Chapter 7-Wireless LAN Topologies

1. Chapter 7-Wireless LAN Topologies • WAN, WLAN, WMAN, etc • Access Points, SSID, BSS, ESS, etc

2. Exam Essentials • Know the four major types of wireless topologies. • Understand the differences between a WWAN, WLAN, WPAN, and WMAN. • Explain the three 802.11 service sets. • Be able to fully expound on all the components, purposes, and differences of a basic service set, an extended service set, and an independent basic service set. Understand how the radio cards interact with each other in each service set. • Identify the various ways in which an 802.11 radio can be used. • Understand that the 802.11 standard expects a radio card to be used either as a client station or inside an access point. Also understand that an 802.11 radio card can be used for other purposes, such as bridging, repeaters, and so on. • Explain the purpose of the distribution system. • Know that the DS consists of two pieces: distribution system services (DSS) and the distribution system medium (DSM). Understand that the medium used by the DS can be any type of medium. Explain the functions of a wireless distribution system (WDS).

3. Exam Essentials • Define SSID, BSSID, and ESSID. • Be able to explain the differences or similarities of all three of these addresses and the function of each. • Describe the various ways in which an ESS can be implemented and the purpose behind each design. • Explain the three ways in which the coverage cells of the ESS access points can be designed and the purpose behind each design. • Demonstrate an understanding of the various nonstandard 802.11 topologies. • Understand that alternative 802.11 topologies such as bridging and mesh networks exist. Further discussion of these nonstandard topologies can be found throughout this book. • Explain access point and client station configuration modes. • Remember all the standard and nonstandard confguration modes of both an AP and a client station.

4. Topology • Physical or logical layout of the network • Three main service sets • Additional non-standard Service sets as well Pg 222

5. Wireless Networking Topologies • Wireless wide area network (WWAN) • Wireless metropolitan area network (WMAN) • Wireless personal area network (WPAN) • Wireless local area network (WLAN) Pg 222

6. Wireless wide area network (WWAN) • Covers larger geographic area • As compared to 802.11 WLAN • Usually cellular phone providers or proprietary solutions • Cell providers and 3G/4G networks are making a bug push • Data transfers are slower than WLAN, but catching up Pg 223

7. Wireless metropolitan area network (WMAN) • Coverage to a city and suburbs • Many different techs • Mesh, 802.11 ESS, etc • 802.16 is a new player • WiMAX • DSL and Cable Speeds • Fixed Wirless?? • Many municipal projects have slowed or stopped • 802.11 didn’t scale well Pg 222

8. Wireless personal area network (WPAN) • For personal devices • Phones, PDA, Laptop, PC, etc • Bluetooth and Zigbee • 802.15 Pg 224

9. Wireless local area network (WLAN) • 802.11-2007 and draft standards • Usually for a building or campus network • LAN vs. WAN • Smaller area usually • Bridging and extenders can change this Pg 226

10. 802.11 Topologies • Radio Card-Station-STA in the standards • In an Access Point (AP) or in a client station • Main Topologies or Service Sets • Basic Service Set (BSS) • Extended Service Set (ESS) • Independent Basic Service Set (IBSS) Pg 226

11. 802.11 Topologies and terminology • In simplex communications, one device is capable of only transmitting, and the other device is capable of only receiving. FM radio is an example of simplex communications. Simplex communications are rarely used on computer networks. • In half-duplex communications, both devices are capable of transmitting and receiving; however, only one device can transmit at a time. Walkie-talkies, or two-way radios, are examples of half duplex technology • In full-duplex communications, both devices are capable of transmitting and receiving at the same time. A telephone conversation is an example of a full-duplex communication. Most IEEE 802.3 equipment is capable of full-duplex communications. The only way to accomplish full-duplex communications in a wireless environment is to have a two-channel setup where all transmissions in one direction are receiving while all transmissions in the other direction are transmitting. Current 802.11 technologies do not employ this technology, contrary to some marketing literature. Pg 226

