Le déploiement d’une solution sous la norme 802.11 Notions de propagation des ondes radio (débits, absorption, réflexion) Les déploiements pratiques 09 déc 2003 - Journée de veille technologique Les réseaux sans fil : point sur les technologies et réflexion sur les usages

Débit variable en fonction de la distance Module 3—Designing and Configuring Wireless LANs Débit variable en fonction de la distance The farther a STA is from an AP, the slower the data rate will be between the STA and the AP, as shown in Figure 3-29. The actual size of each data-rate zone depends on factors such as the antenna used, the amount of interference, transmit power (as permitted by regional law), and the amount of traffic on the AP. © 2001 Intel Corporation 3–2

Zone de couverture Module 6: Basics of IEEE 802.11a The closer a receiver is to the AP, the faster the possible data transmission rate. As shown in Figure 6-7, the range for the IEEE 802.11b maximum data rate of 11 Mbps is larger than the range for the IEEE 802.11a maximum data rate of 54 Mbps. Nevertheless, an IEEE 802.11b client that gets only 2 Mbps because of its distance from the AP would get 12 Mbps from an IEEE 802.11a AP at that same distance. (The actual distance/rate relationship is determined by environmental, usage, and deployment factors that are particular to each space.) © 2002 Intel Corporation 6-3

Comparaison des débits en fonction des fréquences ~4.5x 30 20 Débit (Mbps) 802.11a 10 802.11b ~2.5x 20 30 50 70 80 Distance (m) Source: Atheros Corporation

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Absorption Atténuation du signal lors de la rencontre avec un objet Module 1: Understanding Wireless Technologies Absorption Atténuation du signal lors de la rencontre avec un objet Le signal absorbé est converti en chaleur L’eau absorbe énormement le signal, le métal ne l’absorbe pas mais le dévie. Most of the objects and surfaces with which an RF signal comes into contact— rain, glass, wood, foliage, and even the air itself—tend to reduce signal amplitude. The loss that an RF signal experiences as a result of its encounter with objects is known as insertion loss or attenuation. The process that results in this attenuation is referred to as absorption, because the object absorbs part of the RF signal. The RF energy absorbed is converted to heat, and the object warms up slightly as a result. Because even the air absorbs RF energy, RF signals cannot travel forever. That is why a cellular phone call terminates when the mobile unit moves too far from a base station. If the call is placed on a rainy day, the RF signal is likely to experience attenuation even more quickly. © 2002 Intel Corporation 1-6

Réflexion Le signal est réfléchi par l’objet qu’il rencontre Designing Wireless Solutions: Instructor Guide Réflexion Le signal est réfléchi par l’objet qu’il rencontre Le signal perd de sa puissance à chaque réflexion Angle d’incidence = Angle de réflexion Le métal réfléchit fortement le signal L’eau réfléchit peu le signal La réflexion crée des chemins différents pour le même signal Rather than absorb RF energy, some objects and surfaces that RF signals encounter actually send the signal in another direction. This is known as reflection. RF signals tend to reflect off of objects at the same angle at which they encountered them. In other words, the angle of reflectance of RF waves equals their angle of incidence. 1-7 © 2002 Intel Corporation

Chemins multiples Plusieurs copies du signal arrivent à destination Designing Wireless Solutions: Instructor Guide Chemins multiples Plusieurs copies du signal arrivent à destination Les copies du signal créent des interférences et même des zones d’ombre 1-8 © 2002 Intel Corporation

Les antennes du point d’accès Module 1: Understanding Wireless Technologies Deux antennes Copies du signal envoyées avec une puissance différente Les copies les plus faibles sont rejetées Une antenne peut être dans une zone d’ombre, mais pas les deux Diversity antennas can cancel the effect of nulls. If you do not have diversity antennas and encounter a null, moving the antenna or switching to another channel will help you find the signal again. © 2002 Intel Corporation 1-9

