WIRELESS NETWORKING WHITE PAPER - astro.co.uk · The demand for wireless networking is increasing...

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WIRELESS NETWORKING The future of wireless and what you can do to improve what you have while you are waiting

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+44 (0)203 058 7770 | [email protected] | www.astro.co.uk 2

Table of Contents Introduction ..................................................................................................................................................... 4 The Need for Proper Survey & Survey Tools ................................................................................................. 5

Predictive Software Survey ................................................................................................................ 6 On-Site RF Survey ............................................................................................................................. 6 Active RF Survey ............................................................................................................................... 6

Wireless Security ............................................................................................................................................ 7 Wireless and BYOD ........................................................................................................................................ 8 Wireless Management .................................................................................................................................. 10

On-site Wireless Network Management System ............................................................................. 10 On-site controller based system ...................................................................................................... 10 On-site virtual controller based system ............................................................................................ 10 Cloud based management ............................................................................................................... 10 Hybrid Colocation Hosted ................................................................................................................ 10

The Future of Wireless Networking .............................................................................................................. 11 IEEE 802.11ac Wave 1 .................................................................................................................... 11 IEEE 802.11ac Wave 2 .................................................................................................................... 12 IEEE 802.11ad ................................................................................................................................. 12 IEEE 802.11af .................................................................................................................................. 12 Light-Fidelity - an AP in every light bulb ........................................................................................... 12 Software Defined Networks ............................................................................................................. 13 Frequency Selective Surfaces – if you can’t raise the bridge lower the water ................................. 13

Network Performance Improvements ........................................................................................................... 13 Know your applications and users… ................................................................................................ 14 Maintain balance… .......................................................................................................................... 14 Make a break from the noise… ........................................................................................................ 15 Design for winners… ........................................................................................................................ 15 One, six, eleven, Wi-Fi heaven… .................................................................................................... 16 Don’t be tempted to throw more APs into the mix… ........................................................................ 16 And the (5GHz) band played on… ................................................................................................... 17 External antennas to the rescue, or not… ....................................................................................... 17 LeSS(ID) is best… ........................................................................................................................... 17 Heaven may not be right for you right now… ................................................................................... 18



The view of the (auto channel and power) management… ............................................................. 18 That’s another fine mesh you got me into… .................................................................................... 19 Legacy support for vintage performance… ...................................................................................... 19

Summary ...................................................................................................................................................... 19 About the author ........................................................................................................................................... 20



Introduction The demand for wireless networking is increasing rapidly. The majority of people carry more than one mobile device whether that is a smart phone, tablet, ebook reader, laptop or other work or leisure device. In addition to this, machine to machine communications are now also placing demands on our wireless networks. Many organisations have wireless networks in place to provide public Internet access for staff and guests. Others have wireless networks for specific corporate functions such as warehouse management systems and point of sale systems. Wireless networks now face more complex demands such that may include a combination of corporate network for corporate devices, corporate voice, corporate network for personal devices (BYOD) and guest access. Enterprise wireless networks comprise Access Points (APs) and client devices. APs are connected to the fixed network infrastructure by cabling or if in a meshed wireless installation via another AP. A client device must associate with an AP before it can communicate with the network. A wireless network is surveyed and designed to ensure client devices can associate with APs effectively, and then transmit and receive efficiently and in line with application and user requirements, even when the user and client device are mobile moving from one AP to another. Whether you are considering installing a wireless network for the first time or you are upgrading your existing wireless network to accommodate a new application, mobility requirement or a BYOD strategy, this document outlines important preparation, design and implementation considerations.



The Need for Proper Survey & Survey Tools There are so many environmental factors to be taken into consideration when designing a wireless network. Not least the two frequency bands used for wireless networks have significantly different characteristics. Wireless survey and analysis tools are expensive and many installations are deployed without due diligence. We strongly advise surveying any proposed business wireless network environment, the only exception being small installations of say one to three wireless access points with no specific performance, mobility or service level guarantee requirements.

