Sat Nov 1 06:28:26 2008

Asterisk developer's documentation

---

chan_mgcp.c

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/*
 * Asterisk -- An open source telephony toolkit.
 *
 * Copyright (C) 1999 - 2006, Digium, Inc.
 *
 * Mark Spencer <markster@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.
 */

/*! \file
 *
 * \brief Implementation of Media Gateway Control Protocol
 *
 * \author Mark Spencer <markster@digium.com>
 *
 * \par See also
 * \arg \ref Config_mgcp
 *
 * \ingroup channel_drivers
 */
/*** MODULEINFO
        <depend>res_features</depend>
 ***/

#include "asterisk.h"

ASTERISK_FILE_VERSION(__FILE__, "$Revision: 123113 $")

#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <sys/socket.h>
#include <sys/ioctl.h>
#include <net/if.h>
#include <errno.h>
#include <stdlib.h>
#include <fcntl.h>
#include <netdb.h>
#include <sys/signal.h>
#include <signal.h>
#include <netinet/in.h>
#include <netinet/in_systm.h>
#include <netinet/ip.h>
#include <arpa/inet.h>
#include <ctype.h>

#include "asterisk/lock.h"
#include "asterisk/channel.h"
#include "asterisk/config.h"
#include "asterisk/logger.h"
#include "asterisk/module.h"
#include "asterisk/pbx.h"
#include "asterisk/options.h"
#include "asterisk/lock.h"
#include "asterisk/sched.h"
#include "asterisk/io.h"
#include "asterisk/rtp.h"
#include "asterisk/acl.h"
#include "asterisk/callerid.h"
#include "asterisk/cli.h"
#include "asterisk/say.h"
#include "asterisk/cdr.h"
#include "asterisk/astdb.h"
#include "asterisk/features.h"
#include "asterisk/app.h"
#include "asterisk/musiconhold.h"
#include "asterisk/utils.h"
#include "asterisk/causes.h"
#include "asterisk/dsp.h"
#include "asterisk/devicestate.h"
#include "asterisk/stringfields.h"
#include "asterisk/abstract_jb.h"

#ifndef IPTOS_MINCOST
#define IPTOS_MINCOST 0x02
#endif

/*
 * Define to work around buggy dlink MGCP phone firmware which
 * appears not to know that "rt" is part of the "G" package.
 */
/* #define DLINK_BUGGY_FIRMWARE  */

#define MGCPDUMPER
#define DEFAULT_EXPIRY  120
#define MAX_EXPIRY   3600
#define CANREINVITE  1

#ifndef INADDR_NONE
#define INADDR_NONE (in_addr_t)(-1)
#endif

/*! Global jitterbuffer configuration - by default, jb is disabled */
static struct ast_jb_conf default_jbconf =
{
   .flags = 0,
   .max_size = -1,
   .resync_threshold = -1,
   .impl = ""
};
static struct ast_jb_conf global_jbconf;

static const char tdesc[] = "Media Gateway Control Protocol (MGCP)";
static const char config[] = "mgcp.conf";

#define MGCP_DTMF_RFC2833  (1 << 0)
#define MGCP_DTMF_INBAND   (1 << 1)
#define MGCP_DTMF_HYBRID   (1 << 2)

#define DEFAULT_MGCP_GW_PORT  2427 /*!< From RFC 2705 */
#define DEFAULT_MGCP_CA_PORT  2727 /*!< From RFC 2705 */
#define MGCP_MAX_PACKET    1500 /*!< Also from RFC 2543, should sub headers tho */
#define DEFAULT_RETRANS    1000 /*!< How frequently to retransmit */
#define MAX_RETRANS     5    /*!< Try only 5 times for retransmissions */

/*! MGCP rtp stream modes { */
#define MGCP_CX_SENDONLY   0
#define MGCP_CX_RECVONLY   1
#define MGCP_CX_SENDRECV   2
#define MGCP_CX_CONF    3
#define MGCP_CX_CONFERENCE 3
#define MGCP_CX_MUTE    4
#define MGCP_CX_INACTIVE   4
/*! } */

static char *mgcp_cxmodes[] = {
   "sendonly",
   "recvonly",
   "sendrecv",
   "confrnce",
   "inactive"
};

enum {
   MGCP_CMD_EPCF,
   MGCP_CMD_CRCX,
   MGCP_CMD_MDCX,
   MGCP_CMD_DLCX,
   MGCP_CMD_RQNT,
   MGCP_CMD_NTFY,
   MGCP_CMD_AUEP,
   MGCP_CMD_AUCX,
   MGCP_CMD_RSIP
};

