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Wireless LAN Overview

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

  2. 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 Pietrosemoli, ICTP Feb. 2003

  3. Wireless LAN OverviewAgenda • DSSS Channel Allocation • Access Point Modes and Types • Clients Types • 802.11 Standards • 802.11 Terminology Pietrosemoli, ICTP Feb. 2003

  4. Wireless LAN Overview • DSSS popularity has eclipsed FHSS, although the latter may be more resistant to interference • We will focus on DSSS Pietrosemoli, ICTP Feb. 2003

  5. Channel Overlapping Pietrosemoli, ICTP Feb. 2003

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  10. Access Point Modes • Root Mode • Repeater Mode • Bridge Mode Pietrosemoli, ICTP Feb. 2003

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  18. Repeater and Bridging Functions Pietrosemoli, ICTP Feb. 2003

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  30. Chipset Manufacturers Pietrosemoli, ICTP Feb. 2003

  31. Client Devices Pietrosemoli, ICTP Feb. 2003

  32. Client Devices Pietrosemoli, ICTP Feb. 2003

  33. Client Devices Pietrosemoli, ICTP Feb. 2003

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  38. Common options that most wirelessresidential 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 Pietrosemoli, ICTP Feb. 2003

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  40. 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. Pietrosemoli, ICTP Feb. 2003

  41. 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. Pietrosemoli, ICTP Feb. 2003

  42. Configuration and Managementof 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. Pietrosemoli, ICTP Feb. 2003

  43. Configuration and Managementof 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. Pietrosemoli, ICTP Feb. 2003

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  45. UNII Bands Pietrosemoli, ICTP Feb. 2003

  46. 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. . Pietrosemoli, ICTP Feb. 2003

  47. 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. Pietrosemoli, ICTP Feb. 2003

  48. 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. Pietrosemoli, ICTP Feb. 2003

  49. 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. Pietrosemoli, ICTP Feb. 2003

  50. Power Limits Pietrosemoli, ICTP Feb. 2003