1. Chapter 6 Transmission of Digital Data Interfaces and Modems
Digital Data Transmission
DTE-DCE Interface
Other Interface Standards
Modems

2. Data Transmission
Parallel
Serial
Synchronous
Asynchronous

3. Parallel Transmission

4. Serial Transmission 0 1 1 0 0 0 10 The eight bits are sent
one after another
We need only
one line (wire)
Parallel / Serial
converter
Serial / Parallel
converter

5. Asynchronous Transmission
One start bit is sent at the beginning of each byte and one or more stop bits at the end of each byte.
Asynchronous at the byte level, but the bits are still synchronized
Framing error: False start bit.

6. Synchronous Transmission
Blocks of characters (character-oriented) or bits (bit-oriented) are transmitted without start and stop codes.
SYN characters
Control characters
Control characters
Data characters
Control field
8-bit flag
8-bit Flag
Control fields
Data field

7. DTEs and DCEs
Data Terminal Equipment (DTE): any device that is a source or a destination for binary digital data.
Data Circuit-Terminating Equipment (DCE): any device that transmits or receives data in the form of an analog or digital signal through a network.

8. DTE-DCE interface
The EIA and the ITU-T have been involved in developing DTE-DCE interface standards.
DTE-DCE standard try to define the mechanical
electrical and functional characteristics of connection
between the DTE and DCE

9. EIA-232 Interface Previously called RS-232.
It defines the mechanical, electrical, and functional characteristics of the interface.
Mechanical specification: 25-wire cable with a male and a female DB-25 pin connector.
The pins and tubes are arranged into two rows, with 13 on the top and 12 on the bottom.
Electrical specification: data must be transmitted NRZ-L encoding with 0 (space) 3 to 15 V and 1 (mark) –3 to –15 V.
Maximum bit rate 20 Kbps, maximum distance 15m

10. EIA-232

11. Sending Data

12. Control and Timing
Only 4 wires out of the 25 are used for data functions and the remaining are used for control, timing, grounding, and testing.

13. Data Pins
-Reverse channel (14,16): used to send halt or flow control message to a transmitting device (half-duplex)

14. Control Pins

15. RTS: DTE wishes to transmit.
CTS: DCE is ready to receive, response for RTS.
DCR: DCE is ready to operate.
DTR: DTE is ready to operate.
RLSD (Received Line Signal Detector): DCE is receiving a carrier signal.

16. Timing Pins

17. Other Pins

18. Synchronous Full-Duplex Transmission

19. Synchronous Full-Duplex Transmission

20. Pin Connection With and Without DCEs

21. Pin Connection With and Without DCEs

22. Null Modem