4RF Aprisa SR+, Руководство пользователя

Страница: 30 / 492

30 | About the Radio
Aprisa SR+ User Manual 1.11.1
Repeater Messaging
The Aprisa SR+ uses a routed protocol throughout the network whereby messages contain source and
destination addresses. The remote and repeater stations will register with a base station. In networks with
a repeater, the repeater must register with the base station before the remotes can register with the base
station.
Additionally, based on destination address, messages are designated as either a ‘broadcast’ message,
(mostly originating from a base station) or a ‘unicast’ message (mostly originating from
a remote radio).
In a network with a repeater, or multiple repeaters, the base station broadcasts a message which contains
a source address and a destination address. The repeater receives the message and recognizes it as a
broadcast message, from the destination address and re-broadcasts the message across the network. In IP
routing mode all remote radios in the coverage area will receive the message but only the radio with the
destination address will act upon the message.
Similarly, the remote radio will send a unicast message which contains a unicast destination address (the
base station). The repeater will receive this message; recognize the destination address and forward it to
the appropriate destination address.
In order to prevent repeater-repeate r loops, a detection mechanism of ‘duplicate message’ a nd use of
unicast messaging in remote to base/repeater direction is used.
For example, in the Multiple Repeater Single Hop figure above, the topology is of Base, Repeater 1, Repeater
2 and Remote 1 connected to Repeater 1 in overlapping coverage, where Remote 1 can also hear Repeater
2. When the Base station broadcasts a message, Remote1 will receive this message from both Repeater 1
and Repeater 2 but will drop one of them as ‘duplicate message’. It is possible that Repeater 1, for example,
can also hear the broadcast sent out by Repeater 2. In this case, Repeater 1 will drop this broadcast as a
‘duplicate message’.
T hese phenomena will not happen in the upstream direction as all messages are sent ‘unicast’. Remote 1
will send a packet to Base station, setting the destination address in packet to Base s tation and ‘next hop’
address in packet to Repeater 1. Thus, only Repeater 1 will forward the packet to Base station and Repeater
2 will drop the pack
et as the ‘next hop’ address is not Repeater 2.