Before an RF survey can be completed the wireless technician must have a thorough understanding of the application, device and user profiles. From this information the wireless technician will determine the frequency band to be used and the signal strength and signal to noise ratio limitations for the installation to be successful. At this stage we are more interested in the wireless performance design parameters rather than other aspects such as security, management and monitoring. Another vitally important aspect of the survey is to determine the location of data and/or power outlets for the APs. It is important to note that IEEE 802.11ac APs may require two data outlets if the switch is not PoE+ capable. If the APs do not support PoE or the AP will be part of a wireless mesh power outlets are also required. It is important to understand that an RF environment is constantly changing. The wireless survey is a snap shot at that particular time. In the majority of installations this will be sufficient to allow the wireless technician to develop and effective design. A wireless network design based on the results of an effective survey will enable further adjustments to be made by changing channel or reducing or increasing the transmit power of the APs (within legislative limits). Some wireless vendors automate this process dynamically allocating channels and controlling the power levels to maintain optimum RF cover.



Our wireless technicians use one or more of three wireless survey techniques to gather sufficiently accurate survey results to arrive at an appropriate design to meet specific application requirements:

• Predictive software survey • On site RF survey • Active RF survey

These are outlined below… Predictive Software Survey For an initial survey a wireless technician may use specialist software that allows us to import floor plans and then add some detail about the building materials. The wireless technician can then place virtual APs on the plan. The AP frequency and power levels can be set to allow the software to predict the wireless cover. These software packages are very good tools to provide an estimate of the density and approximate positions of APs required to provide the required cover, and therefore, provide budgetary costs. It is important to understand that predictive software surveys can never be totally accurate. Unless specific performance requirements or service level guarantees are not an issue the results of predictive software surveys should not be used without verification using one of the other survey methods. On-Site RF Survey Our predictive survey software can also be used to plot RF data onto the floor plan while walking around the site. This provides more accurate measurement of the RF signal strength in relation to your position in the building and allows accurate assessments of AP density and position. In addition to using the survey software a wireless technician can also view the RF environment with a spectrum analyser. The spectrum analyser helps the technician understanding of the RF environment in detail. Any signal other than the signal being monitored (i.e. the signal your device is trying to receive at any given time) is noise that will reduce performance. Noise includes signals from all other wireless network APs and devices including those within your own network, as well as external noise sources such as Bluetooth devices, microwave ovens, baby monitors, audio-visual systems, lighting control systems and many more. Noise has a significant effect on the design of a wireless network so it is as important to understand the noise as it is to understand the characteristics of your APs. To provide an accurate view of the environment the technician may erect temporary APs on stands. These are sometimes referred to as ‘AP on a stick’. Active RF Survey Where there is an existing, pervasive wireless network, the wireless technician may use the live APs to carry out an RF survey. However, this method is most commonly used when troubleshooting an existing wireless network.



Wireless Security Wireless security is often the greatest concern for any organisation. Radio frequencies from wireless networks generally spill out way beyond the physical boundaries of an organisation making it possible for a non-authorised user (drive by hacker) to connect to your network from outside the building. In addition to this, non-authorised staff, contractors or visitors may also gain access to the wireless network from within the building. On this last point, a wireless installation configured with the appropriate level of security will be more secure than the majority of wired networks where spare ports are left connected even in meeting rooms and public areas. As with any network security it is important to understand the purpose of the wireless network and understand exactly what it is you are trying to secure. If your wireless network for staff and visitor Internet access will require less security than a wireless network providing access to corporate systems. Most enterprise wireless networks are multi-purpose with two or more networks (SSIDs), if so, each network or SSID will have its own security requirements. For public Internet access only networks, access can be allocated for specific time periods such as one hour, one day or one week. Access may be granted by a receptionist or by someone else in the organisation with authority to grant access. The main reason for security may be to prevent unauthorised use of the organisations Internet bandwidth and to prevent hackers using the public network to attack a third party network. Some organisations choose not to secure their guest networks to remove the administration overhead. However, this overhead can be minimised using simple receipt printers to distribute access codes, or by having pre-printed access codes. The access method will depend on the options offered by each wireless network vendor. Corporate network access security requires careful consideration. When providing access to corporate data it essential to restrict access to authorised users only. Hiding corporate SSIDs or restricting access to a specific group of Ethernet MAC addresses has no real security value. Both can be overcome very easily. The simplest method of securing corporate wireless networks is to use an encryption method with a WPA2 pre-shared key with a minimum of 20 characters. This is a very basic level of security and if it is to be used over a longer term, the pre-shared key must be changed regularly to maintain a reasonable level of wireless security. PSK can be unwieldy especially as all wireless network users are likely to need to change their keys whenever someone leaves the organisation. In practice, it is not uncommon to see pre-shared keys hand written on Post-it notes in workplaces.



