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Textbook attached below. Answer questions for each case study Case Study: 3-1 Interference on WLANs: Page 116 Unlicensed bands are parts of the radio spectrum that are available nationwide to all users without requiring a license. However, a drawback is that, because there are no licenses, there can be interference between devices. Use the Internet to identify a list of devices that can interference with WLANs in either the ISM or UNII bands. Case Study: 3-2 Impact of Propagation Behaviors: Page 117 Absorption, reflection, scattering, refraction, and diffraction can all have an impact on RF signal strength. Using the Internet, identify at least three objects or types of materials in each of the five categories that can impact RF signals. Next, research how much the impact is in terms of loss (either dBm or mW). Case Study: 3-3 Attenuation: Page 117 Attenuation is not limited to wireless LANs, but can also affect wired LANs as well. Research the types of attenuation that can impact wired networks. How can attenuation be measured on a wired network compared to a wireless network? Which is more difficult to uncover? Why? Write a one-page paper on your findings. Writing Requirements Include Abstract APA format and include citations 3 pages in length (excluding cover page, abstract, and reference list) Reference to Textbook attached I have send 2 attachment of the textbook. I split the textbook in half pages 1-282 and pages 282-564 from the channel center, so that they actually consume five overlapping channels (for example, transmitting on channel 6 may cause interference on channels 5 and 7 as well as limited on channels 4 and 8). This leaves only three nonoverlapping (simultaneously usable) 20-MHz channels: 1, 6, and 11. IEEE 802.11a networks have 555 MHz spread across 23 nonover- lapping channels. Channel allocation is covered in Chapter 5. Managing the radio frequency spectrum of 802.11b/g—and to a lesser degree 802.11a—wireless networks can be challenging. Setting all of the APs to the same channel number would result in reduced throughput because each station must wait a longer period of time for its turn to transmit (called cochannel interference). To eliminate this interference it is necessary to arrange the coverage areas of the APs so that one channel does not interfere with an adjacent channel. In Figure 7-6, only channels 1, 6 and 11 are used as nonoverlap- ping channel numbers. Each cell is separated from other cells so that no two adjacent cells have the same channel number in order to reduce interference (known as adjacent channel interference). This type of WLAN is called a multiple-channel architecture or MCA because more than one channel is in the wireless network. One of the keys to an MCA is to have the correct cell size in order to minimize adjacent channel interference. This is especially true when “scaling” or adding additional capacity to the WLAN. The most common approach, called the micro-cell architecture, creates small areas of coverage. Typically, in order to add wireless network capacity, more APs are added while the transmission power of all APs is reduced to minimize potential interference. This can usually provide acceptable network throughput if the site has been properly surveyed to identify the best locations for the APs. In addition, the configuration of BSSIDs and ESSIDs can be made easier in a micro-cell architecture. Single-Channel Architecture (SCA) The fundamental reason why multiple APs in a MCA are necessary is because the interference range of wireless devices exceeds their useful communication range. That is, devices that are too far apart to communicate can still be close enough to interfere with each other. An alter- native to MCA that addresses this weakness is the single-channel architecture (SCA). Instead of having each cell use a different channel as in WCA, WLANs using SCA have all of the APs use the same channel. Each AP has overlapping coverage that forms a continuous region on a single channel, thereby reducing interference. The SCA architecture is accomplished through 6 1 11 116 1 11 6 1 11 6 1 6 1 11 116 1 11 6 1 11 6 1 Figure 7-6 Nonoverlapping cells © Cengage Learning 2013 256 Chapter 7 WLAN Management and Architectures Copyright 2012 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 7 the use of lightweight APs and WLCs. Each lightweight AP broadcasts the same virtual BSSID (instead of multiple BSSIDs) and each has the same configured MAC address. This also serves to eliminate the cochannel interference problem. There are several advantages to SCA. The first advantage is smoother handoffs. A mobile sta- tion must receive an uninterrupted flow of frames when moving from the coverage area of one AP to another AP, especially when using VoIP. With MCA, the station responsible for this pro- cedure monitors the signal strength from multiple APs or data frame error rates. With SCA, the handoff is instead accomplished through coordination between the lightweight APs and the WLC. The stations cannot distinguish which AP is providing the coverage; instead, the net- work decides which AP should transmit and receive data for a particular station. This means that the stations are not involved in any handoff decision from one AP to another. As stations move, the network directs traffic to them via the nearest AP with available capacity. With SCA, the roaming clients are “fooled” into thinking that they are always interacting with the same AP when in reality they may be communicating with several