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Tutorial
MPLS
Traffic Engineering
Calculating
How Much Bandwidth You Need
For
the sake of discussion in these examples, let’s assume that
you know the characteristics of your network. This is a
process of gathering data that is unique to your situation and
has been measured by your team.
Example
One: Two
tunnels with load balanced OC-12 designed for peak busy hour.
Let’s
say that we want to engineer traffic for an OC-12 pipe, which
is 622 Mbps.
You
want to have rapid recovery, so you use two pipes and load
balance each pipe for 45% of capacity.
In this case, if one OC-12 pipe fails, then your rapid
recovery protocol can move traffic from your under-provisioned
pipe to the other, and the total utilization is still
under-provisioned.
Figure
5-5: Sample Network Diagram Example One
Figure
5-6: Sample Network Failure
Figure
5-7 Traffic Trends
We
can work these numbers just like we would in a checkbook.
After we do the math, if we still have money (bits) remaining,
then we are okay. If
our checkbook comes out in the red, then we must go back and
budget our spending.
The
following table helps to simplify the bandwidth budgeting
process, as well as demonstrate some of the calculations
involved in traffic engineering.
Our
traffic trends for peak busy hour show that we have:
| Traffic
Demands |
|
Totals
and subtotals |
| Number
of voice calls |
100 |
|
|
|
b/s/call |
200,000 |
|
|
Total voice
streams in b/s |
20,000,000 |
20,000,000 |
|
| Number
of video calls |
3 |
|
|
|
b/s/call |
500,000 |
|
|
Total video
streams in b/s |
1,500,000 |
1,500,000 |
|
| Committed
information rate |
250,000,000 |
250,000,000 |
|
| Other
traffic |
0 |
0 |
|
| Total
traffic demand |
271,500,000 |
271,500,000 |
BW
required |
| |
|
|
|
| Bandwidth
Available |
|
|
Circuit bandwidth
for OC-12 |
622,000,000 |
|
|
| Percentage used |
45% |
|
Over-
provisioned |
Total BW for
over-provisioned |
279,900,000 |
279,900,000 |
BW
on-hand |
| |
|
271,500,000 |
BW
required |
| Remaining
Bandwidth |
|
8,400,000 |
BW
remaining |
Key
BW = Bandwidth
b/s = bits per second
b/s/call = bits per second for each call |
Figure
5-8: Traffic
Engineering Calculations for Example One
Now
that we understand the basic concept, let’s play with the
figures a bit to achieve the outcomes that we need.
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