enterprise wi-fi review sales & partner training – 2014

Enterprise Wi-Fi Review

Sales & Partner Training – 2014

2© 2014 Avaya Inc. Avaya – ProprietaryDo not duplicate, publish or distribute further without the express written permission of Avaya.

2

Wi-Fi Review

RF Basics

802.11 Standards

Wi-Fi Operation and Medium Contention


3

RF Propagation - Transmission

Transmission Basics– Radio Waves

– Travel at speed of light– Radios tune to specific frequency – Data is modulated and encoded

– Basic Radio Card Components– Antenna– Amplifiers (Transmit and Receive)– Radio – Baseband (converts analog waves to digital “bits” )


4

RF Propagation – Range/Coverage/Capacity

Transmission Basics– Range

• Operating distance between two radios that wish to communicate– Access Point to Station– Station to Station

– Coverage • Total area wherein radios can maintain connection to Access Point

– Range vs. Capacity - The greater the coverage area…– …the more wireless stations can be covered– …the less bandwidth available to each user– …the lower data rates will be at the edge– …the more likely the chances of “hidden nodes”


5

RF Propagation - Inhibitors

Range Inhibitors - Multi-path

- Interference

- Attenuation


6

RF Propagation - Enhancers

Range Enhancers- Additional transmit power

- Better antenna gain

- Better receiver sensitivity


The RF Link – Range Dynamics Fundamentals

– RF Power is measured in dBm• 0dBm = 1 mw of power

• +10dB = 10 times the power

• 20dBm = 100 mw of power (FCC limit)

• -3dBm = ½ power

– Signal Power Dissipation • Inverse of the square of the distance

– Signal Strength • Expected power at receiver

• RSSI = Receive Signal Strength Indicator (dBm)

– Path Loss• Expected Signal Loss between Two Receivers

– Link Budget• TX Power + TX Antenna Gain – Path Loss + RX Antenna Gain =

Expected Useable Signal at Receiver

© 2014 Avaya Inc. Avaya – Confidential & ProprietaryDo not duplicate, publish or distribute further without the express written permission of Avaya.


8

Wi-Fi Review

RF Basics

802.11 Standards


© 2014 Avaya Inc. Avaya – Confidential & ProprietaryDo not duplicate, publish or distribute further without the express written permission of Avaya.


IEEE 802.11a/b/g/n - Overview

802.11b– Ratified in 1999

– Operates in 2.4GHz spectrum

– Data Rates: 1, 2, 5.5, 11Mbps

802.11a– Ratified in 1999

– Operates in 5GHz spectrum

– Data Rates: 6, 9, 12, 18, 24, 36, 48, 54Mbps

802.11g– Ratified in 2003

– Operates in 2.4GHz spectrum

– Data Rates: 1, 2, 5.5, 11, 6, 9, 12, 18, 24, 36, 48, 54Mbps

– Backward compatible with 802.11b

802.11n– Ratified in 2009

– Operates in 2.4GHz and 5GHz spectrum,

– Data Rates: Up to 450Mbps today (600Mbps in spec)

– Backward compatible with 802.11a/b/g


10

802.11a/b/g Data Rates

Data Rates are achieved by using different modulations techniques

The higher the data rate the most sophisticated the modulation and it is more susceptible to errors

Access/Modulation Method 802.11b 802.11a 802.11g

DSSS/DBPSK 1 Mbps 1 Mbps

DSSS/DQPSK 2 Mbps 2 Mbps

CCK/DQPSK 5.5 Mbps – 11 Mbps

5.5 Mbps – 11 Mbps

OFDM/BPSK 6 – 9 Mbps 6 – 9 Mbps

OFDM/QPSK 12 - 18 Mbps 12 - 18 Mbps

OFDM/16-QAM 24 – 36 Mbps 24 – 36 Mbps

OFDM/64-QAM 48 – 54 Mbps 48 – 54 Mbps


11

The RF Link - SNR

Signal to Noise Ratio (SNR)– Indicates how much useable signal is available

– Higher data rates require higher SNR values


802.11a/b/g/n: Channel Breakdown

Note: The above graphic identifies North American channel assignments, channels varies for different countries based on their regulatory domains


