Compaq WL110, Руководство пользователя

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6-18 Optimizing Performance
Designing High Capacity Networks
In networking environments where you have either data intensive users, or a
large number of users in a small area, you may wish to improve the throughput
efficiency and/or load balancing of your Access Points.
This solution described in this section allows you to balance “maximum range
for minimum hardware investments” versus “maximum throughput
performance for higher hardware investments”.
About the CSMA/CA Protocol
In normal network configurations, all equipped devices apply a standard
mechanism to avoid collision of wireless messages. When a station intends
transmitting a message, it will first sense whether no other station is already
transmitting (“using the wireless medium”).
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If no other transmissions are sensed, the station will start its transmission.
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If it does sense another transmission carrier, the station will apply a random
defer timer. After the timer has expired it will start sensing the medium
again to see if it can start transmitting.
This protocol, also referred to as the “Carrier Sense Multiple Access/Collision
Avoidance” (CSMA/CA) protocol works fine in most networking environments.
The user of a wireless computing device will hardly notice the deferral behavior
of the wireless radio.
In network environments with many wireless users in the vicinity of one another
and/or wireless stations that are engaged in heavy data traffic, you may perceive
that wireless stations show a degrading performance, perceived as long network
response times when communicating via the network.
Where poor performance is typically caused by poor radio link quality
(identified by a poor a signal to noise ratio (SNR)), the scenario described above
may also be perceived in areas where:
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Site monitor measurements show an excellent wireless coverage by at least
two Access Points or more on every location.
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Link test measurements at such locations may show:
— An excellent SNR for communications between wireless stations and
the Access Point.
— A large number of messages transmitted at lower rates.
In this type of situations the disappointing network performance might be
caused by the busy wireless traffic in that area, where the CSMA/CA protocol
causes the wireless stations to defer transmissions to often for either:
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Heavy data traffic by other stations in the same wireless cell
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Traffic from stations in neighboring cells, where stations in a location where
wireless cells overlap one another seem to suffer more than the other
stations.