Wireless Networking WLAN Troubleshooting Module-11

Wireless Networking WLAN Troubleshooting Module-11
Jerry Bernardini Community College of Rhode Island 4/16/2017 Wireless Networking J. Bernardini

Presentation Reference Material
CWNA Certified Wireless Network Administration Official Study Guide (PWO-104), David Coleman, David Westcott, 2009, Chapter-12 CWNA Certified Wireless Network Administration Official Study Guide, Fourth Edition, Tom Carpenter, Joel Barrett Chapter-12, page 4/16/2017 Wireless Networking J. Bernardini

Troubleshooting Methodologies
A methodology is a standard way to do something and there are many a troubleshooting methodologies Troubleshooting is the process of discovering the unknown cause of a known problem If you know the solution to a problem you are repairing REACT OSI Model Hardware/software Model Symptom, Diagnosis, and Solution Old System – New System System Thinking 4/16/2017 Wireless Networking J. Bernardini

REACT Methodology-Part 1
Research – Gather facts Check documentation Check Google and read Spend at least 15 minutes researching Engage – ask questions without accusing Has any thing change in the last few days? Don’t say “did you change anything?” Have any strange things happened lately? Have others experience similar problems? Is the problem recent or has it been happening for a while? When was the last time it worked? Is it turned on? 4/16/2017 Wireless Networking J. Bernardini

REACT Methodology-Part 2
Adjust – wrongly, many techs start here previous Try different things to find the cause of the problem Update firmware on AP or STA adapter Install new drivers Change settings or disable features Reinstall OS or drivers Configure Put the system back to the original condition Reinstall and configure settings Take Note - Document your findings (in a journal) Record error messages associated with problem (in a journal) Record step-by-step what you did to locate and fix (in a journal) Document what you have learned (in a journal) Create and organization trouble ticket 4/16/2017 Wireless Networking J. Bernardini

OSI Model Methodology –Part-1
Walk up and down the model and analyze each layer Layer 1 – Physical Layer Are the adapters working? Swap out client adapters Is it a cable issue? Is it the wireless or wired part of the network? RF interference? Use a spectrum analyzer Layer-2 Are switches filtering traffic? VLAN configurations? Bridge configurations? Use a protocol analyzer 4/16/2017 Wireless Networking J. Bernardini

OSI Model Methodology –Part-2
Layer-3 Routing tables? AP configurations for traffic? Test with ping , arp, ipconfig Upper Layers Configurations in applications? Client software configurations? Which applications work and which do not? Have new applications been added? Test with Telnet, http 4/16/2017 Wireless Networking J. Bernardini

Hardware/Software Methodology
Certain problems are commonly hardware and some are commonly software Everything is working except one application >software Multiple applications that use the same hardware are not functioning -----> hardware Consider hardware problem/solution lists Consider software problem/solution lists 4/16/2017 Wireless Networking J. Bernardini

Hardware Problems and Solutions
4/16/2017 Wireless Networking J. Bernardini

Software Problems and Solutions

Symptom, Diagnosis, and Solution
Symptoms are associated with specific problems Symptom - Gathering information about the problem What happen? Where did it happen? What Technology was involved? Which users were involved? Has it always been this way? More questions??? Diagnosis – What is the likely cause? Deal with possible cause at a time Try one fix at a time and evaluate This the path to becoming and “expert” Solution – the potential problem fix Try different hardware and software fixes The more try and remember or document the quicker to “expert” 4/16/2017 Wireless Networking J. Bernardini

Wireless Networking J. Bernardini
System Thinking Process of analyzing all interdependent components Don’t focus on the vendor you may not like focus on the problem (don’t blame Microsoft) However, some operating systems and vendors have a history of certain kinds of problems Ask questions that related to “what makes things work” 4/16/2017 Wireless Networking J. Bernardini

System Thinking Questions

Old System – New System Old system - worked yesterday Probably only a single problem Configuration changes? Added applications? Use REACT or Symptom/Diagnosis/Solution New System - is just being turned on Could be multiple problems Could be hardware, software, configurations Break apart the system and test parts Use system methodology 4/16/2017 Wireless Networking J. Bernardini

WLAN Problem Indicators
Excessive Layer-2 Retransmissions Unicast frames must be resent due a variety of problems Produces increased latency Delay between frame sent and error free received frame Produces increased jitter Variation in latency Produces reduced throughput Low Throughput End indicator of one or more problems Retransmission can be major cause 4/16/2017 Wireless Networking J. Bernardini