different APs. A second advantage to SCA is that the often tedious planning process required for MCA WLANs is no longer needed. All APs are set to the same common RF channel and transmit power, eliminating the need for lengthy and often complex planning regarding the location and unique configuration of each AP. Another advantage to SCA is that because each AP is operating on the same channel, cochan- nel interference is no longer an issue. This can also improve the signal-to-noise ratio (SNR) that in turn increases throughput and reliability. A final advantage is that the SCA architecture provides more network information in order to make informed decisions. With MCA, a station and AP are essentially “in the dark” regarding the overall status of the network. Yet with SCA a more complete knowledge of the conditions at neighboring APs, and even historical information about how stations reacted previously when in similar situations, can be used when deciding which AP a roam- ing client should be associated with. MCA is similar to the centralized handover control of first-generation cellular telephone networks, while today’s 3G and 4G is based on a shared network-client responsibility like SCA. SCA can also support channel stacking. Channel stacking allows for increased capacity by hav- ing more than one SCA operating in an area. Instead of having only one SCA on channel 1, another set of APs operating on channel 6 can also be added using a different BSSID. Stations can then associate with either SCA, thus dramatically increasing the available capacity. This additional capacity can be used for redundancy or to support higher data rates or user density. Instead of installing additional APs, channel stacking can also be accomplished by using APs that support multiple radios. Multiple-Channel Architecture vs. Single-Channel Architecture Models 257 Copyright 2012 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. Wireless Network Management Systems (WNMS) C W N A 4.4.4. Define, describe, and implement a WNMS that manages autonomous APs, WLAN controllers, and mesh nodes. A wireless network management system (WNMS) is a set of hardware and/or software that can be used to provide unified management of a wireless network. This includes configuration man- agement, deployment, and especially troubleshooting. A WNMS can be used to isolate and solve wireless problems, which can have many different root causes (station wireless configuration errors, authentication problems, connectivity issues, problems with wired ports or switches, etc.). The typical features of a WNMS include: ● Configuration management. A new or updated configuration can be “pushed” out to all wireless devices, a single device, or a group of specific devices. These configurations can be designed so that general updates do not override specific configuration settings unique to each device. ● Firmware/Software distribution. As new firmware and software is made available, these can be distributed to all devices from a central management facility, with no need to “touch” each device. ● Intelligent scheduling. To minimize the impact of a new configuration or firmware update, many WNMS can be scheduled to automatically occur late at night or on the weekends when the wireless network usage is low. In addition, recurring tasks can be scheduled to automatically occur on a regular daily, weekly, or monthly basis. ● User and device monitoring. A WNMS can locate a specific user or device on a wire- less network often by WLAN administrator clicking a single button on a Web-based software interface. This allows a wireless technician to monitor historical information and use special diagnostic information to address problems. One of the disadvantages of a WNMS is that it cannot be used to monitor wireless network traffic as it occurs. Power Management C W N A 3.1.3. Explain and apply the power management features of WLANs. Most stations in a WLAN are portable laptop or tablet computers, giving the users the freedom to roam without being tethered to the network by wires. These devices depend upon batteries as their primary power source when they are mobile. To conserve battery power, 258 Chapter 7 WLAN Management and Architectures Copyright 2012 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 7 laptops are usually configured to go into a “sleep” mode after a specific period of time, when functions such as the hard drive or display screen are temporarily powered down by the computer. However, a laptop that is part of a WLAN must remain “awake” in order to receive wireless network transmissions. If a laptop is in sleep mode, it could miss important transmitted infor- mation or even lose the network connection altogether. The dilemma is how to allow the lap- top to power down into sleep mode during idle periods to preserve battery life yet continue to be active to receive network transmissions. The reason a wireless laptop must continue to remain awake to receive network transmissions is because the original IEEE 802 standard assumes that stations are always ready to receive a network message. The answer to the problem is known as power management. Power management allows a station to be in either active mode when it is continuously awake or in power save mode, which turns off the wireless network interface card adapter to conserve battery life but still not miss wireless transmissions. Power management is transparent to all protocols and appli- cations so that it will not interfere with normal network functions. Power save mode is also called continuous aware mode or constantly awake mode. IEEE 802.11 power management can be divided into two categories: basic power manage- ment and enhanced power management techniques. Basic Power Management In a BSS infrastructure WLAN, the steps of power save mode are as follows: 1. A station sends a frame to the AP with the Power Management field set to 1 to indicate that it will go into power save mode after this frame transmission. 