3. Data Transmission Flashcards
What is simplex transmission?
Data can travel in one direction only
+ easiest and most reliable mode of communication
+ most cost effective, as it only requires one communication channel
- only one-way communication is possible
examples: keyboard and monitor
What is half-duplex transmission?
Can go in either direction but only one at a time.
+ efficient use of bandwidth
- can be slower due to turn taking
examples: walkies-talkies
What is full-duplex transmission?
Data can travel in both directions at the same time
+increases performance and speed of the network as both devices can transmit and receive data at the same time
- most expensive as it requires two communication channels
e.g telephone
What is serial transmission?
The data is sent one bit at a time
+ not affected by skew, and there are fewer wires in close proximity which minimises crosstalk
+ uses fewer wires, cheaper to implement and occupies less space
What is parallel transmission?
Allows multiple bits to be sent at the same time
+ works efficiently over short distances and with lower bit rates than serial
The following occur:
Crosstalk - Electromagnetic interference between nearby wires, like parallel links, causes corruption of data and requiring it to be re-sent
Skew - happens when bits are transmitted across parallel link travel at different speeds. This can result in data falling out of sync and therefore not being read correctly
What is multiplexing?
Multiplexing is a way of sending multiple signals over a communications link at the same time in form a single, complex signal
In time division multiplexing (TDM), data is assigned a slot per cycle. Can result in empty slots and under utilisation of the communication channel
In Statistical TDM, if a sending device is not ready to transmit in a cycle, the next sender that is ready can transmit. This reduces the number of wasted slots.
In frequency division multiplexing (FDM), each signal is assigned its own frequency range within a larger band which are often separated to reduce interference.
What is circuit switching?
All the data packets take the same route and will travel sequenitally. If any part of the circuit fails, a ne route will have to be found. Can be inefficient if the reserved bandwidth is not fully used
What is packet switching?
Each packet can take a different route and may arrive out of sequence or may not arrive at all. If a route fails they can take a different one. Can be sent efficiently and individually across less busy routes
Explain how data collisions are detected and resolved in networks.
When data packets collide, these collisions generate a frequency which all devices on the network can detect. The devices wait a random interval of time before resending the packets.
