data transmission Flashcards
paper 2
serial transmission
one bit after another sent in order
eg USB wire
parallel transmission
more than one bit sent at a time
serial connection pros
only one wire needed which makes it cheaper and easier to set up
is less prone to interference over long distances
serial transmission cons
only one bit transmitted at a time so can take longer (less true with high clock speed)
parallel transmission pros
multiple bits sent at a time makes it faster (less true with modern technology)
parallel transmission cons
hardware more expensive
over longer distances there is likely to be interference due to induced currents between wires (crosstalk) which reduces signal quality
bits can travel at different speeds over the wires causing skew
simplex mode of transmission
data can travel in one direction only
eg radio transmission
half duplex mode of transmission
data can travel in both directions but not at the same time
eg two way radios (walkie talkies)
full duplex mode of transission
data can travel in both directions at the same time
eg telephone, ethernet cables
multiplexing
allows independent data sources to be combined into one single communication link which is then transmitted over the same wire simultaneously
switching
process by which the devices forward chunks of data (packets) towards their destination possibly via other devices. switch knows location of nearby devices so can forward data in right direction
frequency division multiplexing
divides spectrum/carrier bandwidth in logical channels and allocates one user to each channel
user can use channel frequency to access data
time division multiplexing
shared channel divided among its users via time slots
each use can transmit data within provided time slot only
high bit rate makes it look as though signals are transmitted simultaneously
internet
a worldwide connection of packet switched networks
contents of a packet
length (number of bits)
order number
source address
destination address
protocols
data
checksum
circuit switching
path across the network is set up in advance and all packets are sent in order down the same route
eg phone netwrok
circuit switching pro
packets will arrive in order
circuit switching cons
if a part of the route is broken the whole circuit will fail and a new circuit must be set up before communication can continue
no other traffic can use that route until communication has ended wasting bandwidth
packet switching
packets take independent routes through the network
packet switching pros
if one route is broken then another route can be found without breaking communication - more stable
bandwidth used more efficiently as no part of the network is reserved
packet switching con
packets might not arrive in order requiring extra processing is needed and each packet needs an order number
collision
when two nodes send data at the same time and the signals interfere with one another
packets are discarded when a collision is detected, a jamming signal is sent to prevent further transmissions and a short, random amount of time is waited before each of the packets is sent
routing
the process of path determination for a packet done by the router
Dijkstra’s shortest path algorithm
designed to find the shortest path between a start node and every other node in a weighted graph
uses priority queue to keep record of which vertex to visit next
assigns temporary distance value to each node (0 at start node and infinity for all other)
bitrate
number of bits transferred between devices in one second
bandwidth
measure of maximum capacity of a given communication channel.
greater the bandwidth the greater the volume of data you can transmitd
data transfer rates
measured in bps (bits per second), Mbps (megabits per second) etc
1. convert from bytes to bits (x8)
2. convert from minutes to seconds (x60)
3. bits divided by seconds
static routing
each router has access to a table that tells it which path to forward data based on destination address
simple to implement but not suitable for networks that change often