2. The AP records that the station is in power save mode to prevent any frames from being sent to that station from the AP. 3. As the AP receives frames specifically for that station (unicast frames) it temporarily stores those frames at the AP (buffering). 4. At prescribed set times, the AP will send out a beacon frame to all stations. At the same time, all stations switch to active mode to receive the frame. This frame contains a list of the stations that have buffered unicast frames waiting at the AP. This list is known as the traffic indication map (TIM). 5. If a station learns from the TIM that buffered frames are waiting for it, that station will request the AP to have those frames forwarded (if it has no buffered frames then it can return to power save mode). Once the buffered frames are received the station can again return to power save mode. This is illustrated in Figure 7-7. Power Management 259 Copyright 2012 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. The amount of power that a wireless network interface card adapter consumes is significant. One typical card requires 450 millionths of an amp (mA) to transmit and 270 mA to receive. While in power save mode it only consumes 15 mA. When a station in power save mode must receive a frame intended for all stations (multicast or broadcast frame) the AP will send a special TIM called a delivery traffic indication message (DTIM). All stations will then change to active mode to receive the frame. Power management for an IBSS is different because there is no AP. Every station in an IBSS must buffer the frames that it attempts to send to another device in case the receiving device is asleep. At a specific period of time, known as the ad hoc traffic indication message (ATIM) window, each station must be awake. At this time a station sends a beacon frame to all other stations. Those stations that previously attempted to send a frame to a sleeping station will now send an ATIM frame, which indicates that the receiving station has pending data to be received and must remain awake (any device that does not receive an ATIM frame can go back to sleep). Finally, the data frames are retrieved from the buffer and sent to the station that is now awake. There are a variety of configuration settings that can be used with power management. For example, different power save levels can be specified for a station in power save mode. One level may require that a station turn off the radio for as long as possible without losing network connectivity for the greatest power savings at the sake of network per- formance, while another setting can require that the station turn off the radio for small periods in order to provide optimal network performance. Enhanced Power Management Although the basic power management features can provide power savings, there are enhanced power management technologies that can provide additional functionality and Station A Power save mode Power save mode Active mode Station B Station C TIM Station A Yes Station C No Access point Send frames request Figure 7-7 Request for frames © Cengage Learning 2013 260 Chapter 7 WLAN Management and Architectures Copyright 2012 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 7 power savings. These include Unscheduled Automatic Power Save Delivery, Power Save Multi-Poll, and Spatial Multiplexing Power Save. Unscheduled Automatic Power Save Delivery (U-APSD) The Unscheduled Automatic Power Save Delivery (U-APSD), which is similar to the Wi-Fi Alliance’s WMM Power-Save (WMM-PS), is often used when a wireless station is using VoIP. With the basic power management settings a device using VoIP for a voice conversation may receive frames every 10–20 milliseconds (ms), while an AP usually sends out a beacon frame every 100 ms. Because the delay is too long, normally a station using VoIP simply could not afford to go into power save mode. With U-APSD, the station would inform the AP that it is operating according to this proto- col, and the AP will then save any frames destined for this station. However, instead of waiting for the AP to send a beacon frame to all stations as with basic power management, whenever the AP sees a frame coming from the station it will immediately release any frames it has been holding for the station. This allows the station to sleep until it needs to send a VoIP frame to the AP, and that frame also serves as an indicator to release any packets des- tined for it. Once the station has received its frames it then goes back into power save mode. There is a slight delay for the station in listen mode when using VoIP with U-APSD while the AP gathers up and sends the frames, at which time the station goes into receive mode. U-APSD improves the efficiency of the basic power management in two ways: it increases the amount of time that a station can be in power save mode and it decreases the number of frames that a station must send and receive in order to download stored frames on the AP. An interesting benefit of U-APSD is that, when higher data rates are used, overall power savings increase. This is because a station will spend less time