Juniper JUNOSE 11.1.X MULTICAST ROUTING, Configuration Manual

Page: 178 / 270

To calculate the measured bandwidth of a stream, the router uses the following
equation:
R = (N
t+5
– N
t
) / 5
Where
R = Calculated bandwidth of the stream during each sampling interval
N
t
= Bytes measured at the start of each sampling period (t seconds)
N
t+5
= Bytes measured at the end of each sampling period (t+5 seconds)
NOTE: When the mroute is first installed in the FC (at t = 0), R
0
is undetermined.
For multicast admission control no joins are admitted until the first bandwidth
measurement is computed (that is, for admission control, R
0
is considered to be
infinite). Similarly, no QoS adjustment occurs until the first bandwidth measurement
is computed (that is, for QoS adjustment, R
0
is considered to be zero [0]).
Using the earlier graph as a reference, the first bandwidth rate (R1
0
) and at time t
5
(N
5
) and the bytes received values are subtracted and divided by the time period T
1
to yield the average rate. This process is repeated every sampling interval, T
2
, to
yield rates R1, R2, R3, and so on.
The first two sampling interval calculations would look like the following:
R
1
= (N
5
- N
0
)/5
R
2
= (N
#+5
- N
#
)/5
The router maintains a history of bandwidth measurements (H) for each mroute, up
to a maximum of M measurements. The actual rate, R, reported to the SRP is the
maximum rate measured in those H samples.
In order to minimize the IC to SRP traffic generated by the rate measurements, the
IC reports a bandwidth change only when a newly computed rate (R#) differs from
the current rate by a specified threshold. When R
s
is computed at time t = 5 seconds,
R is set to R
1
. A rate update occurs whenever a newly calculated rate (R) differs from
R
1
by at least a threshold value (specified as a percentage, P) of the measured peak
bandwidth. This calculation would look like the following:
R = Rt, if and only if the absolute value of (R - Rt) > P * R.
The values assigned to variables associated with this algorithm are as shown in Table
9 on page 156.
Table 9: Adaptive Mode Algorithm Values
Description Units Value Variable
Sampling period; the time in which a sample is taken Seconds 5 T1
156 ■
Defining a Multicast Bandwidth Map
JUNOSe 11.1.x Multicast Routing Configuration Guide