SDPOPS Module

Daniel-Constantin Mierla

Edited by

Daniel-Constantin Mierla


Table of Contents

1. Admin Guide
1. Overview
2. Dependencies
2.1. Kamailio Modules
2.2. External Libraries or Applications
3. Parameters
4. Functions
4.1. sdp_remove_codecs_by_id(list [, mtype])
4.2. sdp_remove_codecs_by_name(list [, mtype])
4.3. sdp_remove_line_by_prefix(string [, mtype])
4.4. sdp_keep_codecs_by_id(list [, mtype])
4.5. sdp_keep_codecs_by_name(list [, mtype])
4.6. sdp_with_media(type)
4.7. sdp_with_active_media(type)
4.8. sdp_remove_media(type)
4.9. sdp_with_transport(type)
4.10. sdp_with_transport_like(type)
4.11. sdp_transport(pv)
4.12. sdp_remove_transport(type)
4.13. sdp_with_codecs_by_id(list)
4.14. sdp_with_codecs_by_name(list)
4.15. sdp_print(level)
4.16. sdp_get(avpvar)
4.17. sdp_content([sloppy])
4.18. sdp_with_ice()
4.19. sdp_get_line_startswith(avpvar, string)

List of Examples

1.1. sdp_remove_codecs_by_id usage
1.2. sdp_remove_codecs_by_name usage
1.3. sdp_remove_line_by_prefix usage
1.4. sdp_keep_codecs_by_id usage
1.5. sdp_keep_codecs_by_name usage
1.6. sdp_with_media usage
1.7. sdp_with_active_media usage
1.8. sdp_remove_media usage
1.9. sdp_with_transport usage
1.10. sdp_with_transport_like usage
1.11. sdp_transport usage
1.12. sdp_remove_transport usage
1.13. sdp_with_codecs_by_id usage
1.14. sdp_with_codecs_by_name usage
1.15. sdp_print usage
1.16. sdp_get usage
1.17. sdp_content usage
1.18. sdp_with_ice usage
1.19. sdp_get_line_startswith usage

Chapter 1. Admin Guide

1. Overview

This module provides functions for checking and managing the SDP payloads of SIP messages.

Examples of functions this module offers: remove codecs from SDP, check the media stream types and return attributes of SDP document. For the full list of the features provided by this module and the implementation state, please read the list of exported functions.

2. Dependencies

2.1. Kamailio Modules

The following modules must be loaded before this module:

  • none.

2.2. External Libraries or Applications

The following libraries or applications must be installed before running Kamailio with this module loaded:

  • None

3. Parameters

The module does not export any config parameters yet.

4. Functions

4.1.  sdp_remove_codecs_by_id(list [, mtype])

Remove the codecs provided in the parameter 'list' from all media streams found in SDP payload. The parameter 'list' must be one item or a comma separated list of numeric codec IDs. The parameter can be a static string or a variable holding the list of numeric codec IDs.

This function can be used from ANY_ROUTE.

Example 1.1. sdp_remove_codecs_by_id usage

...
# remove PCMU
sdp_remove_codecs_by_id("0");
# remove PCMU, PCMA and GSM
sdp_remove_codecs_by_id("0,8,3");
sdp_remove_codecs_by_id("17", "audio");
sdp_remove_codecs_by_id("23", "video");
...

4.2.  sdp_remove_codecs_by_name(list [, mtype])

Remove the codecs provided in the parameter 'list' from all media streams found in SDP payload. The parameter 'list' must be one item or a comma separated list of codec names. The parameter can be a static string or a variable holding the list of codec names.

Optional parameter mtype can be provided to apply the operations only to the streams matching m=mtype.

This function can be used from ANY_ROUTE.

Example 1.2. sdp_remove_codecs_by_name usage

...
# remove PCMU
sdp_remove_codecs_by_name("PCMU");
# remove PCMU, PCMA and GSM
sdp_remove_codecs_by_name("PCMU,PCMA,GSM");
...

4.3.  sdp_remove_line_by_prefix(string [, mtype])

Remove all SDP attribute lines beginning with 'string' in all media streams.

Optional parameter mtype can be provided to apply the operations only to the streams matching m=mtype.