12. Access Point • Half Duplex device • Only one radio card can be transmitting at a time • Basically a hub with a radio card and antenna • The original CWNP definition of an access point (AP) was a half-duplex device with switch like intelligence. That definition can still be used to characterize autonomous access points • Lightweight APs are controlled by a WLAN controller/switch Pg 227

13. Access Point • AP is a WLAN controller that can direct traffic to the backbone (distribution System) or back to the wireless medium • 802.11 Header is designed with 3 MAC Addresses • Can have as many as 4 in some cases to account for forwarding at layer 2 • Layer 3-7 information is called the MAC Service Data Unit (MSDU) • Logic that is used to forward MSDU is known as the Distribution System Services Pg 227

14. Client Station • Radio card not in an AP-usually in a client station • PC, Laptop, PDA, etc • When a client station makes a layer 2 connection with the AP, they are associated Pg 228

15. Integration Service (IS) • Enables delivery of MSDU between the distribution system (DS) and non-802.11 LAN via a portal • Usually done via an AP or WLAN controller • 802.11 to 802.3 for example • The layer 2 information will change • Remove the 802.11 frame and replace with an 802.3 frame • The MSDU information basically stays the same Pg 228

16. Distribution System (DS) • Used to interconnect the Basic Service Sets (BSS) via an integrated LAN to create and Extended Service Set (ESS) • DS Contains: • Distribution system medium (DSM) • A logical physical medium used to connect access points is known as a distribution system medium (DSM). The most common example is an 802.3 medium. • Distribution system services (DSS) • System services built inside an access point usually in the form of software. The distribution system services (DSS) provide the switchlike intelligence mentioned earlier in this chapter. These software services are used to manage client station associations, re-associations, and disassociations. Distribution system services also use the layer 2 addressing of the 802.11 MAC header to eventually forward the layer 3 –7 information (MSDU) either to the integration service or to another wireless client station. level. Pg 228

17. Distribution System (DS) • An AP can act as a portal to other wired and wireless mediums. • APs are translational bridge between two mediums • Generally between 802.11 and 802.3 Pg 229

18. Wireless Distribution System (WDS) • Using a four MAC address frame format • Allowed, but not defined how to use • Called a WDS • Bridging, repeaters, mesh networks all are examples of implementations • Although DS usually goes to wired, it can go to wireless • Wireless backhaul • For connecting APs together Pg 229

19. Wireless Distribution System (WDS) • A WDS may operate by using access points with a single 802.11 radio or dual 802.11 radios • Single radio will limit throughput because while it is sending info to other AP, no additional data can be sent or received • Dual radio allows using WDS and receiving data from Stations • Even better when second radio is different frequency band Pg 230

20. Wireless Repeaters • Used to extend WLAN coverage where no cabled network exists • If a station transmits, the wireless repeater receives and send to Access Point • Repeater provides coverage, but isn’t connected to the wired network • Common option on many APs • Connection between repeater and AP is WDS Pg 230

21. Wireless Repeaters Pg 230

22. Wireless Repeaters • Effectivley increase the size of original cell coverage • Must be on same channel as AP • Must have 50% overlap with AP • Decreases throughput • Generally bad for VoWiFi Pg 231

23. Service Set Identifier (SSID) • Logical name to identify the wireless network • Like a workgroup name • SSID is used to let radio cards find networks • Active and Passive scanning • SSID is configured on APs and Client Stations • 32 characters • Case sensitive • SSID hiding is weak security Pg 232

24. Basic Service Set (BSS) • Single AP with one or more client stations • AP connects to DS • Stations that are members of the BSS are associated • Created a layer 2 connection • Stations do not communicate with each other • Must go through AP Pg 233

25. Basic Service Set Identifier (BSSID) • 48 bit MAC address of the AP’s radio card • Layer 2 ID for the BSS • Usually the MAC address of the AP • Can also customize • Virtual BSSID • Generally found in the Frame Header • Needed for Roaming Pg 234

