I-Frames

When video streams initialize, devices transmit video packets called I-frames (reference frames) that contain information to display a complete picture.

Subsequent video packets, known as P-frames, are smaller and not as complete to consume less bandwidth. Due to packet loss, jitter, or corruption, devices occasionally need to make multiple requests for a complete I-frame in order to reset the full frame, after which devices can revert to P-frame updates.

You can set parameters to control an I-frame request. The following table indicates parameter dependencies and messaging behavior when setting an I-frame request method.

Table 1. I-Frame Parameter Dependencies

video.forceRtcpVideoCodecControl

video.dynamicControlMethod

voIpProt.SDP.offer.rtcpVideoCodecControl

Behavior when requesting video I-frame updates

0

0 (n/a)

0

Only SIP INFO messages are sent. No RTCP-FB is offered in SDP.

0

1 (n/a)

0

Only SIP INFO messages are sent. No RTCP-FB is offered in SDP.

0

0 (n/a)

1

RTCP-FB is offered in SDP. If SDP responses do not contain the required RTCP-FB attribute, then only SIP INFO requests are used.

0

1 (n/a)

1

RTCP-FB is offered in SDP. If SDP responses do not contain the required RTCP-FB attribute, then only SIP INFO requests are used.

1

0

0

The SDP attribute a=rtcp-fb is not included in SDP offers. Both RTCP-FB and SIP INFO messages are attempted.

1

1

0

The SDP attribute a=rtcp-fb is not included in SDP offers. Both RTCP-FB and SIP INFO messages are attempted. If no RTCP-FB messages are received, only SIP INFO messages are sent. If no response is received for SIP INFO messages then, again, both RTCP-FB and SIP INFO messages are attempted.

1

0

1

RTCP-FB is offered in SDP. Even if the SDP response does not include an accepted a=rtcp-fb attribute both RTCP-FB and SIP INFO messages are sent.

1

1

1

RTCP-FB is offered in SDP. Even if the SDP response does not include an accepted a=rtcp-fb attribute both RTCP-FB and SIP INFO messages are sent initially. If no RTCP-FB response is received, only SIP INFO messages are sent afterwards.