Podcast
Questions and Answers
Which technology is typically used in a wireless wide area network (WWAN)?
Which technology is typically used in a wireless wide area network (WWAN)?
- Zigbee
- Bluetooth
- Wi-Fi 6
- General Packet Radio Service (GPRS) (correct)
What is a characteristic of a wireless metropolitan area network (WMAN)?
What is a characteristic of a wireless metropolitan area network (WMAN)?
- Primarily uses fiber optic cables
- Provides RF coverage to a city and surrounding suburbs (correct)
- Operates only in rural areas
- Relies solely on satellite communication
Which wireless technology is often associated with a wireless metropolitan area network (WMAN)?
Which wireless technology is often associated with a wireless metropolitan area network (WMAN)?
- Near Field Communication (NFC)
- RFID
- Long Term Evolution (LTE) (correct)
- Infrared Data Association (IrDA)
What type of technologies do wireless wide area networks (WWANs) typically use?
What type of technologies do wireless wide area networks (WWANs) typically use?
What distinguishes a wireless wide area network (WWAN) from a wireless local area network (WLAN)?
What distinguishes a wireless wide area network (WWAN) from a wireless local area network (WLAN)?
Which wireless technology is NOT typically associated with a wireless wide area network (WWAN)?
Which wireless technology is NOT typically associated with a wireless wide area network (WWAN)?
What does the Duration/ID field in the MAC header represent in 802.11?
What does the Duration/ID field in the MAC header represent in 802.11?
What is the purpose of the Pseudo-Random Backoff Timer in 802.11?
What is the purpose of the Pseudo-Random Backoff Timer in 802.11?
What happens when the backoff timer in 802.11 reaches zero?
What happens when the backoff timer in 802.11 reaches zero?
What is the purpose of the Interframe space (IFS) in 802.11?
What is the purpose of the Interframe space (IFS) in 802.11?
Which interframe space is used for high-priority frames in 802.11?
Which interframe space is used for high-priority frames in 802.11?
What is the Hybrid Coordination Function (HCF) in the 802.11e amendment?
What is the Hybrid Coordination Function (HCF) in the 802.11e amendment?
What is the layer 2 identifier for each individual Basic Service Set (BSS)?
What is the layer 2 identifier for each individual Basic Service Set (BSS)?
What allows station mobility between disjointed cells, where a client station moves from one access point's BSA to another?
What allows station mobility between disjointed cells, where a client station moves from one access point's BSA to another?
What is the topology where 802.11ad stations communicate directly with each other, using the 60 GHz frequency band?
What is the topology where 802.11ad stations communicate directly with each other, using the 60 GHz frequency band?
What is the role of a PBSS control point (PCP) within a PBSS?
What is the role of a PBSS control point (PCP) within a PBSS?
What connects identically configured BSSs through a distribution system medium, enabling seamless roaming within the coverage area?
What connects identically configured BSSs through a distribution system medium, enabling seamless roaming within the coverage area?
What allows client stations to maintain communication within certain signal strength thresholds in the coverage provided by an access point?
What allows client stations to maintain communication within certain signal strength thresholds in the coverage provided by an access point?
What is the cornerstone topology of an 802.11 network?
What is the cornerstone topology of an 802.11 network?
Which 802.11 station serves as a wireless portal for client stations to communicate and provides a distribution system access function (DSAF)?
Which 802.11 station serves as a wireless portal for client stations to communicate and provides a distribution system access function (DSAF)?
What technology facilitates communication between devices in close proximity?
What technology facilitates communication between devices in close proximity?
What is the name identifying an 802.11 wireless network?
What is the name identifying an 802.11 wireless network?
Which standard defines an integration service (IS) for delivering data between the distribution system and non-IEEE-802.11 LAN via a portal?
Which standard defines an integration service (IS) for delivering data between the distribution system and non-IEEE-802.11 LAN via a portal?
What is used in mesh deployments and outdoor bridge links to provide coverage and backhaul connectivity?
What is used in mesh deployments and outdoor bridge links to provide coverage and backhaul connectivity?
What is the fundamental access method of 802.11 communications?
What is the fundamental access method of 802.11 communications?
What are the two forms of contention heavily used in today's networks?
What are the two forms of contention heavily used in today's networks?
What is the purpose of converting AP radio into a sensor radio in a wireless intrusion detection system (WIDS) architecture?
