1. Pietrosemoli, ICTP Feb. 20031 Wireless LAN Overview Abdus Salam ICTP, February 2003 Presented by Ermanno Pietrosemoli Latin American Networking School - ULA

2. Pietrosemoli, ICTP Feb. 20032 Wireless LAN Overview Wireless networks where borne as LANs, but for developing countries applications they are more useful as MANs or even WANs The enormous success of this technology has led to a dramatic price reduction of the equipment, from $750 in 1992 to $60 in 2002

3. Pietrosemoli, ICTP Feb. 20033 Wireless LAN Overview Agenda DSSS Channel Allocation Access Point Modes and Types Clients Types 802.11 Standards 802.11 Terminology

4. Pietrosemoli, ICTP Feb. 20034 Wireless LAN Overview DSSS popularity has eclipsed FHSS, although the latter may be more resistant to interference We will focus on DSSS

5. Pietrosemoli, ICTP Feb. 20035 Channel Overlapping

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10. 10 Access Point Modes Root Mode Repeater Mode Bridge Mode

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18. Pietrosemoli, ICTP Feb. 200318 Repeater and Bridging Functions

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30. Pietrosemoli, ICTP Feb. 200330 Chipset Manufacturers

31. Pietrosemoli, ICTP Feb. 200331 Client Devices

32. Pietrosemoli, ICTP Feb. 200332 Client Devices

33. Pietrosemoli, ICTP Feb. 200333 Client Devices

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38. Pietrosemoli, ICTP Feb. 200338 Common options that most wireless residential gateways include are: Point-to-Point Protocol over Ethernet (PPPoE) Network Address Translation (NAT) Port Address Translation (PAT) Ethernet switching Virtual Servers Print Serving Fail-over routing Virtual Private Networks (VPNs) Dynamic Host Configuration Protocol (DHCP) Server and Client Configurable Firewall

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40. Pietrosemoli, ICTP Feb. 200340 Enterprise Gateway Features Enterprise wireless gateways do have features, such as Role-Based Access Control (RBAC), that are not found in any access points. RBAC allows an administrator to assign a certain level of wireless network access to a particular job position in the company. If the person doing that job is replaced, the new person automatically gains the same network rights as the replaced person. Having the ability to limit a wireless user's access to corporate resources, as part of the "role", can be a useful security feature.

41. Pietrosemoli, ICTP Feb. 200341 Enterprise Gateway Features Class of service is typically supported, and an administrator can assign levels of service to a particular user or role. For example, a guest account might be able to use only 500 kbps on the wireless network whereas an administrator might be allowed 2 Mbps connectivity.

42. Pietrosemoli, ICTP Feb. 200342 Configuration and Management of EG Enterprise wireless gateways are installed in the main the data path on the wired LAN segment just past the access point(s) They are configured through console ports using telnet, internal HTTP or HTTPS servers, etc. Centralized management of only a few devices is one big advantage of using enterprise wireless gateways. An administrator, from a single console, can easily manage a large wireless deployment using only a few central devices instead of a very large number of access points.

43. Pietrosemoli, ICTP Feb. 200343 Configuration and Management of EWG Enterprise wireless gateways are normally upgraded through use of TFTP in the same fashion as many switches and routers on the market today. Configuration backups can often be automated so that the administrator won't have to spend additional management time backing up or recovering from lost configuration files. Enterprise wireless gateways are mostly manufactured as rack-mountable 1U or 2U devices that can fit into your existing data center design.

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45. Pietrosemoli, ICTP Feb. 200345 UNII Bands

46. Pietrosemoli, ICTP Feb. 200346 UNII Middle Band The middle UNII band is bound by 5.25 GHz and 5.35 GHz and is specified at 250 mW of output power by the FCC. The power output specified by IEEE for the middle UNII band is 200 mW. This power limit allows operation of devices either indoors or outdoors and is commonly used for short outdoor hops between closely spaced buildings. In the case of a home installation, such a configuration might include an RF link between the house and the garage, or the house and a neighbor’s house..