Wireless security can be strengthened by introducing an authentication process to gain access to the wireless network. This may be facilitated by a separate RADIUS platform and/or integrated into the organisation’s directory services such as Active Directory. This removes the need to constantly update access keys and as soon as a user leaves the organisation their RADIUS or Active Directory account can be disabled thus blocking wireless access.

RADIUS and Active Directory integration will provide Authentication, Authorisation and Accounting (AAA) providing a good level of access security along with an access audit trail. AAA may be a minimum requirement where formal compliance is required such as PCI DSS (Payment Card Industry Data Security Standard). Some wireless vendors provide an integral compliance reporting facility that enables automatic reporting and report distribution detailing any compliance shortfalls across the network. Network management platforms with compliance reporting may also be available as an add-on but this will depend on certain features being available on the existing wireless infrastructure. Wireless security is often dictated by the client device. If an organisation must use devices with limited security features it is advisable to create a specific network for those devices and restrict access from the devices to the specific systems they need to access using access lists or firewall rules. Some wireless vendors have integral firewall capabilities while others require an external firewall to provide restricted access.

Wireless and BYOD A corporate wireless network is an essential element for a Bring Your Own Device (BYOD) strategy and facility. The Bring Your Own Device phenomenon is changing the way organisations view and address their network access and security arrangements. Some organisations are still taking a firm line and banning use of personal devices on their networks while at the opposite end of the spectrum there are organisations providing cash payments for their staff to buy their own work equipment. The majority of organisations fall somewhere between these two extremes with many poised but unsure how to implement a strategy whilst protecting the organisations customer and client data and intellectual property. Whatever your stance, your policy must support your BYOD strategy whilst maintaining a level or multiple levels of security appropriate to your organisational needs.



There are three main aspects of a BYOD enabled network…

• Authentication • Client Device or End Point Security • Access Control

Authentication is a basic requirement for any network access to maintain confidence that the person accessing our systems and services is the person they say they are. In a BYOD environment we have the added complication that the device is – initially at least - unknown to our organisation. The authentication may be handled by a separate BYOD authentication service, your existing authentication service or a hybrid of both. Managing the security of end points also takes on a new level of complexity when the device is not under the control of the organisation. Additional systems and policies are required to protect corporate data and intellectual property. Typical end point security facilities for BYOD devices include security posture checks to ensure the device is free of any vulnerability or virus and malware infections, and the ability to either factory default the device or specifically remove corporate data in the event of the device being lost. Access Control determines what an authenticated user can have access to depending on other factors such as the device they using, the location they are accessing from and the time of day. Access Control may be implemented specifically for BYOD devices, or it may be a fully implemented Network Access Control facility that controls access to every switch port or wireless access point in the network.

Organisations are unlikely to have the IT resource available to deal with establishing the security status and then on-boarding a plethora of personal devices onto the corporate network. Some wireless and security vendors have addressed this potentially very costly issue by introducing BYOD solutions that automate the on-boarding process. Using a combination of policy management, security posture checking and Network Access Control allows pre-determined, granular policies to be set and maintained to ensure users and their devices are securely on-boarded without IT intervention. When combining on-boarding solutions with Mobile Device Management and Mobile Application Management solutions the demands on IT resource can be minimised.