actively transmitting and receiving and will spend more time in power save mode. A device using U-APSD for VoIP consumes approximately one-sixth of the power compared with not using U-APSD. Power Save Multi-Poll (PSMP) Another enhanced power management mechanism is the Power Save Multi-Poll (PSMP), which can have either a scheduled or an unscheduled component. Scheduled PSMP (S-PSMP) allows an AP to send a transmission schedule to one or more stations in a WLAN. This schedule informs the stations when they should be in active mode to receive frames as well as when they are allowed to begin transmitting. And since a station can only send or receive frames based on the schedule, other stations cannot interfere with the transmissions by attempting to send simultaneously. By using a schedule, stations can be in power save mode for the maximum amount of time without missing any frames. Unscheduled PSMP (U-PSMP) functionality does not replace U-APSD (WMM), but rather extends it to add further functionality. Power Management 261 Copyright 2012 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. Although an improvement over basic power management, S-PSMP still requires a significant amount of overhead. In addition, stations may not be able to be in power save mode for extended periods of time. For example, with VoIP transmissions the time gap for station may be so short that the station must still remain in active mode while other stations are receiving their VoIP packets. Generally speaking, P-SPMP is used only if the number of sta- tions using VoIP associated with a single AP exceeds 15. If fewer than 15 stations are using VoIP, then U-APSD should be used instead. Spatial Multiplexing Power Save (SMPS) Spatial Multiplexing Power Save (SMPS) can be used with IEEE 802.11n devices using Multiple-Input Multiple-Output (MIMO). A device using MIMO may have a 2x3:2 configuration of two transmit antennas and three receive antennas (along with two data spatial streams), each having its own radio chain. Yet it is not necessary for all three of the receive radio chains to be simultaneously awake. This is because the station is only waiting to receive a low data rate beacon that may not be sent with MIMO encoding. SMPS allows the station to change from a 2x3:2 configuration to a 1x1:1 to save power. If the station is plugged into an electrical outlet running on alternating current (AC), it can be configured to run using all radio chains (since conserving power is not a concern). However, if the station begins running on a direct current (DC) battery, it will automatically “down- shift” to 1x1:1 while waiting to receive beacons. The station would then “upshift” back to 2x3:2 when necessary. SMPS is also called Dynamic MIMO Power Save. A device using SMPS can downshift and then tell the AP to prevent it from sending any MIMO-encoded frames to the device with only one receive radio chain. The AP can then send a request to send (RTS) packet that indicates the AP is about to send a MIMO packet so that the device can upshift to receive it. The power savings provided by SMPS can be significant. The ability to dynamically change the MIMO configuration can reduce power consumption by 30 percent when the traffic is low. Chapter Summary ■ The most common type of wireless architecture is an autonomous access point archi- tecture. Each AP is independent or autonomous from all other APs. There are several enhanced features in this type of architecture. Two of the most advanced features are Quality of Service (QoS) and wireless virtual LANs (VLANs). QoS provides the ability to prioritize different types of frames so that those frames that are more time-dependent, such as voice and video, can be given a higher priority (and arrive earlier) than standard data frames. A wireless VLAN is often used to segment traffic. Wireless 262 Chapter 7 WLAN Management and Architectures Copyright 2012 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 7 VLANs can be configured in one of two ways. The difference depends upon which device separates the packets and directs them to different networks. ■ A controller-based architecture uses a wireless LAN controller (WLC) to manage and provide configuration services to the WLAN. Access points in a controller-based architecture are significantly different. A lightweight access point does not contain the management and configuration functions that are found in autonomous access points; instead, these features are contained in the centralized WLC. Lightweight access points only have simplified radios for wireless communication between devices and a media converter for accessing the wired network. A lightweight mesh AP can be used instead of a standard mesh AP. Lightweight mesh APs can also be centrally configured and managed through a WLC. A captive portal AP uses a standard Web browser to pro- vide information, give the wireless user the opportunity to agree to a policy, or present valid login credentials. The WLC is a device that can be centrally configured; these settings are then automatically distributed to all lightweight access points. ■ Besides autonomous access point architectures and control-based architectures, there are other types of WLANs. A WLAN array is a proprietary product that resembles a round consumer-grade smoke detector and replaces a standard WLC installed in a rack in a server closet. The WLAN array contains a WLC that can be directly con- nected to as many as 16 integrated access points. Cooperative control is another proprietary technology marketed architecture that