This function can be used from ANY_ROUTE.

Example 1.3. sdp_remove_line_by_prefix usage

...
if ($si == "2001:DB8::8:800:200C:417A"
        and ( has_body("application/sdp") or has_body("multipart/mixed")))
{
    xlog("L_INFO", "Cleaning ugly SDP from $si\n");
    sdp_remove_codecs_by_name("X-NSE");
    sdp_remove_line_by_prefix("a=X-");
}

...

4.4.  sdp_keep_codecs_by_id(list [, mtype])

Keep only the codecs provided in the parameter 'list' from all media streams found in SDP payload. The parameter 'list' must be one item or a comma separated list of numeric codec IDs. The parameter can be a static string or a variable holding the list of numeric codec IDs.

Optional parameter mtype can be provided to apply the operations only to the streams matching m=mtype.

This function can be used from ANY_ROUTE.

Example 1.4. sdp_keep_codecs_by_id usage

...
# keep only PCMU
sdp_keep_codecs_by_id("0");
# keep PCMU, PCMA and GSM in audio stream
sdp_keep_codecs_by_id("0,8,3", "audio");
...

4.5.  sdp_keep_codecs_by_name(list [, mtype])

Keep only the codecs provided in the parameter 'list' from all media streams found in SDP payload. The parameter 'list' must be one or a comma separated list of codec names. The parameter can be a static string or a variable holding the list of codec names.

Note that you have to explicitly keep 'telephone-event' in the list of names if you want to keep DTMF attributes.

Optional parameter mtype can be provided to apply the operations only to the streams matching m=mtype.

This function can be used from ANY_ROUTE.

Example 1.5. sdp_keep_codecs_by_name usage

...
# keep only PCMU
sdp_keep_codecs_by_name("PCMU");
# keep PCMU, PCMA and GSM
sdp_keep_codecs_by_name("PCMU,PCMA,GSM");
...

4.6.  sdp_with_media(type)

Return true of the SDP has 'media=type ...' line. Useful to check the content of the RTP sessions, such as 'audio' or 'video'. The parameter can be static string or variable holding the media type.

This function can be used from ANY_ROUTE.

Example 1.6. sdp_with_media usage

...
# check for video stream
if(sdp_with_media("video"))
{
    # the session has a video stream
}
...

4.7.  sdp_with_active_media(type)

Return true of the SDP has 'media=type ...' line and the media is active. Useful to check the content of the RTP sessions, such as 'audio' or 'video'. Active media means the port is non-zero and the direction is not "inactive" The parameter can be static string or variable holding the media type.

This function can be used from ANY_ROUTE.

Example 1.7. sdp_with_active_media usage

...
# check for active video stream
if(sdp_with_active_media("video"))
{
    # the session has an active video stream
}
...

4.8.  sdp_remove_media(type)

Remove the streams that match on 'm=type ...' line. The parameter can be static string or variable holding the media type.

Note: If this is executed on a request, the callee should reply without the Media too. However, RFC 3264 mandates, that the reply should contain the exact same number of "m=" lines as the request.

 

6 Generating the Answer

[...]

For each "m=" line in the offer, there MUST be a corresponding "m=" line in the answer. The answer MUST contain exactly the same number of "m=" lines as the offer. This allows for streams to be matched up based on their order. This implies that if the offer contained zero "m=" lines, the answer MUST contain zero "m=" lines.

 
  --RFC 3264

So this may not work with all Endpoints, especially if they follow RFC 3264 precisely (e.g. JSSIP).

This function can be used from ANY_ROUTE.

Example 1.8. sdp_remove_media usage

...
# remove video stream
sdp_remove_media("video");
...

4.9.  sdp_with_transport(type)

Return true of the SDP has 'media=media port type ...' line. Useful to check the transport of the RTP sessions, such as 'RTP/AVP', 'RTP/SAVP', 'RTP/SAVPF' or 'UDP/TLS/RTP/SAVPF'. The parameter can be static string or variable holding the transport type. The function does an exact match of the strings.

This function can be used from ANY_ROUTE.

Example 1.9. sdp_with_transport usage

...
# check for RTP/SAVP stream
if(sdp_with_transport("UDP/TLS/RTP/SAVPF"))
{
    # the session has a UDP/TLS/RTP/SAVPF stream
}
...

