wirelesstopologies3
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Rick Graziani [email protected] 1
Local area networks (LAN)
The basic service set (BSS) is the area of RF coverage provided byone access point.
It is also referred to as a microcell. BSS can be extended by adding another AP. When more than one BSS is connected to a wired LAN, it is referred to
as an extended service set (ESS).
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Rick Graziani [email protected] 2
Local area networks (LAN)
Adding an AP is also a way to add wireless devices and extendthe range of an existing wired system. If a single cell does not provide enough coverage, any number of cells
can be added to extend the range.
It is recommended that adjacent BSS cells have a 10 to 15 percentoverlap.
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Minimal Overlap Coverage Option
By arranging the access points so that the overlap in a coverage areais minimized, a large area can be covered with minimal cost.
The total bandwidth available to each wireless client device depends
on the amount of data each mobile station needs to transfer and thenumber of stations located in each cell.
Seamless roaming is supported as a client device moves in andout of range of each access point, thereby maintaining a constantconnection to the wired LAN.
Each device in the radio network must be configured with the
same SSID to provide roaming capability.
SSID = StudentChannel 6SSID = Student
Channel 6
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Wireless repeater
A wireless repeateris simply an access point that is not connectedto the wired backbone.
This setup requires a 50% overlap of the AP on the backbone andthe wireless repeater. (So they can reach each other.)
The user can set up a chain of several repeater access points. However, the throughput for client devices at the end of therepeater chain will be quite low.
This is because each repeater must receive and then re-transmit eachpacket on the same channel.
Not covered under 802.11
50%
overlap
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Access point coverage and comparison
As a client roams away from the access point, the transmissionsignals between the two attenuate (weaken).
Rather than decreasing reliability, the AP shifts to a slower datarate, which gives more accurate data transfer. This is called data rate ormulti-rate shifting. As a client moves away from an 802.11b access point, the data rate will
go from 11 Mbps, to 5.5Mbps, to 2Mbps, and, finally, to 1Mbps.
This happens without losing the connection, and without any interactionfrom the user.
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Point-to-point configuration
When using point-to-point wireless bridges, two LANs can belocated up to 40 km (25 miles) apart.
The antennas must have line-of-site with each other. Obstacles such as buildings, trees, and hills will cause communicationproblems.
In this configuration, the Ethernet segments in both buildings act asif they are a single segment.
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Point-to-multipoint configuration
Formultipoint bridging, an omni directional antenna is typicallyused at the main site.
Directional antennas are used at the remote sites. In this configuration, again, all the LANs appear as a single segment. Traffic from one remote site to another will be sent to the main site and
then forwarded to the other remote site.
Remote sites cannot communicate directly with one another.
Line of sight must be maintained between each remote site andthe main site.
root
Non-root Non-root