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TELE201 Lecture 10 Data communication interface 1 Lecturer Dr Z. Huang

Overview

!Last Lecture

Transmission modes

Source: chapter 6

!This Lecture

Data communications interface

Source: chapter 6

!Next Lecture

Protocols and architecture (1)

Source: chapter 2

TELE201 Lecture 10 Data communication interface 2 Lecturer Dr Z. Huang

Interfacing

!Data processing devices (or dataterminal equipment, DTE) do not(usually) include data transmissionfacilities

!Need an interface called data circuit

terminating equipment (DCE) e.g. modem, NIC

DCE transmits bits on medium

DCE communicates data and control infowith DTE

Done over interchange circuits

Clear interface standards required

!Characteristics of Interface

Mechanical: physical connection

Connection plugs, male or female

Electrical

Voltage, timing, encoding

Functional: assign meanings to circuits

Data, control, timing, grounding

Procedural

Sequence of events for transmitting data

TELE201 Lecture 10 Data communication interface 3 Lecturer Dr Z. Huang

V.24/EIA-232-F

!ITU-T v.24

!Only specifies functional andprocedural

References other standards for electrical andmechanical

!EIA-232-F (USA)

Alias RS-232

Mechanical ISO 2110

Electrical v.28

Functional v.24

Procedural v.24

TELE201 Lecture 10 Data communication interface 4 Lecturer Dr Z. Huang

Mechanical Specification

!25-pin connector, very often a subsetof 8/9 pins is used

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TELE201 Lecture 10 Data communication interface 5 Lecturer Dr Z. Huang

V.24/EIA-232-F

!Electrical Specification

Digital signals

Values interpreted as data or control,depending on circuit

More than -3v is binary 1, more than +3v isbinary 0 (NRZ-L)

Signal rate < 20kbps

Distance

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TELE201 Lecture 10 Data communication interface 9 Lecturer Dr Z. Huang

Conventional modems

!Dial Up Operation (2)

TELE201 Lecture 10 Data communication interface 10 Lecturer Dr Z. Huang

Null Modem

!For situations where the distancesbetween devices are so close to allowtwo DTEs to signal each otherdirectly

!Both DTEs are fooled to think they

are connected to modems.

TELE201 Lecture 10 Data communication interface 11 Lecturer Dr Z. Huang

RS-449

Replaces RS-232

Uses 37 pin connector, defines pin functions

Relies on RS-422 and RS-423 for electricalstandards (for balanced and unbalancedcircuits)

Higher bit rates over longer distance by usingbalanced circuit

10Mbps over short distance (40 feet)

100Kbps at 4000 feet

TELE201 Lecture 10 Data communication interface 12 Lecturer Dr Z. Huang

Balanced transmission

!Unbalanced circuit

uses one line for signal transmission and acommon ground.

Thus signal voltage levels are relative to thatground

!Balanced circuit

Uses two lines for signal transmission

The transmitting device sends equal but

opposite signals over each line Balanced signals are less susceptible to noise

and allow higher transmission rates overlonger distances

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TELE201 Lecture 10 Data communication interface 13 Lecturer Dr Z. Huang

ISDN Physical Interface Diagram

!Connection between terminalequipment (c.f. DTE) and networkterminating equipment (c.f. DCE)

ISO 8877, taken by X.21

!Cables terminate in matching

connectors with 8 contacts!Transmit/receive carry both data

and control

TELE201 Lecture 10 Data communication interface 14 Lecturer Dr Z. Huang

Summary

!DTE and DCE

!RS-232 standard

Mechanical

Electrical

Functional

Procedural

!Loopback tests in modems

!Null modem

!ISDN physical interface

!Balanced circuit