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Telecommunications Industry Association

TR-30.1/02-12-161

(TIA)










Lake Buena Vista, FL December 11 - 13, 2002





COMMITTEE CONTRIBUTION

Technical Committee TR-30 Meetings
SOURCE: TIA/EIA-825 Editor
CONTACT: Fred Lucas
FAL Associates
3421 Buttonwood Court
Reisterstown, MD 21136-4401
Telephone: 410-239-0248
Email: fred.lucas@ieee.org
TITLE: Draft revision of TIA/EIA-825
PROJECT: PN-4628
DISTRIBUTION: Members of TR-30.1
____________________
ABSTRACT
At the June 2002 meeting of TR-30.1 revised text was agreed to for TIA/EIA-825. This document is the revised standard for TR-30.1 approval and industry ballot.

The Source grants a free, irrevocable license to the Telecommunications Industry Association (TIA) to incorporate text or other copyrightable material contained in this contribution and any modifications thereof in the creation of a TIA Publication; to copyright and sell in TIA's name any TIA Publication even though it may include all or portions of this contribution; and at TIA's sole discretion to permit others to reproduce in whole or in part such contribution or the resulting TIA Publication. The Source will also be willing to grant licenses under such copyrights to third parties on reasonable, non-discriminatory terms and conditions for purpose of practicing a TIA Publication which incorporates this contribution.
This document has been prepared by the Source to assist the TIA Engineering Committee. It is proposed to the Committee as a basis for discussion and is not to be construed as a binding proposal on the Source. The Source specifically reserves the right to amend or modify the material contained herein and nothing herein shall be construed as conferring or offering licenses or rights with respect to any intellectual property of the Source other than provided in the copyright statement above.
The Source agrees that if the Source has changed or added text to the required language in the TIA contribution template as contained in the TIA Engineering Manual, any such change or addition which is inconsistent with such contribution template, is of no force or effect.

ANSI/TIA

STANDARD DRAFT


A FREQUENCY SHIFT KEYED MODEM FOR USE ON THE PUBLIC SWITCHED TELEPHONE NETWORK

TIA/EIA-825-A (SP-3-4628-RV1)

MARCH 2000
TELECOMMUNICATIONS INDUSTRY ASSOCIATION


NOTICE
TIA/EIA Engineering Standards and Publications are designed to serve the public interest through eliminating misunderstandings between manufacturers and purchasers, facilitating interchangeability and improvement of products, and assisting the purchaser in selecting and obtaining with minimum delay the proper product for his particular need. Existence of such Standards and Publications shall not in any respect preclude any member or nonmember of TIA/EIA from manufacturing or selling products not conforming to such Standards and Publications, nor shall the existence of such Standards and Publications preclude their voluntary use by those other than TIA/EIA members, whether the standard is to be used either domestically or internationally.
Standards and Publications are adopted by TIA/EIA in accordance with the American National Standards Institute (ANSI) patent policy. By such action, TIA/EIA does not assume any liability to any patent owner, nor does it assume any obligation whatever to parties adopting the Standard or Publication.
This Standard does not purport to address all safety problems associated with its use or all applicable regulatory requirements. It is the responsibility of the user of this Standard to establish appropriate safety and health practices and to determine the applicability of regulatory limitations before its use.
(From Standards Proposal No. 4628, formulated under the cognizance of the TIA TR-30.1 Subcommittee on Modems.)
Published by

TELECOMMUNICATIONS INDUSTRY ASSOCIATION 2000

Standards and Technology Department

2500 Wilson Boulevard

Arlington, VA 22201
PRICE: Please refer to current Catalog of

EIA ELECTRONIC INDUSTRIES ALLIANCE STANDARDS and ENGINEERING

PUBLICATIONS or call Global Engineering Documents, USA and Canada

(1-800-854-7179) International (303-397-7956)

All rights reserved



Printed in U.S.A.

FOREWORD
(This foreword is not part of this Standard)
This Standard was formulated under the cognizance of TIA Subcommittee TR-30.1 Modems. This Standard specifies a Frequency Shift Keyed (FSK) modem operating at a data signalling rates of 50 and 45.45 symbols/sec. The deaf and hard of hearing generally use this modem for real time 2-way text based communication over the public switched telephone network.

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A FREQUENCY SHIFT KEYED MODEM FOR USE ON THE PUBLIC SWITCHED TELEPHONE NETWORK




1 SCOPE

This standard specifies a FSK modem which operates at a nominal data signalling rates of 50 or 45.45 symbols per second over the switched telephone network.




2 NORMATIVE REFERENCES

ANSI/TIA/EIA-232-F-1997, Interface Between Data Terminal Equipment And Data Circuit Terminating Equipment Employing Serial Binary Data Exchange.

ANSI/EIA/TIA-496-A-1989, Interface between Data Circuit-Terminating Equipment (DCE) and the Public Switched Telephone Network (PSTN)



TIA/EIA/IS-968, Telecommunications, Telephone Terminal Equipment, Technical Requirements for Connection of Terminal Equipment To the Telephone Network
TIA/TSB-121, Cellular Subscriber Interface for TDD

3 DEFINITIONS

3.1 Frequency Shift Keying (FSK) - a transmission method where a signal is applied to the line in response to the pressing of a key (or the electronic equivalent).

