DSTATR

*MENTOF

MERGE

CATKWi

P

NISI

X

4 PUBLICATIONS

\

NBS TECHNICAL NOTE 779

Data Communications System

Throughput Performance Using

High Speed Terminals on the Dial

Telephone Network
NATIONAL BUREAU OF STANDARDS

The National Bureau of Standards1 was established by an act of Congress March 3, 1901. The Bureau's overall goal is to strengthen and advance the Nation's science and

technology and facilitate their effective application for public benefit. To this end, the Bureau conducts research and provides: (1) a basis for the Nation's physical measure- ment system, (2) scientific and technological services for industry and government, (3) a technical basis for equity in trade, and (4) technical services to promote public safety. The Bureau consists of the Institute for Basic Standards, the Institute for Materials Research, the Institute for Applied Technology, the Center for Computer Sciences and

Technology, and the Office for Information Programs.

THE INSTITUTE FOR BASIC STANDARDS provides the central basis within the United States of a complete and consistent system of physical measurement; coordinates

that system with measurement systems of other nations; and furnishes essential services leading to accurate and uniform physical measurements throughout the Nation's scientific community, industry, and commerce. The Institute consists of a Center for Radiation Research, an Office of Measurement Services and the following divisions: Applied Mathematics — Electricity — Mechanics — Heat — Optical Physics —

Linac Radiation - — Nuclear Radiation - — Applied Radiation 2 — Quantum

Electronics :l — Electromagnetics '• — Time and Frequency 3 — Laboratory

Astrophysics '• — Cryogenics 3

. THE INSTITUTE FOR MATERIALS RESEARCH conducts materials research lead- ing to improved methods of measurement, standards, and data on the properties of

well-characterized materials needed by industry, commerce, educational institutions, and

Government; provides advisory and research services to other Government agencies; and develops, produces, and distributes standard reference materials. The Institute consists of the Office of Standard Reference Materials and the following divisions: Analytical Chemistry—Polymers—Metallurgy—Inorganic Materials—Reactor

Radiation—Physical Chemistry.

THE INSTITUTE FOR APPLIED TECHNOLOGY provides technical services to pro- mote the use of available technology and to facilitate technological innovation in industry and Government; cooperates with public and private organizations leading to the development of technological standards (including mandatory safety standards), codes and methods of test; and provides technical advice and services to Government agencies upon request. The Institute also monitors NBS engineering standards activities and

provides liaison between NBS and national and international engineering standards

bodies. The Institute consists of a Center for Building Technology and the following

divisions and offices: Engineering and Product Standards—Weights and Measures—Invention and

Innovation—Product Evaluation Technology—Electronic Technology—Technical Analysis—Measurement Engineering—Building Standards and Code Services4—Housing Technology4 —Federal Building Technology4—Structures, Materials and Life Safety4—Building Environment4—Technical Evaluation and

Application4 —Fire Technology.

THE INSTITUTE FOR COMPUTER SCIENCES AND TECHNOLOGY conducts re- search and provides technical services designed to aid Government agencies in improving cost effectiveness in the conduct of their programs through the selection, acquisition,

and effective utilization of automatic data processing equipment; and serves as the principal focus within the executive branch for the development of Federal standards for automatic data processing equipment, techniques, and computer languages. The Center

consists of the following offices and divisions: Information Processing Standards—Computer Information—Computer Services —Systems Development—Information Processing Technology.

THE OFFICE FOR INFORMATION PROGRAMS promotes optimum dissemination and accessibility of scientific information generated within NBS and other agencies of

the Federal Government; promotes the development of the National Standard Reference Data System and a system of information analysis centers dealing with the broader

aspects of the National Measurement System; provides appropriate services to ensure

that the NBS staff has optimum accessibility to the scientific information of the world,

and directs the public information activities of the Bureau. The Office consists of the following organizational units: Office of Standard Reference Data—Office of Technical Information and

Publications—Library—Office of International Relations.

1 Headquarters and Laboratories at Gaithersburg, Maryland, unless otherwise noted ; mailing address Washington, D.C. 20234.

2 Part of the Center for Radiation Research.

» Located at Boulder, Colorado 80302.

4 Part of the Center for Building Technology.
Data Communications System

Throughput Performance Using

High Speed Terminals on the Dial

Telephone Network

Dana S. Grubb

Institute for Computer Sciences and Technology

National Bureau of Standards

Washington, D.C. 20234

NBS Technical Notes are designed to supplement the Bureau's regular publications program. They provide a means for making available scientific data that are of

transient or limited interest. Technical Notes may be

listed or referred to in the open literature.

U.S. DEPARTMENT OF COMMERCE, Frederick B. Dent, Secretary

NATIONAL BUREAU OF STANDARDS, Richard W. Roberts, Director

Issued May 1973
National Bureau of Standards Technical Note 779

Nat. Bur. Stand. (U.S.), Tech. Note 779, 40 pages (May 197.H) CODEN: NBTNAE

For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402 (Order by SD Catalog No. 03.46:779).

Price $0.65 domestic postpaid or $0.45 G.P.O. Bookstore.
CONTENTS

Page

CONTENTS Ill

ABSTRACT 1

1. INTRODUCTION 1

2. TRIB 1

3. ANSI X3. 28 CONTROL PROCEDURES 2 4. DATA ON ERROR RATES 4

5. MODEMS 4

6. TRIB EQUATION 6

7

.