13

802.11 Channels – Cell Planning

802.11b/g/n Channels Available = 3

– Distance between cells on same channel is less than a across a single cell

– Sensitive to co-channel interference (from other cells on the same channel)

– If energy is weak, seen as interference

– If energy is strong, stations will defer

– Bleed-over retards higher data rates

– Greatly reduces overall network capacity

802.11a/n Channels Available = 24

– High Performance: 8 times the capacity

– Far less interference from cells on same channel

– More channels to avoid interference


14

IEEE 802.11n

A combination of technical improvements to the existing 802.11 standard offers:

Increased data rates up to 600Mbps

MIMO (multiple input, multiple output antennas) technology allowing multiple data streams

Ability to bond two adjacent channels increases speed – Maintain backward compatibility with existing IEEE WLAN

legacy solutions (802.11a/b/g)


15

802.11n: Physical Layer (Traditional)

Classic 802.11 Transmitter – Data Stream sent out of one antenna

– Best antenna on receiver selected


16

802.11n: Spatial Multiplexing

Spatial Multiplexing– Source data stream split

– Sent out over separate antennas at the same time.

– Recombined at receiver using MIMO Signal Processing

– Doubles or triples the data rate


17

802.11n: Physical Layer (MIMO)

MIMO and Signal Processing– Multiple antennas

– Improves receive signal


18

802.11n: Channel Bonding

Bonding Channels Together– Increasing the Bandwidth

– Bonds two 20MHz channels to a 40MHz channel – Slightly more than doubles the bandwidth


19

802.11n: Achieving Higher Data Rates

Higher Data Rates and Enhancements– Higher Encoding Rates (Mandatory)

– Spatial Streams (Mandatory)

– Channel Bonding (Mandatory)

– Shorter Guard Interval (Optional)

– Frame Aggregation

Range and Compatibility– Longer Range or Higher Data Rates

– Wi-Fi Certified data rates 300Mpbs

– Most compatible with 802.11a

– Backwards compatible with 802.11bg


802.11n: Data RatesOne Spatial Stream

Access/Modulation Method

Base Data Rate With Channel Bonding

With Short Guard Interval

MIMO/BPSK 6.5 – 13.5 Mbps 13.5 - 27 Mbps 15 – 30 Mbps

MIMO /QPSK 19.5 – 26 Mbps 40.5 – 54 Mbps 45 – 60 Mbps

MIMO /16-QAM 39 - 52 Mbps 81 - 108 Mbps 90 - 120 Mbps

MIMO /64-QAM 58.5 – 65 Mbps 121.5 – 135 Mbps 135 – 150 Mbps


21

802.11n: Data Rates

All Data rates up to Four Spatial Streams


22

Wi-Fi Review

RF Basics

802.11 Standards



23

CSMA/CA

Listen before you transmit– If media is busy wait random interval

– If media free transmit

Two ways of carrier sense – Physical Carrier sense

– Virtual Carrier sense – Network Allocation Vector

Why are data rates so important?


Wi-Fi Frame Types

Management Frames– Association request

– Association response

– Reassociation request

– Reassociation response

– Probe request

– Probe response

– Beacon

– Announcement traffic indication message (ATIM)

– Disassociation

– Authentication

– Deauthentication

Control Frames– Power Save (PS)-Poll

– Request to send (RTS)

– Clear to send (CTS)

– Acknowledgment (ACK)

Data Frames– Data

– Null Function (no data)


25

Duty Cycle and Channel Utilization Duty Cycle:

– The proportion of time that the media is being used.

– If you see duty cycle of 50% it means you only have ½ of the time available to transmit packets in the air.

