Technical Aspects of Data Communication

1. Asynchronous Communications

Parallel Transmission

Serial Transmission

MARKS and SPACES

START Bit and STOP Bits

Achieving Synchronism

Character Length

Figures Shift and Letters Shift

Baudot and ASCII

A Simplified Asynchronous Receiver

Single Buffering and Double Buffering

Overrun Errors

Framing Errors

A Simplified Asynchronous Transmitter

Caution Concerning Double-Buffered Transmitters


2. A Single Line Asynchronous UART

General Characteristics of a UART

Block Diagram of a UART

Level Converters

Bit Assignments for Registers in a UART and their Function

Break Signals

Programming a UART


3. Interface Standards

How the Need for Standards Arose

EIA

CCITT

Condensed Version of EIA-232-D

Complete CCITT V.28

Mark and Space Distortion

Ground Potential Differences

Condensed Versions of EIA-422-A, EIA-423-A, and EIA-530


4. Beyond Interface Standards

Performance Comparison of EIA-232-D, EIA-423-A, EIA-422-A

Fiber Optic Fundamentals

Line Drivers

Private Lines

2-Wire Versus 4-Wire

300 Bps and 1200 Bps Private Line Modems


5. Private Line Modem Control

List of Interface Circuits Required for Private Line Modems

Comparison of EIA-232-D and CCITT V.24 Definitions

Comments on Clear to Send and Carrier Detect


6. A Single Line Asynchronous UART with Private Line Modem Control

Expansion of the Chapter 2 Block Diagram

Adding Modem Control and Modem Status Bits to the Registers Described in Chapter 2


7. Asynchronous Multiplexers

Single Line Asynchronous Interfaces

Identification of Parts that Could be Shared in a Multiple Line Interface

Additional Features that Could be Added

FIFO

Choice of Line Sizes for Multiplexers

Pros and Cons of Multiplexers


8. Telephone Switching Systems

Historical Development of the Need for Telephone Switching Systems

Magneto Switchboards

Terminology

Common Battery Systems

Strowger

Detection of Service Request

Dialing

Tone Signaling

Speed of connection

COS

Traffic Capacity

Hunt Groups

Noise

Switched Network Structure

VNL and SDN Design

Echo Suppressors

Network Management


9. Modem Control for Switched Network Use

Control Leads Previously Discussed in Chapter 5

Definitions of Additional Leads for Switched Network Use

Reason for those Leads Being Required

Control of Half-Duplex Modems

Reverse Channels

Split Speed Modems


10. Asynchronous Modems for Switched Network Use

Available Frequency Spectrum

Details of the 300 Bps ("103-type") Modem

Originate Mode and Answer Mode

Eye Patterns

Carrier Loss Clamps

A Comparison of Spectrum Utilization by 300 Bps and 1200 bps FSK Modems


11. Automatic Calling Units

Applications

Condensed Versions of EIA-366 and CCITT V.25 References for Parallel Interface Autodiallers

Condensed Versions of CCITT V.25 Bis

AT Command Set

Vadic VA831, and Digital Equipment DF03-AC References for Serial Interface Autodiallers


12. Asynchronous Multiplexers with Modem Control

Programmable Formats and Speeds

Common Terminal Operating Speeds

Direct Memory Transfers

Current Addresses and Byte Counts

Monitoring and Controlling Modems on 16 Lines

Transition Detection Systems

Scanners

Secondary Registers


13. Error Detection

Burst Noise

Parity

VRC and LRC

Cyclic Redundancy Checks (CRC)

Methods of Generating CRC

Why the CRC is Zero for an Error-Free Message

Mathematical Presentation of CRC

Generator Polynomials

Effectivity of CRC

Step-by-Step Examples of CRC Calculation in Both Hardware and Table-Driven Software