Retransmissions Effects
Increased latency Increased jitter Reduced throughput Negative effect on applications Latency produces echoes for VoIP Jitter produces choppy audio for VoWiFi phones Most data applications can tolerate 10% retransmission Time sensitive applications require less than5% retransmission 4/16/2017 Wireless Networking J. Bernardini

Causes of Layer-2 Retransmissions
Multipath Signals RF Interference Low Signal to Noise Ratio SNR) Hidden Node Stations Near/Far Nodes AP and Client Power Mismatching Adjacent Cell Interference 4/16/2017 Wireless Networking J. Bernardini

Abnormally High Retransmission Count

All-Band and Narrowband interference
All-band or wideband – signals that cover all or a large portion of a band of frequencies. Narrowband Interference Wideband Interference 2.4 or 5.0 GHz Devices As WLANs continue to gain in popularity, individuals and businesses often find their wireless network impacted by other, adjacent, wireless networks. Another 2.4 GHz wireless LAN operating in the same area can cause performance issues since WLAN technology is a shared media. When two systems attempt to send data at the same time, failed transmissions can occur. This may require both systems to resend data in order to successfully get information through, compromising the efficiency of the network. Whether the technology is being used in the same location, or if a neighbor has RF energy that bleeds into your facility or campus, it will likely cause problems. In this situation, you may have to work closely with neighbors to make certain that both systems can work simultaneously without creating interference for one another. To guard against interference, as well as security issues, you may also need to perform another survey to ensure that your RF energy is contained (as much as possible) within your coverage area. GHz Phone Systems Today, 2.4 GHz phone systems are a hot item. Unfortunately, 2.4 GHz cordless phone systems and WLANs negatively affect one another. At some point, the 2.4 GHz cordless phone coverage will cause the WLAN user to loose their connection with the access point. This is unacceptable and troubling, especially in an environment where business is conducted. The co-existence of a 2.4GHz WLAN and mobile phone system is a stumbling block. Users of 2.4GHz phone systems may have to change to a 900 MHz phone to accommodate the wireless network. In practical terms, it’s smarter to replace a $200 cordless phone than $10,000 worth of networking equipment. Florescent Lighting & Microwave Ovens There is a new breed of fluorescent lighting that operates in the 2.4GHz band. This technology will make it very difficult to mount wireless LAN equipment at ceiling height (where the lighting is located) without creating issues. Similar to a microwave oven, this lighting uses 2.4 GHz RF to excite electrons. Additionally, an older microwave oven that is not sealed properly will leak RF energy and potentially cause interference (as well as a health risk). If your office encounters what appears to be WLAN interference at approximately noon everyday, you may find the problem to be co-workers firing up a microwave located in close proximity to an access point. These devices compete with a WLAN and must be addressed. Potential solutions are to locate the equipment away from one another or even change the technology being used. Try and avoid the obvious; don’t set an access point on top of a microwave oven. Changing channels is not a viable solution since 2.4 GHz lighting and microwaves use the entire 2.4 GHz spectrum. Bluetooth Devices Keep in mind that Bluetooth devices also share the 2.4 GHz band. If people bring Bluetooth technology into a facility with a wireless network, it may create issues for WLAN users. Because 2.4GHz wireless LANs and Bluetooth are incompatible, you may want to make employees aware that roaming the office with personal Bluetooth devices will compromise the operation of the wireless network. Again, since 2.4 GHz is a shared spectrum, neglecting to take into consideration interference created by microwaves, cordless phone systems, satellite systems, lighting systems, and Bluetooth devices can be a serious oversight. Amplitude Channels Freq.

Eliminating Interference
Walk around with a spectrum analyzer to determine the interference frequencies Locate the source and remove if possible Modify source-frequency band, amplitude Change channels Limit coverage area 4/16/2017 Wireless Networking J. Bernardini

Spectrum Analyzers Scan radio frequency spectrum and provides graphical display of results Typically measure signal-to-noise ratio Single-frequency analyzers measure signal-to-noise ratio at specified frequency Helpful in identifying interference problems Thus, helps properly position/orient AP Costly $500 $50,000 4/16/2017 Wireless Networking J. Bernardini

RF Spectrum Analyzers 2.0 5.0 Frequency, f (GHz) 4/16/2017 Wireless Networking J. Bernardini