TRIB GRAPHS 7 ACKNOWLEDGMENT 14

REFERENCES 15

ILLUSTRATIONS

Figure No. Title

1 TRIB vs. Block Length for 1200 BPS Asynchronous

Modems

2 TRIB vs. Block Length for 2000 BPS Modem

3 TRIB vs. Block Length for 3600 BPS Modem with

150 BPS Secondary Channel

4 TRIB vs. Block Length for 3600 BPS Modem without

Secondary Channel

5 TRIB vs. Block Length for 4800 BPS Modem with

150 BPS Secondary Channel

6 TRIB vs. Block Length for 4800 BPS Modem without

Secondary Channel

7 TRIB vs. Block Length for 50th Percentile of All

Calls

8 TRIB vs. Block Length for 90th Percentile of All

Calls

9 TRIB vs. Burst Error Rate for 1200 PBS Asynchronous

Modem

10 TRIB vs. Burst Error Rate for 2000 BPS Modem

11 TRIB vs. Burst Error Rate for 3600 BPS Modem with

150 BPS Secondary Channel

12 TRIB vs. Burst Error Rate for 3600 BPS Modem without

Secondary Channel

13 TRIB vs. Burst Error Rate for 4800 BPS Modem with

150 BPS Secondary Channel

14 TRIB vs. Burst Error Rate for 4800 BPS Modem without

Secondary Channel

15 TRIB vs. Block Length for 1200 PBS Asynchronous Modem

- Effect of Different Telephone Line Delays

III
Figure No. Title

16 TRIB vs. Block Length for 2000 BPS Modem

Effect of Different Telephone Line Delays

17 TRIB vs. Block Length for 3600 BPS Modem with

150 BPS Secondary Channel - Effect of Different

Telephone Line Delays

18 TRIB vs. Block Length for 4800 BPS Modem with

150 BPS Secondary Channel - Effect of Different

Telephone Line Delays

IV
DATA COMMUNICATIONS SYSTEM THROUGHPUT PERFORMANCE USING

HIGH SPEED TERMINALS ON THE DIAL TELEPHONE NETWORK

Dana S. Grubb

Throughput performance of high speed data terminals using the dial

telephone network is calculated for signaling rate of 1200 to 4800 bits

per second using the ANSI X3. 28-1971 control procedures and measured in

terms of the proposed ANSI standard TRIB described in X3S35/80. The

performance calculations are shown graphically with TRIB as a function

of block length, error rates of the telephone connection, signaling rate

and telephone line delays. Error rates are based on a published survey

involving several hundred telephone connections to geographically

distributed parts of the United States.

Key Words: Data communications; modems; terminals; throughput; TRIB.

1. INTRODUCTION

The rapidly increasing use of terminals with high data rates on the

dial telephone network indicates the need to evaluate their performance

in terms of standard criteria. This report shows the calculated data

throughput of toll calls on the dial telephone network in terms of the

proposed ANSI criteria of TRIB (Transfer Rate of Information Bits) de1/ scribed in XSSSS/SO^- (X3.44 if adopted) with terminals using data

modems in the 1200 to 4800 bit per second range. The use of the ANSI

2/

X3. 28-1971- control procedures is assumed. The error rates used are based on published data for the dial telephone network.

This report is an interim publication to be followed by reports

covering the throughput and residual error rate performance of data

communications systems using data rates to 9600 bits per second and including proposed higher level control procedures.

2

.

TRIB

TRIB is defined in the proposed ANSI standard as "the ratio of the

number of Information Bits accepted by the receiving Terminal Configuration during a single Information Transfer Phase (Phase 3) to the

duration of that Information Transfer Phase. TRIB is expressed in bits

per second.
Information bits are all of the bits contained in information

characters, except those used for parity and as start-stop bits. The

information characters are those in the graphic subset of USASCII, which

are transmitted as the message text, except for those characters used for

control or affecting the format. Characters used in the message heading

are not considered to be information characters.

The information transfer phase begins with the transfer of a SYN

(synchronizing) character, a SOH (start of heading) character, or a STX

(start of text) character. The phase is ended with the transfer of an

EOT (end of transmission) character or DLE EOT (mandatory disconnect)

character sequence. For more detailed information on TRIB see references 1 and 3.

For purposes of performance evaluation it is helpful to consider

TRIB on a block basis. This is a valid simplification and TRIB is defined in this report as the number of information bits per block

divided by the product of the time per block and the ratio of the number

of transmitted blocks to the number of accepted blocks.

3. ANSI X3.28 CONTROL PROCEDURES

2/ The X3.28 control procedures— may be used with either synchronous

or asynchronous systems. The 1200 BPS (bits per second) modem is an asynchronous modem, while the 2000, 3600 and 4800 BPS modems are synchronous modems.

The X3.28 control procedures provide several different modes of

operation including: one-way-only and two-way-alternate, point-to-point

and multi-point connections, switched and non-switched networks, with

and without station identification, with and without message blocking,

with and without replies, single and alternating acknowledgments, with

and without longitudinal checking and other features. This report assumes subcategory 2.1 for point-to-point, two-way-alternate operation

on a switched network without station identification. This report also assumes the complementary subcategory Bl for message blocking with

longitudinal checking, retransmission of unacceptable blocks and single

character acknowledgment. This combination of subcategories provides

for operation on the dial telephone network with both vertical and

longitudinal checking.
The X3.28 control procedures for subcategory 2.1 provide for breaking each message into one or more blocks, so that the number of bits per

transmission may be limited. This permits selecting the number of bits

per transmission block for optimum TRIB. Blocks with less than the

optimum number of bits have a reduced TRIB due to the time spent

reversing the direction of transmission and sending the reply. Blocks

with more than the optimum number of bits per block have such a high

probability of a block containing one or more error bits that too much

time is spent retransmitting the blocks. The optimum number of bits

depends upon several factors and will vary as these factors vary.

The first block of each message is defined by X3.28 as beginning

with a heading. The number of bits used in the heading and the length

of the following message will vary with systems. A typical system might

have a 7-character heading and a 4200-character message. In such a case

the heading comprises .166 percent of the total message aid is negligible.

