Microwave Data Systems MDS entraNET 900, Системное руководство

Страница: 65 / 148

MDS 05-4055A01, Rev. A MDS entraNET 900 System Guide (Preliminary) 57
2. AP Only: Change the
Beacon Period
to
Normal
(508 ms). This will
also reduce the overhead of beacons sent out. On the down side,
association time may be a little longer.
(
Main Menu>Radio Configuration>Beacon Period
)
3. Change the
Fragmentation Threshold
to the maximum of 1600. Longer
packets will be sent over the air reducing overhead. On the down
side, if a packet is corrupted it will take longer to be retransmitted.
(
Main Menu>Radio Configuration>Fragmentation Threshold
)
4. Increase the
RTS Threshold
to 1600. RTS mechanism is used to
reserve a time slot if packets exceed this number. On the down side,
a hidden-node might interfere more often than if RTS is not used.
(
Main Menu>Radio Configuration>RTS Threshold
)
5. Decreasing the
RTS Threshold,
to the 100 to 200 range, will improve
throughput on a busy network. It will add small packets, but reduce
collisions (and resulting re-tries) of large packets.
(
Main Menu>Radio Configuration>RTS Threshold
)
6. Use
Performance Information Menu
to check RSSI by zone.
(Remotes Only /
Main Menu>Performance Information>RSSI by Zone
)
Readings should be close in value (±2 dB). A lower value might
indicate interference. Block the zones at the Access Point that affect
the Remotes. (
Main Menu>Radio Configuration>Skip Zone Option
)
7. Use
Performance Information Menu
to check for errors, retries and
dropped packets. Do the same with Ethernet traffic.
With weak signals, interference, or hidden nodes, the optimal per-
formance may be lower due to collisions and retries.
Data Latency—TCP versus UDP Mode
The latency of data passing through a network will depend on user data
message length, the overall level of traffic on the network, and the
quality of the radio path.
Under ideal conditions—low traffic and good RF signal path—the
latency for units operating in the TCP mode, will typically be around 5
ms in each direction. However, when UDP multicast traffic is trans-
ported, the outbound packet latency (from AP to remote) is dependent
on the beacon period.
UDP multicast packet latency can be minimized by setting the
Beacon
Period
to “
Fast
” (52 ms). Changing beacon rate to
Fast
will result in an
average latency of 29 ms, assuming outbound packets wait for a beacon
transmission 50% of the time (26ms) plus the normal packet latency
(5 ms).