Handheld RF Spectrum Analyzers –Expensive
Frequency range: 100kHz - 6 GHz. Internal preamplifier with frequency range from 100 kHz - 6 GHz. Displayed average noise level typ dBm (RBW 100 Hz). 0.5 dB typ. level accuracy up to 6 GHz. Resolution bandwidths 100 Hz - 1 MHz, 1 and 3 steps. Wide range of detectors; sample, max/min peak, auto peak, RMS. Cost: $13,500 4/16/2017 Wireless Networking J. Bernardini

Laptop RF Spectrum Analyzers
Fluke Cisco Other Cognio (now owned by Cisco) 4/16/2017 Wireless Networking J. Bernardini

Throughput Possible Solutions

System Throughput System Throughput - The actual number of bits, characters, or data blocks passing through a data communication system, or portion of that system in a given time. Bits per second less communication overhead 802.11b 11 Mbps throughput is 5 Mbps 802.11g 54 Mbps throughput id 22 Mbps 1 5 11 Mbps 2 Mbps 100 Mbps Weakest Link = 2 Mbps Half Duplex  45% x ( 2Mbps) System Throughput  900 kbps 4/16/2017 Wireless Networking J. Bernardini

Throughput PHY Limitations
802.11b (DSSS) Mbps 802.11a (OFDM) Mbps 802.11g (OFDM ERP) Mbps 80211n (ERP , Greenfield, protections) – 200 Mbps Mixed modes reduce maximum potential throughput Wired-Side Bandwidth 10 Mbps Ethernet may not be faster enough for 10 users 100 to 1000 Mbps for multiple APs 4/16/2017 Wireless Networking J. Bernardini

Co-Channel and Adjacent-Channel Interference
More than one WLAN attempting to coexist in the same RF coverage area, on the same channel or a channel that is too close System throughput is effected by this problem Non-overlapping channels are supposed to be 1, 6, 11 Adjacent-Channel interference RF-power from channel-1 could be in channel-6 and channel-6 in channel-11 Caused by APs that too close APs and adapters with excessive power levels 4/16/2017 Wireless Networking J. Bernardini

Channel Interference Adjacent Channel interference - Signal impairment to one frequency/channel due to the presence of another signal on a nearby frequency/channel. Amp. 1 2 3 4 This is not co-channel interference. Use a spectrum analyzer to detect adjacent channel interference. Try moving APs or use another non-overlapping channel, (ie. Channel 1 and 11). Channel Guard Band No Guard Band Overlap Freq. Wide Band

same manufacture for the WLAN devices.
Co-Location WLAN 3-Channel System Amplitude CH-1 CH-6 CH-11 Overlapping Sidebands Freq. DSSS there are three non-overlapping channels 1, 6, and 11. There is actually some interference between channels 1, 6 and 6, 11 due to low power sidebands. This overlap can cause a throughput drop of some 20%. You can analysis the user’s requirements to determine if this reduction will be acceptable. Another possibility is two use channels 1 and 11 which do not have any overlap. Two access point can operate at or near the 5.5 Mbps actual throughput and give an aggregate or combined capacity of 11 Mbps. The three access point system would have approximately 4 Mbps for each with a total of 12 Mbps. (Is the 1 Mbps performance improvement worth the cost of adding a third access point?) CH-1 CH-11  Recommend the same manufacture for the WLAN devices. CH-6

Interference Testing and Solutions
Move channels to 1 and 11 Adjust power levels Relocate APs Change antenna Test for retransmission and throughput with one AP off Transmit on Channel-11 and count captured frames on Channels- 8,7,6 (beacon frames could be used for test) Adjust AP power and repeat frame count test 4/16/2017 Wireless Networking J. Bernardini

RF Noise, Noise Floor, RF Interference
RF Noise are signals generated by RF systems other than for the intended communications RF Noise may corrupt frames Noise Floor is the background level of RF noise Signal-to-Noise Ratio is the ratio of desired signal to background noise 40 db SNR means the signal is 40 db higher than the noise (10,000 times higher) Narrow and Wide band interference can corrupt frames Can be detected by checking for CRC errors a with frame analyzer Check for retransmissions Solutions could be reduced data rate or small frames Use the fragment threshold to control frame size 4/16/2017 Wireless Networking J. Bernardini

