Month: November 2014
The main objective is to verify RF Coverage. The goal is to validate or audit the current WLAN deployment in order to enhance its security and performance. Unlike pre installation site surveys, post installation surveys focus more on the entire site environment.
Verify RF footprint of all installed APs. Use Ekahau Survey or AirMagnet Survey PRO.
First use Passive Survey mode
- Conduct a separate passive survey per media type, IEEE 802.11a, 802.11b, 802.11g, 802.11n.
- Verify that all APs are working with the expected level of coverage.
- Verify co-channel interference and separation. Check for co-channel interference by standing near an access point on one channel and watch for other access points that are on the same channel. Check to see if the signal level on other access points heard on the same channel is at least 19 dBm weaker than the access point that you are next to.
- Check to ensure you have adequate signal levels as surveyed.
- Compare the coverage and data rates of the postinstallation survey with the survey that was performed prior to the installation.
- Make any required adjustments that were not accounted for in the preinstallation portion in order to make the network meet user and throughput requirements.
- Survey by SSID to ensure that roaming is taking place.
- For 802.11n active surveys, use Iperf to verify up and down link speeds.
802.11n APs with 100% duty cycle:
- the 2,4 band when oversubscribed with clients communicating at 144 Mbps may consume up to 70 – 75 Mbps on wired side.
- the 5 GHz band when oversubscribed and using 40 MHz channels with clients communicating at 300 Mbps may consume up to 160 – 170 Mbps on wired side.
- Both bands on the Ethernet Side will consume (75 + 170) = 245 Mbps per AP
Antenna – “an intentional radiator of electromagnetic radiation.
Electromagnetic field – a sine wave that has an electric component and a magnetic field component.
Indoor antennas are always vertically polarized but this is not critical. Polarization plays a role in Outdoor links where a polarization mismatch can reduce the received signal by 20 dBm. Polarization may be an advantage or may be an issue. Advantageous when an outdoor link performance is experiencing interference, shifting the antenna by 90 degrees by rotating or changing polarization type may be enough to mitigate the interference issue. Read the rest of this entry »
Options for powering the AP
- AP model-specific Power module (DC Power)
- Power Injector – combine 48-VDC power with the data signal, sending both to the access point or bridge.
- The AIR-PWRINJ3 power injector for Cisco Aironet 1130AG, 1140AG, and 1240AG Series Access Points works with the power supply provided with the access point.
- The Cisco Aironet Power Injector Media Converter (AIR-PWRINJ-FIB) converts fiber media to Category 5 media and combines the resulting data signal with power for delivery to the access point or bridge.
- The AIR-PWRINJ-1000AF provides 802.13af inline PoE. It accepts 100–240 VAC and outputs 48 VDC.
- The AIR-PWRINJ1500 power injector converts AC power into DC power and sends it along with the Ethernet signal to the access point. It is designed to be used with the Cisco Aironet 1500 Series Outdoor Ethernet Cable (AIR-ETH1500-150) to power the Cisco Aironet 1500 Series Lightweight Outdoor Mesh Access Point.
- PoE from the switch
- Cisco Pre-Standard PoE mode
- IEEE 802.3af standardizedPoE
- 15.4 W of power per port for class 3
- Cisco Enhanced Power for 56-VDC power or 802.3at protocol
- Up to 30W per port
- The difference is that the optimized maximum transmitter power drops from 20 dBm (100 mW) to 14 dBm (25 mW)
What happens when you connect an AP to less power than it is intended ( to 802.3at instead of 802.3af)? The AP will function but:
- AP drops to using a single stream for both bands and through a single transmitter
- Throughput is reduced to 72 Mbps over a 20-MHz channel for 2.4 band and 150 Mbps over a 40-MHz channel
Most APs can function with 12.95 W but if we use a long cable, then the power drawn can reach up to 15W 802.3af for Class 3 device.
No AP should be more than 100m away from the wiring closet. 802.11n APs should connect to GE ports
If your access point is connected to Ethernet inline power, do not connect the local power module to the access point. Using two power sources on the access point might cause the access point to shut down to protect internal components and might cause the switch to shut down the port to which the access point is connected.
