Chapter 26: Fundamentals of Wireless Networks

Mesh network

A network of APs used to cover a large area without the need for wired Ethernet cabling; client traffic is bridged from AP to AP over a backhaul network.

Service set identifier (SSID)

A text string that is used to identify a wireless network.

Basic service set identifier (BSSID)

A unique MAC address that is used to identify the AP that is providing a BSS.

Nonoverlapping channels

Successive channel numbers in a band that each have a frequency range that is narrow enough to not overlap the next channel above or below.

Infrastructure mode

The operating mode of an AP that is providing a BSS for wireless clients.

Roaming

The process a wireless client uses to move from one AP to another as it changes location.

Band

A contiguous range of frequencies.

Access point (AP)

A device that provides wireless service for clients within its coverage area or cell, with the AP connecting to both the wireless LAN and the wired Ethernet LAN.

Repeater

A device that repeats or retransmits signals it receives, effectively expanding the wireless coverage area.

Station (STA)

An 802.11 client device that is associated with a BSS.

Point-to-point bridge

An AP configured to bridge a wired network to a companion bridge at the far end of a line-of-sight path.

Workgroup bridge (WGB)

An AP that is configured to bridge between a wired device and a wireless network. The WGB acts as a wireless client.

Channel

An arbitrary index that points to a specific frequency within a band.

Ad hoc network

An impromptu wireless network formed between two or more devices without an AP or a BSS; also known as an ad hoc network.

Independent basic service set (IBSS)

An impromptu wireless network formed between two or more devices without an AP or a BSS; also known as an ad hoc network.

5. Which one of the following can be used to provide wireless connectivity to a nonwireless device? a. Wireless repeater b. Workgroup bridge c. Transparent bridge d. Adaptive bridge

B. A workgroup bridge acts as a wireless client, but bridges traffic to and from a wired device connected to it.

6. Which one of the following is not needed in a Cisco outdoor mesh network? a. A BSS function b. Ethernet cabling to each AP c. A workgroup bridge d. A backhaul network

B. In a mesh network, each mesh AP builds a standalone BSS. The APs relay client traf- fic to each other over wireless backhaul links, rather than wired Ethernet. Therefore, Ethernet cabling to each AP is not required.

4. Which one of the following is used to uniquely identify an AP and the basic service set it maintains with its associated wireless clients? a. SSID b. BSSID c. Ethernet MAC address d. Radio MAC address

B. The AP at the heart of a BSS or cell identifies itself (and the BSS) with a Basic Service Set Identifier (BSSID). It also uses an SSID to identify the wireless network, but that is not unique to the AP or BSS. Finally, the radio MAC address is used as the basis for the BSSID value, but the value can be altered to form the BSSID for each SSID that the AP supports.

2. Devices using a wireless LAN must operate in which one of the following modes? a. Round-robin access b. Half duplex c. Full duplex d. None of these answers

B. WLANs require half-duplex operation because all stations must contend for use of a channel to transmit frames.

8. Which of the following are considered to be nonoverlapping channels? a. Channels 1, 2, and 3 in the 2.4-GHz band b. Channels 1, 5, and 10 in the 2.4-GHz band c. Channels 1, 6, and 11 in the 2.4-GHz band d. Channels 40, 44, and 48 in the 5-GHz band

C and D. In the 2.4-GHz band, consecutively numbered channels are too wide to not overlap. Only channels 1, 6, and 11 are spaced far enough apart to avoid overlapping each other. In the 5-GHz band, all channels are considered to be nonoverlapping.

3. An access point is set up to offer wireless coverage in an office. Which one of the following is the correct 802.11 term for the resulting standalone network? a. BSA b. BSD c. BSS d. IBSS

C. An AP offers a basic service set (BSS). BSA is incorrect because it is a Basic Service Area, or the cell footprint of a BSS. BSD is incorrect because it does not pertain to wireless at all. IBSS is incorrect because it is an Independent BSS, or an ad hoc net- work, where an AP or BSS is not needed at all.

1. Wired Ethernet and Wi-Fi are based on which two IEEE standards, respectively? a. 802.1, 802.3 b. 802.3, 802.1 c. 802.3, 802.11 d. 802.11, 802.3

C. The IEEE 802.3 standard defines Ethernet, while 802.11 defines Wi-Fi.

7. Which of the following are frequency bands commonly used for Wi-Fi? a. 2.5 KHz b. 2.5 MHz c. 5MHz d. 2.5 GHz e. 5GHz

D and E. Wi-Fi commonly uses the 2.5- and 5-GHz bands.

Extended service set (ESS)

Multiple APs that are connected by a common switched infrastructure.

Cell

The area of wireless coverage provided by an AP; also known as the basic service area.

Distribution system (DS)

The wired Ethernet that connects to an AP and transports traffic between a wired and wireless network.

Basic service set (BSS)

Wireless service provided by one AP to one or more associated clients.