Multipath Problems Multipath, or more accurately, multipath propagation - The phenomenon that results in radio signals reaching the receiving antenna by two or more paths. Possible Effects Increased signal amplitude at receiver Decreased signal amplitude at receiver Data corruption Signal nullification Could increase throughput using MIMO (802.11n) 1 2 3 4 Metal Warehouse AP 1 3 2 Because there are obstacles and reflectors in the wireless propagation channel, the transmitted signal arrivals at the receiver from various directions over a multiplicity of paths. Such a phenomenon is called multipath. It is an unpredictable set of reflections and/or direct waves each with its own degree of attenuation and delay. Examples of possible multipath sources: · Standing water, pools or lakes · Flat metal surfaces · Wire fences (particularly chain link) · Large areas of glass (on building fronts) · Large, level areas of concrete paving Multipath is usually described by Line-of-sight (LOS): the direct connection between the transmitter (TX) and the receiver (RX). Non-line-of-sight (NLOS): the path arriving after reflection from reflectors. Multipath propagation occurs when an RF signal takes different paths when propagating from a source (e.g., a radio NIC) to a destination node (e.g., access point). While the signal is en route, walls, chairs, desks, and other items get in the way and cause the signal to bounce in different directions. A portion of the signal may go directly to the destination, and another part may bounce from a chair to the ceiling, and then to the destination. As a result, some of the signal will encounter delay and travel longer paths to the receiver. Multipath delay causes the information symbols represented in an signal to overlap, which confuses the receiver. This is often referred to as intersymbol interference (ISI). Because the shape of the signal conveys the information being transmitted, the receiver will make mistakes when demodulating the signal's information. If the delays are great enough, bit errors in the packet will occur. The receiver won't be able to distinguish the symbols and interpret the corresponding bits correctly. When multipath strikes in this way, the receiving station will detect the errors through 's error checking process. The CRC (cyclic redundancy check) checksum will not compute correctly, indicating that there are errors in the packet. In response to bit errors, the receiving station will not send an acknowledgement to the source. The source will then eventually retransmit the signal after regaining access to the medium. Because of retransmissions, users will encounter lower throughput when multipath is significant. The reduction in throughput depends on the environment. As examples, signals in homes and offices may encounter 50 nanoseconds multipath delay while a manufacturing plant could be as high as 300 nanoseconds. Based on these values, multipath isn't too much of a problem in homes and offices. Metal machinery and racks in a plant, however, provide a lot of reflective surfaces for RF signals to bounce from and take erratic paths. As a result, be wary of multipath problems in warehouses, processing plants, and other areas full of irregular, metal obstacles.

Multipath Wave forms A Distorted upfade Resultant waveform Amplitude B
2 AP 3 A 1 Distorted upfade Resultant waveform Amplitude B The three path waveforms shown in A are vectorially summed at the AP’s antenna. The red wave is from the direct path and the blue and yellow waves are multipath reflected waves. Path 1 (red) is the shortest distance path and the wave arrives the strongest, (less attenuation). Path 2 (blue) is the middle distance path and is shown with reduced amplitude and delayed in time from path 1. Path 3 (yellow) is the longest distance path and shows the smallest amplitude wave with the greatest time delay. The three waveforms in B are showing a different example with the blue wave being 180 degrees out-of-phase with the main red wave. In this example the yellow wave has a greater attenuation. The resulting wave is almost cancelled out due to the red and blue waves being almost equal but with the 180 degree phase shift. The B example would be know as a null point in the illumination field. It is important to note that at different frequencies the resulting waves would change. Up and Downfade have to do with whether the reflecting signal at the receiver is aiding or opposing the direct wave. If the reflected wave increases the signal at the receiver this effect is know as upfade. Delay spread (DS) is a parameter used to signify multipath. The delay of reflected signal is measured in nanoseconds (nsec). The amount of DS varies for indoor home, office and manufacturing environments. For homes, DS is typically < 50 nsec; for offices approximately 100 nsec, and for a manufacturing floor approximately nsec. Distorted downfade Resultant waveform DS Time DS = Delay Spread  10 to 300 nsec