26. Basic Service Area (BSA) • Physical Area of Coverage from the AP • Clients can move in this area an maintain connection/communication with AP • As long as signal strength is above the Received Signal Strength Indicator (RSSI) threshold • Can also switch between rates in this zone • Dynamic rate switching • Shape is affected by other RF sources and interference • Shape is subject to change as well Pg 234

27. Extended Service Set (ESS) • One or more BSS connected through the distribution system (DS) • Generally multiple APs and clients stations united by a single distribution system medium • Often set up with multiple overlapping coverage cells • 15 to 25 % overlap to support roaming Pg 235

28. Extended Service Set (ESS) Pg 235

29. Extended Service Set (ESS) • Roaming is NOT a standards • Common requirement from businesses • Can also have colocation • Multiple totally overlapping cells • Support increased client capacity • Generally all APs will have the same SSID • Also known as the extended service set identifier (ESSID) Pg 235

30. Extended Service Set (ESS) • If APs don’t have same ID, still and ESS • Roaming will not be possible • When APs share the ESSID/SSID each AP still has unique BSSID Pg 235

31. Independent Basic Service Set (IBSS) • Radio cards that make up an IBSS are only client stations • No AP • Can have multiple client stations linked together • Ad-hoc communications • Peer to Peer network • Frames transmitted directly between stations Pg 238

32. Independent Basic Service Set (IBSS) • All stations must use same channel • Must have same SSID • BSSID must be chosen • First station that starts networkgenerates the SSID Pg 238

33. Non Standard Topologies • Wireless bridging • 802.11 radios used to connect two wired networks • Most WDS networks are considered non-standard • Even though 802.11 defines a WDS frame Pg 238

34. Non Standard Topologies • Workgroup Bridge • Gateway for a small wired workgroups • Usually a client station associated to an AP • Repeater is an AP that forwards data to a root access point Pg 238

35. 802.11 Configuration Modes • 802.11-2007 defines all radios as Stations • AP and Client station radio can each be configured in multiple ways • APs • BSS • WDS (non-standard-bridge, repeater, etc.) • Client Station • BSS • IBSS Pg 239

36. AP Modes • Root mode is standard • Serve as a portal to DS • Bridge mode • The AP is converted into a wireless bridge. • Workgroup Bridge mode • The AP is transformed into a workgroup bridge. • Repeater mode • The AP performs as a repeater access point. • Scanner mode • The access point radio is converted into a sensor radio, allowing the access point to integrate into a wireless intrusion detection system (WIDS) architecture. Pg 240

37. Client Station Modes • Infrastructure Mode • Participate in BSS (or ESS) • Find the SSID • Ad Hoc Mode • IBSS • Communicate directly to other client stations Pg 240

38. Exam Essentials • Know the four major types of wireless topologies. • Understand the differences between a WWAN, WLAN, WPAN, and WMAN. • Explain the three 802.11 service sets. • Be able to fully expound on all the components, purposes, and differences of a basic service set, an extended service set, and an independent basic service set. Understand how the radio cards interact with each other in each service set. • Identify the various ways in which an 802.11 radio can be used. • Understand that the 802.11 standard expects a radio card to be used either as a client station or inside an access point. Also understand that an 802.11 radio card can be used for other purposes, such as bridging, repeaters, and so on. • Explain the purpose of the distribution system. • Know that the DS consists of two pieces: distribution system services (DSS) and the distribution system medium (DSM). Understand that the medium used by the DS can be any type of medium. Explain the functions of a wireless distribution system (WDS).

39. Exam Essentials • Define SSID, BSSID, and ESSID. • Be able to explain the differences or similarities of all three of these addresses and the function of each. • Describe the various ways in which an ESS can be implemented and the purpose behind each design. • Explain the three ways in which the coverage cells of the ESS access points can be designed and the purpose behind each design. • Demonstrate an understanding of the various nonstandard 802.11 topologies. • Understand that alternative 802.11 topologies such as bridging and mesh networks exist. Further discussion of these nonstandard topologies can be found throughout this book. • Explain access point and client station configuration modes. • Remember all the standard and nonstandard confguration modes of both an AP and a client station.