In this report the time required to transmit the heading will not be

considered in the calculation of TRIB.

With synchronous modems each block and each reply must be preceded

by SYN (synchronizing) characters, so that the receiving terminal may

achieve synchronization. In this report 4 SYN characters are assumed

for both the message blocks and the replies, as this is an adequate

number for most systems. With asynchronous modems no SYN characters are needed, as the start and stop bits for each character provide the

necessary synchronization for the receiving terminal.

In the first block of each message an SOH (start of heading)

character precedes the heading characters. After the heading characters,

an STX (start of text) character denotes the end of the heading and the

beginning of the text. At the end of each block an ETB (end of transmission block) character denotes the end of the block. It is immediately

followed by the BCC (block check character) character containing the

longitudinal parity bits. The reply consists of either an ACK

(acknowledgment) character denoting that the block was accepted by the

receiving terminal or a NAK (negative acknowledge) character denoting

that the block was not accepted by the receiving terminal. Subsequent
blocks of the message begin with an STX character. At the end of the

last block of the message an ETX (end of text) character is sent instead

of the ETB character.

Therefore, the 1200 BPS asynchronous modem will be assumed to use

3 control characters (STX, ETB or ETX, and BCC) per message block and

1 reply character (ACK or NAK) . The 2000, 3600 and 4800 BPS synchronous

modems will be assumed to use 7 control characters (4 SYN, STX, ETB or

ETX, and BCC) per message block and 5 reply characters (4 SYN and ACK

or NAK).

4. DATA ON ERROR RATES

The error rate data used in this report is from the 1969-70 Connection Survey listed in references 4 and 5.

In this survey, four types of modems were used for toll calls on the

dial telephone network at modem speeds of 1200, 2000, 3600 and 4800 BPS.

The connections were made between telephone end offices in widely distributed cities of the United States and Canada, with 98 different end

office locations used for transmitting and 12 for receiving. These were

chosen by statistical sampling techniques from the approximately 15,000

possible end office choices. The wide geographic dispersion of the end

offices ensured the inclusion of calls from relatively nearby end offices

to those almost three thousand miles away.

The 1200 and 2000 bit per second modems were each tested with over

500 calls of 30 minutes duration each. The 3600 and 4800 bit per second

modems were tested with 277 and 130 calls, respectively, and a call

duration of 20 minutes each. For additional information on this survey

see reference 6.

5. MODEMS

The 1200 BPS modems use a design with frequency shift keying that is

typical for modems in this bit rate class. The 2000 BPS modems use a design with four-level phase shift keying that is typical of their bit rate

class. The 3600 and 4800 BPS modems are the same basic modem with minor

modifications for the bit rate desired. They use a design with multilevel vestigial sideband amplitude modulation. There is more variation

between modem designs in these classes.
The interblock delays in a data communications system depend to a large extent upon the modem design used. For modems up to 2400 BPS the

design usually permits reversing the direction of transmission and

sending the reply at the normal transmission rate. In this case the

delay between the end of a message block and the beginning of a reply

is the sum of the transmission delay (several milliseconds, in most cases)

and the time required for the telephone line to permit transmission in

the reverse direction. On short distance calls it i6- desirable to wait

about .05 seconds for echoes to subside. On longer distance calls

the telephone companies often use echo suppressors to reduce objectionable echoes to voice users. These echo suppressors prevent simultaneous

transmission in both directions and must be reversed, which occurs automatically when transmission ceases. The reversal requires about

.15 to .20 seconds, so modems are usually designed to provide a fixed

delay of about .200 seconds. Therefore, the delay between the end of a message block and the beginning of a reply is the sum of the transmission

delay and .200 seconds. Since the mean delay of long distance calls

(above 725 miles) is .015 seconds, this report uses .215 seconds for

this delay.

For modems with bit rates above 2400, it is usually desirable to use

an adaptive equalizer to reduce the effects of delay and amplitude

distortion on the error rate. The adaptive equalizer on the modem model

tested for 3600 and 4800 BPS required several seconds to recover after

each reversal of the telephone line. For this reason the manufacturer

provided a low speed reverse channel using a narrow portion of the

telephone channel's bandwidth to permit transmission at 150 BPS. While

it takes longer for the reply to be sent at 150 BPS, there is a time

saving in not having to reverse the echo suppressors. Therefore, the

total delay in this case is the transmission delay of .015 seconds.
Since some modems in the over 2400 BPS class are now being built

with digital adaptive equalizers that require only .05 seconds recovery

after a reversal of the direction of transmission, this report also

considers this case. The time delay between the end of a message block

and the beginning of a reply is assumed to be the sum of the transmission

delay (.015 seconds), the reversal of the echo suppressor (.200 seconds),

and the retraining of the digital adaptive equalizer (.05 seconds), for

a total of .265 seconds.

The modems used for the survey have signaling rates that are widely

used. ANSI Standard X3. 1-1969— lists the standard synchronous serial

signaling rates as 600 times N bits per second, where N may be any

positive integer from 1 through 16. The preferred standard signaling

rates for the 1200 to 4800 BPS range are 1200, 2400 and 4800 BPS, while

2000 BPS is listed as an interim standard.

6. TRIB EQUATION

The calculation of TRIB involves the use of several terms, a few of

which are sufficiently minor in their effect as to permit their being

ignored in the TRIB equation without significantly affecting the value of

TRIB. The equation used for the calculation of TRIB must include these

terms: the block length in bits, the number of control characters per

message block, the number of characters in the reply, the delay from the

end of a message block to the beginning of the reply and the corresponding delay from the end of the reply to the beginning of the next message

block, the bit rate for the message block, the bit rate for the reply

(not always the same as for the message block) , the number of bits per

character (which is 8 for the synchronous modems and 10 for the

asynchronous modems) , and the ratio of the number of transmitted blocks

to the number of accepted blocks. The last term accounts for all

retransmissions, including those due to errors in the retransmissions.
As mentioned in the discussion of the control procedure, the effect

of the heading is insignificant, so it is not included in the TRIB

equation. There is a possibility of the reply being in error as well as errors in the recovery from a reply error. Fortunately, the reply has

very few bits relative to the several hundred to many thousands of bits

of the message blocks, so it is reasonable to assume no errors for the

replies. Also, the remote possibility that the parity detection

circuitry does not detect an error due to the particular bit pattern is

insignificant so far as the calculation of TRIB is concerned.