Antenna Diversity Solution to Multipath
Antenna Diversity – using two or more antennas at physically different locations to improve the reception or transmission of an RF signal. In a small building with many reflections antenna diversity may not help AP will select the antenna with the best signal Client Access Point Reflective Surface 1 2 Receive Diversity Modes For clarity, we focus on two receive antennas when we discuss various receive-antenna diversity schemes, but extension to multiple antennas is straightforward. No diversity (single-antenna mode): This is an obvious case where there is only one receive antenna. It allows the simplest implementation and results in the lowest power consumption of all cases. Switched diversity: Only one receive antenna is chosen at any given time during reception, based on some prescribed selection criterion. The antenna connection is switched when the perceived link quality falls below a certain prescribed threshold. Selection diversity: One antenna is chosen whose receive path yields the larger signal-to-noise ratio (SNR) or signal power. The SNR or signal-strength measurement can take place during a preamble period at the beginning of the received packet. So, a single antenna connection is maintained most times, but during the measurement of the SNR/signal strength, both antennas' connections need to be established. The actual selection/switching process can also take place in between packet receptions, and can be done on a packet-by-packet basis or can take place once in a number of receptions or prescribed time period. Full diversity: Both antennas are connected at all times. Since both received paths must be powered up, this mode consumes the largest amount of power, but it also offers the largest performance gain compared with other configurations, especially in severe fading environments with large delay spread. The digital front-end techniques—signal detection, frame synchronization and carrier frequency offset estimation/correction, for instance—can also benefit from the availability of multiple receive paths. The use of multiple antennas is not a new idea and most cellular base stations employ antenna-diversity techniques. However, few mobile phones use antenna diversity. There are two main reasons for this. First, it is difficult to implement multiple antennas in something as small as a handset. Second, the performance of the handset antenna will be degraded by the effects of interantenna coupling, envelope cross-correlation and coupling to biological tissue in the user's head and hand. Simulation software can help designers overcome these problems. It is used to evaluate the individual antennas and the overall handset design. This supports the rapid exploration of design configurations to evaluate the positioning of multiple antennas. Antenna-diversity techniques generally fall into four categories. Spatial diversity involves the use of physically separated identical antennas. The phase centre of each antenna is also spatially separated. Pattern or beam diversity uses co-located antennas that are of different size, shape, orientation and/or material. These antennas have dissimilar radiation patterns and their signals are combined in phase due to their collocation. Polarization diversity uses two antennas oriented at 90° to each other. The result is mutually orthogonal polarization states, such as horizontal and vertical; left-hand circular and right-hand circular; or ±45° slants. The antennas used in polarization diversity schemes are often identical. Finally, transmit/receive diversity schemes employ separate antennas for transmit and receive functions, so frequency filtering is not needed. Antenna diversity can also be introduced by manipulating the way that outputs from multiple antennas are processed. Designers can choose a simple combination of signals from both antennas or a switched selection, which chooses the antenna with the best signal-to-noise ratio (SNR).

Multipath Troubleshooting and Solutions
Can not observe directly Symptoms Links that should work based upon link budget calculations Dead spots in FR coverage during survey High retransmissions RF noise floor when transceivers are off Use a site survey to check for holes/nulls in the illumination field. Use specialized test systems that can check for the possibility of multipath within a wireless local area network or link. If possible try moving the AP and or Client. Use an antenna diversity system.

Narrowband Narrowband - refers to a signal which occupies only a small amount of space on the radio spectrum, the opposite of broadband or wideband. Narrowband Interference In this slide channel 3 of an b DSSS signal is being interfered with buy a narrowband signal. Since narrowband signals have a limited range of frequencies a solution to this type of inherence is to move the communication signal to another channel. Amplitude Channel - 3 Freq.

ALL-Band interference
Microwave Oven 2.4 GHz Phone The slide shows man made interference sources as opposed to natural interference that occur in nature or extraterrestrial. Like many of today's great inventions, the microwave oven was a by-product of another technology. It was during a radar-related research project around 1946 that Dr. Percy Spencer, a self-taught engineer with the Raytheon Corporation, noticed something very unusual. He was testing a new vacuum tube called a magnetron. When he discovered that the candy bar in his pocket had melted. This intrigued Dr. Spencer, so he tried another experiment. This time he placed some popcorn kernels near the tube and, perhaps standing a little farther away, he watched with an inventive sparkle in his eye as the popcorn sputtered, cracked and popped all over his lab. Fluorescent Lighting Bluetooth Devices

Hidden Node Wireless Client Access Points 2 1
Client 1 listens to the medium and does not hear client 2 due to the obstruction/wall. Client 2 is a hidden node to client 1. Client one then assume it may use the shared medium and start to broadcast. However client 2 assumes the same situation and is linking to the AP therefore both data links collided at the AP. The symptoms of this situation is a a slow connection with lower throughput by as much as 40%. Even a well designed system can experience the hidden node problems simply by a client moving into a blind location for other nodes in the system.

