Wireless LAN Design Guide for High Density Client Environments in Higher Education 7DEOH RI &RQWHQWV $ERXW WKH *XLGH 5HODWHG 'RFXPHQWDWLRQ ([HFXWLYH 6XPPDU\ ,QWURGXFWLRQ 7DUJHW (QYLURQPHQWDO &KDUDFWHULVWLFV IRU :/$1V LQ +LJKHU (GXFDWLRQ (QYLURQPHQWV 3ODQQLQJ Design Point #1: Establish and Validate a Per-Connection Bandwidth Requirement 6 Design Point #2: Calculate the Aggregate Throughput Required for the Coverage Area 7 DQG 6FDODELOLW\ +RZ PXFK EDQGZLGWK ZLOO D FHO
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Wireless LAN Design Guide for High Density Client Environments in Higher Education About the Guide 7KLV GHVLJQ JXLGH SURYLGHV HQJLQHHULQJ JXLGHOLQHV DQG SUDFWLFDO WHFKQLTXHV IRU GHVLJQLQJ SODQQLQJ DQG LPSOHPHQWLQJ D ZLUHOHVV /$1 :/$1 ZLWKLQ D KLJK GHQVLW\ HQYLURQPHQW LQ D XQLYHUVLW\ RU FROOHJH FDPSXV +LJK GHQVLW\ LV GHILQHG DV DQ\ HQYLURQPHQW ZLWK D ODUJH FRQFHQWUDWLRQ RI XVHUV VXFK DV D FODVVURRP OHFWXUH KDOO RU DXGLWRULXP ZKHUH WKH XVHUV DUH FRQQHFWHG ZLUHOHVVO\ VKDULQJ DSSOLFDWLRQV DQG XVLQJ
Wireless LAN Design Guide for High Density Client Environments in Higher Education Introduction :KLOH WKHUH KDYH EHHQ JUHDW DGYDQFHV PDGH LQ WKH VSHHG DQG HDVH RI LPSOHPHQWDWLRQ RI :L )L QHWZRUNV WKH EDVLF QDWXUH RI UDGLR IUHTXHQF\ 5) LV JHQHUDOO\ XQFKDQJHG ,QFUHDVLQJ WKH QXPEHU RI XVHUV ZKR FDQ DFFHVV WKH :/$1 LQ D VPDOO SK\VLFDO VSDFH UHPDLQV D FKDOOHQJH 7KH VWHSV DQG SURFHVV IRU D VXFFHVVIXO KLJK XVHU GHQVLW\ :/$1 GHVLJQ WKDW FDQ EH SURYHQ LPSOHPHQWHG DQG PDLQWDLQHG XVLQJ Cisco’s Unified Wirel
Wireless LAN Design Guide for High Density Client Environments in Higher Education )LJXUH &DOFXODWLQJ 8VHU 'HQVLW\ In a high-density environment such as a lecture hall or auditorium, the densities of users in the occupied space increase dramatically. User seating is typically clustered very close together to achieve high occupancy. The overall dimensions of the space are really only useful for getting an idea of the free space path loss of the AP signal.
Wireless LAN Design Guide for High Density Client Environments in Higher Education What is ultimately going to effect the client devices more than any other factor is the degradation of signal-to-noise ratio (SNR) through both co-channel and adjacent channel interference driven by co-located devices. Proper system engineering can minimize the impact by maximizing proper spatial reuse but it cannot be eliminated in highly dense environments entirely.
Wireless LAN Design Guide for High Density Client Environments in Higher Education In all cases, it is highly advisable to test the target application and validate its actual bandwidth requirements. Software designers are often required to pick just one average number to represent the application’s requirements when there are actually many modes and deployment decisions that can make up a more accurate number.
Wireless LAN Design Guide for High Density Client Environments in Higher Education 802.11 and Scalability: How much bandwidth will a cell provide? To scale 802.11 networks to reliably deliver consistent bandwidth to a large number of users in close proximity, it is important to examine certain WLAN fundamentals under reasonably ideal conditions. Once the rules are understood, the ways to manipulate them to maximum advantage will be presented.
Wireless LAN Design Guide for High Density Client Environments in Higher Education )LJXUH 0L[HG :LUHOHVV &OLHQW 3URWRFRO 3HUIRUPDQFH LQ D &HOO D J Q GDWD UDWHV 7KURXSXW RI PL[HG D DQG Q FOLHQWV ZLWK 576 &76 Q Q Q Q D 7KURXJKSXW RI SHU FOLHQW 0ESV 1XPEHU RI FOLHQWV The graph above shows throughput rates under varying mixes of HT20 modulation coding scheme-15 (MCS15) 2SS data rates and legacy 802.
Wireless LAN Design Guide for High Density Client Environments in Higher Education Using legacy data rates as a nominal value, Table 3 shows the relationship between cell bandwidth and per connection bandwidth. 7DEOH 'DWD 7KURXJKSXW DQG 8VHU &RQQHFWLRQV SHU :LUHOHVV 3URWRFRO 3URWRFRO 'DWD 5DWH 0ESV $JJUHJDWH 7KURXJKSXW 0ESV ([DPSOH 8VHU &RXQW $YHUDJH SHU XVHU 7KURXJKSXW E .ESV E .ESV E .
