asterisk/main/udptl.c

/*
 * Asterisk -- A telephony toolkit for Linux.
 *
 * UDPTL support for T.38
 * 
 * Copyright (C) 2005, Steve Underwood, partly based on RTP code which is
 * Copyright (C) 1999-2009, Digium, Inc.
 *
 * Steve Underwood <steveu@coppice.org>
 * Kevin P. Fleming <kpfleming@digium.com>
 *
 * See http://www.asterisk.org for more information about
 * the Asterisk project. Please do not directly contact
 * any of the maintainers of this project for assistance;
 * the project provides a web site, mailing lists and IRC
 * channels for your use.
 *
 * This program is free software, distributed under the terms of
 * the GNU General Public License Version 2. See the LICENSE file
 * at the top of the source tree.
 *
 * A license has been granted to Digium (via disclaimer) for the use of
 * this code.
 */

/*! 
 * \file 
 *
 * \brief UDPTL support for T.38 faxing
 * 
 *
 * \author Mark Spencer <markster@digium.com>
 * \author Steve Underwood <steveu@coppice.org>
 * \author Kevin P. Fleming <kpfleming@digium.com>
 * 
 * \page T38fax_udptl T.38 support :: UDPTL
 *
 * Asterisk supports T.38 fax passthrough, origination and termination. It does
 * not support gateway operation. The only channel driver that supports T.38 at
 * this time is chan_sip.
 *
 * UDPTL is handled very much like RTP. It can be reinvited to go directly between
 * the endpoints, without involving Asterisk in the media stream.
 * 
 * \b References:
 * - chan_sip.c
 * - udptl.c
 * - app_fax.c
 */

/*** MODULEINFO
	<support_level>core</support_level>
 ***/

#include "asterisk.h"

ASTERISK_FILE_VERSION(__FILE__, "$Revision$")

#include <sys/time.h>
#include <signal.h>
#include <fcntl.h>

#include "asterisk/udptl.h"
#include "asterisk/frame.h"
#include "asterisk/channel.h"
#include "asterisk/acl.h"
#include "asterisk/config.h"
#include "asterisk/lock.h"
#include "asterisk/utils.h"
#include "asterisk/netsock.h"
#include "asterisk/cli.h"
#include "asterisk/unaligned.h"

#define UDPTL_MTU		1200

#if !defined(FALSE)
#define FALSE 0
#endif
#if !defined(TRUE)
#define TRUE (!FALSE)
#endif

#define LOG_TAG(u) S_OR(u->tag, "no tag")

static int udptlstart = 4500;
static int udptlend = 4599;
static int udptldebug;	                    /*!< Are we debugging? */
static struct ast_sockaddr udptldebugaddr;   /*!< Debug packets to/from this host */
#ifdef SO_NO_CHECK
static int nochecksums;
#endif
static int udptlfecentries;
static int udptlfecspan;
static int use_even_ports;

#define LOCAL_FAX_MAX_DATAGRAM      1400
#define DEFAULT_FAX_MAX_DATAGRAM    400
#define FAX_MAX_DATAGRAM_LIMIT      1400
#define MAX_FEC_ENTRIES             5
#define MAX_FEC_SPAN                5

#define UDPTL_BUF_MASK              15

typedef struct {
	int buf_len;
	uint8_t buf[LOCAL_FAX_MAX_DATAGRAM];
} udptl_fec_tx_buffer_t;

typedef struct {
	int buf_len;
	uint8_t buf[LOCAL_FAX_MAX_DATAGRAM];
	unsigned int fec_len[MAX_FEC_ENTRIES];
	uint8_t fec[MAX_FEC_ENTRIES][LOCAL_FAX_MAX_DATAGRAM];
	unsigned int fec_span;
	unsigned int fec_entries;
} udptl_fec_rx_buffer_t;

/*! \brief Structure for an UDPTL session */
struct ast_udptl {
	int fd;
	char resp;
	struct ast_frame f[16];
	unsigned char rawdata[8192 + AST_FRIENDLY_OFFSET];
	unsigned int lasteventseqn;
	int nat;
	int flags;
	struct ast_sockaddr us;
	struct ast_sockaddr them;
	int *ioid;
	struct sched_context *sched;
	struct io_context *io;
	void *data;
	char *tag;
	ast_udptl_callback callback;

	/*! This option indicates the error correction scheme used in transmitted UDPTL
	 * packets and expected in received UDPTL packets.
	 */
	enum ast_t38_ec_modes error_correction_scheme;

	/*! This option indicates the number of error correction entries transmitted in
	 * UDPTL packets and expected in received UDPTL packets.
	 */
	unsigned int error_correction_entries;

	/*! This option indicates the span of the error correction entries in transmitted
	 * UDPTL packets (FEC only).
	 */
	unsigned int error_correction_span;

	/*! The maximum size UDPTL packet that can be accepted by
	 * the remote device.
	 */
	int far_max_datagram;

	/*! The maximum size UDPTL packet that we are prepared to
	 * accept, or -1 if it hasn't been calculated since the last
	 * changes were applied to the UDPTL structure.
	 */
	int local_max_datagram;

	/*! The maximum IFP that can be submitted for sending
	 * to the remote device. Calculated from far_max_datagram,
	 * error_correction_scheme and error_correction_entries,
	 * or -1 if it hasn't been calculated since the last
	 * changes were applied to the UDPTL structure.
	 */
	int far_max_ifp;

	/*! The maximum IFP that the local endpoint is prepared
	 * to accept. Along with error_correction_scheme and
	 * error_correction_entries, used to calculate local_max_datagram.
	 */
	int local_max_ifp;

	unsigned int tx_seq_no;
	unsigned int rx_seq_no;

	udptl_fec_tx_buffer_t tx[UDPTL_BUF_MASK + 1];
	udptl_fec_rx_buffer_t rx[UDPTL_BUF_MASK + 1];
};

static AST_RWLIST_HEAD_STATIC(protos, ast_udptl_protocol);

static inline int udptl_debug_test_addr(const struct ast_sockaddr *addr)
{
	if (udptldebug == 0)
		return 0;

	if (ast_sockaddr_isnull(&udptldebugaddr)) {
		return 1;
	}

	if (ast_sockaddr_port(&udptldebugaddr)) {
		return !ast_sockaddr_cmp(&udptldebugaddr, addr);
	} else {
		return !ast_sockaddr_cmp_addr(&udptldebugaddr, addr);
	}
}

