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

Data Transmission Parallel Serial Synchronous Asynchronous

Parallel Transmission

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

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.

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

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.

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

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

EIA-232

Sending Data

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.

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

Control Pins

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.

Timing Pins

Other Pins

Synchronous Full-Duplex Transmission

Synchronous Full-Duplex Transmission

Pin Connection With and Without DCEs

Pin Connection With and Without DCEs

Null Modem