© 2006

The Realities of 802.11 “Wi-Fi”

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The Realities of 802.11 Scarcity of Radio Channels Throughput varies with distance Protocol designed for portability, not mobility Mixed mode (b/g) backward compatibility degrades capacity Voice and data contention degrades capacity and service quality

These traits are inconsequential in small deployments.But have major implications for mid-to-large systems.

The Extricom solution overcomes all of the above constraints.

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1

1

1

802.11 Reality #1:A Frequency Constrained Environment Available non-overlapping channels

• 3 for 802.11b/g (2.4 GHz)• Up to 13 for 802.11a (5GHz)

Frequency re-use rarely happens in practice• Clear Channel Assessment (CCA) is range always greater than useable range• Results in co-channel interference and/or collision domain sharing

Re-usedistance

Re-usedistance

Re-usedistance

6611

111

6

11

APs Closer Together bandwidth stays the same or decreases APs Farther Apart bandwidth decreases

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802.11 Reality #2:Variable Throughput The greater the distance from the AP, the slower the connection

and throughput

Mbps

5.51

11

2418

54

36

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802.11 Reality #3:Portability, Not Mobility Protocol is designed for

portability, not mobility Handoff decision is up

to the client, instead of the infrastructure

36Mbps

11Mbps

Bunching:Clients hold on to an AP, even when a better AP is available.

Inefficient Handoff due to “sticky” clients – a few can drag down all others

11Mbps

Edge Users:2.5X more clients at the edge than in the high speed zone!

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802.11 Reality #4:The Impact of Mixed Mode Mixed mode (b/g) backward compatibility degrades capacity

The first 10% of 802.11b users decreases system throughput by 50%

Aggregate Throughput (Mbps)

10 5.9 6.2 6.5 6.8 7.0 7.2 7.4 7.6 7.8 8.0 8.2

9 5.9 6.2 6.5 6.8 7.1 7.4 7.6 7.8 8.0 8.2 8.3

8 5.9 6.3 6.6 6.9 7.2 7.5 7.7 8.0 8.2 8.4 8.5

7 5.9 6.3 6.7 7.1 7.4 7.7 7.9 8.2 8.4 8.6 8.8

6 5.9 6.4 6.8 7.2 7.6 7.9 8.2 8.4 8.7 8.9 9.1

5 5.9 6.5 7.0 7.4 7.8 8.2 8.5 8.7 9.0 9.2 9.4

4 5.9 6.6 7.2 7.7 8.2 8.5 8.9 9.2 9.4 9.6 9.8

3 5.9 6.8 7.6 8.2 8.7 9.1 9.5 9.7 9.9 10.2 10.4

2 5.9 7.2 8.2 8.9 9.4 9.8 10.2 10.4 10.7 10.9 11.1

1 5.9 8.2 9.4 10.2 10.7 11.1 11.3 11.6 11.7 11.9 12.0

0 0.0 22.1 22.1 22.1 22.1 22.1 22.1 22.1 22.1 22.1 22.1

#802.11b 0 1 2 3 4 5 6 7 8 9 10

Clients Number of 802.11g Clients

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802.11 Reality #5:Voice and Data Contention Different traffic types degrade service quality 802.11e is a statistical answer to QoS

• A statistical method – does not guarantee priority• Requires client support