# A-level Computing 2009/AQA/Computer Systems, Programming and Network Concepts/Introduction to Communication and Networking

Definition of this section is available at , page 19.

## Communication Methods
### Serial

Like a single lane road, all the cars arrive one after another. There is only ever one car going through the check point at any one time.

### Parallel

Multiple cables are arranged to send data simultaneously. However, due to small differences in the wires, the signals can become unsynchronized over longer distances. This is why parallel data transmission is only used over short distances, such as to connect a printer to a computer.

### Baud rate

The rate at which the signal changes in a communication medium, such as a wire. This is either equal to or lower than the bit rate.

### Bit rate

The rate at which bits are transmitted over a communication path. Normally expressed in bits per second (bps). The bit rate should not be confused with the data signaling rate (baud), which measures the rate of a signal changes being transmitted.

### Bandwidth

A measure of information or carrying capacity of a signal, expressed as the width of the spectrum of that signal in Hertz. Or the difference between maximum and minimum frequencies in a given spectrum is called the bandwidth of that spectrum.

### Asynchronous data transmission

The ASYNCHRONOUS (ASYNC) format for data transmission is a procedure or protocol in which each information CHARACTER or BYTE is may be transmitted and received at irregular and independent time intervals. The characters or bytes may also be transmitted as a continuous stream or series of characters.

### Start and stop bits

Describe the purpose of start and stop bits in asynchronous data transmission.

### Parity Bits

Parity is a system in which we use a parity bit to check for errors in a communicating system. Parity bits are generally the most simple way of checking for errors. At the end of a byte sent, an extra bit will be added to the end of the byte. We use two different types of parity bits. These are called even and odd parity bits. If we are using even parity, the bit on the end will ensure that the number of ones sent in the previous data is even. If we are using odd parity, then the bit on the end will ensure that the amount of ones in the sent data is odd.

### Handshaking

Handshaking is an automated process of negotiation that dynamically sets parameters of a communications channel established between two entities before normal communication over the channel begins. It follows the physical establishment of the channel and precedes normal information transfer.
An example for why a handshake is used is a client connecting to a server. To test the connection between the two computers, the client first declares itself to the server. The server now knows that the client can successfully communicate. When the server responds, the client knows that the server received the first message and replied to it, so the server can send and receive data along the data transmission channel. Now the client sends a final message to the server. The server now knows that its message was received. Both parties now know that communication is successful in both directions.

### Protocol

A protocol is a set of rules which computers use to allow them to communicate. There are many different communications protocols, including WiFi (a low level protocol that stipulates how bits should be converted into radio signals), and IP (a higher level protocol which provides addresses for different locations on a WAN, such as the internet).

### Modem

A modem is a piece of electronic equipment that takes data from computers and superimposes it onto the carrier signals of public telecommunications systems. This process is called modulation. The equipment also takes previously modulated data from the public telecommunications system and returns them to state that can be read by computers. This process is called demodulation. Modems can be either built-in units or plugged-in units

## Intranet

Network adapter

## Leased line

==Dial up== networking Candidates should be familiar with LAN topologies but will not be required to know details of their operation. Candidates should be aware of the advantages and disadvantages of each LAN topology. Candidates should be able to compare local area networking with standalone operation.

## Uniform Resource Locator (URL)

Describe the term URL in the context of Internetworking.

### IP addresses

Explain the term domain name and IP address. Describe how domain names are organised