1、 TIA STANDARD ANSI/TIA-825-A-2003 Approved: April 16, 2003 A Frequency Shift Keyed Modem for Use on the Public Switched Telephone Network TIA-825-A (Revision of TIA/EIA-825) APRIL 2003 TELECOMMUNICATIONS INDUSTRY ASSOCIATION Representing the telecommunications industry in association with the Electr
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7、m Standards Proposal No. 3-4628-RV1, formulated under the cognizance of the TIA TR-30.1 Subcommittee on Modems.) Published by TELECOMMUNICATIONS INDUSTRY ASSOCIATION 2003 Standards and Technology Department 2500 Wilson Boulevard Arlington, VA 22201 U.S.A. PRICE: Please refer to current Catalog of TI
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22、rd) 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 signaling 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
23、communication over the public switched telephone network. i This page intentionally left blankii TIA-825-A 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 symbo
24、ls per second over the switched telephone network. 2 NORMATIVE REFERENCES TIA-232-F-1997 Interface Between Data Terminal Equipment And Data Circuit Terminating Equipment Employing Serial Binary Data Exchange. TIA-968-A-2002 Telecommunications, Telephone Terminal Equipment, Technical Requirements for
25、 Connection of Terminal Equipment To the Telephone Network. TIA/TSB121 Cellular Subscriber Unit 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
26、- 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 Signal 4.1 Transmission Mode The transmission mode is character
27、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 20.00 or 22.00 0.40 ms providing nominal data signallin
28、g 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 s
29、top 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 150 ms to 300 ms after th
30、e end of the stop bit(s). Notes: 1 TIA-825-A 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 D
31、CE 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 Tr
32、ansmit Levels When directly connected to the network (see section 5.2.1) the transmit levels shall be in conformity with TIA-968-A. 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 regardle
33、ss 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
34、104 BB Received Data 135 CK Received Energy Present 5.2 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-968-A. 5.2.2 Acoustic Interface The DCE may be equipped with an Acoustic
35、 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. 2 TIA-825-A Annex A (Informative) Table A.1 - Baudot Codes DEC HEX BINARY LETTER FIGURE 0 00 00000 backspace
36、backspace1 01 00001 E 3 2 02 00010 LF LF3 03 00011 A - 4 04 00100 Space Space 5 05 00101 S 6 06 00110 I 87 07 00111 U 7 8 08 01000 CR CR9 09 01001 D $ 10 0A 01010 R 411 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 1001
37、1 W 220 14 10100 H =21 15 10101 Y 622 16 10110 P 023 17 10111 Q 124 18 11000 O 925 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
38、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. 3 TIA-825-A 4 Annex B
39、(Informative) B.1 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
40、 terminals. B.2 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. B.3 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. THE QUICK BROWN FOX JUMPED OVER THE LAZY DOGS 123456789 TEST
