Purpose - to discuss what NTP is, and to discuss coding issues relating to this protocol.
[hopefully one of my comrades in crime will fill in the blanks here as to RFC number, point to standard implementations of say an ntp daemon, etc.]
[Here's a start:-
Firstly, the protocol implemented in the code below is the "daytime" protocol, not NTP. The daytime protocol is described in RFC867 [L1 ].
NTP is a far more sophisticated protocol, version 3 of which is described in RFC1305, created by Dave Mills. More information including links to Dave Mills' implementation is available at http://www.ntp.org
Documentation and other links are at http://www.eecis.udel.edu/~ntp/documentation.html
NTP is implemented via UDP over port 123, and can operate in broadcast and multicast modes, or by direct queries.
--MNO ]
The following code was recently posted to comp.lang.tcl :
## ## good-time - for the correct time, ... ## ## Placed into the public domain by [email protected], January 1999. ## ## usage: good-time [host [port [timezone]]] ## host - defaults to time.nist.gov. ## port - defaults to 13. ## timezone - defaults to nothing, not necessary for NIST format. ## ## After wading through a complicated linux time synchronization ## package, it turned out that the key was to telnet to time.nist.gov ## on port 13. You can do that in tcl, so here it is. ## ## It also turns out that a lot of machines return some kind of time ## service on port 13, so I recognize a few variations in the format ## returned. ## ## See http://www.boulder.nist.gov/timefreq/ for more information and ## links to yet more information. ## # 23Jan02RT - add -set flag set doset 0 if {$argc >= 1 && [string equal [lindex $argv 0] -set]} { incr argc -1 set argv [lrange $argv 1 end] set doset 1 } ## ## choose the host ## # 11Jan02RT TODO use host list # numeric values come from "Atomic Clock Sync v2.5" server menu set hlist { 129.6.15.28 129.6.15.29 132.163.4.101 132.163.4.102 132.163.4.103 128.138.140.44 time-nw.nist.gov time-a.timefreq.bldrdoc.gov time.nist.gov allhoststried } # set host time.nist.gov if {$argc > 0} { set hlist [concat[lindex $argv 0] $hlist] } ## ## choose the port ## set port 13 if {$argc > 1} { set port [lindex $argv 1]; } ## ## choose the timezone ## set timezone {} if {$argc > 2} { set timezone [lindex $argv 2]; } ## ## set a time out ## after [expr 30*1000] { close $sock puts stderr "timed out"; if {[info exists lines]} { puts stderr "no time found in:\n$lines" } exit 1; } ## ## open a socket ## foreach h $hlist { if {[catch {socket $h $port} sock]} { #puts stderr "socket: $sock" #exit 2; puts stderr "host $h - FAILED" continue } break } ## ## read what comes back ## while {[gets $sock line] >= 0} { # # typical daytime response is unix date format without timezone indication # # Mon Sep 16 21:59:22 1996 # set seconds 0 if {[regexp \ {^... ([A-Z][a-z][a-z]) ([ \d]\d) (\d\d:\d\d:\d\d) (\d\d\d\d)$} \ $line all month mday time year]} { set seconds [clock scan "$month $mday, $year $time $timezone"] } # # NIST time service format returned by: # # time.nist.gov # time-nw.nist.gov # time-a.timefreq.bldrdoc.gov # # 50343 96-09-17 05:02:07 50 0 0 50.0 UTC(NIST) * # if {!$seconds && [regexp \ {^..... (\d\d)-(\d\d)-(\d\d) (\d\d:\d\d:\d\d) .. . . ..... UTC\(NIST\)} \ $line all year month day time]} { set seconds [clock scan "$month/$day/$year $time UTC"] } # # USNO master clock format returned by: # # tick.usno.navy.mil # tock.usno.navy.mil # # 50343 261 044932 UTC # if {!$seconds && [regexp {^..... ([ \d][ \d]\d) (\d\d)(\d\d)(\d\d) UTC$} \ $line all doy hour minute second]} { set seconds [clock scan $hour:$minute:$second -gmt true] } if {$seconds} { puts "FETCHED: [clock format $seconds]" puts " LOCAL: [clock format [clock seconds]]" if {$doset} { set newtime [clock format $seconds -format %H%M.%S] exec date.exe $newtime puts "set date to $newtime" } close $sock; exit 0; } # # save unrecognized stuff for final error message # append lines $line\n } ## ## give up ## close $sock; puts stderr "no time found in:\n$lines"; exit 4