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Diffstat (limited to 'src/gprs_codel.h')
| -rw-r--r-- | src/gprs_codel.h | 108 |
1 files changed, 108 insertions, 0 deletions
diff --git a/src/gprs_codel.h b/src/gprs_codel.h new file mode 100644 index 00000000..fb744232 --- /dev/null +++ b/src/gprs_codel.h @@ -0,0 +1,108 @@ +/* gprs_codel.h + * + * This is an implementation of the CoDel algorithm based on the reference + * pseudocode (see http://queue.acm.org/appendices/codel.html). + * Instead of abstracting the queue itself, the following implementation + * provides a time stamp based automaton. The main work is done by a single + * decision function which updates the state and tells whether to pass or to + * drop a packet after it has been taken from the queue. + * + * Copyright (C) 2015 by Sysmocom s.f.m.c. GmbH + * Author: Jacob Erlbeck <jerlbeck@sysmocom.de> + * + * 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, write to the Free Software + * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. + */ + +#pragma once + +#include <sys/time.h> + +/* Spec default values */ +#define GPRS_CODEL_DEFAULT_INTERVAL_MS 100 +#define GPRS_CODEL_DEFAULT_MAXPACKET 512 + +#ifdef __cplusplus +extern "C" { +#endif + +struct gprs_codel { + int dropping; + unsigned count; + struct timeval first_above_time; + struct timeval drop_next; + struct timeval target; + struct timeval interval; + unsigned maxpacket; +}; + +/*! + * \brief Decide about packet drop and update CoDel state + * + * This function takes timing information and decides whether the packet in + * question should be dropped in order to keep related queue in a 'good' state. + * The function is meant to be called when the packet is dequeued. + * + * The CoDel state is updated by this function. + * + * \param state A pointer to the CoDel state of this queue + * \param recv The time when the packet has entered the queue, + * use NULL if dequeueing was not possible because the queue is + * empty + * \param now The current (dequeueing) time + * \param bytes The number of bytes currently stored in the queue (-1 if + * unknown) + * + * \return != 0 if the packet should be dropped, 0 otherwise + */ +int gprs_codel_control(struct gprs_codel *state, const struct timeval *recv, + const struct timeval *now, int bytes); + +/*! + * \brief Initialise CoDel state + * + * This function initialises the CoDel state object. It sets the interval time + * to the default value (GPRS_CODEL_DEFAULT_INTERVAL_MS). + * + * \param state A pointer to the CoDel state of this queue + */ +void gprs_codel_init(struct gprs_codel *state); + +/*! + * \brief Set interval time + * + * This function changes the interval time. + * The target time is derived from the interval time as proposed in the spec + * (5% of interval time). + * + * \param state A pointer to the CoDel state of this queue + * \param interval_ms The initial interval in ms to be used (<= 0 selects the + * default value) + */ +void gprs_codel_set_interval(struct gprs_codel *state, int interval_ms); + +/*! + * \brief Set max packet size + * + * This function changes the maxpacket value. If no more than this number of + * bytes are still stored in the queue, no dropping will be done. + * + * \param state A pointer to the CoDel state of this queue + * \param maxpacket The value in bytes + */ +void gprs_codel_set_maxpacket(struct gprs_codel *state, int maxpacket); + +#ifdef __cplusplus +} +#endif |