The calculation of the ratio of transmitted blocks to accepted blocks

implies a knowledge of the probability of a block being in error. The bit error rates that are obtained by dividing the total number of error bits

by the total number of bits sent are not a realistic measure of the

probability of a block being in error, as bit errors on the dial telephone

network (and their private line counterparts) tend to be clustered into

short bursts. The reason for this is that most errors are not the result

of random (Gaussian) noise, but rather the result of various transient

phenomena that affect several adjacent bits. The largest single cause

of bit errors in data modems in the 1200 to 4800 BPS range is impulse

noise. This noise is thought to be the result of switching in the

telephone network and is usually characterized by several close together

noise spikes each of several milliseconds duration. Since the amplitude

of the noise spike may be high relative to the signal levels, the

probability of error for each of the bits occurring at this time is quite

high and several may be in error for each impulse spike. Rapid phase

changes, sudden gain changes, line dropouts, and other dial telephone

network phenomena of a transient nature tend to have a similar effect.
Since a block is rejected regardless of whether it has one bit in error or a hundred, this clustering of bit errors produces a pessimistic

TRIB if it is used in the calculations; therefore, it is desirable to use an error rate that takes this burst effect into account . In the

1969-70 Connection Survey, the term "burst error rate" is used. It is

defined in that particular study as "a collection of one or more bits

beginning and ending with an error and separated from neighboring bursts

by 50 or more error free bits." Burst error rates in the survey

correlate closely with observed block error rates for all but the very

longest block lengths. In this report, the probability of a bit being

in error is taken from the burst error rate data in the survey. (See

pages 1361 through 1365 of reference 5.)

The burst error rate, P, is related to the probability of the message

block being without error by the expression" (1-P) to the Nth power."

For computer calculation, this is usually solved by using the equality

Y Y * 1 r»Y X = e . Unfortunately, the results are not sufficiently precise

at the larger values of N and P.

For roost values of N, the approximate equality (1-PN) = (1-P) to the

N power may be used, but TRIB becomes pessimistic for the higher values

of N.

The approach used for this report is a five-term binomial expansion.

At very long block lengths and high values of P this expression also

fails, but this is easily detected due to the drastic reversal in the

direction of the curve.
TRIB Equation

TRIB (Transfer Rate of Information Bits) is defined by the equation:

Information bits per block

TRIB =

(rv~- ZT is /No, of transmitted blocks\

I No. of accepted blocks )

"(?)(N - (8)(CC)

)

Information

bits per block

Where 7 = number of information bits per character

F = number of bits per character including parity

and start/stop bits (asynchronous only)

N = block length in bits

CC = number of control characters per message block

Time per block is the summation of the time for transmitting the

message block plus the time for transmitting the reply plus

twice the time between transmissions in opposite directions:

Time per block = ^| +

(F^g

(RY) + (2) (D)

Where RY = number of characters per reply

BP = bit rate for message block

BS = bit rate for reply (not always = BP)

D = transmission delay + echo suppressor reversal

delay + retraining digital adaptive

equalizer (if used)

No of transmitted blocks , 2 .*.<1-E) + 3.E

2

-(1-E)

No. of accepted blocks

+ 4-E3 .(l-E) + ...

where E = probability of block being

in error

= 1 - E + 2E - 2E

2 + 3E2 - 3E

3 + 4E3 - 4E

4

+.

= 1 + E

2 3

+ E + E + .

oo xi Z E

= n=o

(Geometric Series)

1

1 - E
TRIB Equation (cont'd)

Combining these expressions in the original equation for TRIB:

TRIB

h

;; p

WB. + (2)0.))^

- E) |f N - (8) (CC)

_N _,_ (F) (RY)

BP + imsa + (2)(D) \

The expression (1-E) is the only term that is not easily determined in the above equation. It is found from the equality:

(1-E) = (1-P) where P is the probability of a bit being

in error (P burst error rate)

N

The expression (1-P) is evaluated using the binomial expansion.

The binomial expansion of (1 + X) is:

(1 + X) " M1(N - M)l

T

therefore,

n! , „J (1 E) " M1(N-M)1 ( P)

. ! _ N .p + Iffidi P

2 _ N(N-l)(H-2)

p

3

2 2*3

N (N-l) (N-2) (N-3) p

4

+

2-3-4 *•"

Since it is unnecessary to evaluate all of the terms in the

series, it is truncated to the first 5 terms and factored:

(1-E) = 1 + N-P (-i+

(¥pX

i+

(

¥p)(-i+¥p

)))

10
7. TRIB GRAPHS

The TRIB equation was used with FORTRAN programs to generate a series

of graphs showing the variation of TRIB with the various parameters.

