Transcript Competitive Analysis

The Problems With Microcell (1)
How cochannel interference destroys microcell throughput
The Question
What is it about microcell WLAN’s that have
made so many WLAN administrators and end-
users unhappy
and frustrated?
What happens:
WLAN Operation
X
X
AP
Classic Cellular Operation
BTS
WLAN Operation
X
X
AP
Microcell Architecture – 3 channels
2.4 GHz Band
AP
AP
AP
Covering Floor 1 With WLAN
1
2
3
4
5
6
7
8
9
But We Have Only 3 Frequencies
1
6
11
6
11
1
11
1
6
Microcell Architecture: the ugly reality
Cells are actually a lot larger !!
Cochannel interference
zones
Lower rate
transmissions travel
far from the AP.
1
6
11
A client transmitting in this
zone quiets not only his
AP, but also the
neighboring AP.
System throughput is
lowered drastically.
6
11
1
11
1
6
The Reason: RF Energy propagation
Client Connects @ 1 Mbps
Client Connects @ 6 Mbps
Range:
The RF energy does not
stop simply because the
client and AP can no
longer interpret the data,
typical Range may be
2,000 meters
Distance
Client Connects @ 54 Mbps
Client Connects @ 300 Mbps
Radio Coverage:
This is the area a client
can hear an Access Point
and reply successfully –
Typically 10 Metres radius
from the AP at 54 Mbps
Radio Transmission Still Continues
Microcell Architecture: the ugly reality
Cells are actually a lot larger !!
Cochannel interference
zones
Lower rate
transmissions travel
far from the AP.
1
6
11
A client transmitting in this
zone quiets not only his
AP, but also the
neighboring AP.
System throughput is
lowered drastically.
6
11
1
11
1
6
So Instead of This….
1
2
3
4
5
6
7
8
9
We’re Back To This…
AP
AP
AP
Or worse…
Conclusion
Actual microcell throughput is up to
70% lower than expected due to
cochannel interference
And If You Try To Spread Out the Cells
To Lower The Interference…
You get
coverage
holes
1
6
11
6
11
1
11
1
6
And lower air rates
Most of the
coverage area
now has the
lower air rates
So most users
get the lower
rates, and lower
throughput.
1
6
11
6
11
1
11
1
6
Making the
situation even
worse, the users
inside the high
rate areas need
to wait for those
outside to finish
transmitting.
Throughput is
reduced even
further.
And If You Try To Spread Out the Cells
There Is A 2nd Impact:
Most of the
coverage area
now has the
lower air rates
So most users
get the lower
rates, and lower
throughput.
1
6
11
6
11
1
11
1
6
Making the
situation even
worse, the users
inside the high
rate areas need
to wait for those
outside to finish
transmitting.
Throughput is
reduced even
further.
Microcell Architecture: roaming hell
Every time the unit
changes cells, the call
drops!
Mobile device must
cross several cells
as it moves across
the floor.
1
6
11
6
11
1
11
1
6
Disconnect From AP on Channel 6
Request to join AP on Channel 1
Authenticate with central Radius
Connect and start recovering data
Cochannel Interference and Cell Planning:
Even Worse With 802.11n
802.11n RF patterns are
spikey, less predictable
How the competition Tries To Fix The
Inherent Problems of Microcell
Architecture
Its Band aid Time….
 Bandaid #1 TPC
 Transmission power control: does not work so well,
 There is a fundamental hole in the solution: clients do not alter their
power!!
 Bandaid #2: Dynamic Channel Assignment
 Disconnects any VoIP calls in progress
 Sometimes chooses wrong channel, increasing cochannel interference
Cisco RRM: 2.4 GHz case study
RF Experts went into an office and tested RRM. For some reason, instead of
choosing channels 1,6,11, RRM chose channels 1,7,11 and also put two channel 7
cells next to each other. End result might have looked something like this:
Cochannel
interference
between adjacent
cells on same
channel
Classic cochannel
interference
between nearby
cells on same
channel
(unavoidable in
microcell
architecture)
Some interference
between lobes of
7 and 11
1
7
7
11
1
11
7
11
1
Other Attempts To Fix The Inherent
Problems of Microcell Architecture
 Bandaid #3: Beamforming
 a/b/g only
 Independent tests showed no significant impact to throughput
 Clients can’t beamform, so when they transmit it’s omnidirectional
 Bandaid #4: 802.11k
 Attempts to enhance ability of AP’s to hear each other
 Not very effective as number of AP’s and AP density increases:
algorithm does not scale well.
 Bandaid #5: 802.11r
 Attempts to fix the inherent roaming problem of microcell architecture
 Not a very big success.
 Bandaid #6 802.11e (WMM)
 Can cause dropped VoIP calls
Netronics: we don’t like band aid solutions
So we changed the architecture to this:
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Channel Blanket
Architecture
Can Group Cells As Close As Needed
Benefits:
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11
1. Gapless Coverage
2. Higher throughput,
since more users are in
higher air rate areas
(closer to AP’s)
3. Seamless roaming:
no more handoffs!
Avoiding A Single Collision Domain
Stack the Channel Blankets
For Bandwidth Multiplication
Biproduct: built-in quality of service (segregate traffic type per
blanket)
Dividing A Single Collision Domain
True reuse, for even more bandwidth
NetGlide switch can
transmit to 3 clients on
same channel
simultaneously when
those clients are out of
range of each other
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11
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Bandwidth is multiplied
even further
Built-in Uplink Diversity
Client signal is
transmitted to switch by
the AP’s that hear it.
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11
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11
Switch takes care of
redundant packets
Uplink redundancy ideal
for highly mobile,
mission critical
environments like
logistics and healthcare
Uplink redundancy does
not exist in microcell
architectures. In
microcell, only one AP
can receive client’s
transmissions.
Cisco AP’s: Need A Controller
 Cisco AP’s (even though they are layer 3 devices) cannot
function independently in an enterprise setting.
 The Cisco AP’s do not have computing resources for filtering,
policy enforcement, authentication, encryption, that enterprises
must activate to be secure (ie. WPA2)
 Inherent RF problems of microcell architecture require
controller-based monitoring and control of RF environment
 Requires communication between access points and Cisco
wireless controller(s) + Cisco WCS (Wireless Control
Management System)
 Provides access point device discovery, information exchange, and configuration
 Provides access point certification and software control
 Packet encapsulation (L2 mode) and tunneling (L3 mode)
Cisco Lightweight Access Point Protocol
(LWAPP)
 What it does?
 Reduces amount of processing within access points, freeing up their computing
resources to focus exclusively on wireless instead of filtering and policy
enforcement
 Enable centralized traffic handling, authentication, encryption, and policy
enforcement for an entire WLAN system
 Provide a generic encapsulation and transport mechanism for multivendor access
point interoperability, using either a Layer 2 infrastructure or an IP-routed network
 How?
 Requires communication between access points and Cisco wireless controller(s) +
Cisco WCS (Wireless Control Management System)
 Provides access point device discovery, information exchange, and configuration
 Provides access point certification and software control
 Packet encapsulation (L2 mode) and tunneling (L3 mode)
 Aironet 1250 can automatically detect best available controller
The LWAPP Problem:
Heavy traffic between AP’s and controller is driven into
the layer 3 cloud
Thank you
www.netronics-networks.com