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Introduction

Networking means connecting two or more devices forthe purpose of sharing data and resources.

Setting a small network is fairly simple task but once the

network start to grow and become a local area network itmay need to cover more distance than its media canhandle effectively.

When two or more separate networks are connected for

exchanging data or resources, they become aninternetwork (or internet).


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Introduction

There are several way that you can expand networkcapability such as:

Physically extending to support additional computers

Segmenting to filter network traffic

Extending to connect separate LANs

Connecting two separate computing environments


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Networking Devices

Expansion within a single network, callednetwork connectivity. And to expand a singlenetwork the following networking devices can

be used.

Hub

Repeaters

Bridges


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Hub

All networks require a central location to bring mediasegments together.

These central location are called hubs.

A hub organizes the cables and relays signals to the othermedia segments.

There are three main types of hub: Passive, active andintelligent.


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Passive Hub

A passive hub, simply combines the cables of networksegments.

There is no signal processing or regeneration.

Because it absorbs some of the signal, a passive hubreduces by half the maximum cabling distance permitted.

Passive hub merely acts as a connection point and doesnot amplify or regenerate the signal.

Passive hubs do not require electrical power to run.


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Active Hub

Active hubs are like passive hubs except that they haveelectronic components that regenerate or amplify signals.

Because of this, the distance between devices can be

increased.

The hub that regenerates the electrical signal and sends itto all the computers connected to it, is often called amultiport repeater.

Active hub requires electrical power to run.


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Intelligent Hub

In addition to signal regeneration, intelligent hubsperform some network management and intelligent pathselection.


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Repeater

Because of the electrical and mechanical limitations ofany wiring system a network has physical limitations.These are:

1. Attenuation: Loss of signal strength as the signaltravels along a medium.

2. Segment length: longest successful data transmissionthrough a continuous single cable.

3. Node capacity per segment: number of nodes can beconnected on a media


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Repeater

A repeater regenerates the original bit pattern, and putsthe refreshed signals back onto the link.

A repeater allows is to extend only physical length of the

network.

Repeaters operate at the physical layers of the OSI model.

They are unintelligent electronic device unable to

perform any filtering or translation on the actual data.


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Repeater

There is a slight delay as the repeater regenerate thesignal.

The location of a repeater on a link is vital. A repeater

must be placed so that a signal reaches it before any noisechanges the meaning of any of its bits.


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A L L O W S E A S Y E X P A N S I O N O F T H E N E T W O R K O V E R

L A R G E D I S T A N C E .

H A S V E R Y L I T T L E I M P A C T O N T H E S P E E D O F T H E

N E T W O R K .

A L L O W S C O N N E C T I O N B E T W E E N D I F F E R E N T M E D I A .

Strength of Repeater


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Limitations of Repeater

Provide no addressing information.

Can not connect two different architectures.

Does not help ease congestion problem.

The number of repeaters in a network is limited.


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Bridge

Bridges operate in both the physical and data link layer ofOSI model.

Like repeaters, bridges also can be used to connect two

network segments and can connect dissimilar physicalmedia.

Bridges can also limit the traffic on each segment and

eliminate bottlenecks.


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Types of Bridges

To select between segments, a bridge must have a look-uptable that contains the physical addresses of every stationconnected to it.

Bridges can be classified based on look-up tablegeneration and number of segments are connected by asingle bridge.


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Simple Bridges

Simple bridges are the least expensive type of bridge.

Before a simple bridge can be used, operator mustprogram the addresses of every station.

Whenever a new station is added or removed, the tablemust be updated.

Installation and maintenance of simple bridges are timeconsuming and in long run more trouble than the costsavings are worth.


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Learning Bridges

A bridge builds its table of station addresses on its own.

When the learning bridge is first installed, its table is

empty.

As it encounters each packet, it looks at both thedestination and the source addresses.

If it does not yet recognize the destination address, it

relays the packet to all of the station on both segments.

It uses the source address to build its table.

Using the same algorithm, the learning bridge is also

self-updating.


