Networks Unit 3
Networks
A network is a number of computer systems connected together
Advantages
Advantages
Share Software
Share data
Share peripherals (printers)
Centralised backup
Easy to monitor network activity
Access data from any computer
Network requirements and connectivity
Disadvantages
Security problems - files sent between computers could spread a virus
A network manager may need to be employed which is expensive
If the server is down, all workstations on the network are affected
Hackers can gain access to files quicker
Initial cost of servers is also expensive
Connectivity
Connectivity is the process of connecting the parts of a network to allow the data to transfer
Without connectivity, data could not be easily exchanged between computers without the use of removable storage
Wired connections use a wired connection protocol e.g cable using ethernet
Wireless does not use cabling but requires both the transmitting and receiving machine to have wireless network adaptor cards
Wireless is generally slower in terms of bit rate although the advantage of greater freedom can offset this
Lan and wan
A LAN is a network in which the computer systems are all located relatively close to each other, for example, in the same building or on the same site, such as a school.
A WAN is a network in which the computers systems are all located distantly from each other, for example, in different buildings all over the country or in different countries. The Internet is an example of a WAN. Many LANs could be linked using a WAN.
Bus
The computers (nodes) are connected to a single cable on which data can be sent, called the bus.
The bus has terminators on each end, which are needed to close each end of the cable.
The bus carries data packets along the cable.
As the packets arrive at each computer system, it checks the destination address contained in the packet to see if it matches its own.
If the address does not match, the computer system ignores the packet. If the address of the computer system matches that contained in the packet, it processes the data.
Network Topologies
A network topology is the layout of computer systems on a network. There are a number of different network topologies. Some common network topologies include: Bus, Ring, Star and Mesh.
Advantages
Easy to add more computer systems to the network without disrupting the network
Quick and easy to set up – well suited for temporary networks
Cost-effective as less cabling is needed
Disadvantages
It is difficult to troubleshoot the bus if there’s a fault
Limited cable length and number of stations – performance degrades as additional computers are added
If there is a problem with the main cable or connection, the entire network goes down
Low security – all computers on the bus can see all data transmissions
Data collisions are more likely, which causes the network to slow down. A collision is when two computers try to send a packet at the same time
Proper termination is required
Ring
Each node connects to exactly two other nodes, providing a single pathway for signals through each node.
Advantages
The transmission of data is simple as packets travel in one direction only, so no collisions
Data is quickly transferred without a bottleneck – consistent data transfer speeds
Adding additional nodes has very little impact on bandwidth
Disadvantages
If any of the computer systems fail, the ring is broken and data cannot be transmitted efficiently
a problem with the main cable or connection and the entire network goes down
It is difficult to troubleshoot the ring
Because nodes are wired together, to add another you must shut down the network
Star
Where one or more central switch, hub or computer acts as a central conduit to transmit messages
Advantages
Good performance/fast network speed
Easy to set up
Easy to add more computer systems
Disadvantages
Expensive to install as more cable is required
Extra hardware required, such as a hub
Minimal network collisions
failure of workstations will have no
effect on the network
Better security
Sending data over a Star network
Computer A adds computer D’s address to packet
Computer A sends packet to switch
Switch looks at address on packet
Switch compares to stored list of addresses on network
Switch forwards packet to computer D’s address
Mesh
Each node relays data for the mesh network. All mesh nodes cooperate in the distribution of data in the network.
This is very reliable as it can 'self-heal' by reconfiguring around broken paths. This network is complex, expensive and difficult to set up. A large part of the network may be redundant