Unformatted text preview: ation encoded
into a number of layers each to its own multicast group and
the receiver joins or leaves the groups associated with the
layers based on how many packet drops it is experiencing.
We consider a 4 Mbps link traversed by one TCP and three
RLM ows. Each source uses a seven layer encoding, where
layer i sends 2i+4 Kbps; each layer is modeled by a UDP
tra c source. The fair share of each ow is 1Mbps. In the
RLM case this will correspond to each receiver subscribing
to the rst ve layers7 .
The receiving rates averaged over 1 second interval for
each algorithm are plotted in Figure 7. Since in this experiment the link bandwidth is 4 Mbps and the router bu er size
7 More precisely, we have P5 2i+4 Kbps = 0:992 Mbps.
i=1 is 64 KB, we set constants K , K , and Kc to be 250 ms,
i.e., about two times larger than the maximum queue delay. An interesting point to notice is that, unlike DRR and
CSFQ, FRED does not provide fair bandwidth allocation
in this scenario. Again, as discussed in Section 3.2, this is
due to the fact that RLM and TCP use di erent end-to-end
congestion control algorithms. 3.4 Di erent Tra c Models So far we have only considered UDP, TCP and layered multicast tra c sources. We now look at two additional source
models with greater degrees of burstiness. We again consider a single 10 Mbps congested link. In the rst experiment, this link is shared by one ON-OFF source and 19
TCPs. The ON and OFF periods of the ON-OFF source
are both drawn from exponential distributions with means
of 100 ms and 1900 ms respectively. During the ON period
the ON-OFF source sends at 10 Mbps. Note that the ONtime is on the same order as the averaging intervals K , K ,
and Kc which are all 100 ms, so this experiment is designed
to test to what extent CSFQ can react over short timescales.
The ON-OFF source sent 6758 packets over the course of
the experiment. Table 1 shows the number of packets from
the ON-OFF source dropped at the congested link. The
DRR results show what happens when the ON-OFF source
is restricted to its fair sha...
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- Fall '10
- Eugene Ng
- Scheduling algorithm, Round-robin scheduling, Scheduling algorithms, Ow, Fair queuing, ows