User's Manual Part 1

14
2 Product Architecture
The OS-Gemini consists of an identical pair of units deployed one at each end of the link. The
radio link operates on a single frequency channel using Time Division Duplex (TDD). One unit
is deployed as a master and the other as a slave. The master unit takes responsibility for
controlling the link in both directions.
The non-Line-of-Sight (NLOS) aspects of the product are provided by multi-beam space time
coding, coupled with Orthogonal Frequency Division Multiplex (OFDM) modulation with a
dispersion capability of 10 microseconds in both directions.
The OS-Gemini has been developed to operate within license exempt frequency bands, for
example the ETSI 5.8 GHz C band (5.725–5.850 GHz) and the USA 5 GHz ISM band
(5.725-5.850 GHz). The OS-Gemini has been designed to coexist with other users of the band
in an optimal fashion using a combination of Transmit Power Control (TPC), Dynamic
Frequency Selection (DFS) and Antenna beam shape.
In order to maintain link availability, the product employs adaptive modulation techniques that
dynamically reduce the data rate in severe or adverse conditions. To the data network the OS-
Gemini is implemented as a learning bridge. A learning bridge builds up a picture of which
addresses are connected to which port. This means that it will not bridge a packet if it knows
that the destination address is connected to the same port on which the bridge saw the packet.
Figure 6 illustrates the OS-Gemini layer diagram.
Figure 6 OS-Gemini Layer Diagram
The OS-Gemini functionality has been extended to encompass the IEEE 802.1q sub
specification IEEE 802.1p. IEEE 802.1p allows the Ethernet packets to be extended by 4 bytes
to include the IEEE 802.1q VLAN Tag and VLAN Priority/ID with VLAN ID set to 0 and the
packet priority set to 0-7. The OS-Gemini will forward all VLAN tagged packets regardless of