Les types d’antenne Gain des antennes limitées par la législation En intérieur, les antennes du point d’accès sont généralement suffisantes En exterieur (pont), les antennes spécifiques sont requises, soit toriques, soit directionnelles Key Messages: To summarize: WLANs are a hot growth market: Verticals were the early adopters but now everyone is going wireless for the office to home and in between. Resellers recognize this opportunity as key to growing there business…don’t be left behind. Early to market: Intel mobile connectivity solutions are early to market with leading edge technology and innovative form factor designs that help position you ahead of the competition. Seamless mobile experience: Intel® PROSet reduces TCO and provides software innovation that brings our wired and wireless solutions together through a common user interface. Wired to wireless switching means your customer can truly have a seamless mobile experience Increasing your profit potential: Utilize our training and demand generation tools to increase your expertise and maximize your revenue and profit potential

Orientation des Antennes AN363—Designing Flexible Wireless LAN Solutions: Instructor Guide Orientation des Antennes It is important that the rubber duck antennas be positioned vertically, as shown in Figure 3-16, so that the antennas provide nearly omnidirectional coverage. Specialty antennas should also be positioned so that the polarization is correct. 3–11 © 2001 Intel Corporation

Les paramètres du point d’accès Module 3: Designing and Configuring WLANs Canal utilsé (1 à 14) ESSID Mode d’encryption Débit © 2002 Intel Corporation 3-12

Le déploiement d’une solution sous la norme 802.11 Notions de propagation des ondes radio (débits, absorption, réflexion) Les déploiements pratiques

Pontage de 2 segments Ethernet Designing Wireless Solutions: Instructor Guide Pontage de 2 segments Ethernet Note: This slide contains animation. The slide shows the problem; one mouse-click (space bar) causes the solution to appear. The words in yellow show the default interface setting. Two WLAPs can be used to create a wireless bridge between Ethernet segments. Wireless bridges are especially useful for connecting buildings on a campus; with the right antennas, a wireless bridge can have a range of up to 50 kilometers (30 miles). Figure 3-5 shows the settings of two WLAPs that form a bridge between two Ethernet segments. 3-14 © 2002 Intel Corporation

Concentrateur sans fil vers segment Ethernet Module 3: Designing and Configuring WLANs Note: This slide contains animation. The slide shows the problem; one mouse-click (space bar) causes the solution to appear. The words in yellow show the default interface setting. Figure 3-6 shows how WLAPs are configured to bridge Ethernet and wireless LAN segments. Figure 3-6 © 2002 Intel Corporation 3-15

Designing Wireless Solutions: Instructor Guide Pont sans fil Note: This slide contains animation. The slide shows the problem; one mouse-click (space bar) causes the solution to appear. The words in yellow show the default interface setting. Figure 3-7 shows two wireless LANs joined by the wireless interface. This configuration is also an ESS. Figure 3-7 3-16 © 2002 Intel Corporation

Repéteur Ethernet Figure 3-8 Module 3: Designing and Configuring WLANs Note: This slide contains animation. The slide shows the problem; one mouse-click (space bar) causes the solution to appear. The words in yellow show the default interface setting. Figure 3-8 shows how a WLAP can form an intermediate hop between two wireless LANs. There should not be more than two hops between any two WLAPs. Figure 3-8 © 2002 Intel Corporation 3-17

Pontage de sous réseau Figure 3-9 Designing Wireless Solutions: Instructor Guide Pontage de sous réseau Note: This slide contains animation. The slide shows the problem; one mouse-click (space bar) causes the solution to appear. The words in yellow show the default interface setting. Although WLAPs cannot perform layer 3 routing functions, they can bridge two Ethernet subnets if the WLAPs are attached to routers, as shown in Figure 3-9. Figure 3-9 3-18 © 2002 Intel Corporation

Pont Radio Point à multipoint Point à point

Organisation logique du réseau Module 1: Understanding Wireless Technologies Organisation logique du réseau Les choix de l’organisation logique du réseau sans fil La disposition des points d’accès Most of the objects and surfaces with which an RF signal comes into contact— rain, glass, wood, foliage, and even the air itself—tend to reduce signal amplitude. The loss that an RF signal experiences as a result of its encounter with objects is known as insertion loss or attenuation. The process that results in this attenuation is referred to as absorption, because the object absorbs part of the RF signal. The RF energy absorbed is converted to heat, and the object warms up slightly as a result. Because even the air absorbs RF energy, RF signals cannot travel forever. That is why a cellular phone call terminates when the mobile unit moves too far from a base station. If the call is placed on a rainy day, the RF signal is likely to experience attenuation even more quickly. © 2002 Intel Corporation 1-20

