SEC. 6. IBM 3780 BISYNCHRONOUS COMMUNICATION SPECIFICATIONS

.01 Transmissions using IBM 3780 bisynchronous protocols must be in EBCDIC character code. Modems must be compatible with either Bell 208B for 4800 bps transmissions, or AT&T 2296A for 9600 bps transmissions. Both modems are dial-up type modems using the Public Switched Telephone Network. IBM 3780 data compression is acceptable for any bisynchronous transmission. Records may be blocked up to 4096 bytes with INTER RECORD SEPARATORS.

.02 IRS/MCC will accept information returns filed electronically over switched telecommunications network circuits. For 4800 bps, the circuit will be (304) 26 4-7080 . For 9600 bps, the circuit will be (304) 26 4-7040 . Both circuits are equipped for bisynchronous transmission using the IBM 3780 protocol.

.03 The 4800 bps line terminates at a Bell 208B modem. The Bell 208B modem uses phase-shift keying and eight-phase modulation to transmit binary serial data signals over the telephone line in half-duplex mode. The following options have been selected:

• Transmit Level set to –4 dBm

• Compromise Equalizer in (4–Db Slope)

• DSR off in Analog Loop Mode

• Automatic Answer

• Transmitter Internally Timed

• RS–CS Interval of 50 ms .04 The 9600 bps line terminates at an AT&T Dataphone II 2296A modem. The AT&T 2296A modem is a full-duplex, CCITT V.32 compatible unit which operates at 9600 bps or 4800 bps (fallback). The following options have been selected:

• Receiver Responds to Remote Loopback

• Loss-of-Carrier Disconnect

• Received-Space Disconnect

• Send-Space Disconnect

• Automatic Answer

• Answer on Ring 1

• DTR Interlock

• Retrain Enable

• Internal Timing

• CTS Controlled by RTS

• 0-1 ms RTS to CTS Delay

• CTS Dependent on Carrier

• RR Indicates Carrier

• 9600 Trellis Coding

• 4800 bps Fallback

• 4 dB Compromise Equalization

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