/usr/share/doc/nam/examples/ex/adc.README is in nam-examples 1.15-1.
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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 | The attached nam file (adc.nam) shows a simple comparison between a
comparison between measurement-based admission control and
parameter-based admission control. The measurement-based algorithm
is the Measured Sum algorithm given in "Comparison of
Measurement-Based Admission Control Algorithms for Controlled-Load
Service", by Jamin, Shenker and Danzig in Infocomm '97. The
parameter-based algorithm makes admission control decisions based on
reserved rates.
In the animation, there are two bottleneck links with capacity 1Mbps.
Link 6-7 uses the parameter-based algorithm, and Link 0-1 uses the
measurement based algorithm. The remaining links in the topology have
5Mbps capacity and are never congested.
The key point to notice is that when presented with equal average
offered load (in terms of the number of flows requesting reservations)
the measurement-based algorithm, which makes admission decisions based
on the token bucket parameters of the flow requesting service and on
the measurements of traffic sent by flows with existing reservations,
admits more flows and achieves a higher measured utilization on the
bottleneck link than the parameter-based algorithm, which makes
admission decisions using the token bucket parameters of the new flow
and the reserved rate of existing flows.
The 3 magenta nodes on the left are the sources of traffic and the 3
orange nodes on the right are destinations. Flows are started
randomly between pairs of source and destination nodes. When a flow
is started, a reservation request (white packets in the animation) is
sent from the source (Node 8, 2 or 3) to the destination (Node 9, 5 or
4). The token bucket parameters in the reservation packet are r =
64kbps are b = 1. Admission control decisions are made at either node
0 or node 6. Based on the admission control decision, the destination
returns either an Accept packet (green) or Reject packet (red) to the
source. A source that receives an Accept then transmits data (the
data packets are not shown in the animation). After sending its data,
the source transmits a Teardown packet (black) to signal the network
it no longer needs its reservation.
The bottleneck links change color to reflect the last admission
control decision made on the link. When reservation requests are
accepted, the link turns (or remains) green. When a reservation
request is rejected, the link turns (or remains) red.
Monitors associated with the admission control agents at Nodes 0 and 6
display relevant information about the state of the admission control
process and link utilization. Each monitor shows the number of flows
with reservations in place on the adjacent link, and the measured
utilization on the adjacent link (utilization measures are averaged
over 2 second intervals). For the parameter-based admission control
algorithm, the total amount of reserved bandwidth is shown. For the
measurement-based algorithm, the estimated link utilization, which is
an input parameter to the decision process, is shown. (See the
above-reference paper for an explanation of how this estimate is
computed and used.)
Other relevant parameters to the simulation that created this
animation:
Flow inter-arrival times are exponentially distributed with average of
400 ms on each link. Average flow lifetime is 30 seconds (again
exponentially distributed). Flows transmit data according to the
Exponential On/Off source model in the ns-2 simulator. Relevant
parameters are: packet size = 125 bytes, on time = 312.5 msec, off
time = 325 msec, and rate = 64 kbps.
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