Part 3 - Wi-Fi Network Design - Cannonballcannonball.tombridge.com/wp-content/uploads/2016/03/Part 3-Wi-Fi... · Since a spectrum analyzer gets below the level of WiFi, ... Ekahau

WI-FI NETWORK DESIGNFUNDAMENTALS OF WI-FI

WI-FI NETWORK DESIGN

SO MUCH INTERRELATED KNOWLEDGE


ELEMENTS OF A DESIGN PROCESS

▸ Customer requirements

▸ Understanding your site

▸ Radio Frequency (RF) planning

▸ Capacity planning

▸ Equipment

CUSTOMER REQUIREMENTS


In this section we’ll talk about:

1. Client devices2. Applications3. Client density4. Budget


CLIENT DEVICES

▸ Different devices have different WiFi cards, and will therefore behave differently on a given network.

A MacBook Pro may have a 3 x 3: 3 802.11n interface, while a mobile device may be capable of 802.11ac 2 x 2: 2.

Surveying your device population and refresh cycle will help establish your design parameters.


CLIENT DEVICES

▸ Various vendors document device capabilities at different levels of detail.

▸ Sometimes (as with Apple) you have to hunt for information or work your way back from published specs.

Apple also occasionally publishes IT-oriented documents regarding deployment of devices that includes details on the capabilities of its devices, but these become dated quickly, as with Apple’s iOS 6 Deployment Guide at https://www.apple.com/ca/education/docs/ios_6_education_deployment_guide.pdf.

Another trick is to look at FCC compliance paperwork to discover equipment chipsets, then work your way back to the OEM to determine specifications.


CLIENT DEVICES

▸ http://clients.mikealbano.com

Mike Albano runs an ongoing project to document the capabilities of common client devices, documenting not only spatial stream capabilities, but also channels that devices can or can not use.

Always worth checking out what’s going on at http://mikealbano.com.

http://clients.mikealbano.com


APPLICATION REQUIREMENTS

Application Required Throughput

Web Browsing 500 Kbps - 1 Mbps

SD Video Streaming 1 - 1.5 Mbps

AppleTV Streaming 2.5 - 8 Mbps

The detailed chart from which this information is taken is in the Aerohive Design and Configuration Guide for High Density Wi-Fi, by Andrew von Nagy, available from Aerohive at http://docs.aerohive.com/330000/docs/help/english/5.1r2/ref/Aerohive_High-Density_Wi-Fi-Design-Config-Guide_330073-01.pdf


DENSITY

▸ How many devices are you going to have in an area?

▸ How many devices will your users carry?

1. A 600 seat lecture hall is a significant challenge due to the number of people involved.2. If you have a staff each of whom carry a laptop, tablet, and a phone, the design expectation is going to be very different from an environment where you’re designing

for every student having a tablet.3. How many devices an AP can handle is a very specific question; there’s no real standard for this, and the veracity of vendor claims should always be tested to avoid

pain.


DENSITY

▸ Critical when you think about environments such as lecture halls or classrooms

▸ Critical when thinking about the use model for Wi-Fi network


BUDGET

▸ Because of the nature of the 5 GHz band, a 5 GHz network requires more equipment, and thus more money.

▸ A budget constructed prior to a project plan will lead to trouble.

SO SING A SONG OF SIXPENCE.

Lin Manuel-Miranda (as Alexander Hamilton)


And under-budgeted project stands an excellent chance of failing completely, so be careful what you get into.

UNDERSTANDING YOUR SITE


In this section we’ll talk about:

1. Facility Size2. Construction, obstacles, and known interferers3. Usage and key spaces4. Neighboring networks5. Network infrastructure


FACILITY SIZE

▸ Facility size can give you a starting point for estimating the equipment required.

▸ Ceiling heights affect coverage and signal intensity.

▸ Multiple floor facilities require special care due to channel overlap issues.

Per Spock in Wrath of Khan, two dimensional thinking is extremely limiting.


