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Cisco 200-355 > 802.11 Frame Types > Flashcards

802.11 Frame Types Flashcards

1
Q

What are the 1st two 802.11 frame fields and what is their size?

A

Frame Control field (2 bytes)

Duration/ID field (2 bytes)

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2
Q

The To DS and From DS bits indicate the frames direction and are in which 802.11 frame field?

A

Frame Control field

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3
Q

What is DLS?

A

Direct Link Setup

Communication between two host going through an AP .

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4
Q

How many address fields are there in an 802.11 frame and how long are they?

A

There are 4 fields and they are 6 bytes long.

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5
Q

What address is always in the 1st two address fields in 802.11 frame?

A

Address 1 is the receiving address

Address 2 is the transmitting address

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6
Q

What are the 4 directions of an 802.11 frame?

A

Management, control, or DLS (To DS 0 From DS 0)
DS to client (To DS 0 From DS 1)
Client to DS (To DS 1 From DS 0)
Wireless bridge or mesh (To DS 1 From DS 1)

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7
Q

When is the 4th address field used in an 802.11 frame?

A

In a wireless bridge or mesh.

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8
Q

What is DCF?

A

Distributed Coordination Function

The method used by each wireless device to coordinate the use of a wireless channel.

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9
Q

What does CSMA/CA stand for?

A

Carrier Sense Multiple Access / Collision Avoidance

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10
Q

What does the duration in the duration/id field indicate?

A

How much time will be required to send the whole frame, plus and interframe gap, plus a return ACK frame.

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11
Q

Each wireless client must maintain a timer that is used to predict when the channel will become free. What is this timer called?

A

NAV

Network Allocation Vector

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12
Q

What is the purpose of the backup timer?

A

To avoid collisions by backing off and waiting a random time before transmitting.

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13
Q

What is the contention window?

A

It is a range of random timer values for the backup timer.

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14
Q

What happens to the contention window when a transmitted frame fails and what is the maximum of the contention window?

A

The contention window range is doubled the previous range.

The max is 1023 timeslots.

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15
Q

802.11 defines a few different interframe space periods for safety. What is this for?

A

These periods of silence give the channel enough time for signals to dampen.

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16
Q

What is DIFS?

A

Distributed Interframe Space

It is the default period used after most standard priority frame types.

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17
Q

What is EIFS?

A

Extended Interframe Space

The longest interframe space and is used after a collision and before retransmitted frames.

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18
Q

What is SIFS?

A

Short Interframe Space

Used between data frames and ACK frames or CTS 802.11g protected mode control frames

19
Q

How long is the DIFS compared to the SIFS?

A

It is an SIFS plus 2 timeslots.

20
Q

What are the 3 types of 802.11 frames that can be used?

A

Management
Control
Data

21
Q

What are management frames used for?

A

To advertise a BSS and its capabilities and manage clients as they join and leave.

22
Q

There are many types of management frames. What are the five that may be on the CCNA test?

A

Beacon

Probe

Authentication deauthentication

Association, disassociation, reassociation

Action

23
Q

Learning a BSS from listening to beacon frames is called what?

A

Passive Scanning

24
Q

What type of frame is being used when doing active scanning to discover a BSS?

A

Client sends a probe request and the AP sends a probe response.

25
Q

When an AP has multiple SSIDs, how does that affect the quantity of beacon frames?

A

It adds to the number of beacon frames because it has to send beacon frames for each SSID separately. (Beacon frame are sent about 10 times per second)

26
Q

What 2 types of authentication are supported in the authentication management frame?

A

Open System authentication

Wired Equivalent Privacy (WEP) key

27
Q

Who initiates the deauthentication management frame?

A

It can be either the client or AP. If the client wants to deauthenticate, it sends the frame. If the AP wants to force the client to deauthenticate, it sends the frame.

28
Q

Which frame is sent first, association or authentication?

A

Authentication is first. A client cannot associate until it has been authenticated.

29
Q

What type of frame does the AP send after a client sends an association request?

A

If allowed on the BSS, the AP will send an association response with a unique association identifier (AID).

30
Q

What is the reassociation request used for?

A

It is used by a client who is roaming to a new cell. The frame is sent to the new AP.

31
Q

What is an action management frame used for?

A

It provides a way to communicate an extended management action to be taken. (There are 802.11 amendments like 802.11k and 802.11v explain these extended actions)

32
Q

There are many types of control frames. What are the 4 that might be on the CCNA test?

A

ACK
Block ACK
PS-Poll (power save poll)
RTS/CTS

33
Q

Who sends a PS-Poll control frame and why?

A

A client that has powered on its radio to request any frames that were buffered while its radio was down.

34
Q

Is the any payload data in a control frame?

A

No.

35
Q

An AP is configured with a set of data rates it can use. Each data rate can be set to what states?

A

Disabled
Supported
Mandatory

36
Q

A wireless clients sends a frame with a list of its 802.11 capabilities, the SSID it wants to join and a list of data rates and channels it can support. What type of frame is this?

A

Association request

37
Q

Does the client have to support all the data rates that the AP supports?

A

No, but it does have to support the ones the AP lists as mandatory.

38
Q

Amendment 802.11e was certified by Wi-Fi Alliance and is known as what?

A

Wi-Fi Multimedia (WMM)

39
Q

802.11e introduced an QoS mechanism. List the 4 categories (Cisco name).

A

Voice (Platinum)
Video (Gold)
Best Effort (Best Effort)
Background (Background)

40
Q

802.11e also introduced an improved power save mode that is more client-centric. What is this method called?

A

Unscheduled Automatic Power Save Delivery (U-APSD)

41
Q

What is DTIM?

A

Delivery Traffic Indication Message
It is a time period advertised by a beacon telling clients when to wake up for buffered broadcast and multicast frames (original power save mode)

42
Q

What is TIM and what does it tell a client?

A

Traffic Indication Map

Part of a beacon frame that lets a client know if they have buffered frames (original power save mode)

43
Q

What is performed to determine if the channel is busy?

A

Clear Channel Assessment (CCA)

Cisco 200-355 (19 decks)

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