Network HardwareThe term ‘‘computer network’’ to mean a collection of autonomous computers interconnected by a single technology. Two computers are said to be interconnected if they are able to exchange information. The connection need not be via a copper wire; fibre optics, microwaves, infrared, and communication satellites can also be used.

There is no generally accepted taxonomy into which all computer networks fit, but two dimensions stand out as important: transmission technology and scale.

Transmission Technology

Point-to-Point Link:

Point-to-point links connect individual pairs of machines. To go from the source to the destination on a network made up of point-

to-point links, short messages, called packets in certain contexts, may have to first visit one or more intermediateMachines.

Point-to-point transmission with exactly one sender and exactly one receiver is sometimes called unicasting.

Network Hardware

Transmission Technology

Broadcast Link Point-to-Point Link

Scale

Personal Area Network

Local Area Network

Wide Area Network

Metropolitian Area Network

Broadcasting Link:

On a broadcast network, the communication channel is shared by all the machines on the network; packets sent by any machine are received by all the others. An address field within each packet specifies the intended recipient.

Upon receiving a packet, a machine checks the address field. If the packet is intended for the receiving machine, that machine processes the packet; if the packet is intended for some other machine, it is just ignored.

Broadcast systems usually also allow the possibility of addressing a packet to all destinations by using a special code in the address field. When a packet with this code is transmitted, it is received and processed by every machine on the network. This mode of operation is called broadcasting.

Some broadcast systems also support transmission to a subset of the machines, which known as multicasting.

Scale

An alternative criterion for classifying networks is by scale. Distance is important as a classification metric because different technologies are used at different scales.

Personal Area Networks (PAN):

PANs (Personal Area Networks) let devices communicate over the range of a person. A common example is a wireless network that connects a computer with its peripherals.

Without using wireless, this connection must be done with cables. To help these users, some companies got together to design a short-range

Wireless network called Bluetooth to connect these components without wires.The idea is that if your devices have Bluetooth, then you need no cables.

The system unit (the PC) is normally the master, talking to the mouse,Keyboard, etc., as slaves. The master tells the slaves what addresses to use, when they can broadcast, how long they can transmit, what frequencies they can use, and so on.

A completely different kind of PAN is formed when an embedded medical device such as a pacemaker, insulin pump, or hearing aid talks to a user-operated remote control.

Local Area Networks (LAN):

A LAN is a privately owned network that operates within and nearby a single building like a home, office or factory.

LANs are widely used to connect personal computers and consumer electronics to let them share resources (e.g., printers) and exchange information.

When LANs are used by companies, they are called enterprise networks.

Wireless LANs are very popular these days, especially in homes, older office buildings, cafeterias, and other places where it is too much trouble to install cables.

In these systems, every computer has a radio modem and an antenna that it uses to communicate with other computers. In most cases, each computer talks to a device in the ceiling. This device, called an AP (Access Point), wireless router, or base station, relays packets between the wireless computers and also between them and the Internet.

Wired LANs use a range of different transmission technologies. Most of them use copper wires, but some use optical fibre.

LANs are restricted in size, which means that the worst-case transmission time is bounded and known in advance.

Typically, wired LANs run at speeds of 100 Mbps to 1 Gbps, have low delay (microseconds or nanoseconds), and make very few errors.

Ethernet :

The topology of many wired LANs is built from point-to-point links. IEEE 802.3, popularly called Ethernet, is, by far, the most common type of wired LAN.

Each computer speaks the Ethernet protocol and connects to a box called a switch with a point-to-point link. Hence the name.

A switch has multiple ports, each of which can connect to one computer. The job of the switch is to relay packets between computers that are attached to it, using the address in each packet to determine which computer to send it to.

Technical aspects : Network topology describes the layout of interconnections between

devices and network segments. At the Data Link Layer and Physical Layer, a wide variety of LAN

topologies have been used, including ring, bus, mesh and star, but the most common LAN topology in use today is switched Ethernet.

Simple LANs generally consist of one or more switches. A switch can be connected to a router, cable modem, or ADSL modem for Internet access.

Complex LANs are characterized by their use of redundant links with switches using the spanning tree protocol to prevent loops, their ability to manage differing traffic types via quality of service (QoS), and to segregate traffic with VLANs.

A LAN can include a wide variety of network devices such as switches, firewalls, routers, load balancers, and sensors.[13]

LANs can maintain connections with other LANs via leased lines, leased services, or the Internet using virtual private network technologies. Depending on how the connections are established and secured in a LAN, and the distance involved, a LAN may also be classified as a metropolitan area network (MAN) or a wide area network (WAN).

Metropolitan Area Networks (MAN):

A MAN (Metropolitan Area Network) covers a city. The best-known examples of MANs are the cable television networks available in many cities.

A MAN is optimized for a larger geographical area than a LAN, ranging from several blocks of buildings to entire cities.

MANs can also depend on communications channels of moderate-to-high data rates.

A MAN might be owned and operated by a single organization, but it usually will be used by many individuals and organizations.

MANs might also be owned and operated as public utilities. They will often provide means for inter-networking of local networks.

Implementation: MAN links between local area networks have been built

without cables using either microwave, radio, or infra-red laser links. Most companies rent or lease circuits from common carriers because laying long stretches of cable can be expensive.

Distributed-queue dual-bus (DQDB) refers to the metropolitan area network standard for data communication specified in the IEEE 802.6 standard. With DQDB, networks can extend up to 20 miles (30 km) long and operate at speeds of 34–155 Mbit/s

Wide Area Networks (WAN):

A wide area network (WAN) is a network that covers a broad area (i.e., any telecommunications network that links across metropolitan, regional, or national boundaries) using leased telecommunication lines.

This mode of telecommunication allows a business to effectively carry out its daily function regardless of location. The Internet can be considered a WAN as well, and is used by businesses, governments, organizations, and individuals for almost any purpose imaginable.

Working of WAN :

We will follow traditional usage and call these machines hosts. The rest of the network that connects these hosts is then called the

communication subnet, or just subnet for short. The job of the subnet is to carry messages from host to host. In most WANs, the subnet consists of two distinct components:

transmission lines and switching elements. o Transmission lines move bits between machines. They can be

made of copper wire, optical fibre, or even radio links.o Switching elements, or just switches, are specialized computers

that connect two or more transmission lines. When data arrive on an incoming line, the switching element must choose an outgoing line on which to forward them.

o These switching computers have been called by various names in the past; the name router is now most commonly used.

The subnet operator is known as a network service provider. The subnet operator will connect to other networks that are part of the

Internet. Such a subnet operator is called an ISP (Internet Service Provider) and the subnet is an ISP network. Its customers who connect to the ISP receive Internet service.