4.9.1.1 Communication methods Flashcards
What is serial data transmission?
Individual data bits sent one after another along one wire. Used over long distances, fewer wires required which makes it cheaper, no risk of synchronisation issues.
What is parallel data transmission?
Multiple bits are transmitted simultaneously down more than one wire, used for short distances such as data from the hard drive to the processor because it’s faster as the volume of data is greater
Parallel communication requires more wires (and hardware);
Higher cost
More difficult to manage when setting up the system
Parallel communication needs the data to be kept synchronised across wires /
risk of data skew over long distances;
Parallel communication carries the risk of crosstalk between wires;
What are the wires in parallel data transmission used to send?
Data, parity bits, start signal, “ready to send” signal, stop signal
What is synchronous data transmission?
The transmitter and receiver are kept in sync the entire time using synchronising signals
What is asynchronous data transmission?
Receiver and transmitter’s clocks don’t have to be completely synchronised, only during data transmission. Data is sent as soon as possible, using a start bit to synchronise the receiver to the transmitter and the stop bit indicate the transmission has ended and the receiver can process it. A parity bit may also be sent to check for errors.
What is packet switching?
Messages are split into packets of equal sizes which are given a destination address. Each packet is dispatched onto the internet through a router, they travel through any route deemed fastest and are given a sequence number. When the packet reaches a router the router sends it forward until it reaches the destination where the packets are reordered.
What are the advantages of using packet switching?
Transmission is safer from interception because it’s difficult to intercept all packages when they take different routes.
Efficient as each channel is only used for a short time
If there’s an error only a small part of the data has to be resent
Why can emails be more easily intercepted than paper mail?
Emails pass through multiple servers over a network so more computers can make a copy.
The message is vulnerable to being read or copied
Electronic eavesdropping is possible
Email alterations leave no trace
What is the role of the router?
Examines the destination of a packet and forwards them to another network. Manages congestion and chooses the route a packet should go to using a packet’s destination IP address
What is a handshake protocol?
The exchange of signals between devices to show they are ready for communication. It establishes rules like baud rate so that the two devices can understand each other