static int decode_length(uint8_t *buf, unsigned int limit, unsigned int *len, unsigned int *pvalue)
{
	if (*len >= limit)
		return -1;
	if ((buf[*len] & 0x80) == 0) {
		*pvalue = buf[*len];
		(*len)++;
		return 0;
	}
	if ((buf[*len] & 0x40) == 0) {
		if (*len == limit - 1)
			return -1;
		*pvalue = (buf[*len] & 0x3F) << 8;
		(*len)++;
		*pvalue |= buf[*len];
		(*len)++;
		return 0;
	}
	*pvalue = (buf[*len] & 0x3F) << 14;
	(*len)++;
	/* We have a fragment.  Currently we don't process fragments. */
	ast_debug(1, "UDPTL packet with length greater than 16K received, decoding will fail\n");
	return 1;
}
/*- End of function --------------------------------------------------------*/

static int decode_open_type(uint8_t *buf, unsigned int limit, unsigned int *len, const uint8_t **p_object, unsigned int *p_num_octets)
{
	unsigned int octet_cnt = 0;

	if (decode_length(buf, limit, len, &octet_cnt) != 0)
		return -1;

	if (octet_cnt > 0) {
		/* Make sure the buffer contains at least the number of bits requested */
		if ((*len + octet_cnt) > limit)
			return -1;

		*p_num_octets = octet_cnt;
		*p_object = &buf[*len];
		*len += octet_cnt;
	}

	return 0;
}
/*- End of function --------------------------------------------------------*/

static unsigned int encode_length(uint8_t *buf, unsigned int *len, unsigned int value)
{
	unsigned int multiplier;

	if (value < 0x80) {
		/* 1 octet */
		buf[*len] = value;
		(*len)++;
		return value;
	}
	if (value < 0x4000) {
		/* 2 octets */
		/* Set the first bit of the first octet */
		buf[*len] = ((0x8000 | value) >> 8) & 0xFF;
		(*len)++;
		buf[*len] = value & 0xFF;
		(*len)++;
		return value;
	}
	/* Fragmentation */
	multiplier = (value < 0x10000) ? (value >> 14) : 4;
	/* Set the first 2 bits of the octet */
	buf[*len] = 0xC0 | multiplier;
	(*len)++;
	return multiplier << 14;
}
/*- End of function --------------------------------------------------------*/

static int encode_open_type(const struct ast_udptl *udptl, uint8_t *buf, unsigned int buflen,
			    unsigned int *len, const uint8_t *data, unsigned int num_octets)
{
	unsigned int enclen;
	unsigned int octet_idx;
	uint8_t zero_byte;

	/* If open type is of zero length, add a single zero byte (10.1) */
	if (num_octets == 0) {
		zero_byte = 0;
		data = &zero_byte;
		num_octets = 1;
	}
	/* Encode the open type */
	for (octet_idx = 0; ; num_octets -= enclen, octet_idx += enclen) {
		if ((enclen = encode_length(buf, len, num_octets)) < 0)
			return -1;
		if (enclen + *len > buflen) {
			ast_log(LOG_ERROR, "UDPTL (%s): Buffer overflow detected (%u + %u > %u)\n",
				LOG_TAG(udptl), enclen, *len, buflen);
			return -1;
		}
		if (enclen > 0) {
			memcpy(&buf[*len], &data[octet_idx], enclen);
			*len += enclen;
		}
		if (enclen >= num_octets)
			break;
	}

	return 0;
}
/*- End of function --------------------------------------------------------*/

static int udptl_rx_packet(struct ast_udptl *s, uint8_t *buf, unsigned int len)
{
	int stat1;
	int stat2;
	int i;
	unsigned int ptr;	/* an index that keeps track of how much of the UDPTL packet has been processed */
	int seq_no;
	const uint8_t *ifp = NULL;
	const uint8_t *data = NULL;
	unsigned int ifp_len = 0;
	int repaired[16];
	const uint8_t *bufs[ARRAY_LEN(s->f) - 1];
	unsigned int lengths[ARRAY_LEN(s->f) - 1];
	int span;
	int entries;
	int ifp_no;

	ptr = 0;
	ifp_no = 0;
	memset(&s->f[0], 0, sizeof(s->f[0]));

	/* Decode seq_number */
	if (ptr + 2 > len)
		return -1;
	seq_no = (buf[0] << 8) | buf[1];
	ptr += 2;

	/* Break out the primary packet */
	if ((stat1 = decode_open_type(buf, len, &ptr, &ifp, &ifp_len)) != 0)
		return -1;
	/* Decode error_recovery */
	if (ptr + 1 > len)
		return -1;
	if ((buf[ptr++] & 0x80) == 0) {
		/* Secondary packet mode for error recovery */
		if (seq_no > s->rx_seq_no) {
			/* We received a later packet than we expected, so we need to check if we can fill in the gap from the
			   secondary packets. */
			int total_count = 0;
			do {
				unsigned int count;
				if ((stat2 = decode_length(buf, len, &ptr, &count)) < 0)
					return -1;
				for (i = 0; i < count && total_count + i < ARRAY_LEN(bufs); i++) {
					if ((stat1 = decode_open_type(buf, len, &ptr, &bufs[total_count + i], &lengths[total_count + i])) != 0) {
						return -1;
					}
					/* valid secondaries can contain zero-length packets that should be ignored */
					if (!bufs[total_count + i] || !lengths[total_count + i]) {
						/* drop the count of items to process and reuse the buffers that were just set */
						i--;
						count--;
					}
				}
				total_count += i;
			}
			while (stat2 > 0 && total_count < ARRAY_LEN(bufs));
			/* Step through in reverse order, so we go oldest to newest */
			for (i = total_count; i > 0; i--) {
				if (seq_no - i >= s->rx_seq_no) {
					/* This one wasn't seen before */
					/* Decode the secondary IFP packet */
					ast_debug(3, "Recovering lost packet via secondary %d, len %u\n", seq_no - i, lengths[i - 1]);
					s->f[ifp_no].frametype = AST_FRAME_MODEM;
					s->f[ifp_no].subclass.codec = AST_MODEM_T38;

					s->f[ifp_no].mallocd = 0;
					s->f[ifp_no].seqno = seq_no - i;
					s->f[ifp_no].datalen = lengths[i - 1];
					s->f[ifp_no].data.ptr = (uint8_t *) bufs[i - 1];
					s->f[ifp_no].offset = 0;
					s->f[ifp_no].src = "UDPTL";
					if (ifp_no > 0)
						AST_LIST_NEXT(&s->f[ifp_no - 1], frame_list) = &s->f[ifp_no];
					AST_LIST_NEXT(&s->f[ifp_no], frame_list) = NULL;
					ifp_no++;
				}
			}
		}
	}
	else
	{
		int j;
		int l;
		int x;
		/* FEC mode for error recovery */
		/* Our buffers cannot tolerate overlength IFP packets in FEC mode */
		if (ifp_len > LOCAL_FAX_MAX_DATAGRAM)
			return -1;
		/* Update any missed slots in the buffer */
		for ( ; seq_no > s->rx_seq_no; s->rx_seq_no++) {
			x = s->rx_seq_no & UDPTL_BUF_MASK;
			s->rx[x].buf_len = -1;
			s->rx[x].fec_len[0] = 0;
			s->rx[x].fec_span = 0;
			s->rx[x].fec_entries = 0;
		}

		x = seq_no & UDPTL_BUF_MASK;

		memset(repaired, 0, sizeof(repaired));