What is the purpose of converting AP radio into a sensor radio in a wireless intrusion detection system (WIDS) architecture?
What is the function of physical carrier sense in 802.11 communications?
What is the function of physical carrier sense in 802.11 communications?
What is the medium access control (MAC) essential for in network communication?
What is the medium access control (MAC) essential for in network communication?
What is the primary medium access method used in 802.11 communications?
What is the primary medium access method used in 802.11 communications?
What technology is often associated with a wireless metropolitan area network (WMAN)?
What technology is often associated with a wireless metropolitan area network (WMAN)?
Which wireless technology is NOT typically associated with a wireless wide area network (WWAN)?
Which wireless technology is NOT typically associated with a wireless wide area network (WWAN)?
What is the primary medium access method used in 802.11 communications?
What is the primary medium access method used in 802.11 communications?
What is the role of a PBSS control point (PCP) within a PBSS?
What is the role of a PBSS control point (PCP) within a PBSS?
What is the purpose of converting AP radio into a sensor radio in a wireless intrusion detection system (WIDS) architecture?
What is the purpose of converting AP radio into a sensor radio in a wireless intrusion detection system (WIDS) architecture?
What distinguishes a wireless wide area network (WWAN) from a wireless local area network (WLAN)?
What distinguishes a wireless wide area network (WWAN) from a wireless local area network (WLAN)?
What is the layer 2 identifier for each individual Basic Service Set (BSS)?
What is the layer 2 identifier for each individual Basic Service Set (BSS)?
What technology facilitates communication between devices in close proximity?
What technology facilitates communication between devices in close proximity?
What is the function of physical carrier sense in 802.11 communications?
What is the function of physical carrier sense in 802.11 communications?
Which interframe space is used for high-priority frames in 802.11?
Which interframe space is used for high-priority frames in 802.11?
What is the primary medium access method used in 802.11 communications?
What is the primary medium access method used in 802.11 communications?
What is the name identifying an 802.11 wireless network?
What is the name identifying an 802.11 wireless network?
What is the purpose of the network allocation vector (NAV) in 802.11?
What is the purpose of the network allocation vector (NAV) in 802.11?
Which interframe space (IFS) in 802.11 is used after receipt of corrupted frames?
Which interframe space (IFS) in 802.11 is used after receipt of corrupted frames?
What is the primary function of the Point Coordination Function (PCF) in 802.11?
What is the primary function of the Point Coordination Function (PCF) in 802.11?
What distinguishes the Hybrid Coordination Function (HCF) in the 802.11e amendment from the Distributed Coordination Function (DCF)?
What distinguishes the Hybrid Coordination Function (HCF) in the 802.11e amendment from the Distributed Coordination Function (DCF)?
What is the function of the Pseudo-Random Backoff Timer in 802.11?
What is the function of the Pseudo-Random Backoff Timer in 802.11?
At which layer of the OSI model does Virtual Carrier Sense in 802.11 occur?
At which layer of the OSI model does Virtual Carrier Sense in 802.11 occur?
What is the purpose of the Distributed Coordination Function (DCF) in 802.11 communications?
What is the purpose of the Distributed Coordination Function (DCF) in 802.11 communications?
What is the function of physical carrier sense in 802.11 communications?
What is the function of physical carrier sense in 802.11 communications?
What distinguishes Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) from Carrier Sense Multiple Access with Collision Detection (CSMA/CD)?
What distinguishes Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) from Carrier Sense Multiple Access with Collision Detection (CSMA/CD)?
What is the role of a PBSS control point (PCP) within a PBSS?
What is the role of a PBSS control point (PCP) within a PBSS?
What technology facilitates communication between devices in close proximity?
What technology facilitates communication between devices in close proximity?
What is the cornerstone topology of an 802.11 network?
What is the cornerstone topology of an 802.11 network?
What is the function of a PBSS control point (PCP) within a PBSS?
What is the function of a PBSS control point (PCP) within a PBSS?
What is the role of the Distribution System (DS) in 802.11 networks?
What is the role of the Distribution System (DS) in 802.11 networks?
What is the cornerstone topology of an 802.11 network?
What is the cornerstone topology of an 802.11 network?
What technology is used in mesh deployments and outdoor bridge links to provide coverage and backhaul connectivity?
