//
// This file is part of Dire Wolf, an amateur radio packet TNC.
//
// Copyright (C) 2011, 2013 John Langner, WB2OSZ
//
// 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, see .
//
/*------------------------------------------------------------------
*
* Name: dedupe.c
*
* Purpose: Avoid transmitting duplicate packets which are too
* close together.
*
*
* Description: We want to avoid digipeating duplicate packets to
* to help reduce radio channel congestion with
* redundant information.
* Duplicate packets can occur in several ways:
*
* (1) A digipeated packet can loop between 2 or more
* digipeaters. For example:
*
* W1ABC>APRS,WIDE3-3
* W1ABC>APRS,mycall*,WIDE3-2
* W1ABC>APRS,mycall,RPT1*,WIDE3-1
* W1ABC>APRS,mycall,RPT1,mycall*
*
* (2) We could hear our own original transmission
* repeated by someone else. Example:
*
* mycall>APRS,WIDE3-3
* mycall>APRS,RPT1*,WIDE3-2
* mycall>APRS,RPT1*,mycall*,WIDE3-1
*
* (3) We could hear the same packet from multiple
* digipeaters (with or without the original).
*
* W1ABC>APRS,WIDE3-2
* W1ABC>APRS,RPT1*,WIDE3-2
* W1ABC>APRS,RPT2*,WIDE3-2
* W1ABC>APRS,RPT3*,WIDE3-2
*
* (4) Someone could be sending the same thing over and
* over with very little delay in between.
*
* W1ABC>APRS,WIDE3-3
* W1ABC>APRS,WIDE3-3
* W1ABC>APRS,WIDE3-3
*
* We can catch the first two by looking for 'mycall' in
* the source or digipeater fields.
*
* The other two cases require us to keep a record of what
* we transmitted recently and test for duplicates that
* should be dropped.
*
* Once we have the solution to catch cases (3) and (4)
* there is no reason for the special case of looking for
* mycall. The same technique catches all four situations.
*
* For detecting duplicates, we need to look
* + source station
* + destination
* + information field
* but NOT the changing list of digipeaters.
*
* Typically, only a checksum is kept to reduce memory
* requirements and amount of compution for comparisons.
* There is a very very small probability that two unrelated
* packets will result in the same checksum, and the
* undesired dropping of the packet.
*
* References: Original APRS specification:
*
* TBD...
*
* "The New n-N Paradigm"
*
* http://www.aprs.org/fix14439.html
*
*------------------------------------------------------------------*/
#define DEDUPE_C
#include
#include
#include
#include
#include
#include "ax25_pad.h"
#include "dedupe.h"
#include "fcs_calc.h"
#include "textcolor.h"
/*------------------------------------------------------------------------------
*
* Name: dedupe_init
*
* Purpose: Initialize the duplicate detection subsystem.
*
* Input: ttl - Number of seconds to retain information
* about recent transmissions.
*
*
* Returns: None
*
* Description: This should be called at application startup.
*
*
*------------------------------------------------------------------------------*/
static int history_time = 30; /* Number of seconds to keep information */
/* about recent transmissions. */
#define HISTORY_MAX 25 /* Maximum number of transmission */
/* records to keep. If we run out of */
/* room the oldest ones are overwritten */
/* before they expire. */
static int insert_next; /* Index, in array below, where next */
/* item should be stored. */
static struct {
time_t time_stamp; /* When the packet was transmitted. */
unsigned short checksum; /* Some sort of checksum for the */
/* source, destination, and information. */
/* is is not used anywhere else. */
short xmit_channel; /* Radio channel number. */
} history[HISTORY_MAX];
void dedupe_init (int ttl)
{
history_time = ttl;
insert_next = 0;
memset (history, 0, sizeof(history));
}
/*------------------------------------------------------------------------------
*
* Name: dedupe_remember
*
* Purpose: Save information about a packet being transmitted so we
* can detect, and avoid, duplicates later.
*
* Input: pp - Pointer to packet object.
*
* chan - Radio channel for transmission.
*
* Returns: None
*
* Rambling: At one time, my thinking is that we want to keep track of
* ALL transmitted packets regardless of origin or type.
*
* + my beacons
* + anything from a connected application
* + anything digipeated
*
* The easiest way to catch all cases is to call dedup_remember()
* from inside tq_append().
*
* But I don't think that is the right approach.
* When acting as a KISS TNC, we should just shovel everything
* through and not question what the application is doing.
* If the connected application has a digipeating function,
* it's responsible for those decisions.
*
* My current thinking is that dedupe_remember() should be
* called BEFORE tq_append() in the digipeater case.
*
* We should also capture our own beacon transmissions.
*
*------------------------------------------------------------------------------*/
void dedupe_remember (packet_t pp, int chan)
{
history[insert_next].time_stamp = time(NULL);
history[insert_next].checksum = ax25_dedupe_crc(pp);
history[insert_next].xmit_channel = chan;
insert_next++;
if (insert_next >= HISTORY_MAX) {
insert_next = 0;
}
}
/*------------------------------------------------------------------------------
*
* Name: dedupe_check
*
* Purpose: Check whether this is a duplicate of another sent recently.
*
* Input: pp - Pointer to packet object.
*
* chan - Radio channel for transmission.
*
* Returns: True if it is a duplicate.
*
*
*------------------------------------------------------------------------------*/
int dedupe_check (packet_t pp, int chan)
{
unsigned short crc = ax25_dedupe_crc(pp);
time_t now = time(NULL);
int j;
for (j=0; j= now - history_time &&
history[j].checksum == crc &&
history[j].xmit_channel == chan) {
return 1;
}
}
return 0;
}
/* end dedupe.c */