static char context[AST_MAX_EXTENSION] = "default";

static char language[MAX_LANGUAGE] = "";
static char musicclass[MAX_MUSICCLASS] = "";
static char cid_num[AST_MAX_EXTENSION] = "";
static char cid_name[AST_MAX_EXTENSION] = "";

static int dtmfmode = 0;
static int nat = 0;

static ast_group_t cur_callergroup = 0;
static ast_group_t cur_pickupgroup = 0;

static int tos = 0;

static int immediate = 0;

static int callwaiting = 0;

static int callreturn = 0;

static int slowsequence = 0;

static int threewaycalling = 0;

/*! This is for flashhook transfers */
static int transfer = 0;

static int cancallforward = 0;

static int singlepath = 0;

static int canreinvite = CANREINVITE;

static char accountcode[AST_MAX_ACCOUNT_CODE] = "";

static char mailbox[AST_MAX_EXTENSION];

static int amaflags = 0;

static int adsi = 0;

static unsigned int oseq;

/*! Wait up to 16 seconds for first digit (FXO logic) */
static int firstdigittimeout = 16000;

/*! How long to wait for following digits (FXO logic) */
static int gendigittimeout = 8000;

/*! How long to wait for an extra digit, if there is an ambiguous match */
static int matchdigittimeout = 3000;

/*! Protect the monitoring thread, so only one process can kill or start it, and not
    when it's doing something critical. */
AST_MUTEX_DEFINE_STATIC(netlock);

AST_MUTEX_DEFINE_STATIC(monlock);

/*! This is the thread for the monitor which checks for input on the channels
    which are not currently in use. */
static pthread_t monitor_thread = AST_PTHREADT_NULL;

static int restart_monitor(void);

static int capability = AST_FORMAT_ULAW;
static int nonCodecCapability = AST_RTP_DTMF;

static char ourhost[MAXHOSTNAMELEN];
static struct in_addr __ourip;
static int ourport;

static int mgcpdebug = 0;

static struct sched_context *sched;
static struct io_context *io;
/*! The private structures of the  mgcp channels are linked for
  ! selecting outgoing channels */
   
#define MGCP_MAX_HEADERS   64
#define MGCP_MAX_LINES     64

struct mgcp_request {
   int len;
   char *verb;
   char *identifier;
   char *endpoint;
   char *version;
   int headers;         /*!< MGCP Headers */
   char *header[MGCP_MAX_HEADERS];
   int lines;        /*!< SDP Content */
   char *line[MGCP_MAX_LINES];
   char data[MGCP_MAX_PACKET];
   int cmd;                        /*!< int version of verb = command */
   unsigned int trid;              /*!< int version of identifier = transaction id */
   struct mgcp_request *next;      /*!< next in the queue */
};

/*! \brief mgcp_message: MGCP message for queuing up */
struct mgcp_message {
   struct mgcp_endpoint *owner_ep;
   struct mgcp_subchannel *owner_sub;
   int retrans;
   unsigned long expire;
   unsigned int seqno;
   int len;
   struct mgcp_message *next;
   char buf[0];
};

#define RESPONSE_TIMEOUT 30   /*!< in seconds */

struct mgcp_response {
   time_t whensent;
   int len;
   int seqno;
   struct mgcp_response *next;
   char buf[0];
};

#define MAX_SUBS 2

#define SUB_REAL 0
#define SUB_ALT  1

struct mgcp_subchannel {
   /*! subchannel magic string. 
      Needed to prove that any subchannel pointer passed by asterisk 
      really points to a valid subchannel memory area.
      Ugly.. But serves the purpose for the time being.
    */
#define MGCP_SUBCHANNEL_MAGIC "!978!"
   char magic[6]; 
   ast_mutex_t lock;
   int id;
   struct ast_channel *owner;
   struct mgcp_endpoint *parent;
   struct ast_rtp *rtp;
   struct sockaddr_in tmpdest;
   char txident[80]; /*! \todo FIXME txident is replaced by rqnt_ident in endpoint. 
         This should be obsoleted */
   char cxident[80];
   char callid[80];
   int cxmode;
   struct mgcp_request *cx_queue; /*!< pending CX commands */
   ast_mutex_t cx_queue_lock;     /*!< CX queue lock */
   int nat;
   int iseq;                      /*!< Not used? RTP? */
   int outgoing;
   int alreadygone;
   struct mgcp_subchannel *next;  /*!< for out circular linked list */
};