What technology is used in mesh deployments and outdoor bridge links to provide coverage and backhaul connectivity?
What does the Service Set Identifier (SSID) do in an 802.11 wireless network?
What does the Service Set Identifier (SSID) do in an 802.11 wireless network?
What is the purpose of the Interframe space (IFS) in 802.11?
What is the purpose of the Interframe space (IFS) in 802.11?
Which technology is often associated with a wireless metropolitan area network (WMAN)?
Which technology is often associated with a wireless metropolitan area network (WMAN)?
What is the primary medium access method used in 802.11 communications?
What is the primary medium access method used in 802.11 communications?
What is the cornerstone topology of an 802.11 network?
What is the cornerstone topology of an 802.11 network?
What is the function of physical carrier sense in 802.11 communications?
What is the function of physical carrier sense in 802.11 communications?
What is the purpose of the Interframe space (IFS) in 802.11?
What is the purpose of the Interframe space (IFS) in 802.11?
What technology facilitates communication between devices in close proximity?
What technology facilitates communication between devices in close proximity?
Which identifier serves as the layer 2 identifier for each individual Basic Service Set (BSS)?
Which identifier serves as the layer 2 identifier for each individual Basic Service Set (BSS)?
What is the role of an Extended Service Set (ESS) in wireless networking?
What is the role of an Extended Service Set (ESS) in wireless networking?
What is the Logical network name of an ESS known as?
What is the Logical network name of an ESS known as?
What does an Independent Basic Service Set (IBSS) consist solely of?
What does an Independent Basic Service Set (IBSS) consist solely of?
What role does a Mesh Basic Service Set (MBSS) serve in wireless networking?
What role does a Mesh Basic Service Set (MBSS) serve in wireless networking?
What type of wireless network topology is a Personal Basic Service Set (PBSS) associated with?
What type of wireless network topology is a Personal Basic Service Set (PBSS) associated with?
What is the primary medium access method used in 802.11 communications?
What is the primary medium access method used in 802.11 communications?
What is the function of the Pseudo-Random Backoff Timer in 802.11?
What is the function of the Pseudo-Random Backoff Timer in 802.11?
What distinguishes Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) from Carrier Sense Multiple Access with Collision Detection (CSMA/CD)?
What distinguishes Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) from Carrier Sense Multiple Access with Collision Detection (CSMA/CD)?
What is the role of the Distribution System (DS) in 802.11 networks?
What is the role of the Distribution System (DS) in 802.11 networks?
What is the purpose of converting AP radio into a sensor radio in a wireless intrusion detection system (WIDS) architecture?
What is the purpose of converting AP radio into a sensor radio in a wireless intrusion detection system (WIDS) architecture?
What is the purpose of the Interframe space (IFS) in 802.11?
What is the purpose of the Interframe space (IFS) in 802.11?
What is the purpose of the Distribution System (DS) in 802.11 networks?
What is the purpose of the Distribution System (DS) in 802.11 networks?
What technology is used in mesh deployments and outdoor bridge links to provide coverage and backhaul connectivity?
What technology is used in mesh deployments and outdoor bridge links to provide coverage and backhaul connectivity?
What does the Service Set Identifier (SSID) do in an 802.11 wireless network?
What does the Service Set Identifier (SSID) do in an 802.11 wireless network?
What is the function of the Pseudo-Random Backoff Timer in 802.11?
What is the function of the Pseudo-Random Backoff Timer in 802.11?
What is the primary medium access method used in 802.11 communications?
What is the primary medium access method used in 802.11 communications?
What is the cornerstone topology of an 802.11 network?
What is the cornerstone topology of an 802.11 network?
What is the function of the Pseudo-Random Backoff Timer in 802.11?
What is the function of the Pseudo-Random Backoff Timer in 802.11?
What distinguishes the Hybrid Coordination Function (HCF) in the 802.11e amendment from the Distributed Coordination Function (DCF)?
What distinguishes the Hybrid Coordination Function (HCF) in the 802.11e amendment from the Distributed Coordination Function (DCF)?
What happens when the backoff timer in 802.11 reaches zero?
What happens when the backoff timer in 802.11 reaches zero?
What is the purpose of the Distributed Coordination Function (DCF) in 802.11 communications?
What is the purpose of the Distributed Coordination Function (DCF) in 802.11 communications?
