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The script that simulates a Hayes compatible modem.
A copy of vmodem can be also found at Github, at https://github.com/molivil/vmodem
The main script. This script will simulate a modem by answering to standard Hayes commands. It will open the serial port for communication and execute the dialed number as a linux shell script, however you could probably use any execututable with minor modification. For example, if you issue the command ATD12345, the script will look for a file 12345.sh in the working directory and execute it and output contents to console.
This script can be run standalone, or with the accompanying T1.sh and ppp.sh scripts, which will enable point-to-point serial to ethernet connections.
#!/bin/bash # # -------------------------------- # VMODEM - Virtual Modem bootstrap # -------------------------------- # Oliver Molini 2021 # # Billy Stoughton II for bug fixes and contributions # # Licensed under Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International Public License # https://creativecommons.org/licenses/by-nc-sa/4.0/ # Tested working out of box with the following client configurations: # # o Standard VT100 terminal # o HyperTerminal # o PuTTY # # PPP connectivity will initialize correctly under the following configurations: # # o Microsoft Windows 3.1 # - Trumpet Winsock # # o Microsoft Windows 95 OSR 2.5 + DUN 1.4 # - Generic # - Standard 28800 bps Modem # # o Microsoft Windows 98 # - Generic # - Standard 9 600 bps modem # - Standard 33 600 bps modem # - Standard 56 000 bps V90 modem # - Standard 56 000 bps X2 modem # - Standard 56 000 bps K56Flex modem # # Script version vmodver=1.6.0 # CONFIGURATION # ----------------------- # Variable: serport # serport specifies which local serial device to use. # For example, "ttyUSB0" will tell the script to use # to use /dev/ttyUSB0 for communication. # Common values: ttyUSB0 or ttyAMA0 # serport=ttyUSB0 # Variable: baud # baud will tell the script to open the serial port at # specified symbol rate. When connecting, make sure # your client computer uses the same baud than what # has been specified here. # Common baud rates: 9600, 19200, 38400, 57600 # # Default: # baud=57600 # #baud=9600 #baud=38400 baud=57600 # Variable: etherp # Sets the name of the ethernet device for PPP connections. # # eth0 for wired # wlan0 for wireless # etherp=eth0 # Variable: echoser # echoser sets the default behaviour of echoing serial # data back to the client terminal. The default is 1. # echoser=1 # Variable: resultverbose # Controls default behavior when printing Hayes result # codes. # When 0, prints result codes in numerical form. (eg. 0) # When 1, prints result codes in english. (eg. CONNECT) # Default is 1. resultverbose=1 # Variable: TERM # Tells the script and environment which type of terminal to emulate. # It is only useful to change this, if you're using a serial # terminal to connect to this script. If you're connecting form a ANSI # cabable machine such as DOS, you may want to use TERM="ansi" # TERM="vt100" # EXPORT SHELL VARS # ----------------- export serport export baud export etherp export TERM # FUNCTIONS # --------- # #INITIALIZE SERIAL SETTINGS ttyinit () { stty -F /dev/$serport $baud stty -F /dev/$serport sane stty -F /dev/$serport raw stty -F /dev/$serport -echo -icrnl onlcr opost clocal -crtscts } # SEND MESSAGE ON SCREEN AND OVER SERIAL sendtty () { message="$1" # echo -en "$message" # echo -en "${message//\\n/\\r\\n}" > /dev/$serport echo -en "$message" | tee /dev/$serport } export -f sendtty export -f ttyinit # Open serial port for use. Allocate file descriptor # and treat the serial port as a file. ttyinit exec 99<>/dev/$serport sendtty "\n" sendtty "VMODEM - Virtual Modem bootstrap for PPP link v$vmodver\n" sendtty "Connection speed set to $baud baud\n" sendtty "\n" sendtty "TYPE HELP FOR COMMANDS\n" sendtty "READY.\n" # execute hayes commands dohayes () { # default to error result code, if command not recognized result=4 # Debugging #sendtty "COMMAND: $hcmd $hparm\n" # ATA # - A Answer if [[ $hcmd == 'A' ]]; then result=0; fi # ATD Dial a number if [[ $hcmd == 'D' ]]; then if [[ ! -z "$hparm" ]]; then number=$(echo $hparm |tr -dc '0-9') result=0 fi fi # ATE Command echo to host # - E0 Commands are not echoed # - E1 Commands are echoed if [[ $hcmd == 'E' ]]; then if [[ $hparm == '' ]]; then echoser=0; result=0; fi if [[ $hparm == '0' ]]; then echoser=0; result=0; fi if [[ $hparm == '1' ]]; then echoser=1; result=0; fi fi # ATH Hang up of pick-up. # - H0 Go on-hook (Hang up) # - H1 Go off-hook if [[ $hcmd == 'H' ]]; then result=0; fi # ATM Speaker control # - M0 Speaker always off # - M1 Speaker on until carrier detected # - M2 Speaker always on # - M3 Speaker on only while answering if [[ $hcmd == 'M' ]]; then if [[ $hparm == '' ]]; then result=0; fi if [[ $hparm == '1' ]]; then result=0; fi if [[ $hparm == '2' ]]; then result=0; fi if [[ $hparm == '3' ]]; then result=0; fi fi # ATQn Result codes # Q0 Modem returns result codes # Q1 Quiet mode. Modem gives no result codes. if [[ $hcmd == 'Q' ]]; then if [[ $hparm == '' ]]; then resultverbose=0; result=0; fi if [[ $hparm == '0' ]]; then resultverbose=0; result=0; fi if [[ $hparm == '1' ]]; then resultverbose=2; result=0; fi fi # ATV Result codes in numerical or verbose form # - V0 Returns the code in numerical form # - V1 Full-word result codes if [[ $hcmd == 'V' ]]; then if [[ $hparm == '' ]]; then resultverbose=0; result=0; fi if [[ $hparm == '0' ]]; then resultverbose=0; result=0; fi if [[ $hparm == '1' ]]; then resultverbose=1; result=0; fi fi # ATXn Extended result codes # - X0 Disable extended result codes (Hayes Smartmodem 300 compatible result codes) # - X1 Add connection speed to basic result codes (e.g. CONNECT 1200) # - X2 Add dial tone detection (preventing blind dial, and sometimes preventing ATO) # - X3 Add busy signal detection # - X4 Add both busy signal and dial tone detection if [[ $hcmd == 'X' ]]; then if [[ $hparm == '' ]]; then resultverbose=1; result=0; fi if [[ $hparm == '0' ]]; then resultverbose=1; result=0; fi if [[ $hparm == '1' ]]; then resultverbose=0; result=0; fi if [[ $hparm == '2' ]]; then resultverbose=0; result=0; fi if [[ $hparm == '3' ]]; then resultverbose=0; result=0; fi if [[ $hparm == '4' ]]; then resultverbose=0; result=0; fi fi # ATZ Reset modem # - Zn Restore stored profile n if [[ $hcmd == 'Z' ]]; then echoser=1; resultverbose=1; carrierdetect=0; result=0; fi # AT&Cn Carrier-detect # - &C0 Force DCD signal active # - &C1 DCD signal indicates true state of remote carrier signal if [[ $hcmd == '&C' ]]; then if [[ $hparm == '' ]]; then result=0; carrierdetect=0; fi if [[ $hparm == '0' ]]; then result=0; carrierdetect=0; fi if [[ $hparm == '1' ]]; then result=0; carrierdetect=1; fi fi # AT&Dn Data Terminal Ready settings # - &D0 Modem ignores DTR # - &D1 Go to command mode on ON-to-OFF DTR transition. # - &D2 Hang up on DTR-drop and go to command mode # - &D3 Reset (ATZ) on DTR-drop. Modem hangs up. if [[ $hcmd == '&D' ]]; then if [[ $hparm == '' ]]; then result=0; fi if [[ $hparm == '0' ]]; then result=0; fi if [[ $hparm == '1' ]]; then result=0; fi if [[ $hparm == '2' ]]; then result=0; fi if [[ $hparm == '3' ]]; then result=0; fi fi # AT&F Restore factory settings # - &Fn Use profile n if [[ $hcmd == '&F' ]]; then echoser=1; resultverbose=1; carrierdetect=0; result=0; fi # AT&K DTE - MODEM Flow control # - &K0 Local flow control off # - &K1 Not used # - &K2 Not used # - &K3 RTS/CTS # - &K4 XON/XOFF # - &K5 Transparent XON/XOFF # - &K6 RTS/CTS and XON/XOFF if [[ $hcmd == '&K' ]]; then result=0; fi # AT&Sn DSR Override # - &S0 DSR will remain on at all times. # - &S1 DSR will become active after answer tone has been detected and inactive after the carrier has been lost if [[ $hcmd == '&S' ]]; then if [[ $hparm == '' ]]; then result=0; fi if [[ $hparm == '0' ]]; then result=0; fi if [[ $hparm == '1' ]]; then result=0; fi fi } # MAIN LOOP while [ "$continue" != "1" ]; do charhex=`head -c 1 /dev/$serport | xxd -p -` char="`echo -e "\x$charhex"`" #ECHO SERIAL INPUT TO TTY echo -n "$char" #ECHO SERIAL INPUT if [ "$echoser" = "1" ]; then echo -n "$char" > /dev/$serport; fi #CHECK IF NEWLINE IS SENT if [ "$charhex" = "0d" -o "$charhex" = "0a" ]; then line=$buffer # PARSE COMMAND cmd=`echo -en $buffer | tr a-z A-Z` buffer= char= #NEWLINE SENT - ECHO NEWLINE TO CONSOLE if [ "$echoser" = "0" ]; then echo; fi if [ "$echoser" = "1" ]; then sendtty "\n"; fi # # --- HAYES EMULATION --- # if [[ $cmd == AT* ]]; then # Attention! Client issued an AT command # # default to error result code, if command not recognized result=4; resultc=0 if [[ $cmd == AT ]]; then result=0; fi # Get full hayes string and parse it seq=`echo $cmd |cut -b3-` ptr=1 until [ $ptr -gt 64 ]; do hchar=$(echo "$seq" |cut -b$ptr) #sendtty "$ptr $hchar\n" if [[ $hchar =~ [A-Z\&] ]]; then if [[ $hchar == '&' ]]; then hcmd="$hchar" ptr=$((ptr+1)) hchar=$(echo "$seq" |cut -b$ptr) if [[ $hchar =~ [A-Z] ]]; then hcmd="$hcmd$hchar" until [ $hdone ]; do ptr=$((ptr+1)) hchar=$(echo "$seq" |cut -b$ptr) if [[ $hchar =~ [0-9] ]]; then hparm="$hparm$hchar" else ptr=$((ptr-1)) hdone=1 fi done fi elif [[ $hchar =~ [A-CE-Z] ]]; then hcmd="$hcmd$hchar" until [ $hdone ]; do ptr=$((ptr+1)) hchar=$(echo "$seq" |cut -b$ptr) if [[ $hchar =~ [0-9] ]]; then hparm="$hparm$hchar" else ptr=$((ptr-1)) hdone=1 fi done elif [[ $hchar == 'D' ]]; then hcmd="$hcmd$hchar" until [ $hdone ]; do ptr=$((ptr+1)) hchar=$(echo "$seq" |cut -b$ptr) if [[ $hchar =~ [0-9PRT,!] ]]; then hparm="$hparm$hchar" else ptr=$((ptr-1)) hdone=1 fi done fi fi ptr=$((ptr+1)) if [[ ! -z "$hcmd" ]]; then dohayes # preserve