that carries messages in both directions

Types of Networks

Ethernet

The industry standard bus technology for local-area networks

Types of Networks

Wide-area network (WAN)

A network that connects local-area networks over a potentially large geographic distance

Metropolitan-area network (MAN)

The communication infrastructures that have been developed in and around large cities

Gateway

One particular set up to handle all communication going between that LAN and other networks

Types of Networks

Local-area networks connected across a distance to

create a wide-area network

Types of Networks

Internet

A wide area network that spans the planet

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Network Protocols

An agreed-upon format for transmitting data b/w 2 devices.

Protocol determines the following

Type of error checking

Data compression method

Message completion indicated by sender

Message acknowledgement by receiver

Popular protocols – TCP/IP, HTTP, FTP, SMTP, POP

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Network Architecture

Refer to either h/w, s/w or a combination.

Classification : -

Peer-to-peer architecture – each workstation has equivalent capabilities & responsibilities

Client/Server architecture – each computer is either a client or a server.

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Packet Transmission/Switching

Packet

A unit of data sent across a network

Router

A network device that directs a packet between networks toward its final destination

Packet switching

Messages are divided into fixed-sized, numbered packets; packets are individually routed to their destination, then reassembled

Packet Switching

Messages

sent by

packet

switching

Take a message, break it into three packets, and

simulate this process

Hubs

A hub is the place where data converges from one or more directions and is forwarded out in one or more directions.

Seen in local area networks

Switches

Allow different nodes of a network to communicate directly with each other.

Allow several users to send information over a network at the same time without slowing each other down using Media Access Control address (MAC address)

TCP/IP

Transmission Control Protocol (TCP)

Software that breaks messages into packets, hands them off to the IP software for delivery, and then orders and reassembles the packets at their destination

Internet Protocol (IP)

Software that deals with the routing of packets through the maze of interconnected networks to their final destination

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High-Level Protocols

Other protocols build on TCP/IP protocol suite

Simple Mail Transfer Protocol (SMTP) used to specify transfer of electronic mail

File Transfer Protocol (FTP) allows a user to transfer files to and from another computer

Telnet used to log onto one computer from another

Hyper Text Transfer Protocol (http) allows exchange of Web documents

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Which of these have you used?

Firewalls- Network Security

Firewall

A gateway machine and its software that protects a network by filtering the traffic it allows

Access control policy

A set of rules established by an organization that specify what types of network communication are permitted and denied

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Have your messages ever been

returned undelivered, blocked by a firewall?

Firewalls

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A firewall protecting a LAN