#define MGCP_ONHOOK  1
#define MGCP_OFFHOOK 2

#define TYPE_TRUNK 1
#define TYPE_LINE  2

struct mgcp_endpoint {
   ast_mutex_t lock;
   char name[80];
   struct mgcp_subchannel *sub;     /*!< Pointer to our current connection, channel and stuff */
   char accountcode[AST_MAX_ACCOUNT_CODE];
   char exten[AST_MAX_EXTENSION];      /*!< Extention where to start */
   char context[AST_MAX_EXTENSION];
   char language[MAX_LANGUAGE];
   char cid_num[AST_MAX_EXTENSION]; /*!< Caller*ID number */
   char cid_name[AST_MAX_EXTENSION];   /*!< Caller*ID name */
   char lastcallerid[AST_MAX_EXTENSION];  /*!< Last Caller*ID */
   char call_forward[AST_MAX_EXTENSION];  /*!< Last Caller*ID */
   char mailbox[AST_MAX_EXTENSION];
   char musicclass[MAX_MUSICCLASS];
   char curtone[80];       /*!< Current tone */
   char dtmf_buf[AST_MAX_EXTENSION];   /*!< place to collect digits be */
   ast_group_t callgroup;
   ast_group_t pickupgroup;
   int callwaiting;
   int hascallwaiting;
   int transfer;
   int threewaycalling;
   int singlepath;
   int cancallforward;
   int canreinvite;
   int callreturn;
   int dnd; /* How does this affect callwait? Do we just deny a mgcp_request if we're dnd? */
   int hascallerid;
   int hidecallerid;
   int dtmfmode;
   int amaflags;
   int type;
   int slowsequence;       /*!< MS: Sequence the endpoint as a whole */
   int group;
   int iseq; /*!< Not used? */
   int lastout; /*!< tracking this on the subchannels.  Is it needed here? */
   int needdestroy; /*!< Not used? */
   int capability;
   int nonCodecCapability;
   int onhooktime;
   int msgstate; /*!< voicemail message state */
   int immediate;
   int hookstate;
   int adsi;
   char rqnt_ident[80];             /*!< request identifier */
   struct mgcp_request *rqnt_queue; /*!< pending RQNT commands */
   ast_mutex_t rqnt_queue_lock;
   struct mgcp_request *cmd_queue;  /*!< pending commands other than RQNT */
   ast_mutex_t cmd_queue_lock;
   int delme;                       /*!< needed for reload */
   int needaudit;                   /*!< needed for reload */
   struct ast_dsp *dsp; /*!< XXX Should there be a dsp/subchannel? XXX */
   /* owner is tracked on the subchannels, and the *sub indicates whos in charge */
   /* struct ast_channel *owner; */
   /* struct ast_rtp *rtp; */
   /* struct sockaddr_in tmpdest; */
   /* message go the the endpoint and not the channel so they stay here */
   struct mgcp_endpoint *next;
   struct mgcp_gateway *parent;
};

static struct mgcp_gateway {
   /* A gateway containing one or more endpoints */
   char name[80];
   int isnamedottedip; /*!< is the name FQDN or dotted ip */
   struct sockaddr_in addr;
   struct sockaddr_in defaddr;
   struct in_addr ourip;
   int dynamic;
   int expire;    /*!< XXX Should we ever expire dynamic registrations? XXX */
   struct mgcp_endpoint *endpoints;
   struct ast_ha *ha;
/* obsolete
   time_t lastouttime;
   int lastout;
   int messagepending;
*/
/* Wildcard endpoint name */
   char wcardep[30];
   struct mgcp_message *msgs; /*!< gw msg queue */
   ast_mutex_t msgs_lock;     /*!< queue lock */  
   int retransid;             /*!< retrans timer id */
   int delme;                 /*!< needed for reload */
   struct mgcp_response *responses;
   struct mgcp_gateway *next;
} *gateways;

AST_MUTEX_DEFINE_STATIC(mgcp_reload_lock);
static int mgcp_reloading = 0;

