An Investigation into Transport Protocols and Data Transport ...

9.2. Preferential Flow Handling Using DiffServ 226
Drop Probability (percent)
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WRED1
WRED2
WRED3
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Queue Occupancy (percent)
Figure 9.25: WRED profiles.
only and for the most challenging AF allocation of 900Mbit/sec.
The aim of these tests is to smooth out the observed cwnd deviations from
theory by means of configuring different Weighted Random Early Detection
(WRED) [FJ93] drop profiles for the AF class.
Methodology
As the New-TCP algorithms under investigation in this section are loss based
protocols, the cwnd dynamic of each necessarily require the oscillation of
cwnd below the point of congestion. Therefore, it is important not to impose
too great of a random loss upon the AF class as this would correlate to
high(er) loss rates for the single ScalableTCP flow and thus a decrease in
goodput (See Section 5.4.2). As such, a gentle WRED drop profile was used.
From a packet-level perspective, the justification for using WRED is based
on the belief that a smoother distribution of the loss-pattern in the AF queue
will help lower the burst length of SACKs and therefore it will help avoid
deep stalls of cwnd in the TCP sending host.
Using the same network topology and hardware and software configurations
as used previously, three WRED drop profiles are configured on the
Juniper M10 router as shown in Figure 9.25.