Hidden Node Detection and Solution
Symptoms Increase corruption Increased retransmission Use protocol analyzer near to the AP and count corrupted frames Use protocol analyzer near to the STA and count retransmission frames Solutions Use RTS/RTS Increase STA power Remove obstacles and move STA if possible APs and STA at same IEEE h power level 4/16/2017 Wireless Networking J. Bernardini

Near/Far Problem Near/Far Effect – A condition where the AP cannot hear a client because it is being masked by other clients due to: Client has low transmit power Client is a great distance from the AP Fading problems. Symptoms STA can not contact AP STA has low throughput STA adapter looks like it failed Intermittent AP connection Testing Capture retransmissions and corruption frames from STA close to AP

Near/Far Solutions Increase distant STA output power
Decrease close STA output power Move remote STA closer to AP Move AP closer to distant STA Install another AP closer to distant STA 2 1 3 Near Field Far Field

Natural Interference Interference caused by nature.
Smog, Fog, Rain, Snow Wind Lightning Solar Radome radome (radar and dome) is a weatherproof enclosure used to protect an antenna. The Lightning Arrestor shown is up to 3 GHz operation with 350V discharge voltage and .2dB insertion loss. Grid antenna for low wind load. Lightning Arrestor Grid Antenna

Weather Effects In the 2.4 GHz band there are minimal effects to the signal absorption due to Fog – Snow. In the 5.0 GHz band the absorption effects start to increase on the signal. Thunder storms, ice, heavy rain and hail can reduce the quality of RF link Snow can accumulate on building and trees and effect the Fresnel zone Snow , ice and heavy wind can misalign antennas (grid antennas are better in wind) microwave systems operating at 2.4 GHz. Because the wavelength is so much larger than particulate matter and rain drops, even in heavy rain, these effects are minimal. This makes the frequency band between 1 GHz and 4 GHz very useful for radio astronomy and highly reliable communications and navigation systems such as the Global Positioning System (GPS) satellite navigation system and tactical air communications and navigation (TACAN) systems. Below 1 GHz man-made interference, lightening and solar storms cause greater interference, the lower the operating frequency the greater the problem becomes. At high rain intensity (150 mm/hr), the fading of an RF signal at 2.4 Ghz may reach a maximum of 0.02 dB/Km.

Lightning Lightning interference - is sporadic and the primary concern is for survival of the equipment. It can also change the signal path by changing the air (heated by the lightning energy to above 50,000ºF). Lightning Characteristics The conditions necessary for an old-fashioned summer afternoon thunderstorm are lots of moist air from ground level to a few thousand feet, cooler air above with little to no wind, and plenty of sun to heat the air mass near the ground. As the warm, moist air is heated, it rises quickly to heights where the temperature is below freezing, eventually forming a thundercloud. Within the thundercloud, the constant collisions among ice particles driven by the rising air causes a static charge to build up. Eventually the static charge becomes sufficiently large to cause the electrical breakdown of the air—a lightning strike. The average thunderstorm is approximately six miles wide and travels at approximately 25 mph. The anvil shape of the cloud is due to a combination of thermal layer (tropopause) and upper high velocity winds that cause the top of the cloud to mushroom and be pushed forward. The area of imminent danger is the area up to 10 miles in front of the leading edge of the cloud. When a lightning strike does occur, the return stroke rapidly deposits several large pulses of energy along the leader channel. That channel is heated by the energy to above 50,000ºF in only a microsecond and hence has no time to expand while it is being heated, creating extremely high pressure. The high pressure channel rapidly expands into the surrounding air and compresses it. This disturbance of the air propagates outward in all directions. For the first 10 yards or so it propagates as a shock wave (faster than the speed of sound) and after that as an ordinary sound wave—the thunder we hear. During a lightning strike your equipment is subjected to several huge impulses of energy. The majority of the energy is pulsed dc with a substantial amount of RF energy created by the fast rise time of the pulses. A typical lightning strike rise time is 1.8 µS. That translates into a radiated RF signal at 139 kHz. Rise times can vary from a very fast 0.25 µS to a very slow 12 µS, yielding an RF range from 1 MHz down to 20 kHz. However, the attachment point for a direct lightning strike has a time as fast as 10 nS. This RF content of the strike will have a major effect on the design of the protection plan. In addition to the strike pulses, the antennas and feed lines form tuned circuits that will ring when the pulses hit. This is much like striking a tuning fork in that ringing is created from the lightning’s pulsed energy. Average peak current for the first strike is approximately 18 kA (98% of the strikes fall between 3 kA to 140 kA). For the second and subsequent impulses, the current will be about half the initial peak. Yes, there is usually more than one impulse. The reason that we perceive a lightning strike to flicker is that it is composed of an average 3 to 4 impulses per lightning strike. The typical interval between impulses is approximately 50 mS.