Wireless LAN Design Guide for High Density Client Environments in Higher Education )LJXUH 3HU )UDPH &KDQQHO 8WLOL]DWLRQ )UDPH 6L]HV DQG 'DWD 5DWHV LQ D :/$1 The time scale above is in microseconds (µs). At the top end of the chart, a 2048 byte packet is transmitted at 1 Mbps, taking almost .02 seconds of airtime. Only one packet can be in the air at a time, and the faster that packet gets through, the better use made of the time available.
Wireless LAN Design Guide for High Density Client Environments in Higher Education )LJXUH &KDQQHOV RQ 2QH *+] &HOO DQG 5HVXOWLQJ &DSDFLW\ With today’s radio designs, the radio could almost be placed on top of each another, but that would not serve the high-density design well. It would result in the same coverage area of a single cell and likely would not cover the required area, even in a relatively small lecture hall.
Wireless LAN Design Guide for High Density Client Environments in Higher Education What is Co-Channel Interference and Why is it Important in High-density WLANs? CCI is a critical concept to understand when it comes to understanding the behavior and performance of 802.11 WLANs. It is a phenomenon where transmissions from one 802.11 device bleed into the receive range of other 802.11 devices on the same channel, causing interference and reducing the available spectrum and resulting performance.
Wireless LAN Design Guide for High Density Client Environments in Higher Education )LJXUH :/$1 &RYHUDJH 0RGHO %DVHG RQ 'DWD 5DWHV In any Wi-Fi design, the effects of CCI can be limited by isolating the individual cells from one another through the use of non-overlapping channels and natural environment attenuation (walls, ceilings, file cabinets and cubes). We would not place two APs on the same channel directly next to one another intentionally.
Wireless LAN Design Guide for High Density Client Environments in Higher Education The wireless LAN controller maintains two lists of APs, Figure 10, both transmit and receive (TX and RX) neighbors that indicate how other APs hear a selected AP and how a selected AP hears other APs. This can be viewed using the Wireless LAN Controller (WLC) Configuration Analyzer tool and used to tune the resulting network and identify sources of RF as the APs themselves see it.
Wireless LAN Design Guide for High Density Client Environments in Higher Education Additionally, if the WLAN is located in a regulatory domain where the bandwidth to deploy four channels is available (e.g., availability of channel 13 and 14) unless the WLAN is sufficiently isolated from every other network it is likely that someone will deploy using the standard 1, 6, 11 model and drastically increase the interference to the WLAN. If it is necessary to maximize a 2.
Wireless LAN Design Guide for High Density Client Environments in Higher Education 802.11n - 20 MHz or 40 MHz Channels? 802.11n can operate in a 40 MHz channel by bonding two 20 MHz channels together and this significantly increases throughput. However, this is reserved for burst mode transfers only. It is only practical to do this in 5 GHz because 2.4 GHz is already limited by the number of channels available.
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Wireless LAN Design Guide for High Density Client Environments in Higher Education Non Wi-Fi Interference and the High Density Network The important role of non Wi-Fi interference in the high-density network should now be clear. The success of a high-density WLAN will be compromised if any non Wi-Fi interference is operating within the same environment. Non Wi-Fi interference has a much larger impact on throughput in a high-density environment than unmanaged Wi-Fi energy. This is because 802.
Wireless LAN Design Guide for High Density Client Environments in Higher Education Observation and understanding of the requirements of WLAN users and situational requirements will guide the development of reasonable design goals. 500 users in a room who require simultaneous access to a single resource is a different design challenge than 1000 or 1500 users who only occasionally use the wireless network. Also, be aware that user patterns can and do change with time.
Wireless LAN Design Guide for High Density Client Environments in Higher Education $ UHODWHG FRQVLGHUDWLRQ LV KLJK JDLQ YHUVXV ORZ JDLQ RPQLGLUHFWLRQDO DQWHQQDV • Use of a high gain omnidirectional antenna should be avoided. This type of antenna will increase the size of the cell and the number of users that will be sharing the bandwidth. Higher gain in an omnidirectional antenna design generally means increased horizontal beamwidth with a decrease in vertical beamwidth.
Wireless LAN Design Guide for High Density Client Environments in Higher Education MIMO low gain omnidirectional antenna options for the Cisco 802.11n Series APs are shown in Table 7. If the Cisco Aironet 1250, 1260, or 3500e Series AP are to be used, there are several external omnidirectional antenna options to allow broader mounting options and to meet differing aesthetic requirements. Consult the Cisco Aironet Antenna Reference Guide for full details.
Wireless LAN Design Guide for High Density Client Environments in Higher Education Directional Antennas It is not always going to be possible to solve challenges in a high-density environment using strictly omnidirectional antennas. If a WLAN requires channel reuse within the same floor space or if coverage is required for non-standard areas such as indoor or outdoor arenas, mounting options for a usable design may be limited.
