Telnet logger/server for host LL-67(2)

　　CP/CMS is a line at a time system and expects all input to consist of　lines ending with a NL code. Characters received are buffered until　the newline code is received.

　　Since CP/CMS is also a half duplex system, characters are only　examined when the system is expecting input. If the system is not　expecting input, a network interrupt is required to cause the SERVER　to process received characters. On receipt of a network interrupt,　characters received before the TELNET data mark is received are　examined and discarded, except that if a TELNET break code is found,　the appropriate CP/CMS interrupt action is stimulated.

　　On output, EBCDIC codes are mapped into network ASCII if a mapping　exists; otherwise, the codes are mapped into the TELNET control NOP.　A NL code is mapped into CR-LF. The EBCDIC code for bypass maps into　the TELNET control hide-your-input and the EBCDIC code for restore　maps into the TELNET control noecho. Also, the code X'23' maps into　the TELNET control echo and the code X'38' maps into the TELNET　control break.

　　Since CP/CMS is a line at a time, half duplex system the TELNET　control break is transmitted as an end of message signal and also as　an input prompt code. If characters were output without a NL, the　break, as an end of message code, indicates to the user TELNET　operating on a line at a time mode that the characters previously　transmitted should be printed without waiting for the end of line　sequence. If the user TELNET is also operating in a half duplex　mode, the break as an input prompt indicates that the system is ready　for input.

　　If input had been anticipated and sent by a full duplex user TELNET,　the TELNET SERVER will have that input available for immediate　processing. Thus, in the case of a full duplex user TELNET the break　as a prompt should be ignored.

　　Though CP/CMS operates in a half duplex mode, it supports half duplex　terminals with the reverse break feature allowing the system to abort　an input mode in order to transmit a priority output message. In　this situation, the TELNET SERVER transmits a TELNET SYNC. A half　duplex user TELNET should interpret this by aborting the input mode,　i.e., revoking a previous TELNET break which was interpreted as an　input prompt.

　　No codes in the output character stream can cause the TELNET data　mark to be transmitted.

　　LOGOUT

　　When a user logs out from his virtual machine, CP passes the　equivalent of a line disconnect to the LOGGER. The LOGGER then　closes the TELNET send and receive sockets.

　　ASCII ASCII ASCII SYMBOLS EBCDIC EBCDIC

　　DEC OCT HEX HEX DEC

　　0 0 (00) NUL (00) 00

　　1 1 (01) SOH (01) 01

　　2 2 (02) STX (02) 02

　　3 3 (03) ETX (03) 03

　　4 4 (04) EOT (37) 55

　　5 5 (05) ENQ (2D) 45

　　6 6 (06) ACK (2E) 46

　　7 7 (07) BEL (2F) 47

　　8 10 (08) BS (16) 22

　　9 11 (09) HT (05) 05

　　10 12 (0A) LF (25) 37

　　11 13 (0B) VT (0B) 11

　　12 14 (0C) FF (0C) 12

　　13 15 (0D) CR (0D) 13

　　14 16 (0E) SO (0E) 14

　　15 17 (0F) SI (0F) 15

　　16 20 (10) DLE (10) 16

　　17 21 (11) DC1 (11) 17

　　18 22 (12) DC2 (12) 18

　　19 23 (13) DC3 (13) 19

　　20 24 (14) DC4 (3C) 60

　　21 25 (15) NAK (3D) 61

　　22 26 (16) SYN (32) 50

　　23 27 (17) ETB (26) 38

　　24 30 (18) CAN (18) 24

　　25 31 (19) EM (19) 25

　　26 32 (1A) SUB (3F) 63

　　27 33 (1B) CTL (27) 39

　　28 34 (1C) FS (1C) 28

　　29 35 (1D) GS (1D) 29

　　30 36 (1E) RS (1E) 30

　　31 37 (1F) US (1F) 31

　　ASCII/EBCDIC Code Mappings

　　FIGURE 1

　　ASCII ASCII ASCII SYMBOLS EBCDIC EBCDIC

　　DEC OCT HEX HEX DEC

　　32 40 (20) SP (40) 64

　　33 41 (21) ! (5A) 90

　　34 42 (22) " (7F) 127

　　35 43 (23) # (7B) 123

　　36 44 (24) $ (5B) 91

　　37 45 (25) % (6C) 108

　　38 46 (26) &(50) 80

　　39 47 (27) ' (7D) 124