Network Topology

• Compute network:-

Goals:-
1.Resource sharing .
2.Provide High Reliability
3.Distribution of workload
4.Saving Money
5.Expandability
6.Powerful communication Medium.
7.Protecting Information.
8.Preserving Information.

Applications:-
1) Business Applications
2) Home Applications

Network architecture describes how a computer network is configured and what strategies are employed .
Configurations include star, bus, ring, mesh and hierarchical. Strategies include terminal, peer-to-peer and  client-sever.

---

• Network Hardware :-

Broadcasting :-
1.Addressing a packet to all destinations.
2.Received by every machine on network.
3.Multicasting

Point to point:-
1.Network connections between  individual pairs.
2.Packet may visit one more intermediate machines
3.Uni-casting.

A network can be arranged or configured in several different ways.This arrangement is called the network's topology.

---

Network topologies:-  Physical topologies -

---

MESH topology:-
1.Interconnected topology.
2.Point to point link.
3.n(n-1)/2 links for n devices.
4.Direct communication
5.Highest degree of fault tolerance

Advantages:
1.Traffic problems eliminated .
2.Robust
3.Fault identification and fault isolation easy.
4.Privacy.
5.Highest  reliability and security.

Disadvantages:
1Amount of cabling
2.Number of I/O ports.
3.Reconnection is difficult.
4.Installation of new devices is difficult.
5.Expensive.

---

STAR topology:-
1.Point to point link.
2.Hub central controller.
3.Communication through controller.
4.Controller exchange data.

Advantages :
1.Requires only one link and one I/O port
2.Less expensive.
3.Easy to install.
4.Robust.
5.Fault identification and isolation easy.

Disadvantages:
Performance depends on hub.
Therefore if hub fails.
So,Network stops
Since speed depends on hub connections.

In a star network,a number of small computers or peripheral devices are linked to a central unit.This central unit may be a host computer or a file server.
All communications pass through this central unit 
Control is maintained by polling. That is ,each connecting device is asked (polled) whether it has a message to send .Each device is then in turn allowed to send its message.
One particular advantage of the star form of network is that it can be used to provide a time-sharing system. That is , several users can share resources (time) on a central computer.
The star is a common arrangement for linking several microcomputers to a mainframe that allows access to an organization's database.

---

BUS Topology:-

1.Linked by single cable i.e. multi point topology.
2.Devices have Drop lines and taps.
3.Used in LAN.

Advantages:-
1.Easy t install.
2.Cabling requires less compare to mesh and star.

Disadvantages:
1.Limited number of devices support .
2.Difficult to identify and isolate fault.
3.Degradation in quality of signal.
4.Bus cable fault ,stops all transmission.

In bus network each device in the network handles its own communications control.There is no host computer.
All communications travel along a common connecting cable called a bus.
As the information passes along the bus,it is examined by each device to see if the information is intended for it.
The bus network is typically used when only a few microcomputers are to be linked together.This arrangement is common for sharing data stored on different microcomputers.
The bus network is not as efficient as the star network for sharing common resources.
However , a bus network is less expensive and is in very common use.

---

RING topology:-

1.Connected to two devices .
2.Point to point link dedicated .
3.Signal travels in one direction.
4.Device relay ,if not intended.

Advantages:
1.Easy to install or reconfigure.
2.Fault isolation is easy.
3.Token

Disadvantages:-
1.Ring break ,network disable.
2.Number of devices connected and ring length.
3.Unidirectional ,data transfer is slow.

In ring network, each device is connected to two other devices , forming a ring .
There is no central file or computer.Messages are passed around the ring until they reach the correct destination.
With microcomputers, the ring arrangement is the least frequently used of the other networks .
However ,it often is used to link mainframes ,especially over wide geographical areas. These mainframes tend to operate fairly autonomously.
They perform most or all of their  own processing and only occasionally share data and programs with other mainframes.

---

HYBRID topology:-

1.Combination of topologies,not basic topology.
2.Two different basic topologies connection.
3.WAN have it.

---