osmo-pcu/src/pcu_utils.h

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/*
* Copyright (C) 2015 by Sysmocom s.f.m.c. GmbH
*
* 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.
*/
#pragma once
#ifdef __cplusplus
extern "C" {
#endif
#include <osmocom/gsm/gsm_utils.h>
#ifdef __cplusplus
}
#endif
#include <time.h>
#include <stdint.h>
#define FN_UNSET 0xFFFFFFFF
static inline int msecs_to_frames(int msecs) {
return (msecs * (1024 * 1000 / 4615)) / 1024;
}
tbf: Use a hysteresis when discarding DL LLC frames Currently single LLC blocks are discarded when the PDU lifetime expires. If an IP packet has been fragmented either on the IP or on the LLC layer and is therefore distributed over several LLC frames, the kept fragments are transmitted and then discarded by the MS because of the missing PDU. This can cause massive IP packet loss when there are many fragmented packets (e.g. when trying 'ping -s1800' or if the GGSN chops downlink IP packets into several SNDCP packets). On the other hand, discarding too many packets might disturb the congestion handling of TCP. Dropping plain TCP ACKs might also hinder flow control and congestion avoidance. This commit adds a hysteresis algorithm to the LLC discard loop. If an LLC message's age reaches the high water mark, further message's with an age above the low water mark are discarded, too. This is aborted, if a GMM, a non-UI, or a small message is detected. In these cases, that message is kept. The following VTY commands are added (pcu config node): - queue hysteresis <1-65535> set the difference between high (lifetime) and low watermark in centiseconds - no queue hysteresis disable this feature (default) Since the SGSN will most probably send all fragments of a single N-PDU without much delay between them, a value slightly above the average transmission delay jitter between SGSN and PCU is probably a sensible value to discard all fragments of a single IP packet. This is an experimental feature that might be replaced by more advanced means of active queue management in the future. Sponsored-by: On-Waves ehf
2015-03-20 11:02:42 +00:00
static inline uint32_t next_fn(uint32_t fn, uint32_t offset)
{
return (fn + offset) % GSM_MAX_FN;
}
static inline void csecs_to_timespec(unsigned csecs, struct timespec *ts) {
ts->tv_sec = csecs / 100;
ts->tv_nsec = (csecs % 100) * 10000000;
tbf: Use a hysteresis when discarding DL LLC frames Currently single LLC blocks are discarded when the PDU lifetime expires. If an IP packet has been fragmented either on the IP or on the LLC layer and is therefore distributed over several LLC frames, the kept fragments are transmitted and then discarded by the MS because of the missing PDU. This can cause massive IP packet loss when there are many fragmented packets (e.g. when trying 'ping -s1800' or if the GGSN chops downlink IP packets into several SNDCP packets). On the other hand, discarding too many packets might disturb the congestion handling of TCP. Dropping plain TCP ACKs might also hinder flow control and congestion avoidance. This commit adds a hysteresis algorithm to the LLC discard loop. If an LLC message's age reaches the high water mark, further message's with an age above the low water mark are discarded, too. This is aborted, if a GMM, a non-UI, or a small message is detected. In these cases, that message is kept. The following VTY commands are added (pcu config node): - queue hysteresis <1-65535> set the difference between high (lifetime) and low watermark in centiseconds - no queue hysteresis disable this feature (default) Since the SGSN will most probably send all fragments of a single N-PDU without much delay between them, a value slightly above the average transmission delay jitter between SGSN and PCU is probably a sensible value to discard all fragments of a single IP packet. This is an experimental feature that might be replaced by more advanced means of active queue management in the future. Sponsored-by: On-Waves ehf
2015-03-20 11:02:42 +00:00
}
static inline uint32_t rts_next_fn(uint32_t rts_fn, uint8_t block_nr)
{
uint32_t fn = rts_fn + 4;
if ((block_nr % 3) == 2)
fn++;
fn = fn % GSM_MAX_FN;
return fn;
}
static inline unsigned fn2bn(unsigned fn)
{
return (fn % 52) / 4;
}
static inline bool fn_valid(uint32_t fn)
{
uint32_t f = fn % 13;
return f == 0 || f == 4 || f == 8;
}
static inline unsigned fn_next_block(unsigned fn)
{
unsigned bn = fn2bn(fn) + 1;
fn = fn - (fn % 52);
fn += bn * 4 + bn / 3;
return fn % GSM_MAX_FN;
}
#ifdef __cplusplus
template <typename T>
inline unsigned int pcu_bitcount(T x)
{
unsigned int count = 0;
for (count = 0; x; count += 1)
x &= x - 1;
return count;
}
#endif
static inline uint8_t pcu_lsb(uint8_t x)
{
return x & -x;
}
/* Used to store a C++ class in a llist used by C code */
struct llist_item {
struct llist_head list; /* item used by llist */
void *entry;
};