rtp.h

一个开源SIP协议栈

/* $Id: rtp.h 974 2007-02-19 01:13:53Z bennylp $ */
/* 
 * Copyright (C) 2003-2007 Benny Prijono <[e-mail]>
 *
 * 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 
 */
#ifndef __PJMEDIA_RTP_H__
#define __PJMEDIA_RTP_H__


/**
 * @file rtp.h
 * @brief RTP packet and RTP session declarations.
 */
#include <pjmedia/types.h>


PJ_BEGIN_DECL


/**
 * @defgroup PJMED_RTP RTP Session and Encapsulation (RFC 3550)
 * @ingroup PJMEDIA_TRANSPORT
 * @{
 *
 * The RTP module is designed to be dependent only to PJLIB, it does not depend
 * on any other parts of PJMEDIA library. The RTP module does not even depend
 * on any transports (sockets), to promote even more use, such as in DSP
 * development (where transport may be handled by different processor).
 *
 * An RTCP implementation is available, in separate module. Please see 
 * @ref PJMED_RTCP.
 *
 * The functions that are provided by this module:
 *  - creating RTP header for each outgoing packet.
 *  - decoding RTP packet into RTP header and payload.
 *  - provide simple RTP session management (sequence number, etc.)
 *
 * The RTP module does not use any dynamic memory at all.
 *
 * \section P1 How to Use the RTP Module
 * 
 * First application must call #pjmedia_rtp_session_init() to initialize the RTP 
 * session.
 *
 * When application wants to send RTP packet, it needs to call 
 * #pjmedia_rtp_encode_rtp() to build the RTP header. Note that this WILL NOT build
 * the complete RTP packet, but instead only the header. Application can
 * then either concatenate the header with the payload, or send the two
 * fragments (the header and the payload) using scatter-gather transport API
 * (e.g. \a sendv()).
 *
 * When application receives an RTP packet, first it should call
 * #pjmedia_rtp_decode_rtp to decode RTP header and payload, then it should call
 * #pjmedia_rtp_session_update to check whether we can process the RTP payload,
 * and to let the RTP session updates its internal status. The decode function
 * is guaranteed to point the payload to the correct position regardless of
 * any options present in the RTP packet.
 *
 */

#ifdef _MSC_VER
#   pragma warning(disable:4214)    // bit field types other than int
#endif


/**
 * RTP packet header.
 */
#pragma pack(1)
struct pjmedia_rtp_hdr
{
#if defined(PJ_IS_BIG_ENDIAN) && (PJ_IS_BIG_ENDIAN!=0)
    pj_uint16_t v:2;		/**< packet type/version	    */
    pj_uint16_t p:1;		/**< padding flag		    */
    pj_uint16_t x:1;		/**< extension flag		    */
    pj_uint16_t cc:4;		/**< CSRC count			    */
    pj_uint16_t m:1;		/**< marker bit			    */
    pj_uint16_t pt:7;		/**< payload type		    */
#else
    pj_uint16_t cc:4;		/**< CSRC count			    */
    pj_uint16_t x:1;		/**< header extension flag	    */ 
    pj_uint16_t p:1;		/**< padding flag		    */
    pj_uint16_t v:2;		/**< packet type/version	    */
    pj_uint16_t pt:7;		/**< payload type		    */
    pj_uint16_t m:1;		/**< marker bit			    */
#endif
    pj_uint16_t seq;		/**< sequence number		    */
    pj_uint32_t ts;		/**< timestamp			    */
    pj_uint32_t ssrc;		/**< synchronization source	    */
};
#pragma pack()

/**
 * @see pjmedia_rtp_hdr
 */
typedef struct pjmedia_rtp_hdr pjmedia_rtp_hdr;


/**
 * RTP extendsion header.
 */
struct pjmedia_rtp_ext_hdr
{
    pj_uint16_t	profile_data;	/**< Profile data.	    */
    pj_uint16_t	length;		/**< Length.		    */
};

/**
 * @see pjmedia_rtp_ext_hdr
 */
typedef struct pjmedia_rtp_ext_hdr pjmedia_rtp_ext_hdr;


#pragma pack(1)

/**
 * Declaration for DTMF telephony-events (RFC2833).
 */
struct pjmedia_rtp_dtmf_event
{
    pj_uint8_t	event;	    /**< Event type ID.	    */
    pj_uint8_t	e_vol;	    /**< Event volume.	    */
    pj_uint16_t	duration;   /**< Event duration.    */
};

/**
 * @see pjmedia_rtp_dtmf_event
 */
typedef struct pjmedia_rtp_dtmf_event pjmedia_rtp_dtmf_event;

#pragma pack()


/**
 * A generic sequence number management, used by both RTP and RTCP.
 */
struct pjmedia_rtp_seq_session
{
    pj_uint16_t	    max_seq;	    /**< Highest sequence number heard	    */
    pj_uint32_t	    cycles;	    /**< Shifted count of seq number cycles */
    pj_uint32_t	    base_seq;	    /**< Base seq number		    */
    pj_uint32_t	    bad_seq;        /**< Last 'bad' seq number + 1	    */
    pj_uint32_t	    probation;      /**< Sequ. packets till source is valid */
};

/**
 * @see pjmedia_rtp_seq_session
 */
typedef struct pjmedia_rtp_seq_session pjmedia_rtp_seq_session;