Wireless Management There are several options available for wireless management from on-site to cloud managed systems. The available facilities vary from vendor to vendor. A brief outline of some of the management options follows… On-site Wireless Network Management System This is a basic solution using a vendor agnostic Network Management System managing an estate of multi-vendor APs. The major benefit of this solution is that it can be added on to an existing installation. On-site controller based system All APs in the network are managed by a central controller providing security, access control and traffic management capabilities. Some controllers have an integral firewall function providing very secure wireless access. It can be difficult scaling the controller in growing networks. On-site virtual controller based system As for the on-site controller based system but where one of the APs assumes the role of a virtual controller. Cloud based management All APs in the network are managed by a Cloud management solution. This is extremely scalable from a few APs to several thousand (vendor dependent). Some organisations are concerned about security especially as the Cloud management platform could be hosted outside of the UK. Hybrid Colocation Hosted Provides all of the benefits of a Cloud managed solution from the safety of the organisations own data centre.



The Future of Wireless Networking Wi-Fi and mobile communications are merging into one integrated wireless network. Many organisations are using Wi-Fi to supplement mobile phone cover within buildings or in areas beyond reach of a mobile cell. Both Wi-Fi and mobile technologies have their challenges. Telecommunications network developers are constantly up against the laws of physics when trying to achieve more bandwidth from a particular media. Wireless developers have the added complexity of a completely unbounded transmission media. When transmitting over a copper or optical fibre cable, the transmission is contained within the dedicated media. With wireless there are very limited bands within the frequency spectrum allocated to wireless networking and these are shared with many devices. In addition to new wireless standards using new frequency bands and/or modulation techniques, developers are also working on adapting the fabric of buildings to enable wireless technicians to contain or pass certain frequency bands. This section provides a snapshot of some of these developments. IEEE 802.11ac Wave 1 This is the first wave of IEEE 802.11ac products that are currently available. IEEE 802.11ac operates in the 5GHz band only and introduces some very clever techniques to increase throughput and improve efficiency. These include three spatial streams (three antennas, although not all APs or client devices will support this), improved modulation, 80MHz channels doubling the throughput of 802.11n, and Explicit Transmit Beamforming. Beamforming is a very interesting development introduced in 802.11n but with many variables and options making it difficult to implement so it was not widely adopted. The IEEE have resolved this issue in 802.11ac. When a wireless AP transmits to a client device the AP does not know where the client device is located, it only knows it is within range to be heard by the AP. Unless directional antennas are used a responding AP will transmit fairly equally in all directions away from the AP. This is very inefficient and it causes interference to all other APs and devices in the vicinity sharing the same channel. Beamforming enables a wireless AP or device to identify the location of the receiver and direct the transmission to the device. This has the potential of significantly increasing throughput and increasing wireless airspace efficiency by reducing the spread of RF unnecessarily.



IEEE 802.11ac Wave 2 The second generation of 802.11ac products is expected 2015. The second wave further enhances the first wave with four spatial streams, 160MHz channels (more appropriate to single AP home deployments than enterprise installations with multiple APs) and the ability to transmit to more than one device at the same time on the same channel (client device must have this capability so expected 2016 for client support). IEEE 802.11ad IEEE 802.11ad or WiGig uses the unlicensed 60GHz frequency band providing a very high throughput over a short range. Although the limited range of a 60GHz system may seem prohibitive in enterprise wireless networks, it may also be a significant advantage. Severe congestion in the 2.4GHz frequency band and increasing congestion in the 5GHz frequency band are making it difficult to achieve service level guarantees in many installations, 60GHz is relatively free, provides multi-gigabit performance and the shorter range means less co-channel interference between and it is inherently more secure. IEEE 802.11ad may also be useful for short haul inter-building links across a town or campus, although there are specific 60GHz point to point millimetre wave radio systems available on the market. IEEE 802.11af IEEE 802.11af or White-Fi uses White Space Spectrum (TV channels) in the VHF and UHF bands. VHF and UHF have better building material penetration than 2.4GHz and 5GHz. Given the proximity to commercial TV stations there are very tight controls on the use of this spectrum including channel allocation based on geographic location. Single channel data rate over a single spatial stream is around 35Mbps with a capability of over 550Mbps using four spatial streams and channel bonding. Light-Fidelity - an AP in every light bulb Li-Fi or Visual Light Technology has been in development for some time. It has the potential of delivering high speed data wirelessly via low cost LED light bulbs using existing lighting infrastructure. Multiple frequency streams of visible light can be used to transmit data. Visible light is part of the frequency spectrum with much greater bandwidth than the existing Wi-Fi frequency bands, this combined with the fact that it is easy to contain (visible light does not pass through walls) means there is significantly more capacity. Visible light can easily be contained within walls so it is inherently secure.