		/* Save the new IFP packet */
		memcpy(s->rx[x].buf, ifp, ifp_len);
		s->rx[x].buf_len = ifp_len;
		repaired[x] = TRUE;

		/* Decode the FEC packets */
		/* The span is defined as an unconstrained integer, but will never be more
		   than a small value. */
		if (ptr + 2 > len)
			return -1;
		if (buf[ptr++] != 1)
			return -1;
		span = buf[ptr++];
		s->rx[x].fec_span = span;

		/* The number of entries is defined as a length, but will only ever be a small
		   value. Treat it as such. */
		if (ptr + 1 > len)
			return -1;
		entries = buf[ptr++];
		if (entries > MAX_FEC_ENTRIES) {
			return -1;
		}
		s->rx[x].fec_entries = entries;

		/* Decode the elements */
		for (i = 0; i < entries; i++) {
			if ((stat1 = decode_open_type(buf, len, &ptr, &data, &s->rx[x].fec_len[i])) != 0)
				return -1;
			if (s->rx[x].fec_len[i] > LOCAL_FAX_MAX_DATAGRAM)
				return -1;

			/* Save the new FEC data */
			memcpy(s->rx[x].fec[i], data, s->rx[x].fec_len[i]);
#if 0
			fprintf(stderr, "FEC: ");
			for (j = 0; j < s->rx[x].fec_len[i]; j++)
				fprintf(stderr, "%02X ", data[j]);
			fprintf(stderr, "\n");
#endif
		}

		/* See if we can reconstruct anything which is missing */
		/* TODO: this does not comprehensively hunt back and repair everything that is possible */
		for (l = x; l != ((x - (16 - span*entries)) & UDPTL_BUF_MASK); l = (l - 1) & UDPTL_BUF_MASK) {
			int m;
			if (s->rx[l].fec_len[0] <= 0)
				continue;
			for (m = 0; m < s->rx[l].fec_entries; m++) {
				int k;
				int which;
				int limit = (l + m) & UDPTL_BUF_MASK;

				/* only repair buffers that actually exist! */
				if (seq_no <= (s->rx[l].fec_span * s->rx[l].fec_entries) - m) {
					continue;
				}

				for (which = -1, k = (limit - s->rx[l].fec_span * s->rx[l].fec_entries) & UDPTL_BUF_MASK; k != limit; k = (k + s->rx[l].fec_entries) & UDPTL_BUF_MASK) {
					if (s->rx[k].buf_len <= 0)
						which = (which == -1) ? k : -2;
				}
				if (which >= 0) {
					/* Repairable */
					for (j = 0; j < s->rx[l].fec_len[m]; j++) {
						s->rx[which].buf[j] = s->rx[l].fec[m][j];
						for (k = (limit - s->rx[l].fec_span * s->rx[l].fec_entries) & UDPTL_BUF_MASK; k != limit; k = (k + s->rx[l].fec_entries) & UDPTL_BUF_MASK)
							s->rx[which].buf[j] ^= (s->rx[k].buf_len > j) ? s->rx[k].buf[j] : 0;
					}
					s->rx[which].buf_len = s->rx[l].fec_len[m];
					repaired[which] = TRUE;
				}
			}
		}
		/* Now play any new packets forwards in time */
		for (l = (x + 1) & UDPTL_BUF_MASK, j = seq_no - UDPTL_BUF_MASK; l != x; l = (l + 1) & UDPTL_BUF_MASK, j++) {
			if (repaired[l]) {
				//fprintf(stderr, "Fixed packet %d, len %d\n", j, l);
				s->f[ifp_no].frametype = AST_FRAME_MODEM;
				s->f[ifp_no].subclass.codec = AST_MODEM_T38;
			
				s->f[ifp_no].mallocd = 0;
				s->f[ifp_no].seqno = j;
				s->f[ifp_no].datalen = s->rx[l].buf_len;
				s->f[ifp_no].data.ptr = s->rx[l].buf;
				s->f[ifp_no].offset = 0;
				s->f[ifp_no].src = "UDPTL";
				if (ifp_no > 0)
					AST_LIST_NEXT(&s->f[ifp_no - 1], frame_list) = &s->f[ifp_no];
				AST_LIST_NEXT(&s->f[ifp_no], frame_list) = NULL;
				ifp_no++;
			}
		}
	}

	/* If packets are received out of sequence, we may have already processed this packet from the error
	   recovery information in a packet already received. */
	if (seq_no >= s->rx_seq_no) {
		/* Decode the primary IFP packet */
		s->f[ifp_no].frametype = AST_FRAME_MODEM;
		s->f[ifp_no].subclass.codec = AST_MODEM_T38;
		
		s->f[ifp_no].mallocd = 0;
		s->f[ifp_no].seqno = seq_no;
		s->f[ifp_no].datalen = ifp_len;
		s->f[ifp_no].data.ptr = (uint8_t *) ifp;
		s->f[ifp_no].offset = 0;
		s->f[ifp_no].src = "UDPTL";
		if (ifp_no > 0)
			AST_LIST_NEXT(&s->f[ifp_no - 1], frame_list) = &s->f[ifp_no];
		AST_LIST_NEXT(&s->f[ifp_no], frame_list) = NULL;

		ifp_no++;
	}

	s->rx_seq_no = seq_no + 1;
	return ifp_no;
}
/*- End of function --------------------------------------------------------*/

static int udptl_build_packet(struct ast_udptl *s, uint8_t *buf, unsigned int buflen, uint8_t *ifp, unsigned int ifp_len)
{
	uint8_t fec[LOCAL_FAX_MAX_DATAGRAM * 2] = { 0, };
	int i;
	int j;
	int seq;
	int entry;
	int entries;
	int span;
	int m;
	unsigned int len;
	int limit;
	int high_tide;

	seq = s->tx_seq_no & 0xFFFF;

	/* Map the sequence number to an entry in the circular buffer */
	entry = seq & UDPTL_BUF_MASK;

	/* We save the message in a circular buffer, for generating FEC or
	   redundancy sets later on. */
	s->tx[entry].buf_len = ifp_len;
	memcpy(s->tx[entry].buf, ifp, ifp_len);
	
