End-to-End Internet Packet Dynamics

In this paper, the author has used a trace of 20,000 TCP bulk transfers
to study unusual network behaviour(out of order delivery, packet
replciation,
packet corruption), robust bottleneck estimation, packet loss and packet
delay.

Key Points:

1) Internet paths are somtimes subject to a high incidence of reordering,
but the effect is strongly site-dependent and apparently correlated
with route fluttering.
Reordering makes it difficult to determine the TCP duplicate ack
threshold a sender uses to infer that a packet requires retransmission.
Selective ACK can greatly help in the process.

2) Misconfigurations and poor implementations also result in packet
replication.
although rarely.

3) Packet corruption is fairly frequent about 1 in 5000 packets. Data
packets
are more likely to be corrupted than ack packets due to size.

4) Packet pair bottleneck estimation becomes inaccurate due to out-of-order
delivery, capability of clock resolution of the hosts, changes in bottleneck
bandwidth and multi-channel bottleneck links. A more robust bottleneck
estimation improves Packet Pair by using a range of packet bunch sizes
and by allowing for multiple bottleneck values or apparent bottleneck
values.

5) Observing a zero-loss connection is quite a good predictor of zero-loss
connections upto several hours in the future and likewise for lossy
connections.

6) Data stream adapts to the current network conditions but the ack stream
does not and hence the difference between ack and data loss rates. Usually,
loss rates observed follow :
unloaded packets<ack packets< loaded packets (more likely)

7) Packet loss occurs in bursts.

8) Ensuring proper Roundtrip Time out and deploying Selective ACK option
together eliminates virtually all of the avoidable redundant transmissions.

9) Internet delay variations occur primarily on time scales of .1-1
sec but extend out quite frequently to much larger times.

10) Internet connections encounter a broad range of available bandwidths.
Received on Thu Nov 16 2006 - 02:33:14 EST