Software Defined Networks Software Defined Networks (SDN) will inevitably play a big part in the future of wireless networking. SDN could enable a wide range of value added facilities such as QoS, combining elements from different vendors to create a best of breed solution, network optimisation, application delivery and management, Network Access Control, security posture checking and many more features delivered on demand. Frequency Selective Surfaces – if you can’t raise the bridge lower the water

Designing wireless networks with smaller cells can be very challenging due to the RF from one AP interfering with surrounding APs. Where possible, the building materials can be used to contain RF from each AP within a room. The ability to contain the RF from an AP will depend on the fabric of the wall. Plaster board, breeze or even brick may not sufficiently contain RF to prevent interference to the surrounding APs. Whereas, foil backed plasterboard or extrapolated metal lath may provide a very effective block. In many cases when the wireless technician wants the RF to

propagate through walls it is blocked and vice versa. The Wireless Friendly Building Forum (an interdisciplinary team made up of several university and industry members) has been carrying out research and development on Frequency Selective Surfaces. The intention is that Frequency Selective Surfaces are used as part of the building fabric to act as a band pass filter blocking certain frequency bands while allow other bands through. For example, it may be desirable to block the 2.4GHz and 5GHz bands, while allowing the 400MHz emergency services band to pass. They have also developed and tested retrofit devices and film coatings that can be attached to walls and windows as well as carrying out research into frequency selective paint, although these may not be commercially available yet.

Network Performance Improvements There are many factors contributing to the success or failure of your Wi-Fi network. This section offers some basic guidance on the radio frequency (RF) aspects of Wi-Fi installations, and in particular multi-AP installations, primarily for the 2.4GHz band as this band presents the most challenges. It is by no means exhaustive but it may save you some time and pain when deploying a new Wi-Fi network or troubleshooting an existing network. This document does not provide guidance on other aspects of Wi-Fi installations such as safety and security which are both vitally important subjects in their own right and beyond the scope of this guide.



Know your applications and users… Wi-Fi channels are a shared medium, similar to the coaxial Ethernet installations of old but with one major difference the wireless clients are not physically connected to the medium. Wireless clients can drift in and out of AP visibility so the Wi-Fi protocol has to take this into consideration. As a result it is important to understand the applications and users, their individual and collective bandwidth demands and user work habits to ensure the Wi-Fi network can support your business requirements. Your Wi-Fi installation will comprise one or more Service Set ID (SSID), this is the name of the network that spans multiple APs. For every SSID each AP will have a Basic Service Set ID (BSSID) which is an Ethernet MAC address. The number of devices supported by each BSSID will depend on the demands of the applications and users. There are no hard and fast rules so it is important to consult your specific application specifications. The initial discovery may include: the number of users to be supported; concurrency of users; minimum operational bandwidth required; Quality of Service requirements; latency and jitter sensitivity; and anticipated future developments. This will enable the wireless technician to determine the technical parameters including: type of technology to be specified (802.11a/b/g/n/ac); RF channel plan; signal strength requirements; AP positioning, choice of antenna; AP cabling; mesh radio requirements; DHCP requirements; and switching and routing requirements. Maintain balance… Always consider the Wi-Fi client with the weakest transmitter. Access Points typically transmit at a much higher power than a laptop or hand-held device such as a scanner or Point of Sale terminal. If the wireless network design does not take the lower transmit power devices into consideration this gives rise to Unbalanced Power Effect or UPE. UPE is a common wireless network issue where the client can see the AP but the AP cannot see the client. It is important to ensure that the Received Signal Strength Indication (RSSI) is sufficient to meet your application requirements. Modulation rate is RSSI dependent so the stronger the signal the faster the modulation rate and the faster the data transfer. Faster data transfer has the added benefit of reducing the time the transmitting device occupies the air space. Bearing in mind only one device can transmit at a time.



