Communication And Networking Flashcards
Data Transmission
Movement of electrical signals that represent data
Transferring data between two devices over a transmission medium
Transmission medium
Guided : wave travel along physical path e.g fibre optic
Unguided : signal propagated through air using radio waves of varying frequencies
Protocol
Set of rules for data exchange between systems
Bandwidth
Measured in hertz
Difference between highest and lowest frequencies at which a medium can correctly transmit
Typically represented in amount of bits/ bytes …. Gb that can be transmitted in one second
Network bandwidth
Measurement indicating max capacity of a wired or wireless communication link to transfer data over a network connection in a given amount of time
Latency
Time delay which can occur between the moment that something is initiated and moment effect first begins
Serial data transmission
Signal transmitted along wire one bit after another
(A) good for long distance, can regenerate signal along wire
(A) easy to route signal through telecom switches
(A) low cost of cabling, only two needed
(D) transmitter signal reduce in strength over long distance
Bit and Baud Rate
Bit rate - number of bits transferred per second
Baud rate - number signal change per second
(Bit Rate) / number bits per signal change = baud rate
Parallel data transmission
Connecting cable has multiple wires in it . Signal transmitted simultaneously along wire with one bit per wire
(D) only relevant for short distance, expensive for long
(D) skew can occur
Skew
Synchronisation problem, bits set off together but desync due to physical properties of wire
Can lead to wire being read when bit has not arrived
Synchronous Data transmission
Data sent in continuous stream, sender and reciever clock synchronised by common signal
Click in time with one another, may share common clock, data sent in block or frames
(A) fast
(D) costly
(D) have to wait until sending is finished to get a response from server
Asynchronous Data Transmission
Sender and receiver only synchronised for duration of transmission, data sent using serial transmission
Clocks must operate at same speed
Signal change at regular intervals, rate of signal change determined by baud rate
Sender and receiver clock must operate in step- bits read during intervals between signal change
Start and Stop bits must be different to one another
Start bit - wake up receiver
Stop bit - allow for next start bit to be recognised, provides a time interval during which receiver can deal with received bits
(A) sender and receiver use flow control method
(A) sends data in form of character or bytes
(A) do not have to wait till sending finish to get response from server
(D) slow
(D) economical to use