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Multi-Port Bridges

A multiport bridge can be either simple or learning, andis used to interconnect more than two same typesegments.


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Translation Bridges

Translation bridges are available that can connectdifferent types of networks. For example a translation

bridge can be used to connect an Ethernet network to atoken ring network.


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Strength of Bridges

Easy to extend network distances

Can filter traffic to ease congestion

Can connect network with different media

Translation bridges can connect different networkarchitectures


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Internet Working Devices

Expansion that involves and joins two different networks,called internetworking connectivity. Following devicescan be used for internetworking.

Routers

Gateways


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Router

Routers are combination of hardware and software andused to connect separate networks to form aninternetwork.

Router can be used like bridges to connect multiple

network segments and filter traffic.

Also, unlike bridges, routers can be used to connect twoor more independent networks.

For example a FDDI networks and an Ethernet network

can interconnected so that users on each network canshare resources on the other network and still bothnetwork continue to function separately.


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Router

Routers can connect complex networks with multiplepaths between network segments.

Each network segment, also called a subnetwork, is

assigned a network address.

Each node on a subnet is assigned an address as well.

Using a combination of the network and node address,the router can route a packet from the source to adestination.


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Router

Router has access to first three layers(physical, data link, andnetwork).

When the router receives a packet, it analyzes the packets destinationnetwork address and look up that address in its routing table.

Routers can send information over different network architectures.

The router removes the token ring frame, examines the packet todetermine the network address, repackages the data into Ethernet

frames, and sends the data out onto the Ethernet networks.


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Router

Repackaging affect the networks speed.

Unlike bridges routers have ability to select the best paththat is faster and economical.


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Routing Table

Router has a routing table that contains network addresses and theaddress of the routers that handle those networks. Following tableshows a sample routing table for router A. It includes the nexthope(i.e., were transmission will go next) and cost(i.e., number of hopsthe packet must take)

Network Next Hope Cost in Hopes

1 Directly Connected 0

2 Directly Connected 0

3 Router 4 1

4 Router 3 1

5 Router 3 2

6 Router 3 27 Router 4 1

8 Router 4 2

9 Router 4 2


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Static Routing

If router uses static routing, the routing table must beupdated manually by the administrator.

Each individual route must be added by manually.

The router will always use the same path to a destination,even if it is not necessarily the shortest or most efficientroute.


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Dynamic Routing

Dynamic routers communicate with each other and areconstantly receiving and are constantly receiving updatedrouting tables from other routers.

If multiple routes are available to a particular network,the router will decide which route is best and enter thatroute into its routing table.


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Strengths of Routing

Can connect networks of different physical media andnetwork architectures

Can choose the best path for a packet through an

internetwork

Reduces network traffic by not forwarding corruptpackets


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Limitations of Routing

More expensive an more complex than bridges orrepeaters.

Slower than bridge because they perform more complex

calculations on the packet only work with routableprotocols


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Brouters

Brouters combines the best of both bridges and routers.

When brouters receive packets that are routable, they will operate as arouter by choosing the best path for the packet and forwarding it to itsdestination.

However, when a nonroutable packet is received, the brouter functionsas a bridge, forwarding the packet based on hardware address.

To do this brouters maintain both bridging table, which containshardware address, and a routing table, which contains network

address


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Gateway

Gateways operate in all seven layers of OSI model A gateway is a protocol converter. A router itself transfer, accepts, and relays

packets only across network using similar protocols.

A gateway on the other hand, can accept a packet formatted for oneprotocol(e.g. AppleTalk) and convert it to a packet formatted for another

protocol(e.g. TCP/IP) before forwarding it.

A gateway is generally software installed within a router.

The gateway understands the protocol used by each network linked into therouter and is therefore able to translate from one to another.

h f


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Strengths of Gateway

Can connect completely different system.

Dedicated to one task and perform that task well.

Li i i f G


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Limitations of Gateway

More expensive than other devices.

More difficult to install and configure.

Greater processing requirements mean they are slowerthan other devices.


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END

network connecting devices

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