3.2 TTY - A term used by the deaf and hard of hearing for a device which incorporates a FSK modem such as described in this standard. This term originates with the electromagnetic Teletypewriters originally used for this communications.

4 LINE SIGNALS

4.1 Transmission Mode The transmission mode is character oriented Frequency Shift Keying (FSK) using two tones to represent the asynchronous serial data. A binary ONE is represented by 1400 Hz±1% tone and a binary ZERO is represented by 1800 Hz ±1% tone (see Annex B).

4.2 Bit duration A bit duration of 20 or 22.00 ± 0.40 ms providing nominal data signalling rates of 50 or 45.45 symbols/s respectively.

4.3 Character Set The character set conforms to the 5-bit Baudot set (see Annex A). Characters are preceded by a start bit (binary ZERO) and followed by a stop bit (binary ONE). The start bit shall be one bit time in duration. It is desirable that the stop bit be 1.5 bit times in duration (see Note 1). Each key depression causes the transmission of a complete Baudot character including start and stop bits. A binary ONE hold tone also follows the last key depression. In this case the hold tone is transmitted for a period of 150ms to 300 ms after the end of the stop bit(s).

Notes:

  1. Designers should be aware that existing equipment in the field may provide stop bit durations of anywhere from 1 to 2 bit times.


2. The transmitter and receiver should normally start up in the LTRS mode. Additionally, to minimize error propagation, the DCE should re-send the most recent (i.e. last sent) mode character (i.e., LTRS or FIGS) at least every 72 characters.

4.4 Bit Ordering The bit ordering is LSB first with the first data bit corresponding to the Least Significant Bit (LSB) and the fifth data bit to the Most Significant Bit (MSB)

4.5 Transmit Levels When directly connected to the network (see section 5.2.1) the transmit levels shall be in conformity with FCC Part 68. When acoustically coupled to the telephone network the level is typically 108 6 dBSPL.

4.6 Transmit capability The transmitter shall be capable of transmitting regardless of the state of the receiver.

5 INTERFACES

5.1 DTE-DCE Interface The DTE-DCE interface shall support the following circuits (or their logical equivalent) as specified in ANSI/TIA/EIA-232-F-97:

Table 1 -Supported DTE-DCE Interface Circuits





ITU-T V.24 Number

Circuit

Description

103

BA

Transmit Data

104

BB

Received Data

135

CK

Received Energy Present
    1. Line Interface

5.2.1 Direct Connection When the DCE is directly connected to the switched telephone network (land line) the DCE shall provide a jack in conformity with TIA/EIA-968. ANSI/EIA/TIA-496-A-89 should be consulted for guidance on the characteristics of this interface.

5.2.2 Acoustic Interface The DCE may be equipped with an Acoustic interface, the characteristics of which are beyond the scope of this standard.

5.2.3 Wireless Interface When the DCE is connected to a wireless phone the interface shall conform to TSB-121.



Annex A


(Informative)

Table 1A - Baudot Codes




DEC

HEX

BINARY

LETTER

FIGURE


0

00

00000

backspace

backspace

1

01

00001

E

3

2

02

00010

LF

LF

3

03

00011

A

-

4

04

00100

Space

Space

5

05

00101

S




6

06

00110

I

8

7

07

00111

U

7

8

08

01000

CR

CR

9

09

01001

D

$

10

0A

01010

R

4

11

0B

01011

J

'

12

0C

01100

N

,

13

0D

01101

F

!

14

0E

01110

C

:

15

0F

01111

K

(

16

10

10000

T

5

17

11

10001

Z

"

18

12

10010

L

)

19

13

10011

W

2

20

14

10100

H

=

21

15

10101

Y

6

22

16

10110

P

0

23

17

10111

Q

1

24

18

11000

O

9

25

19

11001

B

?

26

1A

11010

G

+

27

1B

11011

FIGS

FIGS

28

1C

11100

M

.

29

1D

11101

X

/

30

1E

11110

V

;

31

1F

11111

LTRS

LTRS

Note: CR and LF may be manually or automatically generated by the DTE. If automatic generated, the sequence may contain an extra (non-printable) character to provide adequate time for older electromechanical TTYs to respond. CR & LF are inserted into the transmitted characters after a maximum of 72 characters to allow for the carriage return of older electromechanical TTYs.


Annex B


(Informative)

Receiver Frequency Tolerance

The Transmitter tolerances on existing devices in the field may vary as much as +/- 4% from the nominal values specified in Section 4.1, therefore receivers should be designed to accommodate these variations to ensure interworking with the broadest range of terminals.



Receiver Stop Bit Tolerance

A receiver should be capable of decoding characters with stop bits of anywhere from 1.0 to 2.0 bit times in length.



Receiver Signal Level Tolerance

A receiver should be capable of correctly decoding the following message, or its equivalent, for at least 120 seconds, with receive levels from –5 dBm to –45 dBm and a signal to noise ratio of 13 dB.



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