NETWORKING DEVICES

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Lesson 04

NETWORKING DEVICES

Topology of a LAN means its physical lay out. There are three main types of Network Topology, namely,

Bus Topology, Star Topology and Ring Topology as shown in Figures 1-3 below. There are two different

approaches to networking Server-based and Peer-to-Peer approach. In server-based approach there is a

centralized server machine that can serve users' requests for the sharing of resources on a network.

Contrarily, in peer-to-peer, the machines on the network have an equal capability which means that they can

act both as a client and a server.

Fig. 1

Fig. 2

Fig. 3

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Networking devices

Hubs

These provide central connection point for a LAN. They organize cables and relay data signals to all

computers. There are ports on the back of a hub used to connect computers. They come in different sizes

and shapes.

Repeaters

Repeaters regenerate signals. A repeater would amplify the entire electric signal it receives. However, it has

no capabilities of directing network traffic.

Bridges

A Bridge is a combination of hardware and software. It has its own operating system. It helps to conserve

the bandwidth of a network. Bandwidth is the speed of a network. It indicates how many bits can be

transmitted across a network in a given time. In case of a bridge, the larger network is physically chopped

into smaller segments. A bridge can read the MAC (Media Access Control) or physical address of a

computer on data packets. MAC address is printed on the Network Interface Card. A bridge matches this

MAC address with the one stored in its table and judges that which particular segment does a data packet

belong to and accordingly sends that packet to such a segment. It does not allow other packets belonging to

other segments to spread to a particular segment and hence conserves the bandwidth. (See Fig. 4 below)

Fig. 4

Switches

A switch is also a combination of hardware and software having its own operating system. Like bridges, the

switches are also used to increase the bandwidth of a network. However, in case of a switch, a network is

virtually divided into small segments called Virtual LANs or VLANs. Similar type of users can be grouped

into a VLAN despite that they have no physical proximity or closeness. A switch would read the MAC

address on a data packet and match it with the list of MAC addresses of the user machines contained in it. It

then sends data packets only to that machine on a VLAN to which these packets relate. Packets belonging

to other VLANs are not allowed to enter into a particular VLAN, hence bandwidth increases.

Routers

Routers use a combination of hardware and software to forward data packets to their destination on the

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internet. They are more efficient and sophisticated than bridges and switches. They can divide large

networks into logical segments called Subnets on the basis of IP addressing scheme. A router can

communicate with another router on the internet with the help of Routing Information Protocol, and thus

it can build a routing table. This routing table contains information about different network addresses and

different routes for delivery of data packets to a host machine on a network. A router is a decision making

device. When a data packet arrives at a router it reads the network addresses from the IP address on the

data packet and determines the shortest possible path through which this packet can be delivered to its

destination.

Following diagram (Fig. 5) explains how routers on the internet backbone forward data packets by

determining the shortest possible path for the destination. In this example a client machine `A' sitting on

network no. 140.57 sends data to a web server `B' hosted at network no. 100. `R1' is the router attached to

network no. 140.57. After consulting its routing table it can find that the shortest possible path for sending

data to machine `B' is to forward data packets to `R2', the router attached to network no. 100. In case there

is a blockade then`R1' can look for the alternative shortest path. Here, the alternative shortest path for the

delivery of data packets to `B' can be R1-R3-R4-R2.

Fig. 5

Cabling options

Cooper-based cables

They are quite commonly used for connecting computers. They have two main types coaxial and twisted

pair. In twisted pair there are two further options unshielded twisted pair (UTP) and Shielded Twisted

Pair (STP).

Fiber optic cables

They are used on the internet. They deliver data at a very high speed. They use glass or plastic filaments and

the pulses of light as a data transfer method.

Telephone and electrical wire networks

They can also be used for connectivity purpose.

Wireless options

Wireless options include radio connectivity (wi fi, bluetooth), infrared connectivity and Satellite microwave

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transmissions.

Address resolution protocols (ARP) and address resolution protocol (RARP)

Each computer on the internet prepares a list of its IP address and corresponding MAC address using ARP.

Through RARP this information is forwarded to a network server. When a data packet arrives at the

destination router, it inquires about the corresponding MAC address form the network server, inserts it and

delivers the packet to that MAC address. A data packet therefore needs both IP and MAC addresses to

reach its destination. (See Fig. 6 below)

Fig. 6

Role of ISPs on internet

Internet Service Providers (ISPs) are those organizations which can provide internet connections, offer

services of web hosting, newsgroups and internet e-mail etc. They work in a hierarchy. The ISP at the top of

the hierarchy which is connected with internet backbone is called Internet Access Provider or IAP. An

internet trunk line or backbone passing through a metropolitan area is also called Metropolitan Area

Ethernet (MAE). IAPs are connected to MAEs at points called Network Access Points (NAPs). Trunk lines

allow IAPs to move data. The actual routing of data packets takes place on internet backbone (see Fig. 7

below).

Fig. 7

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