	/* Build the UDPTLPacket */

	len = 0;
	/* Encode the sequence number */
	buf[len++] = (seq >> 8) & 0xFF;
	buf[len++] = seq & 0xFF;

	/* Encode the primary IFP packet */
	if (encode_open_type(s, buf, buflen, &len, ifp, ifp_len) < 0)
		return -1;

	/* Encode the appropriate type of error recovery information */
	switch (s->error_correction_scheme)
	{
	case UDPTL_ERROR_CORRECTION_NONE:
		/* Encode the error recovery type */
		buf[len++] = 0x00;
		/* The number of entries will always be zero, so it is pointless allowing
		   for the fragmented case here. */
		if (encode_length(buf, &len, 0) < 0)
			return -1;
		break;
	case UDPTL_ERROR_CORRECTION_REDUNDANCY:
		/* Encode the error recovery type */
		buf[len++] = 0x00;
		if (s->tx_seq_no > s->error_correction_entries)
			entries = s->error_correction_entries;
		else
			entries = s->tx_seq_no;
		/* The number of entries will always be small, so it is pointless allowing
		   for the fragmented case here. */
		if (encode_length(buf, &len, entries) < 0)
			return -1;
		/* Encode the elements */
		for (i = 0; i < entries; i++) {
			j = (entry - i - 1) & UDPTL_BUF_MASK;
			if (encode_open_type(s, buf, buflen, &len, s->tx[j].buf, s->tx[j].buf_len) < 0) {
				ast_debug(1, "UDPTL (%s): Encoding failed at i=%d, j=%d\n",
					  LOG_TAG(s), i, j);
				return -1;
			}
		}
		break;
	case UDPTL_ERROR_CORRECTION_FEC:
		span = s->error_correction_span;
		entries = s->error_correction_entries;
		if (seq < s->error_correction_span*s->error_correction_entries) {
			/* In the initial stages, wind up the FEC smoothly */
			entries = seq/s->error_correction_span;
			if (seq < s->error_correction_span)
				span = 0;
		}
		/* Encode the error recovery type */
		buf[len++] = 0x80;
		/* Span is defined as an inconstrained integer, which it dumb. It will only
		   ever be a small value. Treat it as such. */
		buf[len++] = 1;
		buf[len++] = span;
		/* The number of entries is defined as a length, but will only ever be a small
		   value. Treat it as such. */
		buf[len++] = entries;
		for (m = 0; m < entries; m++) {
			/* Make an XOR'ed entry the maximum length */
			limit = (entry + m) & UDPTL_BUF_MASK;
			high_tide = 0;
			for (i = (limit - span*entries) & UDPTL_BUF_MASK; i != limit; i = (i + entries) & UDPTL_BUF_MASK) {
				if (high_tide < s->tx[i].buf_len) {
					for (j = 0; j < high_tide; j++)
						fec[j] ^= s->tx[i].buf[j];
					for ( ; j < s->tx[i].buf_len; j++)
						fec[j] = s->tx[i].buf[j];
					high_tide = s->tx[i].buf_len;
				} else {
					for (j = 0; j < s->tx[i].buf_len; j++)
						fec[j] ^= s->tx[i].buf[j];
				}
			}
			if (encode_open_type(s, buf, buflen, &len, fec, high_tide) < 0)
				return -1;
		}
		break;
	}

	s->tx_seq_no++;
	return len;
}

int ast_udptl_fd(const struct ast_udptl *udptl)
{
	return udptl->fd;
}

void ast_udptl_set_data(struct ast_udptl *udptl, void *data)
{
	udptl->data = data;
}

void ast_udptl_set_callback(struct ast_udptl *udptl, ast_udptl_callback callback)
{
	udptl->callback = callback;
}

void ast_udptl_setnat(struct ast_udptl *udptl, int nat)
{
	udptl->nat = nat;
}

static int udptlread(int *id, int fd, short events, void *cbdata)
{
	struct ast_udptl *udptl = cbdata;
	struct ast_frame *f;

	if ((f = ast_udptl_read(udptl))) {
		if (udptl->callback)
			udptl->callback(udptl, f, udptl->data);
	}
	return 1;
}

struct ast_frame *ast_udptl_read(struct ast_udptl *udptl)
{
	int res;
	struct ast_sockaddr addr;
	uint8_t *buf;

	buf = udptl->rawdata + AST_FRIENDLY_OFFSET;

	/* Cache where the header will go */
	res = ast_recvfrom(udptl->fd,
			buf,
			sizeof(udptl->rawdata) - AST_FRIENDLY_OFFSET,
			0,
			&addr);
	if (res < 0) {
		if (errno != EAGAIN)
			ast_log(LOG_WARNING, "UDPTL (%s): read error: %s\n",
				LOG_TAG(udptl), strerror(errno));
		ast_assert(errno != EBADF);
		return &ast_null_frame;
	}

	/* Ignore if the other side hasn't been given an address yet. */
	if (ast_sockaddr_isnull(&udptl->them)) {
		return &ast_null_frame;
	}

	if (udptl->nat) {
		/* Send to whoever sent to us */
		if (ast_sockaddr_cmp(&udptl->them, &addr)) {
			ast_sockaddr_copy(&udptl->them, &addr);
			ast_debug(1, "UDPTL (%s): NAT, Using address %s\n",
				  LOG_TAG(udptl), ast_sockaddr_stringify(&udptl->them));
		}
	}

	if (udptl_debug_test_addr(&addr)) {
		int seq_no;

		/* Decode sequence number just for verbose message. */
		if (res < 2) {
			/* Short packet. */
			seq_no = -1;
		} else {
			seq_no = (buf[0] << 8) | buf[1];
		}

		ast_verb(1, "UDPTL (%s): packet from %s (seq %d, len %d)\n",
			LOG_TAG(udptl), ast_sockaddr_stringify(&addr), seq_no, res);
	}
	if (udptl_rx_packet(udptl, buf, res) < 1) {
		return &ast_null_frame;
	}

	return &udptl->f[0];
}

static void calculate_local_max_datagram(struct ast_udptl *udptl)
{
	unsigned int new_max = 0;

	if (udptl->local_max_ifp == -1) {
		ast_log(LOG_WARNING, "UDPTL (%s): Cannot calculate local_max_datagram before local_max_ifp has been set.\n",
			LOG_TAG(udptl));
		udptl->local_max_datagram = -1;
		return;
	}

