Cisco Cisco Catalyst 6500 6000 Series Services Maintenance Partition 白皮書
Wireless LAN Design Guide for High Density
Client Environments in Higher Education
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In all cases, it is highly advisable to test the target application and validate its actual bandwidth requirements. Software designers
are often required to pick just one average number to represent the application’s requirements when there are actually many
modes and deployment decisions that can make up a more accurate number. It is also important to validate applications on
a representative sample of the devices that are to be supported in the WLAN. Additionally, not all browsers and operating
systems enjoy the same efficiencies, and an application that runs fine in 100 kilobits per second (Kbps) on a Windows laptop
with Microsoft Internet Explorer or Firefox, may require more bandwidth when being viewed on a smart phone or tablet with an
embedded browser and operating system.
are often required to pick just one average number to represent the application’s requirements when there are actually many
modes and deployment decisions that can make up a more accurate number. It is also important to validate applications on
a representative sample of the devices that are to be supported in the WLAN. Additionally, not all browsers and operating
systems enjoy the same efficiencies, and an application that runs fine in 100 kilobits per second (Kbps) on a Windows laptop
with Microsoft Internet Explorer or Firefox, may require more bandwidth when being viewed on a smart phone or tablet with an
embedded browser and operating system.
Once the required bandwidth throughput per connection and application is known, this number can be used to determine the
aggregate bandwidth required in the WLAN coverage area. To arrive at this number, multiply the minimum acceptable bandwidth
by the number of connections expected in the WLAN coverage area. This yields the target bandwidth needed for the need
series of steps.
aggregate bandwidth required in the WLAN coverage area. To arrive at this number, multiply the minimum acceptable bandwidth
by the number of connections expected in the WLAN coverage area. This yields the target bandwidth needed for the need
series of steps.
Design Point #2: Calculate the Aggregate Throughput Required for the Coverage Area
If this design guide was for a wired rather than wireless network, calculating aggregate throughput requirements would entail
dividing the aggregate capacity by the channel bandwidth available. Then, the number of channels would be established and
these would be plugged into a switch. But in a WLAN, a channel’s speed is effected by multiple factors including protocols,
environmental conditions, and operating band of the adapter. Before calculating aggregate throughput, several things must
be considered.
dividing the aggregate capacity by the channel bandwidth available. Then, the number of channels would be established and
these would be plugged into a switch. But in a WLAN, a channel’s speed is effected by multiple factors including protocols,
environmental conditions, and operating band of the adapter. Before calculating aggregate throughput, several things must
be considered.
In the aggregate throughput calculation, the connections instead of the seats were used as the basis for calculation. The number
of connections in a cell is what determines the total throughput that will be realized per connection instead of the number of
seats. Most users today carry both a primary computing device (such as a smartphone, tablet computer, or laptop) as well as a
second device (such as a smartphone). Each connection operating in the high-density WLAN consumes air time and network
resources and will therefore be part of the aggregate bandwidth calculation. An increase in numbers of device connections is
one of the primary reasons older WLAN designs are reaching oversubscription today.
of connections in a cell is what determines the total throughput that will be realized per connection instead of the number of
seats. Most users today carry both a primary computing device (such as a smartphone, tablet computer, or laptop) as well as a
second device (such as a smartphone). Each connection operating in the high-density WLAN consumes air time and network
resources and will therefore be part of the aggregate bandwidth calculation. An increase in numbers of device connections is
one of the primary reasons older WLAN designs are reaching oversubscription today.
Wi-Fi is a shared medium. Much like an un-switched Ethernet segment, it operates as a half duplex connection. Only one station
can use the channel at a time and both the uplink and downlink operate on the same channel. Each channel or cell used in a
Wi-Fi deployment represents a potential unit of bandwidth much like an Ethernet connection to a hub. In Ethernet, switching
technology was developed to increase the efficiency of the medium by limiting the broadcast and collision domains of a user to a
physical port and creating point-to-point connections between ports on an as-needed basis, dramatically increasing the overall
capacity.
can use the channel at a time and both the uplink and downlink operate on the same channel. Each channel or cell used in a
Wi-Fi deployment represents a potential unit of bandwidth much like an Ethernet connection to a hub. In Ethernet, switching
technology was developed to increase the efficiency of the medium by limiting the broadcast and collision domains of a user to a
physical port and creating point-to-point connections between ports on an as-needed basis, dramatically increasing the overall
capacity.
Users and applications also tend to be bursty (a measure of the unevenness or variations in the traffic flow) in nature and often
access layer networks are designed with a 20:1 oversubscription to account for these variances. Application and end user
anticipated usage patterns must be determined and also accounted for. Some applications, such as streaming multicast video,
will drive this oversubscription ratio down while others may drive this factor even higher to determine an acceptable SLA for each
cell’s designed capacity.
access layer networks are designed with a 20:1 oversubscription to account for these variances. Application and end user
anticipated usage patterns must be determined and also accounted for. Some applications, such as streaming multicast video,
will drive this oversubscription ratio down while others may drive this factor even higher to determine an acceptable SLA for each
cell’s designed capacity.
For 802.11 wireless networks or any radio network in general, air is the medium of propagation. While there have been many
advances in efficiency, it is not possible to logically limit the physical broadcast and collision domain of an RF signal or separate
it’s spectrum footprint from other radios operating in the same spectrum. For that reason, Wi-Fi uses a band plan that breaks up
the available spectrums into a group of non-overlapping channels. A channel represents a cell. Using the analogy of Ethernet, a
cell represents a single contiguous collision domain.
advances in efficiency, it is not possible to logically limit the physical broadcast and collision domain of an RF signal or separate
it’s spectrum footprint from other radios operating in the same spectrum. For that reason, Wi-Fi uses a band plan that breaks up
the available spectrums into a group of non-overlapping channels. A channel represents a cell. Using the analogy of Ethernet, a
cell represents a single contiguous collision domain.
How many users can access an AP comfortably? Hundreds. But the question should not be how many users can successfully
associate to an AP but how many users can be packed into a room and still obtain per-user bandwidth throughput
that is acceptable.
associate to an AP but how many users can be packed into a room and still obtain per-user bandwidth throughput
that is acceptable.