 LINE CALL REQUEST CALL REQUEST ONFIRMATION CONFIRMATION SELECTION SELECTION DIAL PULSES CONNECTED CONNECTED CLEAR CLEAR CLEAR CI FAR CONF IRMATION CONFIRMATION FREE LINE FREE LINE Figure 59.5 Type A and B signalling 59/6 Telex communications eral exist but the ones given in Table 59.1 are generally internation- ally understood. All telex messages should commence with the Table 59.1 Telex protocol (* indicates some of the typical sender's answerback SO that the distant end can easily find the caller. service codes The sequence of setting up a call on the telex network is seizing the line, receiving call confirmation and proceed to select indication Meaning from the telex network. The telex terminal then transmits the ad- dress information and if the call set up is successful the distant * ABS Absent subscriber; power switched off the machine will automatically transmit to the caller the answerback machine code indicating it is ready to accept the message. If the call is I cut off (break the line) unsuccessful for any reason the failure will be indicated by a service Please confirm or I confirm code of up to 3 letters transmitted from the telex network to the originating machine and printed out on the local record of the telex Collation message. Do you receive / I receive The telex network has facilities for testing the telex lines and can detect if a machine has its power disconnected or the line is out of * DER Out of order order, and then send the corresponding service message from the You are in communication with the called network to the originating machine. party You may transmit Telex terminals * INF Subscriber temporarily unavailable; call information service Modern telex terminals are highly sophisticated pieces of equip- Office closed because of holiday ment built around the principles of the personal computer. They comprise a microprocessor, disk drive, keyboard, VDU, and heavy Minutes duty printer with paper roll holder. These machines are still required * MOM Wait for reply to interwork with the olde