Scénarii de déploiement Mode Infrastructure BSS Basic Service Set Un point d’accès ESS Extended Service Set Plusieurs points d’accès Infrastructure Mode An 802.11 networking framework in which devices communicate with each other by first going through an Access Point (AP). In infrastructure mode, wireless devices can communicate with each other or can communicate with a wired network. When one AP is connected to wired network and a set of wireless stations it is referred to as a Basic Service Set (BSS). An Extended Service Set (ESS) is a set of two or more BSSs that form a single subnetwork. Most corporate wireless LANs operate in infrastructure mode because they require access to the wired LAN in order to use services such as file servers or printers.

ESS – Extended Service Set Un Extended Service Set (ESS) est crée par un minimum de deux points d’accès configurés comme faisant partie du même subnet IP avec le même SSID. Cette configuration permet le libre déplacement des clients dans le réseau sans fil All of the BSSs in an ESS have the same Net ID and different BSSIDs. SSID = Service Set Identifier

Mise en place des points d’accès Designing Wireless Solutions: Instructor Guide Mise en place des points d’accès r = 50m ~ 9 Mbps Again, determining how far apart the APs should be deployed is a function of the customer’s needs and environmental conditions. One possible solution is to overlap the APs’ ranges so that the outer range of one AP touches the inner range of the next, as shown in Figure 6-19. r = 15m ~ 54–36 Mbps 6-23 © 2002 Intel Corporation

Répartition dynamique de charge Module 6: Basics of IEEE 802.11a La station client recherche toujours le meilleur débit Les points d’accès contrôlent la charge et peuvent autoritairement terminer l’association avec une station client © 2002 Intel Corporation 6-24

Répartition dynamique de charge Module 6: Basics of IEEE 802.11a In Figure 6-12, three APs with patch antennas provide coverage in one room. The top panel shows an uneven distribution of clients among the APs. This problem was caused by the APs being turned on at different times. AP 1 powered on first, and eight clients associated with it. AP 3 powered on second, and three clients associated with it. One client associated with AP 2, which powered on last. (None of the clients in this example is in motion.) Because the load is unequally distributed, performance for the clients associated with AP 1 will be diminished. © 2002 Intel Corporation 6-25

Répartition dynamique de charge Designing Wireless Solutions: Instructor Guide Client 5, which associated with AP 1 when it powered on, is not close enough to AP 1 to get a data rate better than 36 Mbps. When AP 2 powers on, Client 5 analyzes the signal strength of the beacon from AP 2 and determines that it can get a faster data rate from AP 2 than from AP 1. Client 5 therefore reassociates with AP 2. The second process is carried out by the APs. Client 6, Client 7, and Client 8 cannot get a better data rate than 36 Mbps from any of the APs. However, AP 1 still has a higher load than the other APs. Because the APs are on the same ESS, they are able to communicate with one another. AP 1 determines that there are other APs in the area that can serve the three clients. AP 1 therefore sends Client 6, Client 7, and Client 8 disassociation notices, which force the clients to find other APs. Client 6 and Client 7 associate with AP 2 because it is the closest. Client 8 can associate with either AP 2 or AP 3 and chooses AP 3 because it has the lightest workload. 6-26 © 2002 Intel Corporation

Scanning actif vs. Scanning passif ) ) ) ) ) ) ) ) ) ) ) ) Scanning actif La station client recherche un point d’accès sur les 14 canaux disponibles en émettant Lorsqu’un point d’accès est localisé, la station client essaye de s’y associer Une recherche sur les 14 canaux dure 1/3 de seconde Scanning passif La station cliente écoute l’activité sur ses canaux Une fois un signal détecté, la station émet une demande d’association Un scanning passif de tous les canaux dure 1.5 seconde Our SKU strategy is based on the scanning mechanisms above. Active scanning provides better user experience in Windows XP. Un scanning passif peut retarder l’association sous Windows XP

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