Chapter 26 - Fundamentals of Wireless Networks Flashcards
1
Q
What signals do wireless devices use to communicate?
A
RF (Radio Frequencies)
2
Q
True or False. Wireless devices must operate in Half Duplex mode in order to communicate.
A
True. If multiple signals are sent and/or received on the same channel at the same time, they can interfere with each other.
3
Q
What is a BSS (Infrastructure Service Set)?
A
- BSS (Basic Service Set) - One type of Infrastructure Service Set, A BSS is a closed group of devices that connect to the same WLAN via an AP. The AP determines the characteristics of the BSS and who can and can’t join the closed group. All devices within a BSS must use the same channel to communicate.
4
Q
What is a BSA?
A
- BSA (Basic Service Area) - A BSA is the area around an AP in which its signal is broadcasted. Any devices outside of this area will not be able to connect and use the BSS to communicate with the rest of the WLAN.
5
Q
What is a BSSID?
A
- BSSID (Basic Service Set Identifier) - A unique identifier of a BSS that is based on the relevant APs radio MAC.
6
Q
What is the difference between and SSID and a BSSID?
A
- A BSSID uniquely identifies an AP and is based off of that APs MAC address.
- An SSID identifies a WLAN but is not necessarily unique.
7
Q
What is an association?
A
- Occurs when a device attempts to join a BSS. This is an attempt at an association.
- The AP can either accept or reject this association based off of parameters.
8
Q
What is a DS?
A
- DS (Distribution System) - The wired Ethernet LAN that an AP connects to so that wireless devices can connect with wired devices or other wireless devices within other BSSs.
9
Q
What is an ESS?
A
- ESS (Extended Service Set) - One type of Infrastructure Service Set, an ESS is a large number of APs that are connected via a wired network and all cooperate to ensure that wireless service is consistent and seamless. Generally they should all be able to broadcast the same SSIDs.
- The individual BSSs don’t have to use the same channel.
10
Q
True or False. The BSSID will be the same for every SSID on a single AP.
A
False. In order for wireless devices to communicate with the correct SSID, each SSID must also have its own BSSID. On Cisco APs the BSSID will normally be the APs radio MAC and the last digit will increment by 1 on each SSID.
11
Q
Define Roaming.
A
Seamlessly moving from one AP to another within an ESS. Each AP will have its own BSS and (usually) its own channel as to not cause interference.
12
Q
What is an Independent Basic Service Set?
A
- IBSS (Independent Basic Service Set) - Also known as an Ad Hoc Wireless network, this allows two or more wireless clients to connect directly with each other with no other means of network connectivity. In order to take advantage of this, one device must advertise a network name and the necessary radio parameters. Other devices can then join ad hoc. Not very scalable and tends to fall down as more devices are added.
- An example of this would be AirDrop
13
Q
What is AP Infrastructure Mode
A
- Offers services necessary to form the infrastructure of an APs own wireless network.
14
Q
What is AP Repeater Mode?
A
- As opposed to connecting back to a DS over a wire, a repeater will just extend the coverage of another APs network by retransmiting it in a new cell around the repeating AP. These are generally used when it is not possible to run a wire to an AP but it is still necessary to get coverage to a desired location.
- Repeaters with only a single receiver and transmitter can end up receiving a signal to retransmit from the original AP, and accidentally transmitting it back to the original AP since they are on the same channel. This can have a big impact on throughput as the channel is kept busy for longer. A remedy for this is to get a repeater with 2 receivers and 2 transmitters so that one channel can be used to receive signals from the original AP and the other can be used to transmit signals from the repeater.
15
Q
What is AP Workgroup Bridge Mode?
A
- Allows a device’s wired interface to be connected to a wireless network. Useful when a device doesn’t have a wireless adapter but a wireless connection would be more practical than a wired one.
- The WGB AP itsself becomes a client of another APs BSS.
- Two types of WGB are:
- uWGB (Universal Workgroup Bridge) - A single wired device can be bridged to a wireless network
- WGB - A cisco proprietary implementation that allows multiple wired devices to be bridged to a wireless network
16
Q
What is AP Outdoor Bridge Mode?
A
- Essentially a wireless Point-to-Point link.
- Allows connectivity between WLANs over long distances. There needs to be an AP in this mode at both ends of the link. These are normally used in conjunction with directional antennas that help to focus the signals toward the other AP.
- Point-to-Multipoint links are also possible in this mode by using omnidirectional antennae so that the signal is transmitted equally in all directions. The other points in the link should have directional antennas pointed towards the central omnidirectional antenna.
17
Q
What is Mesh Basic Service Set?
A
- Also known as an MBSS
- Multiple APs over a large area are bridged together in a daisy chain type fashion.
- Mesh APs can use dual radios so that the clients can connect using one channel and the other bridged APs can connect to each other using another channel as to form a backhaul network. A protocol is used to work out the best path through a backhaul network.
- One AP is connected to the wired network called a RAP (Root Access Point).
- All other APs not connected to the wired network directly are called MAPs (Mesh Access Points).