error if one was encountered if [[ $result == '4' ]]; then resultc='4'; fi else break fi hcmd="" hparm="" hdone="" done if [[ $resultc == '4' ]]; then result='4'; fi # ATD Dial number if [[ ! -z "$number" ]]; then if [[ $resultverbose == 1 ]]; then sendtty "RINGING\n"; fi sleep 2 if [ -f "$number.sh" ]; then if [[ $resultverbose == 1 ]]; then sendtty "CONNECT $baud\n"; else sendtty "1\n"; fi # Assert DCD when carrier detection is turned on (for Trumpet Winsock) if [[ $carrierdetect == 1 ]]; then exec 99>&-; fi # Tell the terminal to use CR/LF for newlines instead of just CR. echo -en "\x1b[20h" > /dev/$serport # Run script #/sbin/getty -8 -L $serport $baud $TERM -n -l "./$number.sh" ./$number.sh if [[ $carrierdetect == 1 ]]; then exec 99<>/dev/$serport; fi # Reset serial settings ttyinit result=3 else # Phone number is valid, but no internal script by that name exists result=3 fi number="" fi # # --- PRINT RESULT CODE --- # if [[ $resultverbose == 0 ]]; then sendtty "$result\n"; elif [[ $resultverbose == 1 ]]; then if [[ $result == 0 ]]; then sendtty "OK\n"; fi if [[ $result == 1 ]]; then sendtty "CONNECT\n"; fi if [[ $result == 2 ]]; then sendtty "RING\n"; fi if [[ $result == 3 ]]; then sendtty "NO CARRIER\n"; fi if [[ $result == 4 ]]; then sendtty "ERROR\n"; fi if [[ $result == 5 ]]; then sendtty "CONNECT 1200\n"; fi if [[ $result == 6 ]]; then sendtty "NO DIALTONE\n"; fi if [[ $result == 7 ]]; then sendtty "BUSY\n"; fi if [[ $result == 8 ]]; then sendtty "NO ANSWER\n"; fi fi fi if [[ $cmd = HELP ]]; then sendtty "Command Reference for Virtual Modem Bootstrap v$vmodver\n" sendtty "\n" sendtty "AT......Tests modem link, prints OK if successful\n" sendtty "ATE0....Switch terminal echo off\n" sendtty "ATE1....Switch terminal echo on\n" sendtty "ATD?....Fork program ?.sh and output on terminal\n" sendtty "ATDT1...Open PPPD connection\n" sendtty "ATZ.....Reset modem settings\n" sendtty "HELP....Display command reference\n" sendtty "LOGIN...Fork a new linux login on serial\n" sendtty "EXIT....End this script\n" sendtty "\n" sendtty "To establish connection over PPP, dial 1 using tone dialing (ATDT1)\n" sendtty "\n" sendtty "READY.\n" fi # LOGIN - FORK LOGIN SESSION if [[ $cmd == LOGIN ]]; then exec 99>&- /sbin/getty -8 -L $serport $baud $TERM ttyinit exec 99<>/dev/$serport sendtty "\n"; sendtty "READY.\n" fi # EXIT - EXIT SCRIPT if [ "$cmd" = "EXIT" ]; then sendtty "OK\n"; continue="1"; fi fi buffer=$buffer$char done #Close serial port exec 99>&-
1.sh is a virtual phone number used to establish a PPP connection. 1.sh can be dialed by issuing they Hayes dial command “ATDT1” using vmodem.sh. 1.sh is only a redirect script and will actually just run ppp.sh which will initiate the actual PPP connection.
#!/bin/bash # ./ppp.sh
This script will initiate a PPP session and will present a fake login shell, but will not wait around for user input. The fake login shell is in place for compatibility with Trumpet Winsock 3.0, as it by default expects one, so we're fooling it to make it think that it's logging on. It will then proceed when it receives the expected printouts. The built-in dial-up connection in Windows 95/98/Me by default do not expect a login prompt unless specifically told to do so.