/*! \brief gatelock: mutex for gateway/endpoint lists */
AST_MUTEX_DEFINE_STATIC(gatelock);

static int mgcpsock  = -1;

static struct sockaddr_in bindaddr;

static struct ast_frame  *mgcp_read(struct ast_channel *ast);
static int transmit_response(struct mgcp_subchannel *sub, char *msg, struct mgcp_request *req, char *msgrest);
static int transmit_notify_request(struct mgcp_subchannel *sub, char *tone);
static int transmit_modify_request(struct mgcp_subchannel *sub);
static int transmit_notify_request_with_callerid(struct mgcp_subchannel *sub, char *tone, char *callernum, char *callername);
static int transmit_modify_with_sdp(struct mgcp_subchannel *sub, struct ast_rtp *rtp, int codecs);
static int transmit_connection_del(struct mgcp_subchannel *sub);
static int transmit_audit_endpoint(struct mgcp_endpoint *p);
static void start_rtp(struct mgcp_subchannel *sub);
static void handle_response(struct mgcp_endpoint *p, struct mgcp_subchannel *sub,  
                            int result, unsigned int ident, struct mgcp_request *resp);
static void dump_cmd_queues(struct mgcp_endpoint *p, struct mgcp_subchannel *sub);
static int mgcp_do_reload(void);
static int mgcp_reload(int fd, int argc, char *argv[]);

static struct ast_channel *mgcp_request(const char *type, int format, void *data, int *cause);
static int mgcp_call(struct ast_channel *ast, char *dest, int timeout);
static int mgcp_hangup(struct ast_channel *ast);
static int mgcp_answer(struct ast_channel *ast);
static struct ast_frame *mgcp_read(struct ast_channel *ast);
static int mgcp_write(struct ast_channel *ast, struct ast_frame *frame);
static int mgcp_indicate(struct ast_channel *ast, int ind, const void *data, size_t datalen);
static int mgcp_fixup(struct ast_channel *oldchan, struct ast_channel *newchan);
static int mgcp_senddigit_begin(struct ast_channel *ast, char digit);
static int mgcp_senddigit_end(struct ast_channel *ast, char digit, unsigned int duration);
static int mgcp_devicestate(void *data);
static void add_header_offhook(struct mgcp_subchannel *sub, struct mgcp_request *resp);

static const struct ast_channel_tech mgcp_tech = {
   .type = "MGCP",
   .description = tdesc,
   .capabilities = AST_FORMAT_ULAW,
   .properties = AST_CHAN_TP_WANTSJITTER | AST_CHAN_TP_CREATESJITTER,
   .requester = mgcp_request,
   .devicestate = mgcp_devicestate,
   .call = mgcp_call,
   .hangup = mgcp_hangup,
   .answer = mgcp_answer,
   .read = mgcp_read,
   .write = mgcp_write,
   .indicate = mgcp_indicate,
   .fixup = mgcp_fixup,
   .send_digit_begin = mgcp_senddigit_begin,
   .send_digit_end = mgcp_senddigit_end,
   .bridge = ast_rtp_bridge,
};

static int has_voicemail(struct mgcp_endpoint *p)
{
   return ast_app_has_voicemail(p->mailbox, NULL);
}

static int unalloc_sub(struct mgcp_subchannel *sub)
{
   struct mgcp_endpoint *p = sub->parent;
   if (p->sub == sub) {
      ast_log(LOG_WARNING, "Trying to unalloc the real channel %s@%s?!?\n", p->name, p->parent->name);
      return -1;
   }
   ast_log(LOG_DEBUG, "Released sub %d of channel %s@%s\n", sub->id, p->name, p->parent->name);

   sub->owner = NULL;
   if (!ast_strlen_zero(sub->cxident)) {
      transmit_connection_del(sub);
   }
   sub->cxident[0] = '\0';
   sub->callid[0] = '\0';
   sub->cxmode = MGCP_CX_INACTIVE;
   sub->outgoing = 0;
   sub->alreadygone = 0;
   memset(&sub->tmpdest, 0, sizeof(sub->tmpdest));
   if (sub->rtp) {
      ast_rtp_destroy(sub->rtp);
      sub->rtp = NULL;
   }
   dump_cmd_queues(NULL, sub); /* SC */
   return 0;
}

