Add PJSIP configuration to optimize the size of outgoing SIP messages

[bennylp]

When ICE is enabled, outgoing SIP messages can be bigger than 1500 bytes. This would cause problem with NAT/routers, so it would be desirable to trim outgoing messages down to minimal.

Few ideas that can be done to reduce the SIP message size:

• use compact form of SIP headers
• remove optional headers such as Allow
• don't use User-Agent header

[bennylp]

More ideas:

• don't include SDP rtpmap attribute for static payload types.

[bennylp]

r1389:
Added configuration to send SIP headers in their compact forms.

[bennylp]

Replying to bennylp:

r1389:
Added configuration to send SIP headers in their compact forms.

This can be done in two ways:

1) Using compile time settings in config_site.h:

 #define PJSIP_ENCODE_SHORT_HNAME 1

2) Using run-time setting:

   extern pj_bool_t pjsip_use_compact_form;
 
   // enable compact form
   pjsip_use_compact_form = PJ_TRUE;

[bennylp]

In r1390, added configuration to suppress the inclusion of Allow header in outgoing INVITE. This can be done in two ways:

1) Using compile-time setting in config_site.h:

 #define PJSIP_INCLUDE_ALLOW_HDR_IN_DLG 0

2) Using run-time setting:

   extern pj_bool_t pjsip_include_allow_hdr_in_dlg;
 
   // do not transmit Allow header
   pjsip_include_allow_hdr_in_dlg = PJ_FALSE;

[bennylp]

In r1391, added configuration to control whether SDP rtpmap attribute should be included for static payload types. Default is yes.

Application can change this setting in two ways:

1) Using compile-time setting in config_site.h:

 #define PJMEDIA_ADD_RTPMAP_FOR_STATIC_PT 0

2) Using run-time setting:

    extern pj_bool_t pjmedia_add_rtpmap_for_static_pt;

    // Do not include rtpmap for static payload types (<96)
    pjmedia_add_rtpmap_for_static_pt = PJ_FALSE;

[bennylp]

In r1393, added compile time setting to disable RTCP advertisement in SDP, by setting in config_site.h:

 #define PJMEDIA_ADVERTISE_RTCP 0

When ICE is used, disabling RTCP will reduce SDP by about 65 bytes per network interface. Note that this requires ticket #344 to be applied.

[bennylp]

Summary of the size reductions:

• With compact form of the header: 50 bytes
• Suppressing Allow header: 86 bytes
• Not putting rtpmap for static payload types: 65 bytes
• Not advertising SDP, when ICE is used with three candidates: 235 bytes

Total potential size reduction: 436 bytes

Application can also suppress the User-Agent header for another ~36 bytes reduction.

[bennylp]

Replying to bennylp:

Summary of the size reductions:

• Not advertising SDP, when ICE is used with three candidates: 235 bytes

This should read Not advertising RTCP .. rather than Not advertising SDP ...

Application can also suppress the User-Agent header for another ~36 bytes reduction.

PJSUA-LIB application can do this by setting the pjsua_config.user_agent field.