ND SatCom SKYWAN IDU 7000, Manual

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2010-10-26 Network Design and Engineering Guide 33
General Carrier Design
Essential SkyWAN
®
Satellite Link Layer Features
Despite its numerous limitations NFB-DUB mode is a better choice than MRB-DUB mode if
-
A single star topology is sufficient,
- Master and slave stations are located in different satellite beams interconnected via a
cross-strapped transponder.
If there is no other station located in the same beam as the master, MRB-DUB mode would
require an extra carrier having the same bandwidth as the ’inbound’ carrier (from slave to mas-
ter) just for master synchronization.
2.3.6 Capacity Request and Allocation for User Data
Figure 2-15 Capacity Request
There are two types of capacity requests: stream requests and dynamic requests. Both are
computed for each carrier channel and forwarded to the active master station by means of a
’Request Burst’.
The Sky WAN
®
IDU provides transmit queues. With these queues data to be send via satellite
is treated differently regarding priority measures.
1. Highest priority: Real Time (RT) user data.
2. Less priority: Control data (internal station messaging and network management data)
3. Lowest priority: Non Real Time (NRT) user data.
The queueing principle is shown in figure 2-15. The differentiation is more precise and will be
shown in more detail later. Note, that for each carrier individual queues are used.
Free Slot Assignment
Free Slot Assignment can be enabled per station and per carrier. Every station which
-
is declared to participate in the Free Slot Assignment for a specific carrier and
- is registered in the network
gets empty slots which are not requested by any other station on this carrier. These available
slots are assigned in a round robin fashion among every registered station. If the station has
nothing to transmit it will just transmit „dummy data“. If the station suddenly gets any data pack-
ets in to the transmit queue, then it can transmit them immediately within these slots without