Figure 2-28 Traffic Calculation Example - Erlang B Worksheet - ND SatCom SKYWAN IDU 7000 Manual

General Carrier Design
Network Traffic Estimation
higher than the acceptable value, the number of voice channels has to be incremented until the
blocking probability fulfils the requirement. In the example figure 2-28, 51 voice channels are
required to achieve a blocking probability below 1.5%.
Figure 2-28 Traffic Calculation Example - Erlang B Worksheet
Generally the number of users is derived from the number of voice interfac-
i
es in the network. If the column "voice interfaces per location" on the ca-
pacity calculation worksheet is left blank, the number of users can be
specified in the input field "Alternative Input for # of Users" on the Erlang B
worksheet.
The total traffic requirement for voice is calculated by multiplying the number of (full duplex)
voice channels with 2 x voice channel data rate.
The voice channel data rate depends on the used technology and codec rate, which can be
selected by the input field 'Used Codec'. The most important voice over SkyWAN
VoIP Codecs (with or without header compression) are already predefined in the sheet. If an-
other codec should be used, the data rate for a 'Custom Codec' may be defined in the lookup
table. Note that the data rate must include the network layer overhead up to the IP or Frame
Relay level.
The estimation for the total network traffic would be sufficient for a single carrier SkyWAN
work. If a multi-carrier network is designed, the traffic requirement must be broken down to the
requirements for each individual carrier. The general idea is to calculate a type specific data
rate per station. Then the network designer has to decide how many stations are assigned to
46 Network Design and Engineering Guide
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2010-10-26