ROHC compression/decompression library
Functions | Variables
c_rtp.c File Reference

ROHC compression context for the RTP profile. More...

#include "c_rtp.h"
#include "rohc_traces.h"
#include <assert.h>
Include dependency graph for c_rtp.c:

Functions

int rtp_code_static_rtp_part (struct c_context *context, const unsigned char *next_header, unsigned char *dest, int counter)
 Build the static part of the UDP/RTP headers.
int rtp_code_dynamic_rtp_part (struct c_context *context, const unsigned char *next_header, unsigned char *dest, int counter)
 Build the dynamic part of the UDP/RTP headers.
int rtp_changed_rtp_dynamic (struct c_context *context, const struct udphdr *udp)
 Check if the dynamic part of the UDP/RTP headers changed.
int c_rtp_create (struct c_context *context, const struct ip_packet ip)
 Create a new RTP context and initialize it thanks to the given IP/UDP/RTP packet.
void c_rtp_destroy (struct c_context *context)
 Destroy the RTP context.
int c_rtp_check_context (struct c_context *context, struct ip_packet ip)
 Check if the IP/UDP/RTP packet belongs to the context.
int c_rtp_encode (struct c_context *context, const struct ip_packet ip, int packet_size, unsigned char *dest, int dest_size, int *payload_offset)
 Encode an IP/UDP/RTP packet according to a pattern decided by several different factors.
void rtp_decide_state (struct c_context *context)
 Decide the state that should be used for the next packet compressed with the ROHC RTP profile.

Variables

int rtp_ports [] = { RTP_PORTS, 0 }
 List of UDP ports which are associated with RTP streams.
struct c_profile c_rtp_profile
 Define the compression part of the RTP profile as described in the RFC 3095.

Detailed Description

ROHC compression context for the RTP profile.

Author:
David Moreau from TAS
Didier Barvaux <didier.barvaux@toulouse.viveris.com>

Function Documentation

int c_rtp_check_context ( struct c_context *  context,
struct ip_packet  ip 
)

Check if the IP/UDP/RTP packet belongs to the context.

Conditions are:

  • the number of IP headers must be the same as in context
  • IP version of the two IP headers must be the same as in context
  • IP packets must not be fragmented
  • the source and destination addresses of the two IP headers must match the ones in the context
  • the transport protocol must be UDP
  • the source and destination ports of the UDP header must match the ones in the context
  • IPv6 only: the Flow Label of the two IP headers must match the ones the context
  • the SSRC field of the RTP header must match the one in the context

All the context but the last one are done by the c_udp_check_context() function.

This function is one of the functions that must exist in one profile for the framework to work.

Parameters:
contextThe compression context
ipThe IP/UDP/RTP packet to check
Returns:
1 if the IP/UDP/RTP packet belongs to the context, 0 if it does not belong to the context and -1 if an error occurs
See also:
c_udp_check_context

References c_udp_check_context(), ip_get_inner_packet(), ip_get_next_layer(), ip_get_protocol(), sc_rtp_context::old_rtp, rohc_debugf, c_context::specific, c_generic_context::specific, and rtphdr::ssrc.

int c_rtp_create ( struct c_context *  context,
const struct ip_packet  ip 
)

Create a new RTP context and initialize it thanks to the given IP/UDP/RTP packet.

This function is one of the functions that must exist in one profile for the framework to work.

Parameters:
contextThe compression context
ipThe IP/UDP/RTP packet given to initialize the new context
Returns:
1 if successful, 0 otherwise