Designing the RF network
Define the APs and WLC requirements
This depends on:
- Application requirements
- Data Networks (web browsing)
- 15 to 25 users per AP
- 802.11b users reduce a 802.11g AP throughput dramatically. The 802.11b client still has a maximum data rate of 11 Mb/s per second and a maximum throughput of 7.1 Mb/s.
- Data requires 15 to 20 % overlap
- For an application such as bar code reading, the number of users can increase considerably and this may require using IEEE 802.11g to increase data rates.
- 15 to 25 users per AP
- Location based services
- To avoid co channel interference due to dense deployment, the APs at the edge should be set to monitor mode (only used for location purposes)
- inter-access point separation of between 40 to 70 feet.
- Legacy clients may impact the network and should be taken into account
- Take into consideration protection mechanisms
- Supported channels
- Supported encr yptions
- Data Networks (web browsing)
- Number of users
- Data Rate Supported
- By increasing the access point count and lowering the power, you can improve throughput for users.
Ekahau Site Survey Tool
This tool is used to determine each AP coverage area. It records the signal level, retries, lost packets etc. Ekahau Site Survey comes in a standard version and a Pro version.
- adds the predictive survey which allows us to add obstacles to the map so as to predict how many APs will be needed
- adds the simulated AP features that enables us to add a virtual AP so as to check how coverage would be
- This results in a hybrid between onsite survey and planning mode
CCNP Wireless CUWSS 642-732 Summary Notes 16 : Layer 2 Active Site Survey using AirMagnet Survey Pro
Layer 2 site survey can be performed with AirMagnet Survey PRO to determine the access point placement and coverage. AirMagnet Survey PRO has the capability of doing pre-site surveys (before the install) and post-site surveys (after the install), also known as an audit, to ensure adequate coverage.
In the configuration menu:
- Select the SSID
- Set the Tx power to match that of the AP
- Select Channel Width
- Active Survey – (Default) the wireless network card actively associates itself with the selected access point or SSID, sending and receiving RF packets to and from the access point or SSID. If a specific AP is not selected, then the PC will connect to the AP that has the strongest signal.
- Active with Iperf for greenfield survey – Airmagnet syncs with an Iperf server to test throughput on the uplink and downlink.
- Watch for the following:
- Uplink data rate
- Downlink data rate
- Signal strength
- Signal-to-noise ratio (SNR)
- Percentage of packets lost
- Percentage of packets retried
- Turn power down to at least half of what the 802.11n client supports
- Configure the access point and client for 40-MHz wide channels to improve throughput up to 300 Mb/s. Channel bonding must be enabled on the client and
the access point for 40-MHz high throughput.
- Watch for the following:
iperf -p <port> -s <server>
- Passive – simply listens to the RF data moving through the site, detecting and recording all RF signals and noises in the environment.
When performing a site survey with AirMagnet Survey PRO, at least one active survey of each access point should be completed (two are recommended). When all active access point site surveys are completed, a passive site survey of the floor should be completed.
Pre- Installation Site Survey Procedure:
- Conduct one passive survey of the floor or facility with the SSID set to Any.
- After you have completed coverage of the floor or facility, merge the survey data.
- Merge the survey data by access point
- Then merge the merged access point data files
- Finally, merge the merged access point data file with the passive survey data file.
- review the data for proper placement of additional access points to fill in any null areas.
- Check the AP Noise level
- AP SNR level
- AP Speed
- AP Retry Rate
- Packet loss rate
Active Survey Procedure
- Choose the AP to associate to
- Specify the location of the AP to begin
- walk around the area
- save survey data
Passive Survey Procedure
- Choose passive survey and leave SSID as any
- walk around the area
- save survey data
Generate a Report
AirMagnet can generate 10 different reports:
- Overall Coverage Report by Channel: Contains data about the overall RF signal
coverage on the selected channel
- Overall Coverage Report by SSID: Contains data about the overall RF signal coverage of the selected SSID
- Overall Coverage Report by AP: Contains data about the overall RF signal coverage of the selected access point
- Per Channel Report: Contains signal data of the selected channel
- Per SSID Report: Contains signal data of the selected SSID
- Per AP Report: Contains signal data of the selected access point
- Channel Interference Report: Contains data about the channel interference
- AP Interference Report: Contains data about the interference between the access points
- AirWISE Report: Shows data relating to the AirWISE screen
- Spectrum Analyzer Report: Shows reports on Spectrum Analyzer data
Survey Modes using 802.11n APs.