▸ Look for concrete, rebar, and elevator shaft; also, lathe and plaster with gypsum lathe

▸ Look for heavy or metal furniture

CONSTRUCTION AND OBSTACLES

The last will be maddening, because (1) they’re everyday objects that most people don’t think about very much; (2) they get moved around without a lot of thought to what they might be affecting.


USAGE AND KEY SPACES

▸ Administrative offices may have only minimal use

▸ Classrooms may have consistent heavy use

▸ Conference room may have intermittent heavy use

▸ A 600-seat lecture hall will be a nightmare and is crucial to identify

You want to document all this, and be realistic about it. As you’ll see when we start to talk about airtime, expected usage combines with airtime requirements to help you define your equipment requirements and your channel planning.


NEIGHBORING NETWORKS

Signal strength and channel overlap of neighboring networks can help you decide what channels to avoid in your RF planning, but be aware that the environment will change unpredictably.

A lot of enterprise-grade WiFi equipment will offer to self-select channels on a dynamic basis. This is worth investigating, but also worth mistrusting to some extent.


INTERFERENCE SOURCES AND SPECTRUM UTILIZATION

Spectrum analysis can give you more, though. In this picture we’re seeing the utilization of 2.4 GHz channels in addition to their presence and relative strength. Busier channels show warmer colors (red) and higher utilization levels. Since a spectrum analyzer gets below the level of WiFi, we can see communication that isn’t WiFi.


▸ Does cabling exist already?

▸ Do you have someone to handle cabling?

▸ Is your switching adequate?

▸ (And what about power?)

NETWORK INFRASTRUCTURE (PHYSICAL PLANT)


SITE SURVEY

How are you going to use a site survey to develop a plan?

▸ “AP on a stick” survey

▸ Predictive site survey


▸ Ekahau Site Survey

▸ Fluke Airmagnet

▸ Tamograph Site Survey

(Bring all the dollars)

PREDICTIVE MODELING SOFTWARE

Predictive modeling uses specialized software to estimate coverage using known information about Wi-Fi equipment and gathered information about a facility, e.g. it has pre-programmed attenuation characteristics of construction materials built-in.


▸ Speeds up the planning and design process

▸ Liable to built-in assumptions, e.g. how much attenuation a particular type of wall imposes

PREDICTIVE MODELING SOFTWARE

AP ON A STICK

ACTUALLY DEPLOY AND TEST ONSITE

AP on a stick is useful for gathering basic performance metrics, but becomes difficult to impossible when attempting to gather complex information or plan extremely large installations.


A hybrid process

1. Visit site to gather facility information and perform attenuation and interference testing

2. Run a predictive survey using a planning tool

3. Validate the predictive survey onsite during or following the install, adjusting as necessary.

SO WHAT DO PROFESSIONALS ACTUALLY DO?

RF AND CHANNEL PLANNINGWI-FI NETWORK DESIGN

We want to ensure that our clients receive adequate radio signal and suffer the least possible contention and interference, so in this section we’ll talk about:

1. Channel selection2. Channel width3. DFS (again)

RF PLANNING

CHANNEL SELECTION GOAL

▸ Pick channels to minimize co-channel interference and avoid adjacent channel interference.

RF PLANNING

CHANNEL SELECTION (2.4 GHZ)

▸ 3 non-overlapping 20 MHz channels in North America:

1, 6, 11

11

1

1 6

6

11

11

61

Some equipment vendors in the consumer space provide an option for 40 MHz bonded channels, which removes all ability to prevent channel overlap. You shouldn’t ever do this.

Designing a 2.4 GHz channel plan without overlap is difficult; in a multi-floor environment it’s virtually impossible.

In addition, the attenuation characteristics of 2.4 GHz are such that neighboring networks will impose CCI and ACI from greater distances than you might expact.

Successful design for client density is nearly impossible using only 2.4 GHz channels.

