Subject: [tcpm] [Errata Held for Document Update] RFC5681 (4068)

From: RFC Errata System <[email-masked]>
Date: Mon, 10 Nov 2014 09:01:12 -0800 (PST)

The following errata report has been held for document update 
for RFC5681, "TCP Congestion Control". 

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You may review the report below and at:
http://www.rfc-editor.org/errata_search.php?rfc=5681&eid=4068

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Status: Held for Document Update
Type: Editorial

Reported by: Michael Taylor <[email-masked]>
Date Reported: 2014-08-04
Held by: Martin Stiemerling (IESG)

Section: GLOBAL

Original Text
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Corrected Text
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Notes
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The problem is the use of the phrase "new data" in an imprecise manner to sometimes mean "previously unacknowledged data" and other times mean "never before sent data".

For example, in Section 3.1

   During slow start, a TCP increments cwnd by at most SMSS bytes for
   each ACK received that cumulatively acknowledges new data. 

This should read 

   During slow start, a TCP increments cwnd by at most SMSS bytes for
   each ACK received that cumulatively acknowledges previously 
   unacknowledged data.

I believe that throughout Section 3.1 "new data" refers to "previously unacknowledged data".

However, in Section 3.2 we have

   After the fast retransmit algorithm sends what appears to be the
   missing segment, the "fast recovery" algorithm governs the
   transmission of new data until a non-duplicate ACK arrives.

I believe that here "new data" refers to "previously unsent data".  

This is clearer in the following paragraph from Section 3.2

   1.  On the first and second duplicate ACKs received at a sender, a
       TCP SHOULD send a segment of previously unsent data per [RFC3042]
       provided that the receiver's advertised window allows, the total
       FlightSize would remain less than or equal to cwnd plus 2*SMSS,
       and that new data is available for transmission.

Here we can see the use of "previously unsent data" followed by "new data" 
which refers to the aforementioned "previously unsent data".

While the meaning of "new data" might be clear to those with extensive experience
in TCP it is imprecise and therefore may be quite confusing to those who are learning about the protocol.

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RFC5681 (draft-ietf-tcpm-rfc2581bis-07)
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Title               : TCP Congestion Control
Publication Date    : September 2009
Author(s)           : M. Allman, V. Paxson, E. Blanton
Category            : DRAFT STANDARD
Source              : TCP Maintenance and Minor Extensions
Area                : Transport
Stream              : IETF
Verifying Party     : IESG