When surveying for 802.11n, an Iperf server is used with AirMagnet Survey PRO to measure uplink and downlink data rates.
- Greenfield mode: This means no legacy 802.11 devices. All devices are 802.11n-capable.
- Mixed mode: Mixed mode supports both legacy devices 802.11a/b/g as well as 802.11n. This mode uses both a high-throughput preamble and a legacy preamble.
- Legacy mode: Support for 802.11a/b/g clients, no 802.11n clients.
- CCNP Wireless (642-732 CUWSS) Quick Reference Guide by Jerome Henry
- IPexpert’s CCNP CUWSS Wireless Voice on Demand (642-731)
- CUWSS Studnet Guide v1.0
RF Reflectors and Absorbers in the building
- Each 3-dB attenuation reduces the signal strength by half
- Moving objects may also affect the signal
- Break rooms and test labs may produce 2.4-GHz iinterference and create multipath distortion and RF shadows.
- Elevator shafts block and reflect RF signals.
- Supply rooms with inventory absorb RF signals.
- Interior offices with hard walls absorb RF signals.
- Cubicles absorb and block signals.
- Conference rooms have high-utilization requirements
Cisco Spectrum Expert: Active Site Surveys (Layer 1 Sweep)
Recommended tool of choice – Cisco Spectrum Expert
With Cisco Spectrum Expert, you can detect, classify, locate, and mitigate sources of wireless interference to optimize network performance for mobility applications.
Cisco Spectrum Expert is a combination of both hardware and software. Cisco Spectrum Expert is delivered as hardware in a PC card (CardBus) form factor and is a software install. Read the rest of this entry »
Define the Deliverables
A site survey preassessment form to help determine the length and type of survey, what equipment will be needed, and what questions the engineer will need to ask during the walk through the facility.
- Pre-Assesment Form that summarizes customer requirements
- Customer contact information
- WLAN Objectives
- Building to be covered
- Physical Information and Building Size
- Number Floors and layout
- Each floor that will have Wifi
- Location of closet
- Diagram of existing infrastructure
- Scope of the Survey
- Client Devices
- Arrange to meet up with the all the people that will be involved in the project from the sponsors to the IT to the security team.
- This is when you review and finalize the Statement of Work SoW
- Reconsile contradicting answers. Verify scope of the mission.
- Explain the expectations
- Let them know what will not be covered.
- Notify the team which type of survey is going to be conducted:
- Predictive site survey – using a software tool to estimate the number of APs. usually not very appropriate but is chap and usually used to asses the budget.
- Passive Site Survery – Captures the current state in the RF environment, all the channels etc
- Active site surveys – on one BSSID to determine coverage.
- Notify whether it will be a thorough site survey or sample only.
- Complete the customer questionnaie and especially take contact details prior to site survey.
- Obtain Site and Floor maps for the area to be surveyed.
Site survey could be done in 3 steps:
- Virtual site survey using a planning tool for a general overview
- First add the map of the area to be surveyed.
- Layer 1 sweep to discover existing RF
- Actual survey to establish the placing of the APs.
Design Considerations (especially outdoors)
Consider the data rate required at the edge of the cell
- Larger cells offer binary phase shift keying (BPSK) or quadrature phase shift keying (QPSK) data rates at the edge but require fewer hops to wired network.
- Smaller cells may offer quadrature amplitude modulation (QAM) (16QAM or even 64 QAM) at the edge hence increased performance BUT
- More APs are needed to cover the area
- More APs means more backhaul traffic leading to need for multiple backhauls to increase throughput and reduce hop count to wired closet.