Make a break from the noise… The received signal must be clearly distinguishable from noise. It is vitally important to understand noise in Wi-Fi networks. Noise is any signal other than the ‘signal being monitored’ (i.e. the signal you want to receive). Noise includes transmissions from other APs and user devices within your own network so bear this in mind when considering additional APs.

The background noise (sometimes referred to as the noise floor) will ideally be as near to -100dBm as possible but if the noise floor is above -85dBm getting a working solution can become challenging. The relationship between the ‘signal being monitored’ and noise is referred to as Signal to Noise Ratio or SNR. SNR is one of the most important parameters in telecommunications. In areas where there is a very high density of APs achieving a good SNR can be the most challenging aspect of Wi-Fi network design and installation. Many non-IEEE 802.11 devices can and do cause interference especially in the 2.4GHz band. Common culprits include Bluetooth devices, microwave ovens, DECT phones and mobile phones (if they are close to APs or devices). Design for winners…

Wi-Fi clients need to identify the best AP to associate with when they first connect or move away from one AP towards another, referred to as a ‘clear winner’. Ideally this clear winner will be presenting a signal that is 5dB stronger than any other AP in the vicinity. This gives rise to another important parameter referred to as Signal to Interference Ratio – SIR. SIR is the ratio of the signal being monitored from one AP to competing signals from other APs. Achieving a good SIR can be very difficult and sometimes impossible to achieve in multi AP installations. The client has the responsibility of deciding which AP to associate

with, so if there is no clear winner the client may struggle to decide and may keep changing from one AP to another which reduces performance and reliability. Some wireless vendors move this decision responsibility to the APs in the network. The AP controller can decide which AP is best placed to serve the client.



One, six, eleven, Wi-Fi heaven… There are still many commercial Wi-Fi hand-held devices that only support 2.4GHz. In many areas this is a very congested band so AP placement and channel planning is critical. In the UK we have 13 channels available to use, but to avoid overlapping channels there are typically only three useable – 1, 7 and 13. In the US only 11 channels are available with typically only three useable – 1, 6 and 11. To err on the side of caution and cater for devices with US wireless settings, most multi-AP Wi-Fi networks in the UK use the US channel allocation of 1, 6 and 11. Using three channels allows us to create a cellular design alternating channels. This is sometimes referred to as a ‘poker chip’ design and strictly speaking it should not be used as a design, just as a guide, but more on this in the next tip. Don’t be tempted to throw more APs into the mix… Taking RSSI, SNR and SIR into consideration it is reasonably plain to see that adding APs to a network will have an effect on all of these parameters. If you have an area where you are struggling to achieve your desired RSSI it would be easy to just throw in another AP to increase RF power in

that particular location. However, by doing so you are going to put more strain on adjacent APs by reducing their SNR and SIR. It is important to understand the implications of adding another AP into a network. Co-channel interference can be a big problem for 2.4GHz installations. Co-channel interference is when APs sharing the same channel overlap. In this scenario only one of the APs sharing the channel will be able to transmit at any given time. In effect these APs are contending for the channel air space. This problem is common in 2.4GHz installations as it is

common for organisations to keep adding APs in an attempt to improve performance. In doing so they may solve a problem in a small area adjacent to the new AP but cause bigger problems to the other APs in the installation. This is a particular problem in open environments where it is difficult to contain the RF. This is also a problem with installing a simple poker chip design. Using a simple poker chip design combined with AP placement to support the lowest transmit power devices inevitably leads to AP overlap and potentially a serious co-channel interference issue. In some instances this can be alleviated by reducing the AP power. On this point, it may not be possible to reduce AP power in noisy environments due to the effect this will have on SNR - it will bring the signal closer to the noise floor and reduce SNR.