4.10.  sdp_with_transport_like(type)

Returns true if the SDP has 'media=media port type ...' line, where type contains the string in the parameter. The parameter can be static string or variable holding a string.

This function can be used from ANY_ROUTE.

Example 1.10. sdp_with_transport_like usage

...
# check for SAVPF stream
if(sdp_with_transport_like("SAVPF"))
{
    # the session has a SAVPF stream, e.g., RTP/SAVPF or UDP/TLS/RTP/SAVPF
}
...

4.11.  sdp_transport(pv)

Assigns common media transport (if any) of 'm' lines to pv argument. Returns 1 if common media transport was found, -2 if there was no common media transport, and -1 in case of error.

This function can be used from ANY_ROUTE.

Example 1.11. sdp_transport usage

...
sdp_transport("$avp(caller_rtp_transport)");
...

4.12.  sdp_remove_transport(type)

Remove the streams that match on 'm=media port type ...' line. The parameter can be static string or variable holding the transport type.

This function can be used from ANY_ROUTE.

Example 1.12. sdp_remove_transport usage

...
# remove stream with transport RTP/AVP
sdp_remove_transport("RTP/AVP");
...

4.13.  sdp_with_codecs_by_id(list)

Returns true if any of the codecs provided in the parameter 'list' from all media streams is found in SDP payload. The parameter 'list' must be one or a comma separated list of numeric codec IDs. The parameter can be a static string or a variable holding the list of numeric codec IDs.

This function can be used from ANY_ROUTE.

Example 1.13. sdp_with_codecs_by_id usage

...
# test for PCMU
if(sdp_with_codecs_by_id("0")) { ... }
# test for PCMU, PCMA or GSM
if(sdp_with_codecs_by_id("0,8,3")) { ... }
...

4.14.  sdp_with_codecs_by_name(list)

Returns true if any of the codecs provided in the parameter 'list' from all media streams is found in SDP payload. The parameter 'list' must be one item or a comma separated list of codec names. The parameter can be a static string or a variable holding the list of codec names.

This function can be used from ANY_ROUTE.

Example 1.14. sdp_with_codecs_by_name usage

...
# test for PCMU
if(sdp_with_codecs_by_name("PCMU")) { ... }
# test for PCMU, PCMA or GSM
if(sdp_with_codecs_by_name("PCMU,PCMA,GSM")) { ... }
...

4.15.  sdp_print(level)

Print the SDP internal structure to log 'level'. The parameter can be static integer or variable holding the integer value of the log level.

This function can be used from ANY_ROUTE.

Example 1.15. sdp_print usage

...
# print the SDP
sdp_print("1");
...

4.16.  sdp_get(avpvar)

Store the SDP part of message body in an AVP. Return 1 if SDP is found, -1 on error and -2 if there is no SDP part in the message body.

This function can be used from ANY_ROUTE.

Example 1.16. sdp_get usage

...
sdp_get("$avp(sdp)");
...

4.17.  sdp_content([sloppy])

Return true if the SIP message has SDP body or a SDP part in body. If an argument is given, the function does not parse message body, but returns true if Content-Type is "application/sdp" or if that string exists in "multipart/mixed" body.

This function can be used from ANY_ROUTE.

Example 1.17. sdp_content usage

...
if(sdp_content()) {
    ...
}
...

4.18.  sdp_with_ice()

Return true if the SIP message has SDP body that contains ICE candidate attribute(s).

This function can be used from ANY_ROUTE.

Example 1.18. sdp_with_ice usage

...
if(sdp_with_ice()) {
    ...
}
...

4.19.  sdp_get_line_startswith(avpvar, string)

Store the search part of SDP body message with line beginning with 'string' in an AVP. Return 1 if 'string' is found in SDP, -1 on error and -2 if there is no SDP part in the message body. The second parameter can contain pseudo-variables.

This function can be used from ANY_ROUTE.

Example 1.19. sdp_get_line_startswith usage

...
if(sdp_get_line_startswith("$avp(mline)", "m=")) {
	xlog("m-line: $avp(mline)\n");
}
...