ND SatCom SKYWAN IDU 7000, Руководство пользователя

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36 Network Design and Engineering Guide 2010-10-26
General Carrier Design
Essential SkyWAN
®
Satellite Link Layer Features
2.3.7 Guaranteed Throughput
By default every station is treated identically concerning the allocation of capacity. Optionally it
is possible to define a guaranteed throughput for specific stations on specific carriers. If re-
quested for, the master must allocate these slots even, if it has to reject requests from other
stations.
There are two modes of guaranteed throughput which can be selected individually for every
station:
-
Stream Mode ’Normal’ : In this mode the guarantee only applies to dynamic slot assign-
ment. Concerning stream slot assignment, the stations with guaranteed throughput will still
be treated as every other station. Their requests will be served if there are still slots from
the ’common’ stream pool (specified by the general parameter: ’maximum number of
stream slots’) available on this carrier.
- Stream Mode ’Stream within Guaranteed Throughput’ : In this mode the guarantee also
applies to streaming slots. Stations with a guaranteed throughput will have their ’private’
pool of possible streaming slots: No other station may be allocated streaming slots of this
pool, but the station will also not get any streaming slots from the common pool if its private
pool is already exhausted.
Oversubscription with guaranteed throughput definitions is not allowed. That means, that for
every carrier the sum of guaranteed slots for all stations and the common streaming slot pool
must be smaller or equal to the number of data slots on this carrier.
The master is free to allo-
cate any unrequested data slot as dynamic slot to any station in the network. For the allocation
of streaming slots however, the general restriction is:
- Stations with stream mode Normal may be served out of the common streaming slot
pool.
- Stations with stream mode Stream within Guaranteed Throughput may only be
served out of the private pool as specified by the guaranteed throughput parameter for
this station. That means that a stream slot request may be denied to a station even if
there are currently unused slots in the frame.
Guaranteed Throughput Example Scenarios
To highlight possible applications of the guaranteed throughput in this paragraph we consider
4 scenarios. As general assumption a network is assumed with one carrier having the following
properties, refer to figure 2-19:
- 38 frame slots including 35 data slots.
- Capacity of one data slot: 26 kbps (sufficient for 2 unidirectional voice calls).
- Common stream pool: 12 slots.
- Guaranteed throughput for stations IDU1 and IDU2: 6 slots.
- No guaranteed throughput for all other stations.
Figure 2-19 TDMA Structure of Throughput Example