#!/bin/bash # -*- scheme -*- exec guile --debug -l $0 -e main -- "$@" !# ;; GStreamer ;; Copyright (C) 2005 Andy Wingo <wingo at pobox.com> ;; This program is free software; you can redistribute it and/or ;; modify it under the terms of the GNU General Public License as ;; published by the Free Software Foundation; either version 2 of ;; the License, or (at your option) any later version. ;; ;; This program is distributed in the hope that it will be useful, ;; but WITHOUT ANY WARRANTY; without even the implied warranty of ;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the ;; GNU General Public License for more details. ;; ;; You should have received a copy of the GNU General Public License ;; along with this program; if not, contact: ;; ;; Free Software Foundation Voice: +1-617-542-5942 ;; 59 Temple Place - Suite 330 Fax: +1-617-542-2652 ;; Boston, MA 02111-1307, USA gnu@gnu.org ;;; Commentary: ;; ;; Network clock simulator. ;; ;; Simulates the attempts of one clock to synchronize with another over ;; the network. Packets are sent out with a local timestamp, and come ;; back with the remote time added on to the packet. The remote time is ;; assumed to have been observed at the local time in between sending ;; the query and receiving the reply. ;; ;; The local clock will attempt to adjust its rate and offset by fitting ;; a line to the last N datapoints on hand, by default 32. A better fit, ;; as measured by the correlation coefficient, will result in a longer ;; time before the next query. Bad fits or a not-yet-full set of data ;; will result in many queries in quick succession. ;; ;; The rate and offset are set directly to the slope and intercept from ;; the linear regression. This results in discontinuities in the local ;; time. As clock times must be monotonically increasing, a jump down in ;; time will result instead in time standing still for a while. Smoothly ;; varying the rate such that no discontinuities are present has not ;; been investigated. ;; ;; Implementation-wise, this simulator processes events and calculates ;; times discretely. Times are represented as streams, also known as ;; lazy lists. This is an almost-pure functional simulator. The thing to ;; remember while reading is that stream-cons does not evaluate its ;; second argument, rather deferring that calculation until stream-cdr ;; is called. In that way all times are actually infinite series. ;; ;; Usage: See network-clock.scm --help. ;; ;;; Code: (use-modules (ice-9 popen)) (load "network-clock-utils.scm") (define (time->samples t) (iround (* t *sample-frequency*))) (define (schedule-event events e time) (let lp ((response-time (time->samples time)) (stream events)) (if (zero? response-time) (if (not (stream-car stream)) (stream-cons e (stream-cdr stream)) (stream-cons (stream-car stream) (lp 0 (stream-cdr stream)))) (stream-cons (stream-car stream) (lp (1- response-time) (stream-cdr stream)))))) (define (schedule-send-time-query events time) (schedule-event events (list 'send-time-query) time)) (define (schedule-time-query events l) (schedule-event events (list 'time-query l) (+ *send-delay* (random *send-jitter*)))) (define (schedule-time-response events l r) (schedule-event events (list 'time-response l r) (+ *recv-delay* (random *recv-jitter*)))) (define (network-time remote-time local-time events m b x y t) (let ((r (stream-car remote-time)) (l (stream-car local-time)) (event (stream-car events)) (events (stream-cdr events))) (define (next events m b x y t) (stream-cons (+ (* m l) b) (network-time (stream-cdr remote-time) (stream-cdr local-time) events m b x y t))) (case (and=> event car) ((send-time-query) (cond ((< (random 1.0) *packet-loss*) (debug "; dropped time query: ~a\n" l) (print-event 'packet-lost l (+ (* m l) b)) (next events m b x y (time->samples *timeout*))) (else (debug "; sending time query: ~a\n" l) (print-event 'packet-sent l (+ (* m l) b)) (next (schedule-time-query events l) m b x y (time->samples *timeout*))))) ((time-query) (debug "; time query received, replying with ~a\n" r) (next (schedule-time-response events (cadr event) r) m b x y (and t (1- t)))) ((time-response) (let ((x (q-push x (avg (cadr event) l))) (y (q-push y (caddr event)))) (call-with-values (lambda () (least-squares (q-head x) (q-head y))) (lambda (m b r-squared) (define (next-time) (max (if (< (length (q-head x)) *window-size*) 0 (/ 1 (- 1 (min r-squared 0.99999)) 1000)) 0.10)) (debug "; new slope and offset: ~a ~a (~a)\n" m b r-squared) (print-event 'packet-observed (avg (cadr event) l) (caddr event)) (print-event 'packet-received l (+ (* m l) b)) (next (schedule-send-time-query events (next-time)) m b x y #f))))) (else (cond ((not t) ;; not waiting for a response (next events m b x y t)) ((<= t 0) ;; we timed out (next (schedule-send-time-query events 0.0) m b x y 0)) (else (next events m b x y (1- t)))))))) (define (run-simulation remote-speed local-speed) (let ((absolute-time (arithmetic-series 0.0 (/ 1.0 *sample-frequency*))) (event-stream (stream-of #f))) (let ((remote-time (scale-stream absolute-time remote-speed)) (local-time (scale-stream absolute-time local-speed))) (values absolute-time remote-time local-time (network-time remote-time local-time (schedule-send-time-query event-stream 0.0) 1.0 (stream-car local-time) (make-q (list (stream-car local-time))) (make-q (list (stream-car remote-time))) #f))))) (define (print-simulation) (display "Absolute time; Remote time; Local time; Network time\n") (call-with-values (lambda () (run-simulation *remote-rate* *local-rate*)) (lambda streams (apply stream-while (lambda (a r l n) (<= a *total-time*)) (lambda (a r l n) (format #t "~a ~a ~a ~a\n" a r l n)) streams)))) (define (plot-simulation) (let ((port (open-output-pipe "./plot-data Network Clock Simulation"))) (with-output-to-port port print-simulation) (close-pipe port))) (define-parameter *sample-frequency* 40) (define-parameter *send-delay* 0.1) (define-parameter *recv-delay* 0.1) (define-parameter *packet-loss* 0.01) (define-parameter *send-jitter* 0.1) (define-parameter *recv-jitter* 0.1) (define-parameter *window-size* 32) (define-parameter *local-rate* 1.0) (define-parameter *remote-rate* 1.1) (define-parameter *total-time* 5.0) (define-parameter *timeout* 1.0) (define-parameter *debug* #f) (define-parameter *with-graph* #t) (define (main args) (parse-parameter-arguments (cdr args)) (if *with-graph* (plot-simulation) (print-simulation)) (quit))