User's Manual

SkyGateway/SkyExtender Installation And Configuration Guide
1-4 September 2004
Network Architecture
The SkyPilot system software manages communications protocols at all
levels, from RF to routing. It carefully manages SkyGateWay, SkyExtender,
and subscriber nodes to create the best possible network performance.
SkyProvision software is used to configure the system.
The SkyPilot System operates as a Layer 2 network. All subscriber traffic
goes to and from the network via an external switch or router attached to the
Ethernet bridge in a SkyGateWay basestation. Peer-to-peer communication
is not permitted within a SkyPilot System.
Physical and Link
Layers
Physical Layer . At the RF layer, the components of a SkyPilot System use
standard 802.11a modulation operating in the 5.8GHz range. The Physical
Layer SkyPilot protocol conforms to the 802.11a specifications with the
addition of a synchronous one-second frame. The timing of this frame is
derived from a GPS receiver in each SkyGateWay and SkyExtender. The
frame’s signal is used to control transmission and reception in the network,
and also provides a reference for the “hello message” exchange (a beacon/
response sequence that allows nodes and gateways to establish
connections).
Data Link (MAC) Layer . At the MAC layer, SkyPilot implements a
synchronization protocol that takes advantage of the one-second RF frame
to establish links and exchange secure, rate-controlled data between
devices.
Routing
Above the MAC layer, SkyControl brings into play a dynamic routing protocol
that ensures the most efficient utilization of network resources and provides
for rapid rerouting around link and device failures. SkyControl allows
SkyExtender nodes and SkyConnector subscriber units to join the network
automatically.
When a SkyExtender node connects to the network, it selects an optimum
route to a SkyGateWay. The route selection considers link capacity
(modulation rate), and the number of hops between the node and the
gateway. Once a route is selected, all user traffic is forwarded via this path
unless conditions change. Rerouting is necessary (and automatic) when a
link or node is lost. The SkyPilot system also automatically reroutes traffic
when it determines that a lower cost route is consistently available. (A
connection’s “cost” is determined by the number of hops it requires and the
modulation rates on each of the connection’s component links.)