Wind Wind has no direct impact on a wireless signal. However wind may have a strong indirect effect by moving the antenna. Wind loads are specified for various outside antennas. Wind Load MPH lb. (Based on worst case air temp. -30°F. Windload would be 18% less at +60°F.) 40 6.3 60 14.2 80 25.2 100 39.4 120 56.6 wind load The amount of physical resistance an object presents to the wind. wind survivability The maximum wind speed a given antenna model can experience without damage. Maximum wind velocities are based on a minimum 1.5 factor of safety against structural failure. WIND LOAD is the worst-case wind resistance for the antenna. Using the latest structural analysis, the wind load is either the total element wind load OR the boom windload, whichever is the larger resistance to the wind. Most beams have more element than boom wind load. The figure specified is the effective area, which is the projected area of the elements or boom, multiplied by 2/3 for a cylindrical surface. ROTATING RADIUS is the dimension taken from the mast mounting location to the farthest element tip. This is the maximum clearance needed from the support to the tip. Twice this figure is the total diameter circle that the antenna will cover on one rotation. MAST TORQUE is calculated at 70 mph (20 pounds per square foot wind pressure). It is the amount of "twist" exerted on the tower and rotator in 70 mph winds in the worst-case wind attack angle. The antenna (or stack of antennas) might still want to align one way or the other to the wind. This is because an antenna will usually have more windload in the element or boom plane. Most antennas have more element wind load. This being the case, the additional of an 80 or 40 meter dipole parallel to the boom will minimally increase the wind load on the tower. The added dipole tends to make the entire installation more neutral in the wind, since the boom (plane) wind load has been increased and is now closer to the element load.

Stratification Fog or ionosphere layering. This can cause a bending of the wavefront due to diffraction.

Range Considerations Transmission Power and Frequency
Antenna Type and Placement Environment The top link shows that power has a direct effect on the range of a link. Note higher frequencies have higher absorption losses. The middle link shows using high gain directional antennas at the same reduced power have increased the link range. The bottom link shows environmental noises reducing the reliable range of the link.

VoWLAN Issues A new and growing technology that requires QoS Latency (less than 150 ms)and throughput are important Today use the same vendor for all equipment Common Problems Dropped calls during roaming Dropped call when staying within a BSS Calls not going through to target 4/16/2017 Wireless Networking J. Bernardini

WLAN Analysis Systems Handheld Protocol Analyzers Laptop Protocol Analyzers Basic Protocol Analyzers Handheld RF Spectrum Analyzers Laptop RF Spectrum Analyzers Wireless Intrusion Detection Systems Wireless Intrusion Prevention Systems Distributed RF Spectrum Analyzers 4/16/2017 Wireless Networking J. Bernardini

Handheld Protocol Analyzers
PDA-Based Convenient Low processing power and small screen Medium cost ($1000) PocketPC based applications WiFi PPC, CommView, MiniStumbler, TamoSoft Integrated Specialized Powerful Full featured High cost ($10,000 to $25,000) Fluke OptiView Integrated Network Analyzer 4/16/2017 Wireless Networking J. Bernardini

Laptop Protocol Analyzers
Large choice of applications Wireshark (PC and Linux) Wildpackets Omnipeek AirMagnet Others Wireless adapter Driver Issues Applications only work with certain adapters Obtain application first Download the needed drivers Adapter Choices PCMCIA ExpressCard USB Wireless Networking J. Bernardini 4/16/2017

WiFi Hopper and Netstumbler –Almost free tools
Website: 4/16/2017 Wireless Networking J. Bernardini

Wireless Intrusion Detection Systems
Cisco 4/16/2017 Wireless Networking J. Bernardini

Intrusion Detection System

Wireless Security Articles

Distributed RF Spectrum Analyzers

Spectrum analyzer showing narrowband RF interference

Throughput Testing Tools

Wireless Networking WLAN Troubleshooting Module-11

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