1. FILES, DATA, AND SIGNALS FILE HAMLET. TXT USER DATA
INTERNAL y e a , b
REPRESENTATION
OF USER DATA f r o m b
Internal representation of information stored in n-bit entities
corresponding to a particular character code (e.g., ASCII is
shown here).
Yea, from the table of my memory
I’ll wipe away all trivial fond records

2. FILES, DATA, AND SIGNALS (cont.)
LSB
LSB
LSB
LSB
SIGNAL – External representation of user data
-- Mapping of bits to a signal depends only on choice of
implementer. NonReturn to Zero-Level (NRZ-L) shown,
but other signaling types are possible.

3. PARALLEL TRANSMISSION, y e a b f r o m
Receiver
Transmitter
MSB
LSB
CLOCK
DTE
DTE t0 t1 t2 t3 t4 t5 t6 t7 T8

4. SKEW t0 t1 1 SKEW: The arrival of bits from the same character at1
SKEW: The arrival of bits from the same character at
different times may lead to erroneous reception.

5. SERIAL VS. PARALLEL TRANSMISSION
CPU-peripheral,
internal to computer.
Relative short distance
DTE – DTE.
Longer distances.
APPLICATIONS
Long distances possible.
Easier to implement.
Device-independent.
Very high throughput.
Matches internal architecture.
ADVANTAGES
Extra cable, connectors,
Amplifiers, and
Clock add expense.
Skew limits distance.
Relatively low speeds.
Parallel-to-Serial
Conversion required.
DISADVANTAGE

6. ASYNCHRONOUS TRANSMISSION
STOP
BIT y e
START BIT 1 1 1 1 1 1 1 1
FRAMING
LSB
MSB
FRAMING
Asynchronous transmission:
Timing of each bit is specified within a character
Inter-character time is non-uniform
Each character must be framed

7. SYNCHRONOUS TRANSMISSION
LSB
MSB 1 y e a t
Characters, within a block, are sent contiguously
Each block is framed

8. ASYNCHRONOUS CHARACTER FORMAT
LEAST SIGNIFICANT BIT
SPACE
MARK
START
BIT
STOP INTERVAL
TIME
DATA BITS
LINE
IDLE
Transmitter and receiver must agree on:
Number of data bits per character
Length of a bit time
Length of the stop interval
Signal level
Order of bit transmission
Character code

9. SYNCHRONOUS MESSAGE FORMAT
CHAR (s)
MESSAGE
TRAILER
MESSAGE
HEADER
DATA
BLOCK OR FRAME
All data characters sent as part of a continuous transmission
block (frame)
Transmitter and receiver must agree on:
-- Transmission format
-- Length of a bit time
-- Signal levels
-- SYNC characters
-- Size and content of header and trailer

10. ASYNCHRONOUS VS. SYNCHRONOUS TRANSMISSION
Between a terminal and computer or between low-cost computer – and - computer
High-speed
Device interconnection.
APPLICATIONS
Simple to implement.
Low cost.
Clock resynchronizes
with each character.
High throughput.
High line efficiency
ADVANTAGES
Error detection protocol required.
Self-clocking signaling
Technique required.
High cost.
Low line efficiency
Low speed (<20,000 bps)
DISADVANTAGES

11. A FILE TRANSFER Host B Host A
HAMLET.TXT
Host A
Host B
TRANSMISSION LINK
 FILE TRANSFER: THE STEPS IDENTIFIED IN THIS UNIT
SYNCHRONOUS
HAMLET.TXT CREATED
BY USER AT HOST A
CHARACTER CODE
INTERNAL REPRESENTATION OF FILE
CHOICE OF SIGNAL
EXTERNAL REPRESENTATION
OF DATA
PARALLEL TRANS.
SERIAL TRANS.
ASYNCHRONOUS
 ADDITIONAL AGREEMENTS STILL REQUIRED