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+# 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.
+