Session Description API Overview

The function calls that make up the SDP API are provided by the shared object libcommputil.so.1. The functions in this shared object parse the SDP description and check the description's syntax.

The sdp.h header file defines the sdp_session_t structure, which contains the following members:

typedef    struct sdp_session {
   int             sdp_session_version; /* SDP session verstion */
   int             s_version;           /* SDP version field */
   sdp_origin_t    *s_origin;           /* SDP origin field */
   char            *s_name;             /* SDP name field */
   char            *s_info;             /* SDP info field */
   char            *s_uri;              /* SDP uri field */
   sdp_list_t      *s_email;            /* SDP email field */
   sdp_list_t      *s_phone;            /* SDP phone field */
   sdp_conn_t      *s_conn;             /* SDP connection field */
   sdp_bandwidth_t *s_bw;               /* SDP bandwidth field */
   sdp_time_t      *s_time;             /* SDP time field */
   sdp_zone_t      *s_zone;             /* SDP zone field */
   sdp_key_t       *s_key;              /* SDP key field */
   sdp_attr_t      *s_attr;             /* SDP attribute field */
   sdp_media_t     *s_media;            /* SDP media field */
} sdp_session_t;

The sdp_session_version member tracks the version of the structure. The initial value of the sdp_session_version member is SDP_SESSION_VERSION_1.

The sdp_origin_t structure contains the following members:

typedef struct sdp_origin {
   char        *o_username;  /* username of the originating host */
   uint64_t    o_id;         /* session id */
   uint64_t    o_version;    /* version number of this session */
                             /* description */
   char        *o_nettype;   /* type of network */
   char        *o_addrtype;  /* type of the address */
   char        *o_address;   /* address of the machine from which */
                             /* session was created */
} sdp_origin_t;

The sdp_conn_t structure contains the following members:

typedef struct sdp_conn {
   char    *c_nettype;         /* type of network */
   char    *c_addrtype;        /* type of the address */
   char    *c_address;         /* unicast-address or multicast */
                               /* address */
   int     c_addrcount;        /* number of addresses (case of */
                               /* multicast address with layered */
                               /* encodings */
   struct  sdp_conn *c_next;   /* pointer to next connection */
                               /* structure; there could be several */
                               /* connection fields in SDP description */
   uint8_t c_ttl;              /* TTL value for IPV4 multicast address */
} sdp_conn_t;

The sdp_bandwidth_t structure contains the following members:

typedef struct sdp_bandwidth {
   char                  *b_type; /* info needed to interpret b_value */
   uint64_t              b_value; /* bandwidth value */
   struct sdp_bandwidth  *b_next; /* pointer to next bandwidth structure*/
                                  /* (there could be several bandwidth */
                                  /* fields in SDP description */
} sdp_bandwidth_t;

The sdp_list_t structure is a linked list of void pointers. This structure holds SDP fields. In the case of SDP structure fields such as email and phone, the void pointers point to character buffers. Use this structure to hold information in cases where the number of elements is not predefined, as in the case of repeated offset fields, where the void pointer holds integer values.

The sdp_list_t structure contains the following members:

typedef struct sdp_list {
   void            *value; /* string values in case of email, phone and */
                           /* format (in media field) or integer values */
                           /* in case of offset (in repeat field) */
   struct sdp_list *next;  /* pointer to the next node in the list */
} sdp_list_t;

The sdp_repeat_t structure will always be part of the time structure sdp_time_t. The repeat field does not appear alone in SDP descriptions and is always associated with the time field.

The sdp_repeat_t structure contains the following members:

typedef struct sdp_repeat {
   uint64_t          r_interval; /* repeat interval, e.g. 86400 seconds */
                                 /* (1 day) */
   uint64_t          r_duration; /* duration of session, e.g. 3600 */
                                 /* seconds (1 hour) */
   sdp_list_t        *r_offset;  /* linked list of offset values; each */
                                 /* represents offset from start-time */
                                 /* in the SDP time field */
   struct sdp_repeat *r_next;    /* pointer to next repeat structure; */
                                 /* there could be several repeat */
                                 /* fields in the SDP description */

The sdp_time_t structure contains the following members:

typedef struct sdp_time {
   uint64_t         t_start;   /* start-time for a session */
   uint64_t         t_stop;    /* end-time for a session */
   sdp_repeat_t     *t_repeat; /* points to the SDP repeat field */
   struct sdp_time  *t_next;   /* pointer to next time field; there */
                               /* could there could be several time */
                               /* fields in SDP description */
} sdp_time_t;

The sdp_zone_t structure contains the following members:

typedef struct sdp_zone {
   uint64_t        z_time;    /* base time */
   char            *z_offset; /* offset added to z_time to determine */
                              /* session time; mainly used for daylight */
                              /* saving time conversions */
   struct sdp_zone *z_next;   /* pointer to next zone field; there */
                              /* could be several <adjustment-time> */
                              /* <offset> pairs within a zone field */
} sdp_zone_t;

The sdp_key_t structure contains the following members:

typedef struct sdp_key {
   char   *k_method;   /* key type */
   char   *k_enckey;   /* encryption key */
 } sdp_key_t;

The sdp_attr_t structure contains the following members:

typedef struct sdp_attr {
   char            *a_name;  /* name of the attribute */
   char            *a_value; /* value of the attribute */
   struct sdp_attr *a_next;  /* pointer to the next attribute */
                             /* structure; there could be several */
                             /* attribute fields within SDP description */
} sdp_attr_t;

The sdp_media_t structure contains the following members:

typedef struct sdp_media {
   char              *m_name;     /* name of the media such as "audio", */
                                  /* "video", "message" */
   uint_t            m_port;      /* transport layer port information */
   int               m_portcount; /* number of ports in case of */
                                  /* hierarchically encoded streams */
   char              *m_proto;    /* transport protocol */
   sdp_list_t        *m_format;   /* media format description */
   char              *m_info;     /* media info field */
   sdp_conn_t        *m_conn;     /* media connection field */
   sdp_bandwidth_t   *m_bw;       /* media bandwidth field */
   sdp_key_t         *m_key;      /* media key field */
   sdp_attr_t        *m_attr;     /* media attribute field */
   struct sdp_media  *m_next;     /* pointer to next media structure; */
                                  /* there could be several media */
                                  /* sections in SDP description */
   sdp_session_t     *m_session;  /* pointer to the session structure */
} sdp_media_t;