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Bug #5003

closed

Feature #1624: Design and Implement Congestion Control

Congestion Marking too aggressive

Added by Anonymous about 5 years ago. Updated 12 months ago.

Status:
Closed
Priority:
Normal
Assignee:
-
Category:
Faces
Target version:
v0.7
Start date:
Due date:
% Done:

100%

Estimated time:

Description

The current implementation of the active queue management in GenericLinkService is too agressive, which can cause a drop in throughput.

Example with 2 NFD nodes connected via UDP tunnel (added 10ms RTT): 

klaus@consumer:~/work$ ndncatchunks /100m

All segments have been received.
Time elapsed: 43.3606 seconds
Segments received: 23832
Transferred size: 104858 kB
Goodput: 19.346137 Mbit/s
Congestion marks: 13 (caused 13 window decreases)
Timeouts: 144 (caused 17 window decreases)
Retransmitted segments: 107 (0.446969%), skipped: 37
RTT min/avg/max = 10.520/22.440/427.402 ms

With congestion marks ignored:

klaus@consumer:~/work$ ndncatchunks --ignore-marks /100m


All segments have been received.
Time elapsed: 20.561 seconds
Segments received: 23832
Transferred size: 104858 kB
Goodput: 40.798586 Mbit/s
Congestion marks: 48 (caused 0 window decreases)
Timeouts: 1459 (caused 19 window decreases)
Retransmitted segments: 1389 (5.50732%), skipped: 70
RTT min/avg/max = 10.574/33.479/1006.184 ms
klaus@consumer:~/work$ ndncatchunks /100m

The queuing (and congestion marking) happens mostly inside NFD, since the links are faster than NFD can process (often the case in real networks too).

The solution is to implement a more proper version of CoDel (see https://tools.ietf.org/html/rfc8289), compared to what was done in #4362.

There are two simplifications in the current code:

  1. We measure the queue size (in bytes) rather than queuing delay (ms).
  2. The first mark happens directly after exceeding the threshold, rather than exceeding the threshold for a given time period (100ms).

I think (2) is more significant, and I will look at it first.

Files

retx.pdf (7.82 KB) retx.pdf Timeouts per packet number Anonymous, 10/02/2019 09:40 PM
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