enables APs to communicate and coordinate with each other without the need for a WLC, so that each AP contains the capabilities of a WLC. Wireless mesh access points communicate wirelessly with the next closest mesh access point. ■ A multiple-channel architecture, or MCA, has more than one channel in the wireless network. Each cell is separated from other cells so that no two adjacent cells have the same channel number in order to reduce interference. An alternative to MCA is the single-channel architecture (SCA). Instead of having each cell use a different channel as in WCA, WLANs using SCA have all of the APs use the same channel. Each AP has overlapping coverage that forms a continuous region on a single channel, thereby reducing interference. The SCA architecture is accomplished through the use of lightweight APs and WLCs. ■ A wireless network management system (WNMS) is a set of hardware and/or software that can be used to provide unified management of a wireless network. This includes configuration management, deployment, and especially troubleshooting. A WNMS can be used to isolate and solve wireless problems, which can have many different root causes (station wireless configuration errors, authentication problems, connectivity issues, problems with wired ports or switches, etc.). ■ Power management allows a station to be in either active mode (continuously awake) or in power save mode (turns off the wireless network interface card adapter to con- serve battery life but still not miss wireless transmissions). Power management is transparent to all protocols and applications so that it will not interfere with normal network functions. Basic power management involves the AP temporarily storing frames and then releasing them to the stations. Although the basic power management features can provide power savings, there are enhanced power management technolo- gies that can provide additional functionality and power savings. With Unscheduled Automatic Power Save Delivery (U-APSD) a station informs the AP that it is operating Chapter Summary 263 Copyright 2012 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. according to this protocol, and the AP will then save any frames destined for this station. Whenever the AP sees a frame coming from the station, it will immediately release any frames it has been holding for the station. Power Save Multi-Poll (PSMP) allows an AP to send a transmission schedule to one or more stations in a WLAN. This schedule informs the stations when they should be in active mode to receive frames as well as when they are allowed to begin transmitting. Spatial Multiplexing Power Save (SMPS) allows a station to change from a MIMO configuration to a single radio in order to conserve power. Key Terms active mode A power management state in which the station is continuously awake. ad hoc traffic indication message (ATIM) window A specific period of time that each station must be awake. adjacent channel interference Each cell is separated from other cells so that no two adjacent cells have the same channel number in order to reduce interference. captive portal AP An AP that uses a standard Web browser to provide information, give the wireless user the opportunity to agree to a policy, or present valid login credentials. channel stacking A technology that allows for increased capacity by having more than one SCA operating in an area. cloud management Connecting wireless devices together using the Internet in order to remotely manage them. cochannel interference Reduced throughput caused as a result of all of APs set to the same channel number. cooperative control A proprietary product in which each AP contains the capabilities of a WLC. delivery traffic indication message (DTIM) A special TIM sent by an AP that is used when a station in power save mode must receive a frame intended for all stations. distributed WLAN architecture A wireless architecture configuration in which multiple APs form a non-centralized network through a wireless connection. IEEE 802.11e-2005 The IEEE QoS standards. IEEE 802.1q An IEEE standard for marking VLAN packets. lightweight mesh AP A mesh AP that is centrally configured and managed through a WLC. micro-cell architecture A wireless architecture that creates small areas of coverage. multiple-channel architecture (MCA) A wireless architecture in which more than one channel is used in the wireless network. power management A technology that allows a WLAN to conserve power. power save mode A power management state in which the station turns off the wireless network interface card adapter to conserve battery life. Power Save Multi-Poll (PSMP) An enhanced power management technology that can have either a scheduled or an unscheduled component. Quality of Service (QoS) Prioritizing different types of frames over a network. 264 Chapter 7 WLAN Management and Architectures Copyright 2012 Cengage Learning. All Rights Reserved. May not be copied, scanned, or duplicated, in whole or in part. Due to electronic rights, some third party content may be suppressed from the eBook and/or eChapter(s). Editorial review has deemed that any suppressed content does not materially affect the overall learning experience. Cengage Learning reserves the right to remove additional content at any time if subsequent rights restrictions require it. 7 Scheduled PSMP (S-PSMP) An enhanced power management technology in which the AP sends a transmission schedule to one or more stations in a WLAN. single-channel architecture (SCA) An architecture in which all of the APs use …