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Wireless LAN Design Guide for High Density Client Environments in Higher Education )LJXUH ([DPSOH RI %RUGHU &RYHUDJH =RQH 0DQDJHPHQW XVLQJ 'LUHFWLRQDO 3DWFK DQWHQQD Normal Coverage HD-Coverage Less Sensitivity FTB Ratio Border Area between coverage and HD coverage Table 8 features MIMO directional antenna products for Cisco 802.11n Series APs.
Wireless LAN Design Guide for High Density Client Environments in Higher Education )LJXUH $GMXVWLQJ 'LUHFWLRQDO $QWHQQD XVLQJ 'RZQWLOW 7KH YDOXHV IRU WKH IRUPXOD DERYH DUH • H = height of the antenna • A = downtilt angle • BW = the 3 dB horizontal beamwidth of the antenna By adjusting the downtilt of the antenna, it is possible to “dial in” ― or add WLAN coverage― to specific areas within the coverage zone. APs and RF energy operate much like light cast by lighting fixtures.
Wireless LAN Design Guide for High Density Client Environments in Higher Education AP Placement Options 2YHUKHDG The most common method of achieving even coverage is to evenly space the APs directly over the clients they will serve. There are multiple options to accommodate overhead mounting of the APs in an unobtrusive manner.
Wireless LAN Design Guide for High Density Client Environments in Higher Education Ceiling heights can be much higher in a college lecture hall than they would be in a normal classroom environment. A normal ceiling height may be 8-12 feet but in a lecture hall it could be 20 feet or more. This will impact the resulting RF levels seen at the client’s position if it is not taken into consideration in the design.
Wireless LAN Design Guide for High Density Client Environments in Higher Education )LJXUH $3V 0RXQWHG /RZ WR WKH )ORRU Shadows Features in a room such as support columns or balconies can represent natural shadows within a room. Under normal densities, such features would require an additional AP to ensure coverage for users placed in such a shadow.
Wireless LAN Design Guide for High Density Client Environments in Higher Education Under Floor Mounting Mounting APs under the floor with the intent of radiating through to the users can provide a great deal of attenuation. This in theory will work and will allow the creation of more pico cells within a given environment. However, based on experience, the number of facilities where this has proven practical remains small.
Wireless LAN Design Guide for High Density Client Environments in Higher Education 7KHVH GHSOR\PHQWV UHVXOWHG LQ VLJQLILFDQWO\ GLIIHUHQW XVHU H[SHULHQFHV LQ HDFK URRP • Room A did not have an even balance of clients on all six of the APs, with a pronounced number staying on the AP that was near the entrance to the room indicating that they never roamed. Performance was moderate, but there were no user complaints.
Wireless LAN Design Guide for High Density Client Environments in Higher Education times together, it shows the percentage of time a Wi-Fi station cannot access the channel. As mentioned previously, Wi-Fi is contention based and while signals are present above the CCA threshold no station can access the channel. 100 percent RF duty cycle is bad. In this case, it is attributable to inefficient spectrum use.
Wireless LAN Design Guide for High Density Client Environments in Higher Education Note that for Room A the scale of the swept spectrogram in the lower left corner of the display had the red level set to -39 dBm and in Room B it was adjusted to -50 dBm. Signals were quite a bit hotter in Room A. Room A had fewer channels and the APs were further from the client; this in turn caused the clients to increase their power.
Wireless LAN Design Guide for High Density Client Environments in Higher Education Site Survey • Visually inspect the site for multipath potential and placement options for the APs and antennas • Walking the site using a good survey tool is highly recommended. Using a Live RF tool such as AirMagnet Surveyor will enable an evaluation of RF propagation and the ability to actively transmit data and evaluate range and data rate coverage.
Wireless LAN Design Guide for High Density Client Environments in Higher Education Best practices include: • Use external USB adapters for survey equipment. • The software can usually be licensed to the adapter and moved from platform to platform, keeping the measurement tool consistent. • Always use the same driver software whether from the device manufacturer or from the tool manufacturer on all tools being used to quantify results in a given environment.
Wireless LAN Design Guide for High Density Client Environments in Higher Education Wireless LAN Controller and Feature Specific Configuration Recommendations Here are some specific configuration recommendations and their function for a high-density environment. This is not a list of specific requirements and individual configuration details will likely be different.
Wireless LAN Design Guide for High Density Client Environments in Higher Education Dynamic Channel Assignment (DCA) Algorithm • Defaults should suffice with the following exceptions: o Avoid foreign AP interference. This tells the DCA to accommodate channels in use by a foreign AP and to attempt to work around that assignment. If on the border with another coverage zone under a separate RF group, enable this (default). Disable this if there are other networks operating that are outside of your control.
Wireless LAN Design Guide for High Density Client Environments in Higher Education It is important to have alternate options available, based on changing factors, and to remain flexible in approach as new requirements and challenges are presented. For example, in most venues, aesthetics will be of paramount importance, and anticipating a design response to an aesthetic critique in advance is useful.
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