What distinguishes Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) from Carrier Sense Multiple Access with Collision Detection (CSMA/CD)?
What distinguishes Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) from Carrier Sense Multiple Access with Collision Detection (CSMA/CD)?
What does the Duration/ID field in the MAC header represent in 802.11?
What does the Duration/ID field in the MAC header represent in 802.11?
Match the wireless technology with its typical usage:
Match the wireless technology with its typical usage:
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Match the wireless technology with its associated network type:
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Wireless LAN topologies cover broad geographical boundaries using a wired medium instead of a wireless medium.
Wireless LAN topologies cover broad geographical boundaries using a wired medium instead of a wireless medium.
A wireless wide area network (WWAN) typically uses cellular telephone technologies or proprietary licensed wireless bridging technologies.
A wireless wide area network (WWAN) typically uses cellular telephone technologies or proprietary licensed wireless bridging technologies.
A wireless metropolitan area network (WMAN) provides RF coverage to a metropolitan area, such as a city and the surrounding suburbs.
A wireless metropolitan area network (WMAN) provides RF coverage to a metropolitan area, such as a city and the surrounding suburbs.
The 802.11 draft amendments include general packet radio service (GPRS), code division multiple access (CDMA), time division multiple access (TDMA), Long Term Evolution (LTE), and Global System for Mobile Communications (GSM).
The 802.11 draft amendments include general packet radio service (GPRS), code division multiple access (CDMA), time division multiple access (TDMA), Long Term Evolution (LTE), and Global System for Mobile Communications (GSM).
Data can be carried to a variety of devices, such as laptops, desktop PCs, and gaming consoles.
Data can be carried to a variety of devices, such as laptops, desktop PCs, and gaming consoles.
A wireless wide area network (WWAN) uses a wireless medium instead of a wired medium.
A wireless wide area network (WWAN) uses a wireless medium instead of a wired medium.
An Extended Service Set (ESS) connects identically configured BSSs through a distribution system medium, enabling seamless roaming within the ESS coverage area.
An Extended Service Set (ESS) connects identically configured BSSs through a distribution system medium, enabling seamless roaming within the ESS coverage area.
Nomadic roaming allows station mobility between disjointed cells, where a client station moves from one access point's BSA to another.
Nomadic roaming allows station mobility between disjointed cells, where a client station moves from one access point's BSA to another.
An Independent Basic Service Set (IBSS) consists solely of client stations with no access point, akin to a wired crossover cable.
An Independent Basic Service Set (IBSS) consists solely of client stations with no access point, akin to a wired crossover cable.
A Personal Basic Service Set (PBSS) is an 802.11 WLAN topology where 802.11ad stations communicate directly with each other, using the 60 GHz frequency band.
A Personal Basic Service Set (PBSS) is an 802.11 WLAN topology where 802.11ad stations communicate directly with each other, using the 60 GHz frequency band.
Quality of service (QoS) mechanisms can be implemented within all 802.11 service sets, with most enterprise deployments considering each basic service set as a QoS basic service set (QBSS).
Quality of service (QoS) mechanisms can be implemented within all 802.11 service sets, with most enterprise deployments considering each basic service set as a QoS basic service set (QBSS).
A Mesh Basic Service Set (MBSS) provides wireless distribution of network traffic through mesh portal stations connected to the upstream wired medium, with mesh points forwarding traffic through the wireless backhaul.
A Mesh Basic Service Set (MBSS) provides wireless distribution of network traffic through mesh portal stations connected to the upstream wired medium, with mesh points forwarding traffic through the wireless backhaul.
802.11 stations include access points (AP) and client stations, each identified by a unique MAC address.
802.11 stations include access points (AP) and client stations, each identified by a unique MAC address.
The 802.11-2020 standard defines an integration service (IS) for delivering data between the distribution system and non-IEEE-802.11 LAN via a portal.
The 802.11-2020 standard defines an integration service (IS) for delivering data between the distribution system and non-IEEE-802.11 LAN via a portal.
Wireless Distribution System (WDS) is used in mesh deployments and outdoor bridge links to provide coverage and backhaul connectivity.
Wireless Distribution System (WDS) is used in mesh deployments and outdoor bridge links to provide coverage and backhaul connectivity.
Service Set Identifier (SSID) is a logical name identifying an 802.11 wireless network and is configurable on all 802.11 radios.