Except where they are shown as variables in the graphs, the following

values are used for each of the parameters: 10 bits per character for

the 1200 BPS asynchronous modem and 8 bits per character for the

synchronous modems; 3 control characters and 1 reply character for the

asynchronous modem, and 7 control characters and 5 reply characters for

the synchronous modems; a delay from the end of transmission in one direction to the beginning of transmission in the other direction of

.215 seconds for the 1200 and 2000 BPS modems, .015 seconds for the

3600 and 4800 BPS modems when used with the secondary channel, and .265

seconds for the 3600 and 4800 BPS modems when used without the secondary

channel (assumes a digital adaptive equalizer) ; a 150 BPS rate for the

secondary channel (when used) ; and the burst error rate for the 50th

percentile of the calls. The burst error rate data is from the burst

error rate graphs in the 1969-70 Connection Survey. (These graphs show

a rapidly increasing burst error rate for calls above the 90th percentile,

while the variation in the error rate is much less marked for calls below

about the 90th percentile )The accuracy of the TRIB values for extremely

long block lengths of 50,000 and 100,000 bits may be less than that for

block lengths of 10,000 bits or less, as error burst rate to block error

rate relationship in the survey is only shown for block lengths through

10,000 bits.

Burst Error Rate Data from the 1969-70 Connection Survey

Bur s t_ E_r ror Rates_f or_Percent iles_o f_ Toil_Ca_lls_on the_

_Dial Teie£.no_n£ Network XBe.s ^. ^l^-r^P^-P^S^BPl?-^_

Modem Bit Rate

in BPS 50th Percenti

6.0 x

10~ 7 le 90th Percent:

7.0 x 10"6

Lie 95th Percentile

1200 2.0 x

10"5

2000 4.5 x 10" 7 4.5 x

10~6

1.0 x 10"5

3600 1.0 x 10"6

1.0 x

10~5 3.2 x10"5

4800 1.7 x 10"6 3.0 x 10"5 1.0 x

10"4

11
Figures 1 through 6 show TRIB versus block length for each of the

four modem types. There are two graphs each for the 3600 and 4800 BPS

modems, so that TRIB can be shown both with and without the secondary

channel. On each graph curves are shown for the 50th, 90th and 95th

percentiles of the telephone calls, as ranked by their burst error rates.

(Users may prefer to hang up and dial again for calls in the top 5 or 10

percentiles.)

The optimum block length varies with the burst error rates and with

modem bit rate. At very short block lengths TRIB is quite low due to

the fixed line turnaround delays and to the fixed time required for

transmitting the replies. At very long block lengths TRIB drops due to

the increasing probability of one or more bits in the block being in error and the message block being retransmitted. The optimum block

length choice would certainly depend upon whether it is feasible to hang

up and dial again for calls with high error rates.

TRIB, as a percentage of the bit rate of the synchronous modems, is

limited to 87.5 percent by the X3.28 requirement of a parity bit for each

character, while with asynchronous modems this drops to 70 percent due

to the start and stop bits. (A control procedure using a polynomial code

would not require a parity bit for each character and would have a substantially higher TRIB.) At the 50th percentile and a block length

of 10,000 bits; the 1200 BPS modem has an efficiency of 66 percent, the

2000 BPS modem an efficiency of 79 percent, the 3600 BPS modem has

efficiencies of 78 and 72 percent with and without the secondary channel,

and the 4800 BPS modem has efficiencies of 75 and 68 percent with and

without the secondary channel.

The graphs are discontinuous when the next computed value for TRIB is

invalid due to the high values of N and P in the binomial expansion.

Figure 7 shows TRIB versus block length for the four modems on the same graph with the burst error rates of each modem at the 50th percentile and with the use of the secondary channel for the 3600 and 4800

BPS modems. Figure 8 shows the same curves for each modem, but with the

burst error rates at the 90th percentile. The 4800 BPS modem offers a substantial performance improvement over the 3600 BPS modem at the 50th

percentile, but at the 90th percentile offers a minimal improvement and

12
a greatly increased sensitivity to block length.

Figures 9 through 14 show TRIB as a function of burst error rate for

each of the modems, with separate curves for block lengths of 1,000,

10,000 and 100,000 bits. Since error rates tend to be in the range of

-7 -4

10 to 10 , the ends of the graphs are shown only to illustrate the

effect of the error rate on TRIB. When data transmission must take place

on telephone lines with high error rates, the use of short block lengths

is desirable and in extreme cases virtually essential.

Figures 15 through 18 show TRIB as a function of block length for

burst error rates at the 50th percentile and with curves for different

telephone line delays. With the 1200 and 2000 BPS modems, the delays

are: for calls only to nearby locations (no echo suppressor); for use with any dial call, but showing a lower echo suppressor delay for

illustration ; any dial call with the usual echo suppressor delay

setting for the modem; and for calls via satellite with an estimated

.300 seconds transmission delay for the satellite link. With the 3600

and 4800 BPS modems, the delays are: for calls to nearby locations;

calls to locations several hundred miles away; and for calls via

satellite. (All of these delays are doubled in the TRIB equation for

the two line reversals needed for each block.) As might be expected,

the effect of variations in the delay is greatest with the shorter block

lengths and almost insignificant with very long blocks. At moderate

block lengths, the effect is quite significant.

This initial report on a specialized aspect of data communications

performance is to be followed by more extensive reports in

collaboration with the Institute for Basic Standards. These reports

will cover a much broader area of data communications and will involve

both the measurement of parameters influencing digital data transmission

and the optimization of systems performance.

13
ACKNOWLEDGMENT

Grateful acknowledgment is made to Mr. Robert T.

Elbourn, Mr. Selden Stewart, and Mr. Justin Walker

for their technical assistance.

14
REFERENCES

1. X3S35/80 Dept. X3

The American National Standards Institute, Inc.

1430 Broadway, New York, N. Y. 10018

2. X3. 28-1971 Dept. X3

The American National Standards Institute, Inc.

1430 Broadway, New York, N. Y. 10018

3. Determination of Performance of Digital Data Communication

Systems by R. T. Moore, IEEE International Conference on Communications, June 1971

4. Analog Transmission Performance on the Switched Telecommunications

Network by F. P. Duffy and T. W. Thatcher, Jr., Bell System

Technical Journal, Volume 50, No. 4, April, 1971, page 1311.

