User's Manual

12
2 Product Architecture (More Detail About The OS-Gemini)
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 OFDMmodulation with a dispersion capability of 10 microseconds in both
directions.
The OS-Gemini has been developed to operate in license exempt frequency bands for example
the ETSI 5.8 GHz C band (5.725–5.875 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
reduce the data rate in severe or adverse conditions.
The OS-Gemini operates as a standard IEEE 802.3 Ethernet bridge as defined in IEEE 802.1. 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 re-transmit a packet if it knows
that the destination address is connected to the same port on which the bridge saw the packet.
Figure 7 illustrates the OS-Gemini layer diagram.
Ethernet
PHY
DLC
Bridging
Network(IP)
Transport(TCP, UDP)
DLC
PHY
http
5 GHz Wireless
PHY
DLC
Bridging
Network(IP)
Transport(TCP, UDP)
DLC
PHY
Ethernet
http
Figure 7 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 8 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 the VLAN ID value.
Each unit in the link is manageable through an IP connection. Standard IP protocols are utilised
for all management functions e.g. HTTP, TFTP, etc. The OS-Gemini is fully software upgrade-
able. New software images are first downloaded from the Orthogon Systems support web site