Types of Transmission - Comparison

ASYNCHRONOUS TRANSMISSION

1.Used for short bit sequences
2.Idle = No signal, negative voltage, 1
3.One Start bit, 7 or 8 data bits
4. One parity bit: Odd, Even, None
5.  Minimum Gap = Stop bits = 1, 1.5, or 2 bits
6. Efficiency = data bits/total bits

8N1 = 1 Start bit + 8 Data bits + 1 Stop bit + 1 parity bit (even 
though the parity is not being used by this site)
⇒ 8/(1+8+1+1) = 73%

7.  Faster clock: 7% ⇒ 56% off on 8th bit ⇒ Error
8.  Framing error ⇒ False start/end of a frame

SYNCHRONOUS TRANSMISSION


1. Used for longer bit sequences
2.  Requires clock transmission
Use codes with clock information (Manchester)
3.  Begining of block indicated by a preamble bit pattern called
“Syn”
4.  End of block indicated by postamble bit pattern
5. Character-oriented transmission: Data in 8-bit units
6. Bit-oriented transmission: Preamble = Flag
7. Efficiency: Data bits/(Preamble+Data+Postamble)
8. High-Level Data Link Control (HDLC) uses bit-oriented
synchronous transmission. 8 bit of overhead for 1000 data bits
⇒ 48/1048 = 4.6% overhead