5. High-Speed Voiceband Data Transmission Performance on the

Switched Telecommunications Network , by M. D. Balkovic,

H. W. Klancer, S. W. Klare, and W. G. McGruther, Bell System

Technical Journal, Volume 50, No. 4, April 1971, page 1349.

6. Thruput of High Speed Data Transmission Systems Using Block

Retransmission Error Control Schemes over Voicebandwidth Channels , by W. G. McGruther, IEEE International Conference on Communications, June 1972.

7. X3. 1-1969 Dept. X3

The American National Standards Institute, Inc.

1430 Broadway, New York, N. Y. 10018

15

, , , r 1 1 r w w w

hJ hJ h-J 1-H M I-) g g H

53

Www

cj o u

ei Pi Pi w w w

Ph P-, Pn aa sc so

fr< t-< Irl o o m in o> cr*

WW s

<U •aos w CO o 3Oc

rM on

J2u

CO &CO o HM < o « CO o P-I m S3M mo r-l A o H CM at O i-l u

S3 3 w u 60 J o •H

14-1 fn

w

CJ .c o o u o J 00 o « a

cm a>oo

t-H PQ oo « o (0

•-i >M

psH ooir>

OOO

O

O o O

O

O o o o o O o O O o o O o o o o

K* CM o CO \£> sf CM

O CO vO v* CM

CM CM CM rH t-i f-1 rH i-l ami
w

W

W

.-1 iJ l-l M M M g H

55

H

S3

wWw o O u

Pi Prf erf w w W

P-. Pi PL.

PC S3 nc H H H O O LO

u-i c^ Ol

wooo

fc4 o

CMoooomooo

CMooooo

in

•z

l-l H

S3wOo

35 eOs

CO

Pmmooo

r-j § to Oo

CQ

pa

PiH

Oo

CMOO o o O O o o o o o o o o o o O O o o o o o o o o

-* CM

O 00 vO <r CM o 00 VO ^r ci

CM CM CM 1-t l-l rH 1-1 r-\ aiHi
uoo

•-i w

<Ucc

c« .C

M <_> o >> H c8eoo

COCO o Ph o w o

«o om

CO iH HM .C « 4-1 •H 53 s M e W CJ 00 o H 13 o rl O CU o S3 .4J t-J CS W w J

60

a. •H

i4

w ta CJo

.JM oo

vO

co ooo <4-l 43

4-1 MC

co

l-J o ^5 mo om

CO>MMH

O o o o o o o o o o O o o o o o o o o o o o O o

00 < o VO C-4 CO ~tf o vO CS 00 -*

-* ~* -* CO CO cs CN CN rH

H

aim
w

w

w

1-1 hJ nJ M H M g g g w W W u u u

OS erf PS w w w

CM Pm P4

paa 33

HH

H

OO iri

m ON ON

wHMMMHO

S3WuoM

(1) IUu

tf ocou

<u3o

X.B

<u T3Os

P*

PQO

vOCOuo

<** 43U

60c

01yo

CO>«M

erf H

M

00 o o o o o o o O o o o o o o o o o o o o o o o o

00 -tf o NO CM 00 ~3- o vO CM 00 ~*

-* -* «•* CO CM CM CM 1-1 <-i

SIHI
COH

0)Cc

CO un

(0 "Ocoo

<u CO

CO«

l-l (D

ffi Ci H

O o C9 o z COm

cn

w

l-I

CJoJ oo

00 ooo uo

M-l

cu

)-l 3

00

•H

00c

cuuo> o o o o o o O o O O O o o o o o o o o o O O o o

00 -* o vo CN 00 -* o vO CN 00 sf -* -* sr tn <*-> CM CN CN t-l t~) ami
COHHo

53WooM

(Ucc

ca .CCJ

<d -ocoo

<D CO

4J3o

4=ag vO o * o

00srMO

t)0 guo

CO>

PQ

l-l PiH o o O O O o o o O o o o o o o O O o o o O o o o

00 •<r o vO CnJ 00 <r o SO Cn| 00 vf sr Sf sT d en CN cs CM r-\ rH ami
ooCO * oo

IS

to o

4-1 o o o 01 lA i-H •H

t/i

U

HM

PQ o

25M P-l r~. K 43

O

H 4-1 <u O O u o ta in 3 m w 00 J M •H o fe w IW

CJo 43

hJ 4J pq COc o <u o hJ o

iH 4»ioo

i-H m

CO> oo m in

PiH

arai
u

CO CO

Phpa o o

u-i

r-i

c/1 pa

CO

PL, M

CO

PM CO

Pw

pa oocm

t-l ooocm oo

co oo

CO o o o

CJo (1) ir\ CO 4J H n l-l (it pa o

(J 53 V M Ph as 43 o H 4-1 o o o o !rf <3\ CM WM uo W <4-l CJO ,c

>-i 4-1 w 60

O <u o J O

r-t

uo

0)3

pa>

pa o o o o o o o o o o o o o o o o

00 -tf o vo CM CO -3- o

^r <f <J" CO CO CM CM CM o o o o o o o o

vO CM CO -3-

SIcII
wHCO

pq 6

<u

CO3oco

>-l 43o

CO <i

en

Ph

PQO

erf o

CM

cd

erfo

S-i w

•P

COH3

PQ

CO>

PQM

frf H

0\

CUu

00 o o o O O O O O O O o O o o o O O o O O O O o O

•<r CM o CO vO >* CM

O 00 NO -3- CM

CM CM CM iH tH iH iH «H

aiHi
<J1 H

PQaM

ffi H o O o o

53 o o W O o #1 J o •> o o o o W iH rH *-i uo

PQ

O • D

"1 o

4- &-J-

-3-1 o

rH e

a> T3OSw

CM

pq

m oO o

rH o

CMuo o

erf

•u

rd OS

O

rH

CDu

w rl 3 o C>0 H u •H

53

um

pK 1 « u

CO

O

u

H 53• CO>

PQM

&> I o

rH

00I o o o O o o O o O O o o o o o O o O O o O o o o o

<t CM o 00 vO <t CM

O 00 vO <r CM

CM CM CM rH rH rH rH rH

9IHI
w$

PiO

Pi

PiwH

en

Pi« Io

>>

tdcoo

<u w

co

PhPQo

4JSoaw

PQ

CO>

PQ

l-l PiHO PW

CO Pn Uo

cauon

J-J w

4-) CO

V-i o o o o o o o o o o o o o o o o o o o o o o o o CO ^-r o V£> CM 00 <t o vO CM 00 -cf