Service Set Identifier (SSID) is a logical name identifying an 802.11 wireless network and is configurable on all 802.11 radios.
The basic service set (BSS) is the cornerstone topology of an 802.11 network, consisting of one AP radio with one or more client stations, forming a wireless domain for communication.
The basic service set (BSS) is the cornerstone topology of an 802.11 network, consisting of one AP radio with one or more client stations, forming a wireless domain for communication.
The 802.11-2020 standard defines multiple service sets, including basic service set (BSS), extended service set (ESS), independent basic service set (IBSS), personal basic service set (PBSS), mesh basic service set (MBSS), and QoS basic service set (QBSS).
The 802.11-2020 standard defines multiple service sets, including basic service set (BSS), extended service set (ESS), independent basic service set (IBSS), personal basic service set (PBSS), mesh basic service set (MBSS), and QoS basic service set (QBSS).
Virtual Carrier Sense in 802.11 occurs at layer 2 of the OSI model and utilizes the Duration/ID field in the MAC header to prevent interruptions during frame exchange.
Virtual Carrier Sense in 802.11 occurs at layer 2 of the OSI model and utilizes the Duration/ID field in the MAC header to prevent interruptions during frame exchange.
Pseudo-Random Backoff Timer in 802.11 selects a random backoff value using a pseudo-random backoff algorithm before transmission, distinct from the NAV timer.
Pseudo-Random Backoff Timer in 802.11 selects a random backoff value using a pseudo-random backoff algorithm before transmission, distinct from the NAV timer.
Interframe space (IFS) in 802.11 consists of ten types, with the Reduced interframe space (RIFS) being the highest priority and the Extended interframe space (EIFS) used after receipt of corrupted frames.
Interframe space (IFS) in 802.11 consists of ten types, with the Reduced interframe space (RIFS) being the highest priority and the Extended interframe space (EIFS) used after receipt of corrupted frames.
The Point Coordination Function (PCF) is an optional 802.11 media access method that uses polling and has yet to be implemented by any vendors.
The Point Coordination Function (PCF) is an optional 802.11 media access method that uses polling and has yet to be implemented by any vendors.
The Hybrid Coordination Function (HCF) in the 802.11e quality-of-service amendment enhances DCF with QoS capabilities and allows an 802.11 radio to send multiple frames during contention for the medium.
The Hybrid Coordination Function (HCF) in the 802.11e quality-of-service amendment enhances DCF with QoS capabilities and allows an 802.11 radio to send multiple frames during contention for the medium.
Unsuccessful frame transmissions cause the contention window (CW) size to increase exponentially up to a maximum value after each retransmission.
Unsuccessful frame transmissions cause the contention window (CW) size to increase exponentially up to a maximum value after each retransmission.
802.11 wireless networking uses CSMA/CD to avoid collisions, as wireless radios cannot transmit and receive at the same time.
802.11 wireless networking uses CSMA/CD to avoid collisions, as wireless radios cannot transmit and receive at the same time.
Unicast acknowledgment in 802.11 involves the transmitting radio sending a unicast frame and the receiver radio sending an L2 ACK frame upon successful reception.
Unicast acknowledgment in 802.11 involves the transmitting radio sending a unicast frame and the receiver radio sending an L2 ACK frame upon successful reception.
802.11 radios use two separate Clear Channel Assessment (CCA) thresholds - Signal Detect (SD) and Energy Detect (ED) - when listening to the RF medium, with approximately 4 microseconds needed for both assessments during the CCA.
802.11 radios use two separate Clear Channel Assessment (CCA) thresholds - Signal Detect (SD) and Energy Detect (ED) - when listening to the RF medium, with approximately 4 microseconds needed for both assessments during the CCA.
Physical carrier sense in 802.11 determines whether a frame transmission is inbound for a station to receive and checks whether the medium is busy before transmitting.
Physical carrier sense in 802.11 determines whether a frame transmission is inbound for a station to receive and checks whether the medium is busy before transmitting.
Distributed Coordination Function (DCF) is the fundamental access method of 802.11 communications, using CSMA/CA protocol with four main components: physical carrier sense, virtual carrier sense, pseudo-random backoff timer, and interframe spaces.
Distributed Coordination Function (DCF) is the fundamental access method of 802.11 communications, using CSMA/CA protocol with four main components: physical carrier sense, virtual carrier sense, pseudo-random backoff timer, and interframe spaces.
