SLR 20 - communication

Question 1

What is a symbol?

Answer 1

A symbol is a particular bit pattern represented by a signal e.g., a symbol of four bits might be 1101

Question 2

What is baud rate?

Answer 2

a communication of system’s Baud rate is the number of signal changes in the medium per second. 1 Baud (or1bd) is equal to 1 symbol change per second

Question 3

What is bit rate?

Answer 3

the number if bits that are transmitted over the medium per second - often calculated in bits per second

Question 4

What is the calculation of bit rate?

Answer 4

baud rate x number of bits per second

Question 5

When would the bit rate be higher than its baud rate

Answer 5

if there is more than one bit sent per signal

Question 6

What is bandwidth?

Answer 6

• its expressed in Hertz
• it relates to the range of frequencies that a communication medium is capable of transmitting
• there is a direct relationship between bandwidth and bit rate
• higher bandwidth = higher bit rate

Question 7

What is latency?

Answer 7

• the difference in time between an action being initiated and its effect being noticed
• measured in milliseconds
• latency increases with distance

Question 8

What is a protocol?

Answer 8

• a set of rules relating to communication between devices
• international organisations decide on and publish protocols which allow devices to be made by different manufacturers but still communicate seamlessly

Question 9

What is synchronous transmission?

Answer 9

• data is transferred at regular intervals that are times by the clocking signal
• allows for constant and reliable transmission for time sensitive data e.g., real-time video and vice
• Parallel communications is the main user of this type of transmission e.g., the signal clock

Question 10

What is asynchronous transmission?

Answer 10

• one byte is sent at a time by using start and stop bits
• The start bit alerts the receiving device which synchronizes the receiving devices internal clock - if this is not done, the Baud rate will not match between sender and receiving devices internal clock
• The stop bit will continue until the next byte is sent, hence why the start/stop bit are always opposite
  The start and stop bit can be either way around, unless specified (these bits are not included in the parity check)

Question 11

What is the problem with parallel data transmission?

Answer 11

• each individual wire has slight different properties e.g., material and temp, which causes a small variation in speeds
• this limits its use to short distances e.g., inside a computer because it is faster

Question 12

Advantages of serial data transmission

Answer 12

• lower costs because the complexity of connections is reduced
• avoids cross talk - occurs in parallel transmission - connections close together result in corrupted data
• serial links are more reliable over greater distances
• higher frequencies can be sent over serial connectors