vj- <r ^r CO CO CM CM CM !-*• tH aiHi
Pio

£3wH

CO

0)a§

>>Coo

<D COu3ouS

<U H3OX

CO

PL, PQO

vO

enno

<J-I

<u uouuw

4-1 CO

PQ

CO>

PQM

PSH

CN

•H

FL4

aiHi
COHH

PQ

!ZH

suH o O o o

!S o o w o o * hJ o m o o o o ^ iH rH iH ao

r-l o • D I o

r-l ( 4~i—#i -& IoI o

•H

Noi o H

ft! O&wHCO

!=> PQ I o

COIo oo

00

-4- o o o o «* o oo

vO

CO oo

CM ooCO

CM ooCM oooCM oo

«o ooCM

rH oo

00 oo cc

>>u

tooo

cu COCO

PnPQom6

a)oS

CO

Pd

PQO

00Uo

IW

a) M

CTJ Prf

!-i O

r-l

r-l W

4J

CO

r-l 3

PQ

CO>

PQMH

(U

r-l 3

00

ami
wH$

Pio

01ec

CO ,C

03 •acoo

a> CO

•u3O

.C

4-) •H

J*6

0) •aos

CO 9

PL4 PQ

0)u3 O on

H

O •H CO 00 fe Pi «*

t>« U

0) 4J

at PS

(^ouw

COM

PQ

CO>

PQM

PiH

aiHi
ww

J o s

0) T3Oa

w CO CO o 3ocouo

0)

•-i a

CD

CO CO e

•HJ

H <; o M 01 o c

eq

w o FN o in a PQ .C M a. in O ID -H

PC o .H H CM 01 0) U H H M z 3 w M *J 60 (J o C H M-l at Pn w Ij o Xl <u

O o 4J y-i J &o IH o P9 c •H (^ CD .JOO

PQ ooo0) o M-l o • U-l o CO w rH >

pqM

PiH ooin

O

O

OOO o O

O o o O o o o o O O o O O o O o o

*<« CM o 00 \0 •* CM

O 00 vO sr CM CM CM CM i-l t-i r-l rH rH

flIHI
«

CO w e a) o T1 iH

rH

C/J

os

CO

PL. W

o

0) Q

a)C

•H H o 0) o M o c M CS o o J2 m S3M O 0) vO

<4-l rH iH

35H .C H 0) O u

S3w

J

60e

iJ

u

a

<uu

oo •H o

o

o MHH

o o H-1 o o PQ rH

CM

(0>M

14-1 o

4-1 o

<u

4-1 O

o

<Xi <4-l w o

o

o

CM o

o

o

o

o o

o o

00 VO

r4 rH

O

o

o o

o o

CM O

.-H t-\ O

CO o

o

vO o

o

o

o

aim
cc

ca GU

!>% U

ca •acoo

(11 03 rn S»> n)

C/1 t-H Pn (U

r-Q f-1

00HH

0)C

•Hco

a> rH

ai H

0)M

(U

M-l

PiH

PhPQoO

coMOC J-1 4J CJ 60 I) c "w

^!oo o o o o O o o o O O O o o o o o O o o o o O O o

00 -o- o VO CM 00 <t o vD CM 00 St

<r <r vi- ro ro CN CN CM iH r-l ami
w

w

wocn

4)c

c

td W o O

CO •oc

o

CJ

cu co

CO

CO

r-l O

o PQ

CU o o o 01 "> m c

C/> iH •HJ HM 4=

4J CU m •H C ^

s o

4= M 6

<u a 00

CU iH w 13 iH o H O CU CU o O H t-l o !a 3

C-4 w CO 4-1 60

-i p.

C •H w CU fa w u u o <u o o M-l hJ 00 M-l m -* H

Q O u

o

4-1 O M-l O

iH

4-1 60C

4-1 o

<u

M-l M-l w O U

O

siki

* U. S. GOVERNMENT PRINTING OFFICE : 1 973--5I 1 -326/259
r R. : '4BS-114A d-7i>

U.S. DEPT. OF COMM. BIBLIOGRAPHIC DATA

SHEET

1. PUBLICATION OR REPORT NO. NBS. TN-779

2. Gov't Accession No.

3. Recipient's Accession No.

4. TITLE AND SUBTITLE

DATA COMMUNICATIONS SYSTEM THROUGHPUT PERFORMANCE USING

HIGH SPEED TERMINALS ON THE DIAL TELEPHONE NETWORK

5. Publication Date May"1973

6. Performing Organization Code

650.01

7. AUTHOR(S)

Dana S. Grubb

8. Performing Organization

10. Project/Task/Work Unit No. Project 6502131

9. PERFORMING ORGANIZATION NAME AND ADDRESS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

WASHINGTON, D.C. 20234

11. Contract/Grant No. RTS

12. Sponsoring Organization Name and Address

Same as 9.