	/* calculate the amount of space required to receive an IFP
	 * of the maximum size supported by the application/endpoint
	 * that we are delivering them to (local endpoint), and add
	 * the amount of space required to support the selected
	 * error correction mode
	 */
	switch (udptl->error_correction_scheme) {
	case UDPTL_ERROR_CORRECTION_NONE:
		/* need room for sequence number, length indicator, redundancy
		 * indicator and following length indicator
		 */
		new_max = 5 + udptl->local_max_ifp;
		break;
	case UDPTL_ERROR_CORRECTION_REDUNDANCY:
		/* need room for sequence number, length indicators, plus
		 * room for up to 3 redundancy packets
		 */
		new_max = 5 + udptl->local_max_ifp + 2 + (3 * udptl->local_max_ifp);
		break;
	case UDPTL_ERROR_CORRECTION_FEC:
		/* need room for sequence number, length indicators and a
		 * a single IFP of the maximum size expected
		 */
		new_max = 5 + udptl->local_max_ifp + 4 + udptl->local_max_ifp;
		break;
	}
	/* add 5% extra space for insurance, but no larger than LOCAL_FAX_MAX_DATAGRAM */
	udptl->local_max_datagram = MIN(new_max * 1.05, LOCAL_FAX_MAX_DATAGRAM);
}

static void calculate_far_max_ifp(struct ast_udptl *udptl)
{
	unsigned new_max = 0;

	if (udptl->far_max_datagram == -1) {
		ast_log(LOG_WARNING, "UDPTL (%s): Cannot calculate far_max_ifp before far_max_datagram has been set.\n",
			LOG_TAG(udptl));
		udptl->far_max_ifp = -1;
		return;
	}

	/* the goal here is to supply the local endpoint (application
	 * or bridged channel) a maximum IFP value that will allow it
	 * to effectively and efficiently transfer image data at its
	 * selected bit rate, taking into account the selected error
	 * correction mode, but without overrunning the far endpoint's
	 * datagram buffer. this is complicated by the fact that some
	 * far endpoints send us bogus (small) max datagram values,
	 * which would result in either buffer overrun or no error
	 * correction. we try to accomodate those, but if the supplied
	 * value is too small to do so, we'll emit warning messages and
	 * the user will have to use configuration options to override
	 * the max datagram value supplied by the far endpoint.
	 */
	switch (udptl->error_correction_scheme) {
	case UDPTL_ERROR_CORRECTION_NONE:
		/* need room for sequence number, length indicator, redundancy
		 * indicator and following length indicator
		 */
		new_max = udptl->far_max_datagram - 5;
		break;
	case UDPTL_ERROR_CORRECTION_REDUNDANCY:
		/* for this case, we'd like to send as many error correction entries
		 * as possible (up to the number we're configured for), but we'll settle
		 * for sending fewer if the configured number would cause the
		 * calculated max IFP to be too small for effective operation
		 *
		 * need room for sequence number, length indicators and the
		 * configured number of redundant packets
		 *
		 * note: we purposely don't allow error_correction_entries to drop to
		 * zero in this loop; we'd rather send smaller IFPs (and thus reduce
		 * the image data transfer rate) than sacrifice redundancy completely
		 */
		for (;;) {
			new_max = (udptl->far_max_datagram - 8) / (udptl->error_correction_entries + 1);

			if ((new_max < 80) && (udptl->error_correction_entries > 1)) {
				/* the max ifp is not large enough, subtract an
				 * error correction entry and calculate again
				 * */
				--udptl->error_correction_entries;
			} else {
				break;
			}
		}
		break;
	case UDPTL_ERROR_CORRECTION_FEC:
		/* need room for sequence number, length indicators and a
		 * a single IFP of the maximum size expected
		 */
		new_max = (udptl->far_max_datagram - 10) / 2;
		break;
	}
	/* subtract 5% of space for insurance */
	udptl->far_max_ifp = new_max * 0.95;
}

enum ast_t38_ec_modes ast_udptl_get_error_correction_scheme(const struct ast_udptl *udptl)
{
	return udptl->error_correction_scheme;
}

void ast_udptl_set_error_correction_scheme(struct ast_udptl *udptl, enum ast_t38_ec_modes ec)
{
	udptl->error_correction_scheme = ec;
	switch (ec) {
	case UDPTL_ERROR_CORRECTION_FEC:
		udptl->error_correction_scheme = UDPTL_ERROR_CORRECTION_FEC;
		if (udptl->error_correction_entries == 0) {
			udptl->error_correction_entries = 3;
		}
		if (udptl->error_correction_span == 0) {
			udptl->error_correction_span = 3;
		}
		break;
	case UDPTL_ERROR_CORRECTION_REDUNDANCY:
		udptl->error_correction_scheme = UDPTL_ERROR_CORRECTION_REDUNDANCY;
		if (udptl->error_correction_entries == 0) {
			udptl->error_correction_entries = 3;
		}
		break;
	default:
		/* nothing to do */
		break;
	};
	/* reset calculated values so they'll be computed again */
	udptl->local_max_datagram = -1;
	udptl->far_max_ifp = -1;
}

void ast_udptl_set_local_max_ifp(struct ast_udptl *udptl, unsigned int max_ifp)
{
	/* make sure max_ifp is a positive value since a cast will take place when
	 * when setting local_max_ifp */
	if ((signed int) max_ifp > 0) {
		udptl->local_max_ifp = max_ifp;
		/* reset calculated values so they'll be computed again */
		udptl->local_max_datagram = -1;
	}
}

unsigned int ast_udptl_get_local_max_datagram(struct ast_udptl *udptl)
{
	if (udptl->local_max_datagram == -1) {
		calculate_local_max_datagram(udptl);
	}

	/* this function expects a unsigned value in return. */
	if (udptl->local_max_datagram < 0) {
		return 0;
	}
	return udptl->local_max_datagram;
}

void ast_udptl_set_far_max_datagram(struct ast_udptl *udptl, unsigned int max_datagram)
{
	if (!max_datagram || (max_datagram > FAX_MAX_DATAGRAM_LIMIT)) {
		udptl->far_max_datagram = DEFAULT_FAX_MAX_DATAGRAM;
	} else {
		udptl->far_max_datagram = max_datagram;
	}
	/* reset calculated values so they'll be computed again */
	udptl->far_max_ifp = -1;
}

unsigned int ast_udptl_get_far_max_datagram(const struct ast_udptl *udptl)
{
	if (udptl->far_max_datagram < 0) {
		return 0;
	}
	return udptl->far_max_datagram;
}

unsigned int ast_udptl_get_far_max_ifp(struct ast_udptl *udptl)
{
	if (udptl->far_max_ifp == -1) {
		calculate_far_max_ifp(udptl);
	}