References c_create_sc(), c_create_wlsb(), c_generic_create(), c_generic_destroy(), C_WINDOW_WIDTH, c_generic_context::code_dynamic_part, c_generic_context::code_static_part, c_generic_context::code_UO_packet_head, c_generic_context::code_UO_packet_tail, c_generic_context::compute_crc_dynamic, c_generic_context::compute_crc_static, c_generic_context::decide_state, c_generic_context::init_at_IR, ip_get_inner_packet(), ip_get_next_layer(), ip_get_protocol(), rtp_tmp_variables::m_set, c_generic_context::next_header_len, c_generic_context::next_header_proto, rtp_tmp_variables::nr_ts_bits, sc_rtp_context::old_rtp, sc_rtp_context::old_udp, rohc_debugf, rtp_code_dynamic_rtp_part(), rtp_code_static_rtp_part(), rtp_compute_crc_dynamic(), rtp_compute_crc_static(), rtp_decide_state(), sc_rtp_context::rtp_pt_change_count, rtp_tmp_variables::rtp_pt_changed, rtp_tmp_variables::send_rtp_dynamic, c_context::specific, c_generic_context::specific, rtp_tmp_variables::timestamp, sc_rtp_context::tmp_variables, sc_rtp_context::ts_sc, rtp_tmp_variables::ts_send, sc_rtp_context::ts_window, sc_rtp_context::udp_checksum_change_count, and udp_code_UO_packet_tail().

void c_rtp_destroy ( struct c_context *  context)

Destroy the RTP context.

This function is one of the functions that must exist in one profile for the framework to work.

Parameters:
contextThe RTP compression context to destroy

References c_destroy_sc(), c_generic_destroy(), c_context::specific, c_generic_context::specific, and sc_rtp_context::ts_sc.

int c_rtp_encode ( struct c_context *  context,
const struct ip_packet  ip,
int  packet_size,
unsigned char *  dest,
int  dest_size,
int *  payload_offset 
)

Encode an IP/UDP/RTP packet according to a pattern decided by several different factors.

Parameters:
contextThe compression context
ipThe IP packet to encode
packet_sizeThe length of the IP packet to encode
destThe rohc-packet-under-build buffer
dest_sizeThe length of the rohc-packet-under-build buffer
payload_offsetThe offset for the payload in the IP packet
Returns:
The length of the created ROHC packet

References c_generic_encode(), ip_get_inner_packet(), ip_get_next_layer(), ip_get_protocol(), sc_rtp_context::old_rtp, sc_rtp_context::old_udp, PACKET_IR, PACKET_IR_DYN, generic_tmp_variables::packet_type, rohc_debugf, rtp_changed_rtp_dynamic(), rtp_tmp_variables::send_rtp_dynamic, c_context::specific, c_generic_context::specific, rtp_tmp_variables::timestamp, rtphdr::timestamp, sc_rtp_context::tmp_variables, and c_generic_context::tmp_variables.

int rtp_changed_rtp_dynamic ( struct c_context *  context,
const struct udphdr *  udp 
)

Check if the dynamic part of the UDP/RTP headers changed.

Parameters:
contextThe compression context
udpThe UDP/RTP headers
Returns:
The number of UDP/RTP fields that changed

References rtphdr::cc, rtphdr::m, rtp_tmp_variables::m_set, MAX_IR_COUNT, sc_rtp_context::old_rtp, sc_rtp_context::old_udp, rtphdr::pt, rohc_debugf, sc_rtp_context::rtp_pt_change_count, rtp_tmp_variables::rtp_pt_changed, c_context::specific, c_generic_context::specific, rtphdr::ssrc, rtphdr::timestamp, rtp_tmp_variables::timestamp, sc_rtp_context::tmp_variables, and sc_rtp_context::udp_checksum_change_count.

Referenced by c_rtp_encode().

int rtp_code_dynamic_rtp_part ( struct c_context *  context,
const unsigned char *  next_header,
unsigned char *  dest,
int  counter 
)

Build the dynamic part of the UDP/RTP headers. 


 Dynamic part of UDP header (5.7.7.5):

    +---+---+---+---+---+---+---+---+
 1  /           Checksum            /   2 octets
    +---+---+---+---+---+---+---+---+

 Dynamic part of RTP header (5.7.7.6):

    +---+---+---+---+---+---+---+---+
 2  |  V=2  | P | RX|      CC       |  (RX is NOT the RTP X bit)
    +---+---+---+---+---+---+---+---+
 3  | M |            PT             |
    +---+---+---+---+---+---+---+---+
 4  /      RTP Sequence Number      /  2 octets
    +---+---+---+---+---+---+---+---+
 5  /   RTP Timestamp (absolute)    /  4 octets
    +---+---+---+---+---+---+---+---+
 6  /      Generic CSRC list        /  variable length
    +---+---+---+---+---+---+---+---+
 7  : Reserved  | X |  Mode |TIS|TSS:  if RX = 1
    +---+---+---+---+---+---+---+---+
 8  :         TS_Stride             :  1-4 octets, if TSS = 1
    +---+---+---+---+---+---+---+---+
 9  :         Time_Stride           :  1-4 octets, if TIS = 1
    +---+---+---+---+---+---+---+---+

Parts 6 & 9 are not supported yet. The TIS flag in part 7 is not supported.