/* modified for new transport mechanism */
static int __mgcp_xmit(struct mgcp_gateway *gw, char *data, int len)
{
   int res;
   if (gw->addr.sin_addr.s_addr)
      res=sendto(mgcpsock, data, len, 0, (struct sockaddr *)&gw->addr, sizeof(struct sockaddr_in));
   else 
      res=sendto(mgcpsock, data, len, 0, (struct sockaddr *)&gw->defaddr, sizeof(struct sockaddr_in));
   if (res != len) {
      ast_log(LOG_WARNING, "mgcp_xmit returned %d: %s\n", res, strerror(errno));
   }
   return res;
}

static int resend_response(struct mgcp_subchannel *sub, struct mgcp_response *resp)
{
   struct mgcp_endpoint *p = sub->parent;
   int res;
   if (mgcpdebug) {
      ast_verbose("Retransmitting:\n%s\n to %s:%d\n", resp->buf, ast_inet_ntoa(p->parent->addr.sin_addr), ntohs(p->parent->addr.sin_port));
   }
   res = __mgcp_xmit(p->parent, resp->buf, resp->len);
   if (res > 0)
      res = 0;
   return res;
}

static int send_response(struct mgcp_subchannel *sub, struct mgcp_request *req)
{
   struct mgcp_endpoint *p = sub->parent;
   int res;
   if (mgcpdebug) {
      ast_verbose("Transmitting:\n%s\n to %s:%d\n", req->data, ast_inet_ntoa(p->parent->addr.sin_addr), ntohs(p->parent->addr.sin_port));
   }
   res = __mgcp_xmit(p->parent, req->data, req->len);
   if (res > 0)
      res = 0;
   return res;
}

/* modified for new transport framework */
static void dump_queue(struct mgcp_gateway *gw, struct mgcp_endpoint *p)
{
   struct mgcp_message *cur, *q = NULL, *w, *prev;

   ast_mutex_lock(&gw->msgs_lock);
   prev = NULL, cur = gw->msgs;
   while (cur) {
      if (!p || cur->owner_ep == p) {
         if (prev)
            prev->next = cur->next;
         else
            gw->msgs = cur->next;

         ast_log(LOG_NOTICE, "Removing message from %s transaction %u\n", 
            gw->name, cur->seqno);

         w = cur;
         cur = cur->next;
         if (q) {
            w->next = q;
         } else {
            w->next = NULL;
         }
         q = w;
      } else {
         prev = cur, cur=cur->next;
      }
   }
   ast_mutex_unlock(&gw->msgs_lock);

   while (q) {
      cur = q;
      q = q->next;
      free(cur);
   }
}

static void mgcp_queue_frame(struct mgcp_subchannel *sub, struct ast_frame *f)
{
   for(;;) {
      if (sub->owner) {
         if (!ast_mutex_trylock(&sub->owner->lock)) {
            ast_queue_frame(sub->owner, f);
            ast_mutex_unlock(&sub->owner->lock);
            break;
         } else {
            DEADLOCK_AVOIDANCE(&sub->lock);
         }
      } else
         break;
   }
}

static void mgcp_queue_hangup(struct mgcp_subchannel *sub)
{
   for(;;) {
      if (sub->owner) {
         if (!ast_mutex_trylock(&sub->owner->lock)) {
            ast_queue_hangup(sub->owner);
            ast_mutex_unlock(&sub->owner->lock);
            break;
         } else {
            DEADLOCK_AVOIDANCE(&sub->lock);
         }
      } else
         break;
   }
}

static void mgcp_queue_control(struct mgcp_subchannel *sub, int control)
{
   struct ast_frame f = { AST_FRAME_CONTROL, };
   f.subclass = control;
   return mgcp_queue_frame(sub, &f);
}

static int retrans_pkt(const void *data)
{
   struct mgcp_gateway *gw = (struct mgcp_gateway *)data;
   struct mgcp_message *cur, *exq = NULL, *w, *prev;
   int res = 0;

   /* find out expired msgs */
   ast_mutex_lock(&gw->msgs_lock);

   prev = NULL, cur = gw->msgs;
   while (cur) {
      if (cur->retrans < MAX_RETRANS) {
         cur->retrans++;
         if (mgcpdebug) {
            ast_verbose("Retransmitting #%d transaction %u on [%s]\n",
               cur->retrans, cur->seqno, gw->name);
         }
         __mgcp_xmit(gw, cur->buf, cur->len);

         prev = cur;
         cur = cur->next;
      } else {
         if (prev)
            prev->next = cur->next;
         else
            gw->msgs = cur->next;

         ast_log(LOG_WARNING, "Maximum retries exceeded for transaction %u on [%s]\n",
            cur->seqno, gw->name);

         w = cur;
         cur = cur->next;

         if (exq) {
            w->next = exq;
         } else {
            w->next = NULL;
         }
         exq = w;
      }
   }