	if (udptl->far_max_ifp < 0) {
		return 0;
	}
	return udptl->far_max_ifp;
}

struct ast_udptl *ast_udptl_new_with_bindaddr(struct sched_context *sched, struct io_context *io, int callbackmode, struct ast_sockaddr *addr)
{
	struct ast_udptl *udptl;
	int x;
	int startplace;
	int i;
	long int flags;

	if (!(udptl = ast_calloc(1, sizeof(*udptl))))
		return NULL;

	udptl->error_correction_span = udptlfecspan;
	udptl->error_correction_entries = udptlfecentries;
	
	udptl->far_max_datagram = -1;
	udptl->far_max_ifp = -1;
	udptl->local_max_ifp = -1;
	udptl->local_max_datagram = -1;

	for (i = 0; i <= UDPTL_BUF_MASK; i++) {
		udptl->rx[i].buf_len = -1;
		udptl->tx[i].buf_len = -1;
	}

	if ((udptl->fd = socket(ast_sockaddr_is_ipv6(addr) ?
					AF_INET6 : AF_INET, SOCK_DGRAM, 0)) < 0) {
		ast_free(udptl);
		ast_log(LOG_WARNING, "Unable to allocate socket: %s\n", strerror(errno));
		return NULL;
	}
	flags = fcntl(udptl->fd, F_GETFL);
	fcntl(udptl->fd, F_SETFL, flags | O_NONBLOCK);
#ifdef SO_NO_CHECK
	if (nochecksums)
		setsockopt(udptl->fd, SOL_SOCKET, SO_NO_CHECK, &nochecksums, sizeof(nochecksums));
#endif
	/* Find us a place */
	x = (udptlstart == udptlend) ? udptlstart : (ast_random() % (udptlend - udptlstart)) + udptlstart;
	if (use_even_ports && (x & 1)) {
		++x;
	}
	startplace = x;
	for (;;) {
		ast_sockaddr_copy(&udptl->us, addr);
		ast_sockaddr_set_port(&udptl->us, x);
		if (ast_bind(udptl->fd, &udptl->us) == 0) {
			break;
		}
		if (errno != EADDRINUSE && errno != EACCES) {
			ast_log(LOG_WARNING, "Unexpected bind error: %s\n", strerror(errno));
			close(udptl->fd);
			ast_free(udptl);
			return NULL;
		}
		if (use_even_ports) {
			x += 2;
		} else {
			++x;
		}
		if (x > udptlend)
			x = udptlstart;
		if (x == startplace) {
			ast_log(LOG_WARNING, "No UDPTL ports remaining\n");
			close(udptl->fd);
			ast_free(udptl);
			return NULL;
		}
	}
	if (io && sched && callbackmode) {
		/* Operate this one in a callback mode */
		udptl->sched = sched;
		udptl->io = io;
		udptl->ioid = ast_io_add(udptl->io, udptl->fd, udptlread, AST_IO_IN, udptl);
	}
	return udptl;
}

void ast_udptl_set_tag(struct ast_udptl *udptl, const char *format, ...)
{
	va_list ap;

	ast_free(udptl->tag);
	udptl->tag = NULL;
	va_start(ap, format);
	if (ast_vasprintf(&udptl->tag, format, ap) == -1) {
		udptl->tag = NULL;
	}
	va_end(ap);
}

int ast_udptl_setqos(struct ast_udptl *udptl, unsigned int tos, unsigned int cos)
{
	return ast_netsock_set_qos(udptl->fd, tos, cos, "UDPTL");
}

void ast_udptl_set_peer(struct ast_udptl *udptl, const struct ast_sockaddr *them)
{
	ast_sockaddr_copy(&udptl->them, them);
}

void ast_udptl_get_peer(const struct ast_udptl *udptl, struct ast_sockaddr *them)
{
	ast_sockaddr_copy(them, &udptl->them);
}

void ast_udptl_get_us(const struct ast_udptl *udptl, struct ast_sockaddr *us)
{
	ast_sockaddr_copy(us, &udptl->us);
}

void ast_udptl_stop(struct ast_udptl *udptl)
{
	ast_sockaddr_setnull(&udptl->them);
}

void ast_udptl_destroy(struct ast_udptl *udptl)
{
	if (udptl->ioid)
		ast_io_remove(udptl->io, udptl->ioid);
	if (udptl->fd > -1)
		close(udptl->fd);
	if (udptl->tag)
		ast_free(udptl->tag);
	ast_free(udptl);
}

int ast_udptl_write(struct ast_udptl *s, struct ast_frame *f)
{
	unsigned int seq;
	unsigned int len = f->datalen;
	int res;
	/* if no max datagram size is provided, use default value */
	const int bufsize = (s->far_max_datagram > 0) ? s->far_max_datagram : DEFAULT_FAX_MAX_DATAGRAM;
	uint8_t buf[bufsize];

	memset(buf, 0, sizeof(buf));

	/* If we have no peer, return immediately */
	if (ast_sockaddr_isnull(&s->them)) {
		return 0;
	}

	/* If there is no data length, return immediately */
	if (f->datalen == 0)
		return 0;
	
	if ((f->frametype != AST_FRAME_MODEM) ||
	    (f->subclass.codec != AST_MODEM_T38)) {
		ast_log(LOG_WARNING, "UDPTL (%s): UDPTL can only send T.38 data.\n",
			LOG_TAG(s));
		return -1;
	}

	if (len > s->far_max_ifp) {
		ast_log(LOG_WARNING,
			"UDPTL (%s): UDPTL asked to send %u bytes of IFP when far end only prepared to accept %d bytes; data loss will occur."
			"You may need to override the T38FaxMaxDatagram value for this endpoint in the channel driver configuration.\n",
			LOG_TAG(s), len, s->far_max_ifp);
		len = s->far_max_ifp;
	}

	/* Save seq_no for debug output because udptl_build_packet increments it */
	seq = s->tx_seq_no & 0xFFFF;

	/* Cook up the UDPTL packet, with the relevant EC info. */
	len = udptl_build_packet(s, buf, sizeof(buf), f->data.ptr, len);

	if ((signed int) len > 0 && !ast_sockaddr_isnull(&s->them)) {
		if ((res = ast_sendto(s->fd, buf, len, 0, &s->them)) < 0)
			ast_log(LOG_NOTICE, "UDPTL (%s): Transmission error to %s: %s\n",
				LOG_TAG(s), ast_sockaddr_stringify(&s->them), strerror(errno));
		if (udptl_debug_test_addr(&s->them))
			ast_verb(1, "UDPTL (%s): packet to %s (seq %u, len %u)\n",
				LOG_TAG(s), ast_sockaddr_stringify(&s->them), seq, len);
	}
		
	return 0;
}

void ast_udptl_proto_unregister(struct ast_udptl_protocol *proto)
{
	AST_RWLIST_WRLOCK(&protos);
	AST_RWLIST_REMOVE(&protos, proto, list);
	AST_RWLIST_UNLOCK(&protos);
}

int ast_udptl_proto_register(struct ast_udptl_protocol *proto)
{
	struct ast_udptl_protocol *cur;

