How To Expanding A Networks

Network Connectivity Devices:  

To expand a single network without breaking it into new parts or connecting it to other networks, we can use the following devices:

•  Hubs
•  Repeaters
•  Bridges
•  Multiplexers

Hub:

• All networks require a central location to bring media segments together
• The central locations are called hubs
•  A hub organizes the cables and relays signals to the other media segments.
• Important things about hub:
• There is a limit to the number of hubs that can be connected to each other to extend a network.
• When possible, connect each hub directly to a server network card rather than to another hub.
• Label the connection on the hub.
• The more hubs data passes through, the slower the connection.
• Passive hubs
• A passive hub simply combines the signals of network segments.
• There is no signal processing or regeneration.
• As it does not boost the signal and absorb some of the signal, it reduces by half of maximum cabling distance permitted.

Here, each computer receives the signals sent from all the other computers connected to the hub.

Active hub:

• It regenerates or amplify signals.
• The distance between devices can be increased.
• They also amplify the noise as well.
• They are more expensive than passive hub.
• Bcz some active hubs function as repeaters, they are sometimes called multi-port repeaters.

Intelligent hub:

Intelligent hubs can regenerate signals but it can perform some network management and intelligent path selection.

A switching hub chooses only the port of the device where the signal needs to go, rather than sending the signal along all paths.

Many switching hubs can choose which alternative path will be the quickest and send the signal that way.

Repeaters:

• All transmission media attenuate the electromagnetic waves that travel through them.
• Adding a device that amplifies the signal can allow it to travel farther, increasing the size of the network.
• Devices that amplify the signals in this way are called repeaters.
• Repeaters fall into two categories: amplifier and signal-regenerating repeaters.
• Amplifiers simply amplify the entire incoming signal and amplify both signal and noise.
• Signal regenerating repeaters create an exact duplicate of incoming data by identifying it amidst the noise, reconstructing it and retransmitting only the desired information.
• The original signal is duplicated, boosted to its original strength and sent.

Bridges:

Bridges connect network segments.

The use of bridge increases the maximum possible size of your network.

A bridge selectively determines the appropriate segment to which it should pass a signal.

It does this by reading the address of all the signals it receives.

The bridge reads the physical location of the source and destination computers from this address.

The process works like:

A bridge receives all the signals from both segment A and segment B.

The bridge reads the addresses and discards all signals from segment A that are addressed to segment A, bcz they do not need to cross the bridge.

Signals from segment A addressed to a computer on segment B are retransmitted to segment B.

The signals from segment B are treated in the same way

Through address filtering, bridges can divide busy networks into segments and reduce network traffic.

Network traffic will be reduced if most signals are addressed to the same segment and do not cross the bridge.

Two types of bridges:

• Transparent bridges keep a table of addresses in memory to determine where to send data
• Source-routing bridges require the entire route to be included in the transmission and do not route packets intelligently.
• Multiplexing allows you to use more bandwidth of the medium by combining two or more separate signals and transmitting them together.
• The original signals can then be extracted at the other end of the medium. This is demultiplexing.
• Multiplexing provides a way of sharing a single medium segment by combining several channels for transmission over that segment.

Three major methods of multiplexing are:

1. Frequency division 

2. Time division 

3. Statistical time division

Frequency-Division multiplexing:

FDM uses separate frequencies to combine multiple data channels onto a broadband medium.

You can use FDM to separate traffic traveling in different directions in a broadband LAN.

Time-division multiplexing:

• TDM divides channel into time slots.
• Each of the devices communicating over this multiplexed line is allocated a time slot in a round-robin fashion.
• If a device does not use its time slot, that slot is wasted.

Statistical Time-division multiplexing:

• TDM systems can be inefficient if many slot times are wasted.
• StatTDM provides an intelligent solution to this problem by dynamically allocating time slots to devices on a first-come, first-serve basis.
• The number of time slots allocated to a particular device depends on how busy it is.
• You can use priorities to allow on device greater access to time slots than another.
• For the multiplexer on the receiving end to determine which signal a particular time slot is carrying, there must be a control field tat identifies the owner attached to the data.