Client stations can operate in infrastructure mode, allowing communication via an access point, or ad hoc mode, participating in an IBSS topology without an access point.
Client stations can operate in infrastructure mode, allowing communication via an access point, or ad hoc mode, participating in an IBSS topology without an access point.
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Study Notes
802.11 Medium Access Control and Configuration Modes
- AP radio can be converted into a sensor radio, operating in continuous listening state and scanning between multiple channels, as part of a wireless intrusion detection system (WIDS) architecture.
- Other optional operational modes for APs include bridge mode, workgroup bridge mode, and AP as a client mode, each with specific functionalities.
- Client stations can operate in infrastructure mode, allowing communication via an access point, or ad hoc mode, participating in an IBSS topology without an access point.
- Medium access control (MAC) is essential for network communication and includes rules for controlled and efficient access to the network medium.
- Two forms of contention heavily used in today's networks are Carrier Sense Multiple Access with Collision Detection (CSMA/CD) and Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA).
- CSMA/CD is used for 802.3 Ethernet networks, where nodes check for collisions over the Ethernet cable before transmitting.
- 802.11 wireless networking uses CSMA/CA to avoid collisions, as wireless radios cannot transmit and receive at the same time.
- Unicast acknowledgment in 802.11 involves the transmitting radio sending a unicast frame and the receiver radio sending an L2 ACK frame upon successful reception.
- Distributed Coordination Function (DCF) is the fundamental access method of 802.11 communications, using CSMA/CA protocol with four main components: physical carrier sense, virtual carrier sense, pseudo-random backoff timer, and interframe spaces.
- Physical carrier sense in 802.11 determines whether a frame transmission is inbound for a station to receive and checks whether the medium is busy before transmitting.
- 802.11 radios use two separate Clear Channel Assessment (CCA) thresholds - Signal Detect (SD) and Energy Detect (ED) - when listening to the RF medium, with approximately 4 microseconds needed for both assessments during the CCA.
- The text includes study guide references and modified notes from "CWNA Certified Wireless Network Administrator: Official Study Guide" for the Wireless Networks course.
Wireless Networking Topologies and 802.11 Stations
- Wireless personal area network (WPAN) facilitates communication between devices in close proximity using technologies like Bluetooth and infrared.
- Wireless local area network (WLAN) is suitable for building or campus environments, commonly using the 802.11 standard.
- 802.11 stations include access points (AP) and client stations, each identified by a unique MAC address.
- Client stations, not used in access points, contend for the RF medium and can be associated with an access point when having a layer 2 connection.
- An AP station serves as a wireless portal for client stations to communicate and provides a distribution system access function (DSAF).
- The 802.11-2020 standard defines an integration service (IS) for delivering data between the distribution system and non-IEEE-802.11 LAN via a portal.
- The distribution system (DS) in 802.11 networks interconnects basic service sets to create an extended service set (ESS) and consists of distribution system medium (DSM) and distribution system service.
- Wireless Distribution System (WDS) is used in mesh deployments and outdoor bridge links to provide coverage and backhaul connectivity.
- The 802.11-2020 standard defines multiple service sets, including basic service set (BSS), extended service set (ESS), independent basic service set (IBSS), personal basic service set (PBSS), mesh basic service set (MBSS), and QoS basic service set (QBSS).
- Service Set Identifier (SSID) is a logical name identifying an 802.11 wireless network and is configurable on all 802.11 radios.
- The basic service set (BSS) is the cornerstone topology of an 802.11 network, consisting of one AP radio with one or more client stations, forming a wireless domain for communication.
802.11 Wireless Medium Access Control Techniques
- Clear Channel Assessment (CCA) thresholds in the 802.11-2020 standard are somewhat ambiguous, leading to varying interpretations among WLAN manufacturers.
- Receive sensitivity differences between radios can cause variations in noise floor perception and consequently, in the CCA thresholds.
- Virtual Carrier Sense in 802.11 occurs at layer 2 of the OSI model and utilizes the Duration/ID field in the MAC header to prevent interruptions during frame exchange.
- The Duration/ID value in the MAC header represents the time required for an active frame exchange process, preventing other radios from contending for the medium.
- Virtual Carrier Sense uses a timer mechanism called the network allocation vector (NAV) to predict future traffic and inform other stations about the busy medium.