And the (5GHz) band played on… The 5GHz band has been available for many years but despite there being many more available and useable channels in the 5GHz band there are a number of reasons why it does not solve all of our problems, the most important being the lack of client device 5GHz commercial hand-held devices. 5GHz does not propagate as far as 2.4GHz nor does it penetrate building materials as well as 2.4GHz so 5GHz cell sizes are smaller. Smaller cells require more APs which increases the cost of deployment. Later Wi-Fi technologies such as IEEE 802.11n (802.11n can use 2.4GHz and 5GHz) and IEEE 802.11ac (5GHz only) make more efficient use of 5GHz than the earlier IEEE 802.11a but this does not increase cell size nor does it solve the problem of client device support. An important point to consider when designing for 2.4GHz and 5GHz installations using dual band APs is the effect of the higher AP count on the 2.4GHz network – power settings will need to be checked and adjusted to reduce co-channel interference problems. If a dual band system is deployed it is recommended to use band steer if this is available. This will force client devices with 5GHz capability from 2.4GHz onto the 5GHz channel to reduce congestion in the 2.4GHz band. External antennas to the rescue, or not… Use of external directional antennas needs careful consideration. APs with integral antennas are generally fit for most internal purposes. Installing directional antennas is a specialist operation requiring detailed survey results including spectrum analysis of the area before and after the antennas are installed. Directional antennas can be used to increase the working range of a cell as the higher gain antenna will increase both the transit range and the receive sensitivity and may help overcome UPE issues. Directional antennas are also useful to reduce the spread of RF and may be used in certain circumstances to reduce co-channel interference. An alternative to using directional antennas is to use building fabric to shield the RF from a particular AP. You are unlikely to completely block the RF from the AP in any particular direction (other than if you can hide the AP behind a steel lined life shaft or equivalent) but you may be able to reduce the power enough to reduce co-channel interference. When using external antennas the gain of the antenna and the loss of any antenna cabling must be taken into consideration to ensure maximum emitted power levels for each band (relevant to specific countries) are not exceeded. LeSS(ID) is best… You need to keep the number of SSIDs on each radio to a minimum. Every SSID appears as a wireless network device with its own management traffic. Try to keep your Wi-Fi installation to three SSIDs maximum. You can have more but you need to bear in mind the negative effect the additional management traffic will have on performance.



Heaven may not be right for you right now…

In Tip 4 above we discussed the use of channels 1, 6 and 11 for multi AP installations. But what if you really can’t get a working solution due to the number of adjacent APs that are completely out of your control? The main argument for sticking with a structured channel plan based on channels 1, 6 and 11 is that APs in the near vicinity can