/**
 * RTP session descriptor.
 */
struct pjmedia_rtp_session
{
    pjmedia_rtp_hdr	    out_hdr;    /**< Saved hdr for outgoing pkts.   */
    pjmedia_rtp_seq_session seq_ctrl;   /**< Sequence number management.    */
    pj_uint16_t		    out_pt;	/**< Default outgoing payload type. */
    pj_uint32_t		    out_extseq; /**< Outgoing extended seq #.	    */
    pj_uint32_t		    peer_ssrc;  /**< Peer SSRC.			    */
    pj_uint32_t		    received;   /**< Number of received packets.    */
};

/**
 * @see pjmedia_rtp_session
 */
typedef struct pjmedia_rtp_session pjmedia_rtp_session;


/**
 * This structure is used to receive additional information about the
 * state of incoming RTP packet.
 */
struct pjmedia_rtp_status
{
    union {
	struct flag {
	    int	bad:1;	    /**< General flag to indicate that sequence is
				 bad, and application should not process
				 this packet. More information will be given
				 in other flags.			    */
	    int badpt:1;    /**< Bad payload type.			    */
	    int badssrc:1;  /**< Bad SSRC				    */
	    int	dup:1;	    /**< Indicates duplicate packet		    */
	    int	outorder:1; /**< Indicates out of order packet		    */
	    int	probation:1;/**< Indicates that session is in probation
				 until more packets are received.	    */
	    int	restart:1;  /**< Indicates that sequence number has made
				 a large jump, and internal base sequence
				 number has been adjusted.		    */
	} flag;		    /**< Status flags.				    */

	pj_uint16_t value;  /**< Status value, to conveniently address all
				 flags.					    */

    } status;		    /**< Status information union.		    */

    pj_uint16_t	diff;	    /**< Sequence number difference from previous
				 packet. Normally the value should be 1.    
				 Value greater than one may indicate packet
				 loss. If packet with lower sequence is
				 received, the value will be set to zero.
				 If base sequence has been restarted, the
				 value will be one.			    */
};

/**
 * @see pjmedia_rtp_status
 */
typedef struct pjmedia_rtp_status pjmedia_rtp_status;


/**
 * This function will initialize the RTP session according to given parameters.
 *
 * @param ses		The session.
 * @param default_pt	Default payload type.
 * @param sender_ssrc	SSRC used for outgoing packets.
 *
 * @return		PJ_SUCCESS if successfull.
 */
PJ_DECL(pj_status_t) pjmedia_rtp_session_init( pjmedia_rtp_session *ses,
					       int default_pt, 
					       pj_uint32_t sender_ssrc );

/**
 * Create the RTP header based on arguments and current state of the RTP
 * session.
 *
 * @param ses		The session.
 * @param pt		Payload type.
 * @param m		Marker flag.
 * @param payload_len	Payload length in bytes.
 * @param ts_len	Timestamp length.
 * @param rtphdr	Upon return will point to RTP packet header.
 * @param hdrlen	Upon return will indicate the size of RTP packet header
 *
 * @return		PJ_SUCCESS if successfull.
 */
PJ_DECL(pj_status_t) pjmedia_rtp_encode_rtp( pjmedia_rtp_session *ses, 
					     int pt, int m,
					     int payload_len, int ts_len,
					     const void **rtphdr, 
					     int *hdrlen );

/**
 * This function decodes incoming packet into RTP header and payload.
 * The decode function is guaranteed to point the payload to the correct 
 * position regardless of any options present in the RTP packet.
 *
 * @param ses		The session.
 * @param pkt		The received RTP packet.
 * @param pkt_len	The length of the packet.
 * @param hdr		Upon return will point to the location of the RTP header
 *			inside the packet.
 * @param payload	Upon return will point to the location of the
 *			payload inside the packet.
 * @param payloadlen	Upon return will indicate the size of the payload.
 *
 * @return		PJ_SUCCESS if successfull.
 */
PJ_DECL(pj_status_t) pjmedia_rtp_decode_rtp( pjmedia_rtp_session *ses, 
					     const void *pkt, int pkt_len,
					     const pjmedia_rtp_hdr **hdr,
					     const void **payload,
					     unsigned *payloadlen);

/**
 * Call this function everytime an RTP packet is received to check whether 
 * the packet can be received and to let the RTP session performs its internal
 * calculations.
 *
 * @param ses	    The session.
 * @param hdr	    The RTP header of the incoming packet.
 * @param seq_st    Optional structure to receive the status of the RTP packet
 *		    processing.
 */
PJ_DECL(void) pjmedia_rtp_session_update( pjmedia_rtp_session *ses, 
					  const pjmedia_rtp_hdr *hdr,
					  pjmedia_rtp_status *seq_st);


/*
 * INTERNAL:
 */

/** 
 * Internal function for creating sequence number control, shared by RTCP 
 * implementation. 
 *
 * @param seq_ctrl  The sequence control instance.
 * @param seq	    Sequence number to initialize.
 */
void pjmedia_rtp_seq_init(pjmedia_rtp_seq_session *seq_ctrl, 
			  pj_uint16_t seq);


/** 
 * Internal function update sequence control, shared by RTCP implementation.
 *
 * @param seq_ctrl	The sequence control instance.
 * @param seq		Sequence number to update.
 * @param seq_status	Optional structure to receive additional information 
 *			about the packet.
 */
void pjmedia_rtp_seq_update( pjmedia_rtp_seq_session *seq_ctrl, 
			     pj_uint16_t seq,
			     pjmedia_rtp_status *seq_status);

/**
 * @}
 */

PJ_END_DECL


#endif	/* __PJMEDIA_RTP_H__ */