   if (!gw->msgs) {
      gw->retransid = -1;
      res = 0;
   } else {
      res = 1;
   }
   ast_mutex_unlock(&gw->msgs_lock);

   while (exq) {
      cur = exq;
      /* time-out transaction */
      handle_response(cur->owner_ep, cur->owner_sub, 406, cur->seqno, NULL); 
      exq = exq->next;
      free(cur);
   }

   return res;
}

/* modified for the new transaction mechanism */
static int mgcp_postrequest(struct mgcp_endpoint *p, struct mgcp_subchannel *sub, 
                            char *data, int len, unsigned int seqno)
{
   struct mgcp_message *msg = malloc(sizeof(struct mgcp_message) + len);
   struct mgcp_message *cur;
   struct mgcp_gateway *gw = ((p && p->parent) ? p->parent : NULL);
   struct timeval tv;

   if (!msg) {
      return -1;
   }
   if (!gw) {
      return -1;
   }
/* SC
   time(&t);
   if (gw->messagepending && (gw->lastouttime + 20 < t)) {
      ast_log(LOG_NOTICE, "Timeout waiting for response to message:%d,  lastouttime: %ld, now: %ld.  Dumping pending queue\n",
         gw->msgs ? gw->msgs->seqno : -1, (long) gw->lastouttime, (long) t);
      dump_queue(sub->parent);
   }
*/
   msg->owner_sub = sub;
   msg->owner_ep = p;
   msg->seqno = seqno;
   msg->next = NULL;
   msg->len = len;
   msg->retrans = 0;
   memcpy(msg->buf, data, msg->len);

   ast_mutex_lock(&gw->msgs_lock);
   cur = gw->msgs;
   if (cur) {
      while(cur->next)
         cur = cur->next;
      cur->next = msg;
   } else {
      gw->msgs = msg;
   }

   if (gettimeofday(&tv, NULL) < 0) {
      /* This shouldn't ever happen, but let's be sure */
      ast_log(LOG_NOTICE, "gettimeofday() failed!\n");
   } else {
      msg->expire = tv.tv_sec * 1000 + tv.tv_usec / 1000 + DEFAULT_RETRANS;

      if (gw->retransid == -1)
         gw->retransid = ast_sched_add(sched, DEFAULT_RETRANS, retrans_pkt, (void *)gw);
   }
   ast_mutex_unlock(&gw->msgs_lock);
/* SC
   if (!gw->messagepending) {
      gw->messagepending = 1;
      gw->lastout = seqno;
      gw->lastouttime = t;
*/
   __mgcp_xmit(gw, msg->buf, msg->len);
      /* XXX Should schedule retransmission XXX */
/* SC
   } else
      ast_log(LOG_DEBUG, "Deferring transmission of transaction %d\n", seqno);
*/
   return 0;
}

/* modified for new transport */
static int send_request(struct mgcp_endpoint *p, struct mgcp_subchannel *sub, 
                        struct mgcp_request *req, unsigned int seqno)
{
   int res = 0;
   struct mgcp_request **queue, *q, *r, *t;
   ast_mutex_t *l;

   ast_log(LOG_DEBUG, "Slow sequence is %d\n", p->slowsequence);
   if (p->slowsequence) {
      queue = &p->cmd_queue;
      l = &p->cmd_queue_lock;
      ast_mutex_lock(l);
   } else {
      switch (req->cmd) {
      case MGCP_CMD_DLCX:
         queue = &sub->cx_queue;
         l = &sub->cx_queue_lock;
         ast_mutex_lock(l);
         q = sub->cx_queue;
         /* delete pending cx cmds */
         while (q) {
            r = q->next;
            free(q);
            q = r;
         }
         *queue = NULL;
         break;

      case MGCP_CMD_CRCX:
      case MGCP_CMD_MDCX:
         queue = &sub->cx_queue;
         l = &sub->cx_queue_lock;
         ast_mutex_lock(l);
         break;

      case MGCP_CMD_RQNT:
         queue = &p->rqnt_queue;
         l = &p->rqnt_queue_lock;
         ast_mutex_lock(l);
         break;

      default:
         queue = &p->cmd_queue;
         l = &p->cmd_queue_lock;
         ast_mutex_lock(l);
         break;
      }
   }

   r = (struct mgcp_request *) malloc (sizeof(struct mgcp_request));
   if (!r) {
      ast_log(LOG_WARNING, "Cannot post MGCP request: insufficient memory\n");