see the management activity on the channel and respond accordingly. Unfortunately, responding accordingly in congested environments generally means it will back off and hold up transmission while another AP using the same channel transmits. This also means the APs will have to deal with a lot of Wi-Fi management traffic within the contended channel space. The major benefit here is that although this is noise, it is noise that the AP understands. On the other hand, if we use the intermediate channels (2 -5, 7 – 10), because these overlap with their surrounding channels, any transmission on 1, 6 or 11 will be seen as noise but it will not be noise the AP understands and therefore the AP cannot partake in any management traffic dialogue. As this adjacent channel noise isn’t directly in line with its neighbouring channels there is a chance that the performance will be better than trying to live in the over-crowded 1, 6, 11 jungle. There are different opinions on this subject but when you are faced with having to deliver a network to support your business applications (this is more suited to low demand clients) you need to make use of every tool in the box. The view of the (auto channel and power) management… Many vendors have auto channel assignment and power management facilities that constantly monitor the RF environment and dynamically change the AP configurations to maintain a healthy Wi-Fi network, including configuring around failed APs to ensure the network remains operational. These facilities work very well in the majority of installations but they should never be taken for granted and should always be checked regularly. How often you need to monitor your RF managers view of the network will be dictated by the complexity of your network, it could be weekly for congested networks. Auto channel assignment and power configuration software can make some bad decisions leaving your network exposed to a range of the aforementioned problems, especially co-channel interference. It is not uncommon to find all or most of the APs in a multi-AP installation configured for the same channel while transmitting at maximum power – co-channel interference at its worst! APs have been automatically set to a channel where there is excessive interference, rendering the channel out of action. APs may have their power set so high they are taking out APs belonging to other businesses in the area. There are some instances where the auto management system needs a restart or needs some guidance through configuration and in extreme circumstances a manual configuration is required. If a manual configuration is your only option this will also need to be monitored closely throughout the life of the installation to ensure the configuration is maintained in an optimum state. You will also need to remember that in the event of an AP failure you will need to replace the AP or manually reconfigure the surrounding APs to restore service while a replacement is organised.



That’s another fine mesh you got me into… Wireless mesh is used when it is impossible or cost prohibitive to connect the AP to the network with a data cable. Ideally, as many APs as possible will be physically connected to the network. Any remaining APs will connect to the network wirelessly via neighbouring APs. If the APs are only equipped with a single radio, all radios in the mesh must use the same channel. Therefore, all radios in the mesh and client devices are contending for one channel. Using APs in a mesh configuration should only be used as a last resort, especially in congested environments as you are adding to the RF noise with mesh or back link channels. If you really must use wireless mesh, use dual radios and keep the mesh or backhaul channels away from the Wi-Fi client channels to reduce the impact on client performance. Mesh wireless may not be supported by all vendor equipment. Legacy support for vintage performance… Wireless APs may be configured to support legacy 802.11b protocols by default. This can come at a huge cost. Firstly, if an old 802.11b device associates with an AP that AP has to reduce its performance to the lowest common denominator at the cost of any later generation devices associated to the same AP. There are so few 802.11b devices around now that this is often overlooked as a very low risk. However, an AP configured to support 802.11b will also suffer more from the surrounding noise and that will also affect performance to the point where it can make the network unstable even when there are no 802.11b for miles. If there is an option to remove legacy support, unless legacy support is specifically required, it is best to switch it off.

Summary Wireless networks are becoming a vital element in the enterprise infrastructure and the demands have never been greater with many people carrying several wireless devices. If a wireless installation is designed and installed effectively it will serve your organisation well without a major impact on IT resource. In wireless networking RF surveying is essential to successful wireless network implementation. The survey by far is the most important element in the whole design and implementation process, the key to a success wireless network deployment.



About the author Steve Smith started out in the industry in 1973 as a Post Office Telecommunications Apprentice. After six years he joined Cable & Wireless UK Services and embarked on a retraining exercise at the C&W training school in Porthcurno. In January 1985 Steve co-founded Astro Communications with Rob, who was a colleague at C&W at the time. Steve has been responsible for the design and delivery of some very innovative technology solutions including a satellite overlay system for Wide Area Networks, safety systems for the North Sea Oil industry and many others. As CTO at Astro Steve still loves the industry and the daily challenges it provides. Steve is a Freeman of the City of London, a Liveryman in the Information Technologists Livery Company and is a member of The ITP, The IET and The IEEE.

www.astro.co.uk

+44 (0)203 058 7770 [email protected]

WIRELESS NETWORKING WHITE PAPER - astro.co.uk · The demand for wireless networking is increasing...

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Transcript of WIRELESS NETWORKING WHITE PAPER - astro.co.uk · The demand for wireless networking is increasing...