14. Synchronous Communication

Efficiency of Synchronous Communication vs. Asynchronous Communication

Synchronization Search

Synchronizing on One Character or Two

Modulation Processes

Phase Modulation Operation in a 2400 Bps Modem

Product Modulators

Demodulation of Phase Modulated Signals

Operation of 9600 Bit Per Second Modems

Interface Leads for Synchronous Modems

Signal Quality Detector and Clock Leads


15. A Single Line Synchronous USRT

USRT Chips for Synchronous Interfaces

Overrun Errors

Underrun Errors

Block Diagram and Bit Assignments for a Single Line USRT

Modem Control Leads for a USRT

Sync Character Stripping

Maintenance Features

Loop Around

Receiver Blinding for Half-Duplex

Parity

Pad Characters

Request to Send and Line Turn-Around


16. Protocols

Requirement for Protocols

The ISO Layered Model

Functions of the Layers

Existing Types of Protocols


17. BISYNC and Character Oriented Protocols

General Format of a Message

Transparent Text

Typical Data Exchange

Definitions of the Special Characters

Error Checking Codes Used

Flow Charts of Transmission and Reception


18. DDCMP and Byte Count Oriented Protocols

Use of Character Counts for Transparent Transmissions

General Format of a Message

Sequencing Messages

Reply Wait

Message Classes

Message Format Detail for Various Classes of Message

Introduction to the Kermit Protocol


19. SDLC and Bit Oriented Protocols

General Format of a Message

Function of Flags

Message Fields

Poll and Final Bits

Control Field Formats

Sequencing of Messages

Definitions of Control Commands and Responses

Abort


20. A Single Line Synchronous USRT for Bit-Oriented Protocols

Block Diagram

Register Bit Assignments for Serving BISYNC and DDCMP

Additional Bits for Serving SDLC

CRC Error Detection

Start of Message

End of Message

Secondary Station Addressing


21. Multiplexer Enhancements

Self-Test Diagnostics

Receiver FIFO Timer

Automatic XON/XOFF

Transmitter FIFOs

The Need for Intelligent DMA

Methods of Achieving Intelligent DMA

Linked Lists

Ring Buffers


22. Sophisticated Modems

List of CCITT Modem Recommendations

Echo Cancelling

Trellis Coding

Error-Correcting Modems

Microcom Networking Protocol (MNP)


23. Digital Transmission

History of Carrier Telephony

Sampling Theory

Tl Carrier

Framing

Robbedbit Signalling

Common Channel Interoffice Signalling (CCIS)

Clear Channel

Zero Suppression

European Systems (CEPT)


24. Packet Switching

Comparison with Circuit and Message Switching

Telecom Canada's Datapac

Sample X.25 Packet Formats


25. ISDN

Definition

Bearer Channels

Data Channels

Basic Rate Interface

Primary Rate Interface

Equipment NT1, NT2, TA, TE1, and TE2


26. Special Problems

Connection of Two Pieces of Data Terminal Equipment Via Null Modems

Clocking of Synchronous Modems and Terminals

Effect of Clock Skew in Asynchronous Transmission

Active and Passive 20 Milliampere Devices

Use of Optical Couplers


27. CCITT Recommendations X.20 and X.21

Trends in Quantity of Interface Leads

Summaries of X.20, X.20 bis, X.21, X.21 Bis


28. Local Area Networks

Large Computers Versus Personal Computers

Sharing File and Printer Services

Definition of Local Area Network (LAN)

Star, Ring, and Bus Topologies

Access Control Via Polling, Tokens, ALOHA, and CSMA/CD

Appendixes

A. How Far—How Fast?

Speed Versus Distance Tables for Various Types of Interface Circuits

B. Modem Options

A List of Modem Options and their Functions

C. Codes

Tables of Baudot, ASCII, and Other Communication Codes

D. Universal Synchronous Asynchronous Receiver Transmitter (USART)

Explanation of the USART, Bit Assignments and Signal Functions

E. Format and Speed Table for Asynchronous Communication

A List of Character Formats, Character Rates, and Baud Rates for Various Terminals

F. Channel Conditioning

Parameters for Private Line Conditioning Offered by AT&T

G. Interface Connector Pinning

Pinning Assignment for the 25-Pin D-Subminiature Connector as Used in EIA-232-D and EIA-530

H. Hayes Smartmodem 1200™ and Hayes Smartmodem 2400™ Dialling Commands and Responses

An Excerpt from the Quick Reference Cards for These Products Showing the Flexibility and Complexity of Modern Serial Interface Dialling

I. Where to Get More Information

A List of Addresses and Telephone Numbers for Obtaining EIA, CCITT, ISO, ANSI, and AT&T Documents

Glossary

Index