- Approximate AP radius per speed offered and area of the cell
- AP with QPSK at the edge can have 0.619 m radius (in open space)
- 16-QAM rate AP offers 0.324-m radius per cell at the edge
- 64-QAM rate AP offers 0.226-m radius per cell at the edge
- Common distances
- MAP to MAP: 100 to 200 m
- Client to MAP: 80 to 150 m
- RAP to first MAP: 200 to 800 m ( If RAP is high, APs at the foot of the building are in the shadow area, and need to go through another MAP to reach the RAP)
- Maximum recommended number of hops to RAP is 4
- AP cell area can be approximated as
Area = Pi (3.14159) x Square of the radius
- For Mesh, neighbouring APs overlap forming a hexagon with aan AP on each side
Indoor Mesh Networks
This is an excellent way of providing coverage in hard to wire environments or where cables cannot be used or if cable length is too long (> 100 m).
Indoor mesh access points:
- Cisco Aironet 1130 Series – controller based
- Cisco Aironet 1240 Series – controller based
The APs deliver network access to users over the 2.4-GHz frequency and use the 5-GHz band to backhaul traffic.
The APs use AWPP (Adaptive Wireless Path Protocol) which is Cisco Proprietary for communication. Because it dynamically learns the best way to route traffic wirelessly across multiple hops back to the wired network, the AWPP ensures maximum network availability. Read the rest of this entry »
Point to Point Wireless Links
Cisco Aironet 1500 Series Access Point can use its backhaul radio to bridge two wired segments in point to point mode. Its a mesh network with only one MAP and no WLAN clients. If Ethernet bridging is enabled, then wireless client access can be provided but is not recommended if the MAP is too high on the rooftop. Read the rest of this entry »
Data Only Coverage
- Does not require a large amount of overlap due to rate shifting; generally 5 to 10 percent, with 10 – 15 % overlap between the cells
- Separation of access points is typically 120 to 130 feet ( 37 to 40 m)
- 2.4 band 802.11b/g propagates through floors. The 5-GHz waveform of 802.11a has approximately half the tendency for a given power to transmit suitable amounts of energy through walls because of its higher frequency. avoid overlapping cells on adjacent floors too.
- All the client devices using 5 GHz must have the hardware support for all 23 channels before RRM should be allowed to configure all 23 channels. (this feature can be disabled for the 5GHz band)
- If no legacy clients then 1-Mbps and 2-Mbps data rates should be turned off
- Ladder and Aerial Lift Safety – horizontal distance from the top support to the footoftheladder is about one-fourth of the working lengthoftheladder. Do not exceed the lift maximum load, taking into account the worker, the materials, and the tools.
- Self-supporting (foldout) and portable ladders that are not self-supporting (leaning) must be able to support at least four times the maximum intended load.
- The angle of the ladder should be such that the top of the ladder covers a fourth of the working length of the ladder
- If you need access to the ceiling for access point placement do
not use a forklift; use an aerial lift with a safety harness.
- Site-Specific Safety – It might require safety clothing and training so one needs to prepare before hand.
- FCC Safety Rules – OSHA 1910.97 has listed RF as a hazardous environment so safety should be taken when dealing with wireless equipment.
- Enterprise-Specific Safety – there may be specific safety requirements for some businesses.
- AP-Related Safety – Read the Cisco Installation Guide for your AP before installation and also follow the grounding procedures.
Several countries use the same regulatory rules, forming regulatory domains. They define such things as power of transmission, antenna gain and frequency used.
- A domain – US, Taiwan, Puerto Rico etc – Follow Federal Communication Commision rules
- E domain – Europe, Israel, Mexico, Singapore etc – follow Europe Telecommunication Standard Institute Rules
- Japan – follow Ministry of Communication Rules and their applications are managed by Telec
When performing a survey for 802.11n, signal strength is not an accurate predictor of 802.11n performance. Multipath can actually enhance performance with 802.11n clients.
Disadvantage of non-802.11 hardware is that they may have 2 antennas per band but they both are connected to the same radio circuit so when they receive a signal, the receiver tests each antenna and uses the one that provides the best signal (diversity) thus limits impact of multipath on the received signal. The same antenna that was used to receive the signal is the same one that is used to send
Data rate is just the link speed and not the throughput (download speed).
- 802.11b at an 11-Mbps data rate offers on average a 5.5-Mbps throughput. 11b usually degrades performance for other devices in the other bands. Avoid using this band, unless you have old devices.