47. Pietrosemoli, ICTP Feb. 200347 UNII Upper Band The upper UNII band is reserved for outdoor links and is limited by the FCC to 1 Watt of output power. This band occupies the range of frequencies between 5.725 GHz and 5.825 GHz, and is often confused with the 5.8 GHz ISM band. The IEEE specifies the maximum output power for this band as 800 mW, which is plenty of power for almost any outdoor implementation, except for large campuses or long-distance RF links.

48. Pietrosemoli, ICTP Feb. 200348 Power Limits PtMP links have a central point of connection and two or more non-central connection points. PtMP links are typically configured in a star topology. The central connection point may or may not have an omnidirectional antenna It is important to note that when an omnidirectional antenna is used, the FCC automatically considers the link a PtMP link. Regarding the setup of a PtMP link, the FCC limits the EIRP to 4 Watts in both the 2.4 GHz ISM band and upper 5 GHz UNII band. The power limit set for the intentional radiator (the device transmitting the RF signal) in each of these bands is 1 Watt. If the transmitting wireless LAN devices are adjustable with respect to their output power, then the system can be customized to the needs of the user.

49. Pietrosemoli, ICTP Feb. 200349 Power Limits Suppose a radio transmitting at 1 Watt (+30 dBm) is connected directly to a 12 dBi omnidirectional antenna. The total output power at the antenna is about 16 Watts, which is well above the 4 Watt limit. The FCC stipulates that for each 3 dBi above the antenna's initial 6 dBi of gain, the power at the intentional radiator must be reduced by 3 dB below the initial +30 dBm. For our example, since the antenna gain is 12 dBi, the power at the intentional radiator must be reduced by 6 dB. This reduction will result in an intentional radiator power of +24 dBm (30 dBm – 6 dB), or 250 mW and an EIRP of 36 dBm (24 dBm + 12 dBi), or 4 Watts. Clearly this rule can become confusing, but the end result must be that the power at the intentional radiator must never be more than 1 Watt and the EIRP must never be above 4 Watts for a PtMP connection.

50. Pietrosemoli, ICTP Feb. 200350 Power Limits

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57. Pietrosemoli, ICTP Feb. 200357 IEEE 802.11g 802.11g provides the same maximum speed of 802.11a,coupled with backwards compatibility for 802.11b devices. This backwards compatibility will make upgrading wireless LANs simple and inexpensive. IEEE 802.11g specifies operation in the 2.4 GHz ISM band. To achieve the higher data rates found in 802.11a, 802.11g compliant devices utilize Orthogonal Frequency Division Multiplexing (OFDM) modulation technology. These devices can automatically switch to QPSK modulation in order to communicate with the slower 802.11b- and 802.11- compatible devices. With all of the apparent advantages, 802.11g’s use of the crowded 2.4 GHz band could prove to be a disadvantage.

58. Pietrosemoli, ICTP Feb. 200358 Wireless Ethernet Compatibility Alliance The Wireless Ethernet Compatibility Alliance (WECA) promotes and tests for wireless LAN interoperability of 802.11b devices and 802.11a devices. WECA’s mission is to certify interoperability of Wi-Fi™ (IEEE 802.11) products and to promote Wi-Fi as the global wireless LAN standard across all market segments. As an administrator, you must resolve conflicts among wireless LAN devices that result from interference, incompatibility, or other problems.

59. Pietrosemoli, ICTP Feb. 200359 Wireless Ethernet Compatibility Alliance

60. Pietrosemoli, ICTP Feb. 200360 European Telecommunications Standards Institute

61. Pietrosemoli, ICTP Feb. 200361 European Telecommunications Standards Institute The website for ETSI is www.etsi.org

62. Pietrosemoli, ICTP Feb. 200362 Wireless LAN Association The Wireless LAN Association's mission is to educate and raise consumer awareness regarding the use and availability of wireless LANs and to promote the wireless LAN industry in general. The Wireless LAN Association (WLANA) is an educational resource for those seeking to learn more about wireless LANs. WLANA can also help if you are looking for a specific wireless LAN product or service. WLANA has many partners within the industry that contribute content to the WLANA directory of information. It is this directory, along with the many white papers and case studies that WLANA provides, that offer you valuable information for making your own decisions about wireless LAN implementation. The website for WLANA is www.wlana.org