13. Type of Report & Period Covered Interim Publication

14. Sponsoring Agency Code

15. SUPPLEMENTARY NOTES

16. ABSTRACT (A 200-word or less factual summary of most significant information. If document includes a significant bibliography or literature survey, mention it here.) Throughput performance of high speed data terminals using the dial telephone network

is calculated for signaling rate of 1200 to 4800 bits per second using the ANSI

X3. 28-1971 control procedures and measured in terms of the proposed ANSI strand TRIB

described in X3S35/80. The performance calculations are shown graphically with TRIB

as a function of block length, error rates of the telephone connection, signaling rate

and telephone line delays. Error rates are based on a published survey involving

several hundred telephone connections to geographically distributed parts of the

United States.

17. KEY WORDS (Alphabetical order, separated by semicolons)

Data communications; modems; terminals; throughput; TRIB.

18. AVAILABILITY STATEMENT

f^l UNLIMITED.

I I FOR OFFICIAL DISTRIBUTION. DO NOT RELEASE

TO NTIS.

19. SECURITY CLASS

(THIS REPORT)

UNCLASSIFIED

20. SECURITY CLASS

(THIS PAGE)

UNCLASSIFIED

21. NO. OF PAGES

40

22. Price

$.65 Domestic postpaid

$.45 G.P.0. Bookstore

USCOMM-DC 66244-P71

NBS TECHNICAL PUBLICATIONS

PERIODICALS JOURNAL OF RESEARCH reports National Bureau of Standards research and development in

physics, mathematics, and chemistry. Comprehensive

scientific papers give complete details of the work,

including laboratory data, experimental procedures,

and theoretical and mathematical analyses. Illustrated with photographs, drawings, and charts. Includes

listings of other NBS papers as issued.

Published in two sections, available separately:

• Physics and Chemistry (Section A)

Papers of interest primarily to scientists working in these fields. This section covers a broad range of

physical and chemical research, with major emphasis on standards of physical measurement, fundamental

constants, and properties of matter. Issued six times a year. Annual subscription: Domestic, $17.00; Foreign, $21.25.

• Mathematical Sciences (Section B)

Studies and compilations designed mainly for the mathematician and theoretical physicist. Topics in mathematical statistics, theory of experiment design,

numerical analysis, theoretical physics and chemistry,

logical design and programming of computers and

computer systems. Short numerical tables. Issued quarterly. Annual subscription : Domestic, $9.00 ; Foreign,

$11.25.

TECHNICAL NEWS BULLETIN

The best single source of information concerning the Bureau's measurement, research, developmental, co- operative, and publication activities, this monthly

publication is designed for the industry-oriented

individual whose daily work involves intimate contact with science and technology-^/or engineers, chemists,

physicists, research managers, product-development

managers, and company executives. Includes listing of

all NBS papers as issued. Annual subscription: Domestic, $6.50; Foreign, $8.25.

NONPERIODICALS Applied Mathematics Series. Mathematical tables, manuals, and studies. Building Science Series. Research results, test methods, and performance criteria of building materials, components, systems, and structures. Handbooks. Recommended codes of engineering

and industrial practice (including safety codes) de- veloped in cooperation with interested industries, professional organizations, and regulatory bodies. Special Publications. Proceedings of NBS conferences, bibliographies, annual reports, wall charts, pamphlets, etc. Monographs. Major contributions to the technical

literature on various subjects related to the Bureau's

scientific and technical activities. National Standard Reference Data Series.

NSRDS provides quantitative data on the physical

and chemical properties of materials, compiled from

the world's literature and critically evaluated. Product Standards. Provide requirements for sizes, types, quality, and methods for testing various industrial products. , These standards are developed co- operatively with interested Government and industry groups and provide the basis for common understanding of product characteristics for both buyers and

sellers. Their use is voluntary.

Technical Notes. This series consists of communications and reports (covering both other-agency and

NBS-sponsored work) of limited or transitory interest. Federal Information Processing Standards

Publications. This series is the official publication within the Federal Government for information on

standards adopted and promulgated under the Public Law 89-306, and Bureau of the Budget Circular A-86

entitled, Standardization of Data Elements and Codes

in Data Systems.

Consumer Information Series. Practical information, based on NBS research and experience, covering areas of interest to the consumer. Easily understandable language and illustrations provide useful background knowledge for shopping in today's tech- nological marketplace.

BIBLIOGRAPHIC SUBSCRIPTION SERVICES

The following current-awareness and literature-survey bibliographies are issued periodically by the Bureau

:

Cryogenic Data Center Current Awareness Service (Publications and Reports of Interest in Cryogenics).

A literature survey issued weekly. Annual subscription: Domestic, $20.00; foreign, $25.00.

Liquefied Natural Gas. A literature survey issued quarterly. Annual subscription: $20.00. Superconducting Devices and Materials. A literature survey issued quarterly. Annual subscription : $20.00. Send subscription orders and remittances for the preceding bibliographic services to the U.S. Department

of Commerce, National Technical Information Service, Springfield, Va. 22151.

Electromagnetic Metrology Current Awareness Service (Abstracts of Selected Articles on Measurement

Techniques and Standards of Electromagnetic Quantities from D-C to Millimeter-Wave Frequencies). Issued monthly. Annual subscription: $100.00 (Special rates for multi-subscriptions). Send subscription order and

remittance to the Electromagnetic Metrology Information Center, Electromagnetics Division, National Bureau

of Standards, Boulder, Colo. 80302. Order NBS publications (except Bibliographic Subscription Services) from: Superintendent of Documents, Government Printing Office, Washington, D.C. 20402.
U.S. DEPARTMENT OF COMMERCE

National Bureau of Standards

Washington. D.C. 20234

OFFICIAL BUSINESS

Penalty for Private Use. $300

POSTAGE AND FEES PAID

U.S. DEPARTMENT OF COMMERCE COM-215