ND SatCom SKYWAN IDU 7000, Manual

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42 Network Design and Engineering Guide 2010-10-26
General Carrier Design
Network Traffic Estimation
Voice traffic has in principle the same nature as real-time data traffic. However it has a few
characteristics requiring a different treatment concerning the traffic estimation:
- Individual voice calls consume a relative low bandwidth, but there are many simultaneous
calls possible.
- The voice capacity (streaming capacity) is not constantly in use.
- A certain amount of blocked calls due to insufficient network capacity is acceptable.
Therefor the network capacity needed for voice calls is not calculated by the number of voice
interfaces multiplied with the bandwidth per call, but the maximum number of simultaneous
calls in the network is estimated. This might be done by ’educated guessing’ taking into account
the customer’s experience with the voice network or by an explicit statistical calculation (“Er-
lang calculation”) based on average usage rates of telephones.
Traffic Estimation Example Scenario
The following pictures represent an example for the traffic estimation of a network consisting
of 50 stations. Four different station groups (station types) are defined: head offices, big sites,
medium sites and small sites.
In figure 2-24 the non real-time traffic flow between stations of specific types is sketched.
Keep in mind that the numbers here do not represent maximum but committed data rates for
individual flows. For example, a small site will typically be able to send more non real-time data
than 1 kbps to the head office, because it is unlikely that all other stations would be active si-
multaneously. The type of non real-time raffic assumed in this example is LAN (i.e. IP) data,
but the approach would be not different for non real-time Frame Relay data. In this case the
numbers in the traffic pattern sketch could be used to define the Frame Relay station param-
eter ’Committed Information Rate’ for each Frame Relay Circuit.
Figure 2-24 Traffic Estimation Scenario IP Traffic
A graphical representation of the real-time data requirements is given in figure 2-25. There is
a bidirectional videoconference planned between the head offices and voice calls based on
Frame Relay (
Sky WAN
®
FAD) functionality. For the voice calls the traffic pattern is also spec-
ified. The total number of simultaneous voice calls required in this network has to be estimated
additionally.