COMPUTER NETWORKS

WHAT IS A COMPUTER NETWORK

A Computer Network is a group of two or more independent computers connected in an organized manner such that they can communicate with each other .Computers on a network are sometimes called nodes.

WHY A COMPUTER NETWORK?

The main reasons are:

Distribute pieces of computation among computers (nodes)

Coordination between processes running on different nodes

Remote I/O Devices

WHY A COMPUTER NETWORK?

Remote Data/File Access

Personal communications (like e-mail, chat, audio/video conferencing)

Advantages & Disadvantages of Computer Networks

Advantages: Price/Performance Ratio. Performance Quality. Reliability. Accessible Resources. Incremental Growth of Computing Power.

contd..

Advantages &Disadvantages of Computer Networks (contd..)

Disadvantages:Disk space management.Resource management.Network Architecture management.

Characteristics used to categorize different types of networks:

Area of location: Based on geographical areas covered as Networks can be divided into : LAN, MAN,& WANTopology : According to the geometric arrangement of computers the different topologies are BUS,STAR, RING & WIRELESS

Characteristics used to categorize different types of networks:

Protocol : The protocol defines a common set of rules and signals that computers on the network use to communicate.Some of the popular protocols are ETHERNET & TOKEN-RING NETWORK.Architecture : Networks can be broadly classified as using either a CLIENT/SERVER or PEER-TO-PEER architecture

LANs : Local Area Networks

Developed in 1970s. Typically connects computer in a single building or

campus. Medium : optical fibers, coaxial cables, twisted

pair, wireless. Speeds adequate for most distributed systems High speed networks (0.2 to 100 Mb/sec).

MANs : Metropolitan Area Networks

Developed in 1980s. Generally covers towns and cities (50 kms) Medium : optical fibers, cables. Data rates adequate for distributed computing

applications.

WANs : Wide Area Networks

Developed in 1960s. Generally covers large distances (states, countries,

continents). Medium : communication circuits connected by

routers. .

WANs : Wide Area Networks

Problems with delays if using satellites. Typical speed : 20 - 2000 Kbits/s. Not (yet) suitable for distributed

computing.

BUS TOPOLOGY

On the bus network illustrated here, the electrical signal representing the packet travels away from the sending station in both directions on the shared cable. All stations will see the packet, but only the station it is addressed to will pay attention to it.

STAR TOPOLOGY

In a star topology all stations are wired to a central wiring concentrator called a hub.Similar to a bus topology, packets sent from one station to another are repeated to all ports on the hub.

STAR TOPOLOGY

This allows all stations to see each packet sent on the network, but only the station a packet is addressed to pays attention to it.

RING TOPOLOGY

The ring topology used in Token Ring networks is a collapsed ring that looks like a physical star. Each station is connected to a Token Ring wiring connector by a single twisted pair cable with two wire pairs.

RING TOPOLOGY

One pair serves as the "inbound" portion of the ring (also known as the receive pair) and the other pair serves as the "outbound" or transmit pair.

WIRELESS TOPOLOGY

Wireless Topology components generally include a PC, a transmitter/receiver, and a software program loaded into the PC. Wireless Topology is normally very slow compared to

other topologies. Wireless LANs are more limited in distance, and

usually work well in large open areas.

Ethernet is an open network standard developed by Intel, Digital Equipment and Xerox.Ethernet is the most common network. It offers support for a variety of protocols and computer platforms and is relatively lower in cost. Ethernet LANs use a bus topology.

Ethernet Local Area Networks

Network Medium

Once you have the network cards installed and interfaced in your computer, you need a way to connect them to each other.The network media used can be:wire ( Bounded) orwireless (Unbounded).

Network Medium (contd…)

Bounded Media:Wires or network cables are referred to as bounded media because the signal travels through a physical media shielded on the outside (bounded)by some material.Bounded media are great for LANs because they offer good speed, good security and low cost.Examples of bounded media CO-AXIAL,TWISTED PAIR & OPTICAL FIBER.

Network Medium (contd…)

Unbounded or Wireless media:This does not use any physical connectors between the two communicating devices. Usually the transmission is sent through the atmosphere, but sometimes it can be just across a room.Wireless media is used when a physical obstruction or distance blocks the use of normal cable media. The three main types of Wireless Media areradio wave, microwave and infrared.

