data transmission

Question 1

serial transmission

Answer 1

one bit after another sent in order
eg USB wire

Question 2

parallel transmission

Answer 2

more than one bit sent at a time

Question 3

serial connection pros

Answer 3

only one wire needed which makes it cheaper and easier to set up
is less prone to interference over long distances

Question 4

serial transmission cons

Answer 4

only one bit transmitted at a time so can take longer (less true with high clock speed)

Question 5

parallel transmission pros

Answer 5

multiple bits sent at a time makes it faster (less true with modern technology)

Question 6

parallel transmission cons

Answer 6

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

Question 7

simplex mode of transmission

Answer 7

data can travel in one direction only
eg radio transmission

Question 8

half duplex mode of transmission

Answer 8

data can travel in both directions but not at the same time
eg two way radios (walkie talkies)

Question 9

full duplex mode of transission

Answer 9

data can travel in both directions at the same time
eg telephone, ethernet cables

Question 10

multiplexing

Answer 10

allows independent data sources to be combined into one single communication link which is then transmitted over the same wire simultaneously

Question 11

switching

Answer 11

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

Question 12

frequency division multiplexing

Answer 12

divides spectrum/carrier bandwidth in logical channels and allocates one user to each channel
user can use channel frequency to access data

Question 13

time division multiplexing

Answer 13

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

Question 14

internet

Answer 14

a worldwide connection of packet switched networks

Question 15

contents of a packet

Answer 15

length (number of bits)
order number
source address
destination address
protocols
data
checksum

Question 16

circuit switching

Answer 16

path across the network is set up in advance and all packets are sent in order down the same route
eg phone netwrok

Question 17

circuit switching pro

Answer 17

packets will arrive in order

Question 18

circuit switching cons

Answer 18

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

Question 19

packet switching

Answer 19

packets take independent routes through the network

Question 20

packet switching pros

Answer 20

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

Question 21

packet switching con

Answer 21

packets might not arrive in order requiring extra processing is needed and each packet needs an order number

Question 22

collision

Answer 22

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

Question 23

routing

Answer 23

the process of path determination for a packet done by the router

Question 24

Dijkstra’s shortest path algorithm

Answer 24

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)

Question 25

bitrate

Answer 25

number of bits transferred between devices in one second

Question 26

bandwidth

Answer 26

measure of maximum capacity of a given communication channel.
greater the bandwidth the greater the volume of data you can transmitd

Question 27

data transfer rates

Answer 27

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

Question 28

static routing

Answer 28

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