1. Communications Networks

2. What is a Network?

An arrangement of two or more computers interconnected to enable sharing of resource and data.

A true network is characterised by having its processing distributed across the various processors which constitute the network itself.

3. Advantages of Networks

Sharing of data

Sharing of resources

• hardware and software

Communication

Easier resource management and security.

4. Servers

A server is a computer that is designed to support a computer network.

File Server

• an entire file is sent to the requesting computer and it does the processing.

Client Server

• processing is done on the server before the file is transmitted.

5. Networks

LANS - Local Area Networks

MANS - Metropolitan Area Networks

WANS - Wide Area Networks

WINS - Wireless In-building Networks

6. LANS

Restricted area - room, building.

Privately owned transmission systems - cable based media.

Doesnt cross public roads.

High transmission rate.

7. LANs - peer to peer

LANs do not have to use a single server but may use a peer to peer network.

Peer to peer networks allow any computer to share the resources with any other computer on the network.

• Microsoft's Home Networking and Apples AppleTalk are examples of this.

8. MANS

Network spans a municipality.

Transmission is left to Public Access Utility Carriers (Telstra)

Area covers a town, city or bigger.

WANS 9. WINS

High speed communications among PCs and other equipment within one site.

Use radio frequency that can carry a large amount of data at high speed.

Possible security problems.

10. The Internet

The internet is a worldwide network of computer networks.

The Internet has millions of users and can be used for:

• email, file transfer, research, discussion groups and entertainment

11. Network Topologies

STAR

RING

BUS

12. STAR

Each node is connected to the network controller (or host) by a separate transmission medium.

All communication between nodes must first be directed to the controller where it is re-addressed.

• e.g. PABX, Time sharing Main Frame

13. STAR NETWORK Server Nodes 14. Star network

Expensive

• due to amount of cabling

Other nodes can continue if one link is broken.

No contention for access to lines.

Capacity of network determined by the speed of the controller.

15. BUS Network

A single link (the bus) traversing the area of the network. Each node is tapped into the passing bus line forming a multidropped configuration.

All nodes share a common transmission medium.

Messages and destination address are broadcast to all nodes, but only the addressee accepts it.

16. BUS NETWORK

ETHERNET is the most common example of the bus.

17. Bus network

Usually uses twisted pair or coaxial cable.

Easy to add extra nodes.

Easy installation.

Performance degrades if network gets busy.

Requires medium access control.

Usual transmission speed 10Mbps.

18. RING NETWORK

A number of point-to-point links between nodes with the first and last being joined to form a loop.

Each node shares the transmission line.

Each message must be addressed.

19. Ring Network 20. Ring Network

A common type of ring network is the TOKEN ring network.

Nodes that want send data must first get the token (an electronic signal) to gain access to the communication channel.

21. Ring Network

The token is attached to the messageand when received correctly an acknowledgement signal is sent back.

The token is then released back onto the network.

Only one token is available at any one time.

22. Ring Network

Data only travels in one direction.

Requires medium access control.

Typical speed 1-10Mbps