RF PLANNING

CHANNEL SELECTION (5 GHZ)

▸ Many more channel options

▸ Many more caveats

RF PLANNING


▸ 9 x 20 MHz channels + 15 x 20 MHz DFS channels

▸ Options for wider channels (40 MHz and 80 MHz), which can provide higher performance*

▸ Wider channels reduce the number of channels available

*Assuming your clients can take advantage of that higher performance.

Wider channels provide for faster connections, but reduce the number of channels available.

RF PLANNING

AVAILABLE 5 GHZ CHANNELS (UNITED STATES)

Note how as channels get wider, the number available falls. Pay particular attention to the 160 MHz channels.

RF PLANNING

▸ Keep in mind that 5 GHz signals attenuate more quickly than 2.4 GHz signals.

Courtesy NASA/JPL/CalTech


5 GHZ AND DFSWAIT, THERE’S A WRINKLE

15 of the 24 available 20 MHz channels in the 5 Ghz band share frequencies with a variety of civilian and military radar systems, including the Terminal Doppler Weather Radar (TDWR) used at major airports to improve takeoff and landing safety by detecting wind shear associated with thunderstorms

RF PLANNING

APs on these channels must dynamically change their channel if they detect radar emissions.

UNII-2: 52, 56, 60, and 64

UNII-2 Ext: 100, 104, 108, 112, 116, 120, 124, 128, 132, 136, 140

5 GHZ AND DFS

As an example, Aerohive’s cloud controller won’t even allow you to access these channels for use unless you also enable Dynamic Frequency Selection.

In addition, FCC regulations disallow DFS channels within 35 km of Terminal Doppler Weather Radar systems.

Are you in the Pacific Northwest? You’re probably cool.Are you east of the Mississippi? You’ve got some more problems.

RF PLANNING

DFS AND 5GHZ

▸ Excluding DFS vastly reduces the number of available channels of each width.

9 x 20 MHz channels4 x 40 MHz channels2 x 80 MHz channels

CAPACITY PLANNINGWI-FI NETWORK DESIGN

Planning for capacity has superseded coverage as the holy grail of Wi-Fi network design.

1. Equipment specs and limitations2. Power3. Network throughput4. Installation and mounting5. Density6. Airtime

NETWORK DESIGN

CAPACITY PLANNING

▸ Capacity planning can move us away from Wi-Fi standards, and toward reliance on vendor implementations

▸ Standards simply do not exist here

CAPACITY PLANNING

VENDOR REQUIREMENTS

▸ Controllers have upper limits to the number of client devices and APs that they can handle

▸ Controllers are often licensed for a specified # of APs

▸ There isn’t a quantifiable standard for AP capacity.

Ruckus 3025 controller can handle approximately 1000 concurrent clients

CAPACITY PLANNING

NETWORK THROUGHPUT

▸ Wireless APs can move more than 100 Mbps

▸ Check whether your switches can handle speeds required; in many cases you will need gigabit


CLIENT COUNT (DENSITY)

▸ Vendors make various claims about clients per-AP

▸ Many of these claims are “best case”

▸ Ruckus says 500 until you ask about encryption, then says 100 per-radio.

▸ Aerohive claims 100 per-radio

▸ Meraki classifies 40+ devices on an AP as “high density”

Ruckus note at https://forums.ruckuswireless.com/ruckuswireless/topics/max_client_per_apAerohive note at https://community.aerohive.com/aerohive/topics/ap230_maximum_concurrent_user


DENSITY

▸ Wi-Fi is more complicated than an environment in which you connect clients to a switch until you run out of ports.

TEXT

DENSITY AND AIRTIME

▸ The sharing of the bandwidth in an AP makes things more analogous to use of an Ethernet hub.

AIRTIMETHE WEIRD TURN PRO


AIRTIME

Calculated percentage of available time a client device will utilize; determining this requires:

1. Known application bandwidth requirement

2. Known real client performance

We start with the assumption that the TX rate is double the truth.

AIRTIME CALCULATION

Airtime required is expressed as a percentage of available airtime.