- Pseudo-Random Backoff Timer in 802.11 selects a random backoff value using a pseudo-random backoff algorithm before transmission, distinct from the NAV timer.
- The backoff timer counts down slots, and when it reaches zero, the client can reassess the channel and begin transmitting if it is clear.
- Unsuccessful frame transmissions cause the contention window (CW) size to increase exponentially up to a maximum value after each retransmission.
- Interframe space (IFS) in 802.11 consists of ten types, with the Reduced interframe space (RIFS) being the highest priority and the Extended interframe space (EIFS) used after receipt of corrupted frames.
- SIFS and DIFS are the two most common interframe spaces, with SIFS being used for high-priority frames and DIFS for most other 802.11 frames.
- The Point Coordination Function (PCF) is an optional 802.11 media access method that uses polling and has yet to be implemented by any vendors.
- The Hybrid Coordination Function (HCF) in the 802.11e quality-of-service amendment enhances DCF with QoS capabilities and allows an 802.11 radio to send multiple frames during contention for the medium.
Wireless Networking Topologies and 802.11 Stations
- Wireless personal area network (WPAN) facilitates communication between devices in close proximity using technologies like Bluetooth and infrared.
- Wireless local area network (WLAN) is suitable for building or campus environments, commonly using the 802.11 standard.
- 802.11 stations include access points (AP) and client stations, each identified by a unique MAC address.
- Client stations, not used in access points, contend for the RF medium and can be associated with an access point when having a layer 2 connection.
- An AP station serves as a wireless portal for client stations to communicate and provides a distribution system access function (DSAF).
- The 802.11-2020 standard defines an integration service (IS) for delivering data between the distribution system and non-IEEE-802.11 LAN via a portal.
- The distribution system (DS) in 802.11 networks interconnects basic service sets to create an extended service set (ESS) and consists of distribution system medium (DSM) and distribution system service.
- Wireless Distribution System (WDS) is used in mesh deployments and outdoor bridge links to provide coverage and backhaul connectivity.
- The 802.11-2020 standard defines multiple service sets, including basic service set (BSS), extended service set (ESS), independent basic service set (IBSS), personal basic service set (PBSS), mesh basic service set (MBSS), and QoS basic service set (QBSS).
- Service Set Identifier (SSID) is a logical name identifying an 802.11 wireless network and is configurable on all 802.11 radios.
- The basic service set (BSS) is the cornerstone topology of an 802.11 network, consisting of one AP radio with one or more client stations, forming a wireless domain for communication.
802.11 Medium Access Control and Configuration Modes
- AP radio can be converted into a sensor radio, operating in continuous listening state and scanning between multiple channels, as part of a wireless intrusion detection system (WIDS) architecture.
- Other optional operational modes for APs include bridge mode, workgroup bridge mode, and AP as a client mode, each with specific functionalities.
- Client stations can operate in infrastructure mode, allowing communication via an access point, or ad hoc mode, participating in an IBSS topology without an access point.
- Medium access control (MAC) is essential for network communication and includes rules for controlled and efficient access to the network medium.
- Two forms of contention heavily used in today's networks are Carrier Sense Multiple Access with Collision Detection (CSMA/CD) and Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA).
- CSMA/CD is used for 802.3 Ethernet networks, where nodes check for collisions over the Ethernet cable before transmitting.
- 802.11 wireless networking uses CSMA/CA to avoid collisions, as wireless radios cannot transmit and receive at the same time.
- Unicast acknowledgment in 802.11 involves the transmitting radio sending a unicast frame and the receiver radio sending an L2 ACK frame upon successful reception.
- Distributed Coordination Function (DCF) is the fundamental access method of 802.11 communications, using CSMA/CA protocol with four main components: physical carrier sense, virtual carrier sense, pseudo-random backoff timer, and interframe spaces.
- Physical carrier sense in 802.11 determines whether a frame transmission is inbound for a station to receive and checks whether the medium is busy before transmitting.
- 802.11 radios use two separate Clear Channel Assessment (CCA) thresholds - Signal Detect (SD) and Energy Detect (ED) - when listening to the RF medium, with approximately 4 microseconds needed for both assessments during the CCA.
- The text includes study guide references and modified notes from "CWNA Certified Wireless Network Administrator: Official Study Guide" for the Wireless Networks course.
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