transmisson modes

1. Transmission Modes
Different ways of characterizing the
transmission.
Nofeel

2. Timing of the transmission
of the data bits
• Serial
– Data bits transmitted at
different times
– One bit after the other
• Parallel
– Multiple bits transmitted
simultaneously (same time)
– Typically with different data
“lines” for each bit
0
1
0
1
1
1 1 0 1 0
0
1
0
1
1
0
1
0
1
1

3. Timing between
transmitter and receiver
• All transmissions are synchronized somehow
– once per bit (Manchester)
– once per byte
– once per frame …..
• Asynchronous (means without synchronization)
but DOES synchronize once per BYTE.
• Awful name
ASYNCHRONOUS

4. So what is Synchronous?
• Synchronizes
– once per block of data not per byte
• Typically faster rates
• USB ports on a PC (find rates on www)
– see www.pcs.cnu.edu/~dgame/cs335/topics/usb.ppt
– easier to understand after protocols
• More complex framing (each of these are bytes typically)
(end) errordetect DATA control sync sync

5. Sync byte/string
• A pattern with which receiver can
established synchronization
• The longer it is (to a point) the greater the
reliability of the synchronization
• Like a start bit
• (e.g. ) 0 1 1 1 1 1 1 0
• No idle times between bytes(bits) in the
frame.

6. Character/bit stuffing
• What if timing/framing flags in beginning
or ending?
• AND they are part of the data itself!
• Stuff extra symbols if in data
• Stuff even if “stuffed” version is in the data

7. Character stuffing
SYN SYN STX
Data
ETX
SYN SYN STX ETXETX
Expected End of Data
SYN SYN STX ETXETXDLE
ETX in data
DLEDLEDLE
ETX in data DLE in data
Receiver discards!

8. Bit Stuffing
Basically the same!
5 zeros in a row, insert extra 0

9. Asynchronous
Synchronous
Isochronous
Different arrival rates of bytes

10. Asynchronous
Synchronous
Isochronous
Different arrival rates of bytes