TEXT

AIRTIME: IPAD 2

SD Video = 1 Mbps

65 Mbps max TX = 30 Mbps actual performance

Question: If iPad 2 can only provide 65 Mbps theoretical throughput, how much does a 1300 Mbps-capable AP help network performance?

TEXT

AIRTIME: IPAD 2

Ultimately, it sometimes will not matter how fast your APs are, because the client airtime requirements do so much to determine the need.


AIRTIME: IPAD 2

▸ In theory then, 30 iPad 2 units stream 1 Mbps video would chew up all the available airtime on a single access point.

▸ Note how this assumes no performance loss from interference, attenuation, or other sources.

▸ In addition, this assumes no degradation from client transmission collisions.


AIRTIME: ANOTHER WRINKLE

▸ iPad Mini 3 will work on 20 MHz and 40 MHz channels

40 MHz = 300 Mbps TX = ~135 Mbps real

20 MHz = 144 Mbps TX = ~65 Mbps real

Remember to refer to your MCS Index charts for the maximum TX available for a device in a given environment.

AIRTIMEMIX DEVICE CAPABILITIES, AND THINGS GET REAL COMPLICATED.

Think about what happens if you have a requirement for 6 Mbps bandwidth, and a mixed group of iPad mini 3 and iPad 2 devices. Each iPad 2 device will require 20% airtime, which means that 5 iPad 2 devices will chew up all the airtime available.

EQUIPMENTWI-FI NETWORK DESIGN

The equipment considerations we’ll discuss are

1. Power2. Cabling3. Network4. Installation and mounting

EQUIPMENT CONSIDERATIONS

POWER

▸ Access points require power, but are typically installed in hard-to-reach locations.

▸ Power over Ethernet solves this, but requires infrastructure and knowledge to implement successfully.


POWER OVER ETHERNET

802.3af 802.3at

Nickname PoE PoE+ (plus)

Wattage/port 15.4W 34.2W

Wattage/guaranteed 12.95W 25.5W

Two different PoE standards exist, providing different amounts of power per-port. Access points will

802.11ac access points running 3 x 3:3 tend to require PoE+ for full functionality; otherwise they step down to a lower performance level, e.g. 2 x 2:2.


POE BUDGETS

▸ Zyxel GS1900-8

8 ports

802.3af and 802.3at-capable

70W power budget

▸ So how many APs is that?


POE BUDGETS

▸ Zyxel GS1900-8

8 ports

802.3af and 802.3at-capable

70W power budget

▸ So how many APs is that?

2 x 25.4W APs

5 x 12.95W APs


POE BUDGETS

A final consideration for power budgeting is that different manufacturers’ access points draw different amounts of power via PoE, which could make your calculations against power budgets more complex.

Clockwise from top-left, these are the power draw figures for a Cisco Meraki MR42, and Aruba AP105, and a Ruckus R500.

NETWORK AND CABLING



NETWORK AND CABLING

▸ APs will require ethernet cabling for data and power, but how much?

▸ Also note that 100 Mbps will likely be too slow for modern access points and TX rates.

▸ IEEE standards require Category 5 cabling, so beware of Category 3.

Enterprise APs often come with more than one Ethernet port, for several reasons, primarily to provide link-aggregation via two connections. Note that on this Aerohive AP230, PoE is only available on a single ethernet port.

INSTALLATION AND MOUNTING



▸ Vendors typically use omnidirectional antennas in APs, which generate a specific radiation pattern.

▸ In general, vendors design enterprise grade APs for wall or ceiling mounting to provide best coverage

Usually, that means “not like this”.


MORE LIKE THIS

CONCLUSIONSWI-FI NETWORK DESIGN

We’ve seen how a number of elements can influence your design process.

1.Customer requirements2.Understanding your site3.Radio Frequency (RF) planning4.Capacity planning5.Equipment

But what does it all mean?

Documents

Part 3 - Wi-Fi Network Design - Cannonballcannonball.tombridge.com/wp-content/uploads/2016/03/Part 3-Wi-Fi... · Since a spectrum analyzer gets below the level of WiFi, ... Ekahau