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diff --git a/third_party/libwebrtc/docs/native-code/rtp-hdrext/transport-wide-cc-02/README.md b/third_party/libwebrtc/docs/native-code/rtp-hdrext/transport-wide-cc-02/README.md new file mode 100644 index 0000000000..8dc82612c7 --- /dev/null +++ b/third_party/libwebrtc/docs/native-code/rtp-hdrext/transport-wide-cc-02/README.md @@ -0,0 +1,62 @@ +# Transport-Wide Congestion Control + +This RTP header extension is an extended version of the extension defined in +<https://tools.ietf.org/html/draft-holmer-rmcat-transport-wide-cc-extensions-01> + +**Name:** "Transport-wide congenstion control 02" + +**Formal name:** +<http://www.webrtc.org/experiments/rtp-hdrext/transport-wide-cc-02> + +**Status:** This extension is defined here to allow for experimentation. Once +experience has shown that it is useful, we intend to make a proposal based on +it for standardization in the IETF. + +The original extension defines a transport-wide sequence number that is used in +feedback packets for congestion control. The original implementation sends these +feedback packets at a periodic interval. The extended version presented here has +two changes compared to the original version: +* Feedback is sent only on request by the sender, therefore, the extension has + two optional bytes that signals that a feedback packet is requested. +* The sender determines if timing information should be included or not in the + feedback packet. The original version always include timing information. + +Contact <kron@google.com> or <sprang@google.com> for more info. + +## RTP header extension format + +### Data layout overview +Data layout of transport-wide sequence number + 1-byte header + 2 bytes of data: + + 0 1 2 + 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | ID | L=1 |transport-wide sequence number | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + +Data layout of transport-wide sequence number and optional feedback request + 1-byte header + 4 bytes of data: + + 0 1 2 3 + 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + | ID | L=3 |transport-wide sequence number |T| seq count | + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ + |seq count cont.| + +-+-+-+-+-+-+-+-+ + +### Data layout details +The data is written in the following order, +* transport-wide sequence number (16-bit unsigned integer) +* feedback request (optional) (16-bit unsigned integer)<br> + If the extension contains two extra bytes for feedback request, this means + that a feedback packet should be generated and sent immediately. The feedback + request consists of a one-bit field giving the flag value T and a 15-bit + field giving the sequence count as an unsigned number. + - If the bit T is set the feedback packet must contain timing information. + - seq count specifies how many packets of history that should be included in + the feedback packet. If seq count is zero no feedback should be be + generated, which is equivalent of sending the two-byte extension above. + This is added as an option to allow for a fixed packet header size. + |