ND SatCom SKYWAN IDU 7000, Manual

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2010-10-26 Network Design and Engineering Guide 27
General Carrier Design
Essential SkyWAN
®
Satellite Link Layer Features
2.3.3 SkyWAN
®
MF-TDMA functionality
Sky WAN
®
networks are based on a time division technique on multiple carriers which is called
’Multi-Frequency Time Division Multiple Access’ (MF-TDMA). Up to eight carriers can be de-
fined for one
Sky WAN
®
network. The bandwidth of individual carriers is shared by multiple sta-
tions by assigning discrete time slots to each station. This assignment is not static and may be
changed according to the current traffic on each station. This allows a flexible bandwidth on
demand allocation of the carrier bandwidth for an optimal utilization of precious satellite capac-
ity. Since multiple stations receive the same carrier, multicast forwarding of data without packet
duplication is possible.
TDMA Frame
The following picture represents the TDMA structure of a single carrier (channel 1). The TDMA
frame starts with a time slot (furthermore notated as ’slot’) which is allocated to the active mas-
ter to transmit the reference burst. The following slot is assigned to slave stations for transmis-
sion of their request bursts. The rest of the TDMA frame consists of time slots for user traffic
data bursts which are allocated on demand to various stations (indicated by color) in the net-
work.
The allocation of slots to stations is defined by the master and signalled to the slave stations
via the frame plan, which is transmitted as part of the reference burst. Note that the duration of
each time slot (’base slot’) within the TDMA frame is identical. Multiple request bursts may be
defined in one base slot whereas the reference burst will use one or multiple base slots. The
maximum number of base slots per frame is 256 (
Sky WAN
®
IDU Software Release 7.10).
The frame time is the time between two reference bursts. This frame time and the size of an
individual time slot can be defined by network configuration. One major task of the
Sky WAN
®
carrier design is the optimal definition of these parameters.