Parameters:
contextThe compression context
next_headerThe UDP/RTP headers
destThe rohc-packet-under-build buffer
counterThe current position in the rohc-packet-under-build buffer
Returns:
The new position in the rohc-packet-under-build buffer

References c_bytesSdvl(), c_encodeSdvl(), rtphdr::cc, rtphdr::extension, get_ts_stride(), INIT_STRIDE, INIT_TS, is_ts_constant(), rtphdr::m, c_context::mode, PACKET_IR, generic_tmp_variables::packet_type, rtphdr::padding, rtphdr::pt, rohc_debugf, ROHC_TRUE, sc_rtp_context::rtp_pt_change_count, SEND_SCALED, rtphdr::sn, c_context::specific, c_generic_context::specific, ts_sc_comp::state, rtphdr::timestamp, c_generic_context::tmp_variables, sc_rtp_context::ts_sc, sc_rtp_context::udp_checksum_change_count, and rtphdr::version.

Referenced by c_rtp_create().

int rtp_code_static_rtp_part ( struct c_context *  context,
const unsigned char *  next_header,
unsigned char *  dest,
int  counter 
)

Build the static part of the UDP/RTP headers. 


 Static part of UDP header (5.7.7.5):

    +---+---+---+---+---+---+---+---+
 1  /          Source Port          /   2 octets
    +---+---+---+---+---+---+---+---+
 2  /       Destination Port        /   2 octets
    +---+---+---+---+---+---+---+---+

 Static part of RTP header (5.7.7.6):

    +---+---+---+---+---+---+---+---+
 3  /             SSRC              /   4 octets
    +---+---+---+---+---+---+---+---+

Parts 1 & 2 are done by the udp_code_static_udp_part() function. Part 3 is done by this function.

Parameters:
contextThe compression context
next_headerThe UDP/RTP headers
destThe rohc-packet-under-build buffer
counterThe current position in the rohc-packet-under-build buffer
Returns:
The new position in the rohc-packet-under-build buffer
See also:
udp_code_static_udp_part

References rohc_debugf, rtphdr::ssrc, and udp_code_static_udp_part().

Referenced by c_rtp_create().

void rtp_decide_state ( struct c_context *  context)

Decide the state that should be used for the next packet compressed with the ROHC RTP profile.

The three states are:

  • Initialization and Refresh (IR),
  • First Order (FO),
  • Second Order (SO).
Parameters:
contextThe compression context

References change_state(), decide_state(), FO, INIT_STRIDE, INIT_TS, IR, is_ts_constant(), MAX_IR_COUNT, rohc_debugf, rtp_tmp_variables::send_rtp_dynamic, c_context::specific, c_generic_context::specific, ts_sc_comp::state, c_context::state, sc_rtp_context::tmp_variables, sc_rtp_context::ts_sc, and sc_rtp_context::udp_checksum_change_count.

Referenced by c_rtp_create().

Variable Documentation

struct c_profile c_rtp_profile
Initial value:
{
        IPPROTO_UDP,         
        rtp_ports,           
        ROHC_PROFILE_RTP,    
        "alpha",             
        "RTP / Compressor",  
        c_rtp_create,        
        c_rtp_destroy,
        c_rtp_check_context,
        c_rtp_encode,
        c_generic_feedback,
}

Define the compression part of the RTP profile as described in the RFC 3095.

int rtp_ports[] = { RTP_PORTS, 0 }

List of UDP ports which are associated with RTP streams.

Generated on Mon May 20 2013 18:18:02 for ROHC compression/decompression library by   doxygen 1.7.6.1