Performance Notes; Wireless Bridge; Distance-Throughput Relationship - GE MDS iNET 900 Reference Manual

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4.4 PERFORMANCE NOTES

The following is a list of points that are useful for understanding the per-
formance of the radio in your installation.

4.4.1 Wireless Bridge

The transceiver acts as a bridge. If any radio in your network is con-
nected to a large LAN, such as may be found in a large office complex,
there may be undesired multicast/broadcast traffic over the air. As a
bridge, the radios transmit this type of frame.
The radio goes through a listening and learning period at start-up before
it will send any packets over either of its ports. This is about 10 seconds
after the CPU's operating system has finished its boot cycle.
The bridge code in the transceiver operates and makes decisions about
packet forwarding just like any other bridge. The bridge code builds a
list of source MAC addresses that it has seen on each of its ports.
There are a few general rules that are followed when a packet is received
on any port:
• If the destination address is a multicast or broadcast address,
forward the packet to all remotes.
• If the destination address is not known, forward the packet to
all remotes.
• If the destination address is known, forward the packet to the
port that the destination is known to be on (usually the RF
port).
• The bridge code uses Spanning Tree Protocol (STP) to pre-
vent loops from being created when connecting bridges in
parallel. For example, connecting two remotes to the same
wired LAN could create a loop if STP was not used. Every
bridge running STP sends out Bridge Protocol Data Units
(BPDUs) at regular intervals so that the spanning tree can be
built and maintained. BPDUs are 60-byte multicast Ethernet
frames.

4.4.2 Distance-Throughput Relationship

Distance affects throughput. Because of timers and other components of
the protocol, there is a practical distance limit of 30 miles (48 km) for
reliable operation. After this, although data still flows, the throughput
will begin to drop and latency will increase, due to additional retries
between the radios. Packets may start to be dropped. Some applications
may tolerate this; others may not. Repeater stations may be used to
extend the range.
iNET Series Reference Manual 05-2806A01, Rev. J