	AST_RWLIST_WRLOCK(&protos);
	AST_RWLIST_TRAVERSE(&protos, cur, list) {
		if (cur->type == proto->type) {
			ast_log(LOG_WARNING, "Tried to register same protocol '%s' twice\n", cur->type);
			AST_RWLIST_UNLOCK(&protos);
			return -1;
		}
	}
	AST_RWLIST_INSERT_TAIL(&protos, proto, list);
	AST_RWLIST_UNLOCK(&protos);
	return 0;
}

static struct ast_udptl_protocol *get_proto(struct ast_channel *chan)
{
	struct ast_udptl_protocol *cur = NULL;

	AST_RWLIST_RDLOCK(&protos);
	AST_RWLIST_TRAVERSE(&protos, cur, list) {
		if (cur->type == chan->tech->type)
			break;
	}
	AST_RWLIST_UNLOCK(&protos);

	return cur;
}

int ast_udptl_bridge(struct ast_channel *c0, struct ast_channel *c1, int flags, struct ast_frame **fo, struct ast_channel **rc)
{
	struct ast_frame *f;
	struct ast_channel *who;
	struct ast_channel *cs[3];
	struct ast_udptl *p0;
	struct ast_udptl *p1;
	struct ast_udptl_protocol *pr0;
	struct ast_udptl_protocol *pr1;
	struct ast_sockaddr ac0;
	struct ast_sockaddr ac1;
	struct ast_sockaddr t0;
	struct ast_sockaddr t1;
	void *pvt0;
	void *pvt1;
	int to;
	
	ast_channel_lock(c0);
	while (ast_channel_trylock(c1)) {
		ast_channel_unlock(c0);
		usleep(1);
		ast_channel_lock(c0);
	}
	pr0 = get_proto(c0);
	pr1 = get_proto(c1);
	if (!pr0) {
		ast_log(LOG_WARNING, "Can't find native functions for channel '%s'\n", c0->name);
		ast_channel_unlock(c0);
		ast_channel_unlock(c1);
		return -1;
	}
	if (!pr1) {
		ast_log(LOG_WARNING, "Can't find native functions for channel '%s'\n", c1->name);
		ast_channel_unlock(c0);
		ast_channel_unlock(c1);
		return -1;
	}
	pvt0 = c0->tech_pvt;
	pvt1 = c1->tech_pvt;
	p0 = pr0->get_udptl_info(c0);
	p1 = pr1->get_udptl_info(c1);
	if (!p0 || !p1) {
		/* Somebody doesn't want to play... */
		ast_channel_unlock(c0);
		ast_channel_unlock(c1);
		return -2;
	}
	if (pr0->set_udptl_peer(c0, p1)) {
		ast_log(LOG_WARNING, "Channel '%s' failed to talk to '%s'\n", c0->name, c1->name);
		memset(&ac1, 0, sizeof(ac1));
	} else {
		/* Store UDPTL peer */
		ast_udptl_get_peer(p1, &ac1);
	}
	if (pr1->set_udptl_peer(c1, p0)) {
		ast_log(LOG_WARNING, "Channel '%s' failed to talk back to '%s'\n", c1->name, c0->name);
		memset(&ac0, 0, sizeof(ac0));
	} else {
		/* Store UDPTL peer */
		ast_udptl_get_peer(p0, &ac0);
	}
	ast_channel_unlock(c0);
	ast_channel_unlock(c1);
	cs[0] = c0;
	cs[1] = c1;
	cs[2] = NULL;
	for (;;) {
		if ((c0->tech_pvt != pvt0) ||
			(c1->tech_pvt != pvt1) ||
			(c0->masq || c0->masqr || c1->masq || c1->masqr)) {
				ast_debug(1, "Oooh, something is weird, backing out\n");
				/* Tell it to try again later */
				return -3;
		}
		to = -1;
		ast_udptl_get_peer(p1, &t1);
		ast_udptl_get_peer(p0, &t0);
		if (ast_sockaddr_cmp(&t1, &ac1)) {
			ast_debug(1, "Oooh, '%s' changed end address to %s\n", 
				c1->name, ast_sockaddr_stringify(&t1));
			ast_debug(1, "Oooh, '%s' was %s\n", 
				c1->name, ast_sockaddr_stringify(&ac1));
			ast_sockaddr_copy(&ac1, &t1);
		}
		if (ast_sockaddr_cmp(&t0, &ac0)) {
			ast_debug(1, "Oooh, '%s' changed end address to %s\n", 
				c0->name, ast_sockaddr_stringify(&t0));
			ast_debug(1, "Oooh, '%s' was %s\n", 
				c0->name, ast_sockaddr_stringify(&ac0));
			ast_sockaddr_copy(&ac0, &t0);
		}
		who = ast_waitfor_n(cs, 2, &to);
		if (!who) {
			ast_debug(1, "Ooh, empty read...\n");
			/* check for hangup / whentohangup */
			if (ast_check_hangup(c0) || ast_check_hangup(c1))
				break;
			continue;
		}
		f = ast_read(who);
		if (!f) {
			*fo = f;
			*rc = who;
			ast_debug(1, "Oooh, got a %s\n", f ? "digit" : "hangup");
			/* That's all we needed */
			return 0;
		} else {
			if (f->frametype == AST_FRAME_MODEM) {
				/* Forward T.38 frames if they happen upon us */
				if (who == c0) {
					ast_write(c1, f);
				} else if (who == c1) {
					ast_write(c0, f);
				}
			}
			ast_frfree(f);
		}
		/* Swap priority. Not that it's a big deal at this point */
		cs[2] = cs[0];
		cs[0] = cs[1];
		cs[1] = cs[2];
	}
	return -1;
}

static char *handle_cli_udptl_set_debug(struct ast_cli_entry *e, int cmd, struct ast_cli_args *a)
{
	switch (cmd) {
	case CLI_INIT:
		e->command = "udptl set debug {on|off|ip}";
		e->usage = 
			"Usage: udptl set debug {on|off|ip host[:port]}\n"
			"       Enable or disable dumping of UDPTL packets.\n"
			"       If ip is specified, limit the dumped packets to those to and from\n"
			"       the specified 'host' with optional port.\n";
		return NULL;
	case CLI_GENERATE:
		return NULL;
	}