– Half of the time means half of the available bandwidth. Instead of 20Mbps you only have 10Mbps.

– You can call duty cycle also channel utilization. But the complementary of duty cycle is available or free air time. That is what you want to have.

Factors that affect free air time

– Number of beacons and number of SSIDs

– Near APs in the same channel

– Low data rates due to Bcast, Mcast

– Weak clients signal at low data rate

– Retransmissions

– Interference

– Simply Traffic!!


26

The Impact of Beaconing – The permanent DC

Beacon size:

– 225 bytes in 11n and around 170 bytes in 11bg

Usual beacon data rate in 2.4GHz:

– 1Mbps

Beacon interval:

– 100ms

Used bandwidth:

– 0.000001x225x8x10= 0.018 sec– Around 2% of the bandwidth is used.

Now: If we have 4 SSIDs configured and we can see 3 radios on the same channel from a particular location that means:

– 2% x 4 x 3 = 24% Ouch!!

Is this a problem?

– It depends on the usage. E.x. one Laptop cart vs 1:1


27

Duty Cycle – Is it fixed or variable?

I see 31 different APs, with 4 SSIDs it is more than 6 Avaya IAP radios in Channel 11 in this location. Crazy!!!

Total packets 10,047 : Management frames 8,062 : Data 242

Percentage of management frames 80%

80% Management of the total is not a problem per se. When there are no users at all, the management frames % would be even bigger.

Duty Cycle of 50% without knowing the data/management distribution is not a problem either

The problem is that the duty cycle is 50% and it is based out of Management frames

Consider also the probe request induced traffic.


28

Congestion – The Variable Duty Cycle

The air is being used by 802.11 traffic to a point that the performance is not optimal. The congestion is time of the day dependant.

It can be caused by:– Too many stations for the amount of channels

– Unnecessary broadcasts from the wire and wireless

– Traffic from rogues devices in the vicinity

– Just traffic


29

Congestion – Broadcast on the Wire Testing for wired congestion

– Use Wireshark on the wire and sniff for a period of 2 minutes

In that switch port you are only supposed to see broadcast, multicast (if IGMP snooping is not enabled) and unicast addressed to you.

Captured in those 2 minutes 1,000,000 multicast and broadcast bytes combined. For a 250 byte packet is only 33 packet/s (not too much for a wired switch (100BT or GigE)

Now the same traffic in the air transmitting through a 11bg radio

– 1,000,000 x 8 x 0.000001 = 8 seconds out of 2 minutes is 6.5% duty cycle now if there 4 array radios seen in that location in the same channel that means more than 25% utilization in the air is due to broadcast in the air

How do you fix it? – Several options

– Segment wired from wireless traffic

– Avaya Clean Air Filters

– Use Broadcast optimization in the array

– Use 11g only (if OK with customer)

– Arp filter (pass-thru or proxy)


30

CCA (Clear Channel Assessment) – Rx Threshold

Clear Channel Assessment happens in the physical layer and determines the current state of use of a wireless medium.

There is a threshold of energy detected (coherently) that determines whether the media is busy or not and triggers the CSMA algorithm. This is the basis for contention avoidance.

Lesson of the day: when the energy in the channel is higher than the CCA threshold You wait !!

You can’t directly set the CCA in the AP, same thing for the wireless client. But you can tune the Rx sensitivity which directly impacts the CCA. The CCA is 2 to 3 db higher than the Rx sensitivity. If Rx sen = -85dbm CCA = -83dbm

Case example


32

Wi-Fi Getting Connected: RF Level

Client Association– Clients join the Wi-Fi infrastructure through an

authentication/association process

– Probe Requests/Responses sent periodically by stations to update information about wireless environment

enterprise wi-fi review sales & partner training – 2014

Documents

avaya proprietary

avaya confidential proprietary

review rf basics

attenuation slide

medium contention slide

signal loss

mw of power fcc limit

station station