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65. Pietrosemoli, ICTP Feb. 200365 Bluetooth

66. Pietrosemoli, ICTP Feb. 200366 Bluetooth

67. Pietrosemoli, ICTP Feb. 200367 Bluetooth

68. Pietrosemoli, ICTP Feb. 200368 Bluetooth

69. Pietrosemoli, ICTP Feb. 200369 The website for IrDA is www.irda.org

70. Pietrosemoli, ICTP Feb. 200370 Locating a Wireless LAN

71. Pietrosemoli, ICTP Feb. 200371 Service Set Identifier

72. Pietrosemoli, ICTP Feb. 200372 Beacons Beacons (short for beacon management frame) are short frames that are sent from the access point to stations (infrastructure mode) or station-to-station (ad hoc mode) in order to organize and synchronize wireless communication on the wireless LAN. Beacons serve several functions, including the following:

73. Pietrosemoli, ICTP Feb. 200373 Time Synchronization Beacons synchronize clients by way of a time-stamp at the exact moment of transmission. When the client receives the beacon, it changes its own clock to reflect the clock of the access point. Once this change is made, the two clocks are synchronized. Synchronizing the clocks of communicating units will ensure that all time- sensitive functions, such as hopping in FHSS systems, are performed without error. The beacon also contains the beacon interval, which informs stations how often to expect the beacon.

74. Pietrosemoli, ICTP Feb. 200374 FH or DS Parameter Sets Beacons contain information specifically geared to the spread spectrum technology the system is using. For example, in a FHSS system, hop and dwell time parameters and hop sequence are included in the beacon. In a DSSS system, the beacon contains channel information.

75. Pietrosemoli, ICTP Feb. 200375 SSID Information Stations look in beacons for the SSID of the network they wish to join. When this information is found, the station looks at the MAC address of where the beacon originated and sends an authentication request in hopes of associating with that access point. If a station is set to accept any SSID, then the station will attempt to join the network through the first access point that sends a beacon or the one with the strongest signal strength if there are multiple access points.

76. Pietrosemoli, ICTP Feb. 200376 Traffic Indication Map (TIM) The TIM is used an as indicator of which sleeping stations have packets queued at the access point. This information is passed in each beacon to all associated stations. While sleeping, synchronized stations power up their receivers, listen for the beacon, check the TIM to see if they are listed, then, if they are not listed, they power down their receivers and continue sleeping..

77. Pietrosemoli, ICTP Feb. 200377 Supported Rates With wireless networks, there are many supported speeds depending on the standard of the hardware in use. For example, an 802.11b compliant device supports 11, 5.5, 2, & 1 Mbps speeds. This capability information is passed in the beacons to inform the stations what speeds are supported on the access point.

78. Pietrosemoli, ICTP Feb. 200378 Passive Scanning Passive scanning is the process of listening for beacons on each channel for a specific period of time after the station is initialized. These beacons are sent by access points (infrastructure mode) or client stations (ad hoc mode), and the scanning station catalogs characteristics about the access points or stations based on these beacons. The station searching for a network listens for beacons until it hears a beacon listing the SSID of the network it wishes to join. The station then attempts to join the network through the access point that sent the beacon.

79. Pietrosemoli, ICTP Feb. 200379 Active Scanning Active scanning involves the sending of a probe request frame from a wireless station. Stations send this probe frame when they are actively seeking a network to join. The probe frame will contain either the SSID of the network they wish to join or a broadcast SSID. If a probe request is sent specifying an SSID, then only access points that are servicing that SSID will respond with a probe response frame. If a probe request frame is sent with a broadcast SSID, then all access points within reach will respond with a probe response frame. The point of probing in this manner is to locate access points through which the station can attach to the network. Once an access point with the proper SSID is found, the station initiates the authentication and association steps of joining the network through that access point..

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81. Pietrosemoli, ICTP Feb. 200381 Active Scanning

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