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| author | Laurent Bercot <ska-skaware@skarnet.org> | 2014-12-15 23:08:59 +0000 |
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| committer | Laurent Bercot <ska-skaware@skarnet.org> | 2014-12-15 23:08:59 +0000 |
| commit | e0fc82203d677a6f1e808e9a1a46176c109d89be (patch) | |
| tree | e9609209b755e3f7a8480aea86601ffe9d4ca540 /doc/s6-taiclock.html | |
| download | s6-networking-e0fc82203d677a6f1e808e9a1a46176c109d89be.tar.xz | |
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diff --git a/doc/s6-taiclock.html b/doc/s6-taiclock.html new file mode 100644 index 0000000..bbdc680 --- /dev/null +++ b/doc/s6-taiclock.html @@ -0,0 +1,114 @@ +<html> + <head> + <meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /> + <meta http-equiv="Content-Language" content="en" /> + <title>s6-networking: the s6-taiclock program</title> + <meta name="Description" content="s6-networking: the s6-taiclock program" /> + <meta name="Keywords" content="s6-networking s6-taiclock tai clock tai64 tai64n tai64na client" /> + <!-- <link rel="stylesheet" type="text/css" href="http://skarnet.org/default.css" /> --> + </head> +<body> + +<p> +<a href="index.html">s6-networking</a><br /> +<a href="http://skarnet.org/software/">Software</a><br /> +<a href="http://skarnet.org/">skarnet.org</a> +</p> + +<h1> The <tt>s6-taiclock</tt> program </h1> + +<p> +<tt>s6-taiclock</tt> is a client for the +<a href="http://cr.yp.to/proto/taiclock.txt">TAICLOCK</a> protocol. +It connects to a TAICLOCK server, computes an estimated discrepancy +between the local clock time and the absolute time given by the server, +and outputs it on stdout. +</p> + +<h2> Interface </h2> + +<pre> + s6-taiclock [ -f ] [ -v <em>verbosity</em> ] [ -r <em>roundtrips</em> ] [ -t <em>triptimeout</em> ] [ -h <em>throttle</em> ] [ -T <em>totaltimeout</em> ] [ -e <em>errmax</em> ] [ -p <em>port</em> ] <em>ipaddress</em> | s6-clockview +</pre> + +<ul> + <li> s6-taiclock exchanges TAICLOCK messages with a server such as +<a href="s6-taiclockd.html">s6-taiclockd</a> +listening on <em>ipaddress</em>, UDP port 4014. +<em>ipaddress</em> can be IPv4 or IPv6. </li> + <li> It computes the mean difference between the absolute time +given by the system clock and the one given by the server. </li> + <li> It prints the difference to stdout in a format understood +by <a href="s6-clockadd">s6-clockadd</a> and +<a href="s6-clockview">s6-clockview</a>. It then exits 0. </li> +</ul> + +<h2> Options </h2> + +<ul> + <li> <tt>-f</tt> : force. Normally, s6-taiclock exits 111 if it cannot +compute a time with a smaller uncertainty than <em>errmax</em>. If this +option is set, it will output a time difference and exit 0 even if the +error is too big. </li> + <li> <tt>-v <em>verbosity</em></tt> : be more or less verbose. +By default, <em>verbosity</em> is 1. 0 means only print fatal error +messages; 2 means print advanced warnings. </li> + <li> <tt>-r <em>roundtrips</em></tt> : perform <em>roundtrips</em> +exchanges with the server. By default, <em>roundtrip</em> is 10. A lower +value yields a higher time uncertainty; a higher value puts more load on +the server. </li> + <li> <tt>-t <em>triptimeout</em></tt> : if a TAICLOCK exchange with +the server takes more than <em>triptimeout</em> milliseconds, abort this +exchange and move on to the next one. By default, <em>triptimeout</em> +is 2000. </li> + <li> <tt>-h <em>throttle</em></tt> : wait <em>throttle</em> +milliseconds between exchanges with the server. A lower value gets the +final result earlier, but exerts more load on the server. A higher +value puts a lighter load on the server, but delays the computation. +By default, <em>throttle</em> is 0. It is recommended to set it to a +reasonable nonzero value when increasing <em>roundtrips</em>. </li> + <li> <tt>-T <em>totaltimeout</em></tt> : if the whole +operation takes more than <em>totaltimeout</em> milliseconds, abort +and exit 1. By default, <em>totaltimeout</em> is 10000. </li> + <li> <tt>-e <em>errmax</em></tt> : accept a maximum time +uncertainty of <em>errmax</em> milliseconds. By default, <em>errmax</em> +is 100. </li> + <li> <tt>-p <em>port</em></tt> : contact a server on port +<em>port</em>. By default, <em>port</em> is 4014. </li> +</ul> + +<h2> Notes </h2> + +<h3> On the usage of NTP vs. TAICLOCK </h3> + +<ul> + <li> TAICLOCK is not as generic or failproof as NTP. It is not as +resistant to network latency. It has been designed to broadcast +time on a local area network, whereas NTP has been designed to +broadcast time over the whole Internet. </li> + <li> TAICLOCK will produce faster results on a LAN; moreover, the +point of TAICLOCK is to broadcast TAI instead of UTC, so it is +more accurate around a leap second. </li> + <li> The Internet is much more reliable latency-wise today +than it was when dialout connections and broken routing protocols +were the norm. So it is possible to use TAICLOCK +across a WAN if the accuracy expectations are not too strict. </li> + <li> TAICLOCK is much easier to implement. The +<a href="s6-sntpclock.html">s6-sntpclock</a> client binary code +(statically linked on a i386) is 50% bigger than the s6-taiclock +client. Also, the <a href="s6-taiclockd.html">s6-taiclockd</a> +server is extremely small (close to 50% smaller than the client), +whereas NTP servers, even SNTP servers, are behemoths requiring +a project of their own. </li> +</ul> + +<h3> Related work </h3> + +<ul> + <li> The <a href="http://cr.yp.to/clockspeed.html">clockspeed</a> package +is the original inspiration for the clock management part of s6-networking. +Unfortunately, it is unmaintained. </li> +</ul> + +</body> +</html> |