When Trumpet Winsock is in PPP mode, by default it will expect the following output after dialing the ISP's number and establishing a connection:
This script has been tested with the default installation of Trumpet Winsock 3.0 revision D with PPP mode switched on. This script has also been tested with the default dial-up utility of Windows 95 and Windows 98 with PPP enabled.
I've added a parameter to send an LCP echo to the client to test if the connection is still up. If the connection has abruptly been closed, pppd will know this by not receiving an echo reply, and will exit and relinquish control back to the vmodem.sh script. The only reason the timeout is in there, is because it seems like Trumpet Winsock 3.0 doesn't know how to tell pppd to terminate a PPP session from within a PPP session, and it will just hang up the call. As a result, pppd daemon will be left running indefinitely and won't ever give control back to vmodem. This is obviously not preferred, so LCP echo is added to let pppd know when the link has been cut. If you can think of better ways to accomplish this check, feel free to send tips on how to improve the script.
#!/bin/bash # RUN PPPD DAEMON # # Oliver Molini 2021 # # Billy Stoughton II for bug fixes and contributions # # Licensed under Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International Public License # https://creativecommons.org/licenses/by-nc-sa/4.0/ # # Note on PPPD settings: # - Make sure the noauth option is set (instead of auth) # - Make sure DNS servers are defined (add ms-dns 1.2.3.4 twice) # # Variable: etherp # Override the ethernet device to use to connect to your network. # This is set in vmodem.sh, but can be overridden here. # # Default: #etherp=eth0 (commented out) #etherp=eth0 # Variable: lcpidle # Specifies the idle timeout period in seconds for lcp-echo-interval. # This is to ensure that pppd will not run indefinitely after sudden # hangup and will relinquish control back to the vmodem.sh. # # Default: lcpidle=5 lcpidle=10 # # Trumpet Winsock 3.0 revision D for Windows 3.1 # by default requires a fake login shell. # # Windows 95 and 98 will not care for a login shell # unless specifically told to expect one. # sleep 2 sendtty "\n\n`uname -sn`****\n\n" sendtty "Username: "; sleep 1; sendtty "\n" sendtty "Password: "; sleep 1; sendtty "\n" sendtty "Starting pppd...\n" sendtty "PPP>" # End of fake login prompt. # Set the kernel to router mode sysctl -q net.ipv4.ip_forward=1 # Share eth0 over ppp0 iptables -t nat -A POSTROUTING -o $etherp -j MASQUERADE iptables -t filter -A FORWARD -i ppp0 -o $etherp -m state --state RELATED,ESTABLISHED -j ACCEPT iptables -t filter -A FORWARD -i $etherp -o ppp0 -j ACCEPT # Run PPP daemon and establish a link. pppd noauth nodetach local lock lcp-echo-interval $lcpidle lcp-echo-failure 3 proxyarp ms-dns 8.8.4.4 ms-dns 8.8.8.8 10.0.100.1:10.0.100.2 /dev/$serport $baud # Flush iptables iptables -t filter -F FORWARD iptables -t nat -F POSTROUTING printf "\nPPP link terminated.\n"
This example script demonstrates how easy it is to make simple dial-up services, such as BBS's. To call this script, from the serial console, type “ATD2”.
#!/bin/bash # echo "Hello World Demo Box!" echo "---------------------" echo echo "You have just successfully dialed this virtual box!" echo echo "Please enter your name: " read -e -p "User? " username echo echo "Hello, $username!" echo echo "Thank you for visiting! Bye!" sleep 2
This example script allows VT100 compatible terminal access to the web by way of running lynx as soon as the number “3” is dialed with “ATD3”. It demonstrates how to add a Linux based web browser for simple terminals.
#!/bin/bash # sendtty "Terminal type set to $TERM. Running Lynx ..." lynx