1、 THIS DOCUMENT CONTAINS PAGES. Licensed by Information Handling ServicesFED-STD-1005A TE 7777777 0002Li74 7 FED-STD-I 005A June 2, 1986 Supercedes January 20, 1977 FED-STD-1005 FEDERAL STANDARD TELECOMMUNICATIONS: CODING AND MODULATION REQUIREMENTS FOR 2,400 BIT/SECOND MODEMS This standard is issued
2、 by the General Services Administration pursuant to the Federal Property and Administrative Services Act of 1949, as amended. 1. Scope 1 .I gescription. This standard establishes coding and modulation requirements for 2,400 bit/s modems owned or leased by the Federal government for use over analog t
3、ransmission channels other than those derived from high-frequency radio facilities. It is based upon techniques described in CCITT Recommendations V.22 bis, V.26, and 1.2 Purpose. This standard is to facilitate interoperability between telecommunication facilities and systems of the Federal governme
4、nt. I .3 Application. This standard shall be used by all Federal agencies in the design and procurement of 2,400 bit/s modems for use with switched or dedicated nominal 4 kHz channels with the following exception. Secure (i.e. encrypted) voice terminals conforming to North Atlantic Treaty Organizati
5、on (NATO) Standardization Agreement 4291 may deviate from the requirements of this standard. V.26 bis. 2. Kequirements 2.1 Ovrview. .This standard describes two alternative modem types (1) a 2-wire half-duplex and/or 4-wire duplex moaem7s2.2) with optional fallback to 1,200 bit/s operation (section
6、2.3) and (2) a 2-wire duplex modem with optional fallback to 1,200 bit/s operation (section 2.4). Section 2.5 describes general characteristics. 2.2 2.2.1 2,400 Bit/s, 2-wke Half-duplex and 4-wire Duplex Operation- Carrier Frequency. The transmit carrier frequency shall be 1,8001 Hz. 2.2.2 rate shal
7、l be 1,200 baud 5.01 percent. gata and Modulation Rates. The data rate shall be 2,400 bits/s .O1 percent. The modulation (symbol) 2.2.3 Encoding Bits. The data stream to be modulated shall be divided into pairs of consecutive bits (dibits). Each aibit shall be encoded as a phase change of the 1,800
8、Hz carrier relative to the phase of the carrier during transmission of the immediately preceding dibit as indicated below. D IBIT PHASE CHANGE O0 o1 II 10 + 45O +135O +225O +315O The phase change is the actual on-line phase shift in the transition region from the center of one signal element to the
9、center of the following signal element. At the demodulator, the dibits are decoded and the bits are reassembled in the correct order. The left-most bit of each dibit is the one occurring first-in the data stream upon entering the modulator portion of the modem. 2.2.4 Synchronization. During the inte
10、rval between Request to Send indication (e.g. CCITT Interchange Circuit 105 ON) fromassociated data terminal equipment and Clear to Send indication (e+ CCITT Interchange Circuit 106 ON) from the modem, continuous 225 phase changes (dibit II) shall be transmitted. Modems capable of 2-wire, halfduplex
11、 operation shall have the ability to delay Clear to Send indication for a period of at least 185 ms following the receipt of Request to Send indication. During 2-wire, half-duplex operation using the above delay, modems shall also withhold Receiver Ready indication (e for the Hiph Channel. 2.4.2 telephone (202) 472-2205. Please call in advance for pickup service. 8 i i c. i e Licensed by Information Handling Services