	if (a->argc < 4 || a->argc > 5)
		return CLI_SHOWUSAGE;

	if (a->argc == 4) {
		if (!strncasecmp(a->argv[3], "on", 2)) {
			udptldebug = 1;
			memset(&udptldebugaddr, 0, sizeof(udptldebugaddr));
			ast_cli(a->fd, "UDPTL Debugging Enabled\n");
		} else if (!strncasecmp(a->argv[3], "off", 3)) {
			udptldebug = 0;
			ast_cli(a->fd, "UDPTL Debugging Disabled\n");
		} else {
			return CLI_SHOWUSAGE;
		}
	} else {
		struct ast_sockaddr *addrs;
		if (strncasecmp(a->argv[3], "ip", 2))
			return CLI_SHOWUSAGE;
		if (!ast_sockaddr_resolve(&addrs, a->argv[4], 0, 0)) {
			return CLI_SHOWUSAGE;
		}
		ast_sockaddr_copy(&udptldebugaddr, &addrs[0]);
			ast_cli(a->fd, "UDPTL Debugging Enabled for IP: %s\n", ast_sockaddr_stringify(&udptldebugaddr));
		udptldebug = 1;
		ast_free(addrs);
	}

	return CLI_SUCCESS;
}


static struct ast_cli_entry cli_udptl[] = {
	AST_CLI_DEFINE(handle_cli_udptl_set_debug, "Enable/Disable UDPTL debugging")
};

static void __ast_udptl_reload(int reload)
{
	struct ast_config *cfg;
	const char *s;
	struct ast_flags config_flags = { reload ? CONFIG_FLAG_FILEUNCHANGED : 0 };

	cfg = ast_config_load2("udptl.conf", "udptl", config_flags);
	if (cfg == CONFIG_STATUS_FILEMISSING || cfg == CONFIG_STATUS_FILEUNCHANGED || cfg == CONFIG_STATUS_FILEINVALID) {
		return;
	}

	udptlstart = 4500;
	udptlend = 4999;
	udptlfecentries = 0;
	udptlfecspan = 0;
	use_even_ports = 0;

	if (cfg) {
		if ((s = ast_variable_retrieve(cfg, "general", "udptlstart"))) {
			udptlstart = atoi(s);
			if (udptlstart < 1024) {
				ast_log(LOG_WARNING, "Ports under 1024 are not allowed for T.38.\n");
				udptlstart = 1024;
			}
			if (udptlstart > 65535) {
				ast_log(LOG_WARNING, "Ports over 65535 are invalid.\n");
				udptlstart = 65535;
			}
		}
		if ((s = ast_variable_retrieve(cfg, "general", "udptlend"))) {
			udptlend = atoi(s);
			if (udptlend < 1024) {
				ast_log(LOG_WARNING, "Ports under 1024 are not allowed for T.38.\n");
				udptlend = 1024;
			}
			if (udptlend > 65535) {
				ast_log(LOG_WARNING, "Ports over 65535 are invalid.\n");
				udptlend = 65535;
			}
		}
		if ((s = ast_variable_retrieve(cfg, "general", "udptlchecksums"))) {
#ifdef SO_NO_CHECK
			if (ast_false(s))
				nochecksums = 1;
			else
				nochecksums = 0;
#else
			if (ast_false(s))
				ast_log(LOG_WARNING, "Disabling UDPTL checksums is not supported on this operating system!\n");
#endif
		}
		if (ast_variable_retrieve(cfg, "general", "T38FaxUdpEC")) {
			ast_log(LOG_WARNING, "T38FaxUdpEC in udptl.conf is no longer supported; use the t38pt_udptl configuration option in sip.conf instead.\n");
		}
		if (ast_variable_retrieve(cfg, "general", "T38FaxMaxDatagram")) {
			ast_log(LOG_WARNING, "T38FaxMaxDatagram in udptl.conf is no longer supported; value is now supplied by T.38 applications.\n");
		}
		if ((s = ast_variable_retrieve(cfg, "general", "UDPTLFECEntries"))) {
			udptlfecentries = atoi(s);
			if (udptlfecentries < 1) {
				ast_log(LOG_WARNING, "Too small UDPTLFECEntries value.  Defaulting to 1.\n");
				udptlfecentries = 1;
			}
			if (udptlfecentries > MAX_FEC_ENTRIES) {
				ast_log(LOG_WARNING, "Too large UDPTLFECEntries value.  Defaulting to %d.\n", MAX_FEC_ENTRIES);
				udptlfecentries = MAX_FEC_ENTRIES;
			}
		}
		if ((s = ast_variable_retrieve(cfg, "general", "UDPTLFECSpan"))) {
			udptlfecspan = atoi(s);
			if (udptlfecspan < 1) {
				ast_log(LOG_WARNING, "Too small UDPTLFECSpan value.  Defaulting to 1.\n");
				udptlfecspan = 1;
			}
			if (udptlfecspan > MAX_FEC_SPAN) {
				ast_log(LOG_WARNING, "Too large UDPTLFECSpan value.  Defaulting to %d.\n", MAX_FEC_SPAN);
				udptlfecspan = MAX_FEC_SPAN;
			}
		}
		if ((s = ast_variable_retrieve(cfg, "general", "use_even_ports"))) {
			use_even_ports = ast_true(s);
		}
		ast_config_destroy(cfg);
	}
	if (udptlstart >= udptlend) {
		ast_log(LOG_WARNING, "Unreasonable values for UDPTL start/end ports; defaulting to 4500-4999.\n");
		udptlstart = 4500;
		udptlend = 4999;
	}
	if (use_even_ports && (udptlstart & 1)) {
		++udptlstart;
		ast_log(LOG_NOTICE, "Odd numbered udptlstart specified but use_even_ports enabled. udptlstart is now %d\n", udptlstart);
	}
	if (use_even_ports && (udptlend & 1)) {
		--udptlend;
		ast_log(LOG_NOTICE, "Odd numbered udptlend specified but use_event_ports enabled. udptlend is now %d\n", udptlend);
	}
	ast_verb(2, "UDPTL allocating from port range %d -> %d\n", udptlstart, udptlend);
}

int ast_udptl_reload(void)
{
	__ast_udptl_reload(1);
	return 0;
}

/*!
 * \internal
 * \brief Clean up resources on Asterisk shutdown
 */
static void udptl_shutdown(void)
{
	ast_cli_unregister_multiple(cli_udptl, ARRAY_LEN(cli_udptl));
}

void ast_udptl_init(void)
{
	__ast_udptl_reload(0);

	ast_cli_register_multiple(cli_udptl, ARRAY_LEN(cli_udptl));

	ast_register_atexit(udptl_shutdown);
}