Communications and Networks

A Network is a group of devices connected to each other.

A LAN is a small-scale network of computers commonly used by schools, small businesses etc.

The advantages of LANs are:

• Allows communications between people 
  
• Allows resources to be shared
• Peripherals can be shared
• Computers can be upgraded more easily

Data is too large to be sent over the internet in one go, so it is divided into packets.

Each packet contains snippets of the original data as well as logging information about the recipient and the sender.

The source address is the IP address of the computer which sent the data.

The destination address is the IP address of the computer which will recieve the data.

The Network Interface Card (NIC) provides access to the network, as well as providing an address to each individual node.

The Hub connects each node together to form one segment. The hub passes on information from one node to all other nodes. If two nodes transmit information at the same time, a data collision may occur which means data will need to be retransmitted.

A Switch connects one node to another directly without any other nodes being involved. Data can be sent directly from one node to another, minimising any risk of data collisions.

A Router forwards data packets from one network to another. It extracts the routing information from the data packet and uses its routing policy to move the packet onto the next network. This continues until the packet reaches its final destination.

A Wireless Access Point (WAP) connects a node to a network without the use of wires. It uses electrical signals in the form of Wi-Fi or bluetooth etc.

A Peer-to-Peer network is a setup by which each node is connected to each other in a line. This is usually prominent on small networks.

Each computer stores its own programs and data rather than storing it on a central server.

Computers send data to other computers, but this causes data collisions.

In a Client Server, a central server stores all the data and information, and carries out most of the processing jobs as well as holding data to access peripherals and the internet.

The Central Server is a high specification machine which holds all the data & information, carries out the processing of shared files and allows access to peripherals and the internet.

Clients are each computer (node) which connects to the network via the server. Clients send requests to the central server.

A Network Topology is a term used to describe the layout of a network.

A Ring Toplogy is where all the nodes are interconnected in one linking cable.

Data passes in one direction only. As a result, the performance is faster.

However, if one node fails, the whole network of nodes fails.

A Star Toplogy is where each node has an individual cable linking to the central server.

There are fewer data collisions in a star network. The individual connections mean the network runs faster. 

However, the network is expensive to install. If one hub or switch fails, the other nodes might not be able to connect to the network.

A Bus Network is where one cable links every node and the server together, however each node has its own cable divulging off the main cable.

This setup is cheap to install.

However, if the main linking cable breaks, all the nodes will lose connection to the network. There will be lots of data collisions and the network can slow down during periods of heavy traffic.

A Wide Area Network (WAN) is a network which is on a large scale. The largest known WAN is the internet.

A Local Area Network (LAN) is a network which is on a smaller scale. For example, a school will use a LAN.

A WAN consists of two or more LANs connected via a satellite or telephone cable or fibre-optic cable etc.

Network Protocols are rules which enable different computers to communicate with each other.

Transmission Control Protocol (TCP) enables the interaction of two computers.

Internet Protocol (IP) enables the transmission of data packets over the internet.

An IP Address is a unique address given to each node on a network using IP.

It consists of four numbers separated by full stops.

These four numbers are converted into 8-bit binary numbers when transmitted over the network.

Examples include: (92.123.76.17) 

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A MAC (Media Access Control) Address is a unique number indentifying a Wi-Fi adapter or Network Interface Card (NIC).

A MAC can be used to restrict user acccess to a network.

User Access Levels are permissions granted to users of a network which determine how much access they obtain.

When a user logs on to a network, their username and password are matched against a database of authorised users. Appropriate permissions will be given based on rules set by the network admin. If user access levels were not implemented, users would be able to access the server itself as well as every other computer, which could jeopardise the network.

Passwords are secure hidden phrases used to prevent outside unauthorised users gaining access to a network. Users are recommended to use a mixture of upper and lower cases, character types and numbers in order to prevent hackers using brute force software to gain access to the password. 

Encryption is where data is rewritten during transmission in order to keep it secure and hidden from unauthorised access. Only the destination and sender will be able to decrypt the data. This is needed to avoid data being stolen or viewed against the sender/recipient's will.

Network Policies are written rules by which users should abide by. These are set by the admin.

Acceptable Usage Policy is the main policy set by the administrator which determines how users should use the network. Usual rules are that users must not interact with any inappropriate content and they must not gain unauthorised access to private data or information.

Disaster Recovery Plans are plans which determine how a network will run in the event of a server or component failing. They aim to reduce disruption and the amount of data and money lost. The plans should contain preventive measures which aim to stop a disaster happening in the first place, detective measures to attempt to detect problems before they become larger in scale and corrective measures to rectify the problem.

Failover is the ability to transfer the data from a failed server to a standby emergency server.

Backup is the ability to make copies of data from the server so they can be saved in the event of a disaster.

Archiving is storing files in a server over a long period of time.

The Internet is a world-wide connection of computer networks using the TCP/IP to connect with each other.

The internet is the largest WAN currently in use. It consists of a variety of other WANs and LANs connecting to it to form one large WAN.