Coaxial Cable

Used extensively in LANs. Single central conductor

surrounded by a circular insulation layer and a conductive shield. High quality of data

transmission. Max. used data rates : 100

Mbits/s. Problems : signal loss at

high frequencies.

Twisted Pair Cable

Extensively used in telephone circuits, where several wires are insulated and put together.

Low signal to noise ratio (cross talk) -> Low data rate.

Good for short-distance communications.

UTP and 10BaseT are Used in LANs and have much higher bandwidth.

Optical Fiber

High quality and high bandwidth data transmission applications. Use light instead of

electric pulses for message transmission. Very high frequency

ranges (20,000 Mhz). Single fiber can support

over 30,000 telephone lines.

Optical Fiber (Contd..)

Data transmission rates of 400 Mbits/s and more.

Becoming very popular for MAN and LAN, also used for intercontinental links.

High signal to noise ratio, difficulty in tapping (security).

Cost is the single biggest drawback (currently).

Wireless Media

For WANs satellites provide global communication over the world, receiving signals from transmitters and relaying them back to the receivers.

For MANs microwave radio technology is widely used (2 to 24 Mbit/s).

Wireless Media

For LANs Spread Spectrum radio technology is becoming very popular (up to 2 Mbit/s).

Infrared : Line of sight limitation.

Common Hardware Requirements for Computer Networking

Common Hardware Requirements for Computer Networking

NetworkInterface Card : Also known as network adapter, interfaces a computer board with the network medium. Repeater : two-ports electronic device that just repeats what it receives from one port to the other. Bridge : a more sophisticated repeater with logic capabilities that filters packets

contd..

Common Hardware Requirements for Computer Networking (contd..)

Hub : multi-port repeater. Switch : multi-port bridgeRouter : links two or more networks (different types too), passing messages with appropriate routing information. It operates at OSI level 3.

Common Hardware Requirements for Computer Networking (contd..)

Modem :Device that converts digital data originating from a terminal or computer, to analog signals used by voice communication networks such as the telephone systemFirewalls : Firewalls are systems that establish access control policies among networks.

NETWORK INTERFACE CARD

Often abbreviated as NIC, an expansion board you insert into a computer so the computer can be connected to a network. Most NICs are designed for a particular type of network, protocol, and media, although some can serve multiple networks. .

Repeaters

A communications device that amplifies or regenerates the data signal in order to extend the transmission distance.

Available for both analog and digital signals, it is used extensively in long distance transmission.

Repeaters

Repeaters work at layer 1 of the OSI model However the amount of Repeaters that can be chained

together is limited

Bridges

•A Bridge is an electrical device which connects and passes packets between two network segments. In general, a bridge will forward or discard an incoming frame based on the MAC address of that frame.

Bridges

Unlike routers, bridges are protocol -independent. They simply forward packets without analyzing and re- routing messages.

Hubs

Hub's major function is to replicate data it receives from one device attached to it to all others.

Hubs

Characteristics :Hubs come in many flavors. They differ in the amount of devices that can connect to them, the length of wire that can transmit on, and the type of media they support.

Switches

Switch is a device used to link several separate LANs and provide packet filtering between them.

Switches

In effect, it acts like a very fast multiport bridge packets are filtered by the switch based on the destination address. Switches can also support numerous transmissions

simultaneously.

Routers

A device that forwards data packets from one local area network (LAN) or wide area network (WAN) to another.

Routers

Based on routing tables and routing protocols,routers read the network address in each transmitted frame and make a decision on how to send it based on the most expedient route (traffic load, line costs, speed, bad lines, etc.).

Modems

The word "Modem" stands for "MOdulator-DEModulator". A modem is a device that converts digital data originating from a terminal or computer, to analog signals used by voice communication networks such as the telephone system.

Contd..

Modems

At one end, modems convert the digital pulses to audible tones and convert audio tones back to digital pulses at the other.

Contd..

Modems (contd..)

Characteristics : Transmission speed Internal/External Error detection and correction Compression

Firewall

Firewalls are systems that establish access control policies among networks. They can block information from entering a network or from getting out of that network, they can permit different users to perform different kinds of operations, according to the user's authorizations.

Firewall

There are two general types of firewalls: Packet Level Firewalls and Application Level Firewalls.

Firewall (contd..)

There are two general types of firewalls: Packet Level Firewalls, which examine packets and decide according to filtering rules whether to pass them to the network. Application Level Firewalls, which monitor specific applications protocols.