802.11 Flashcards

1
Q

What are the commonly used wi-fi bands

A

2.4 Ghz, 5.7 Ghz

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2
Q

True/False - In a wireless environment a wireless unit cannot tx/rx at the same time

A

True

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3
Q

Describe the hidden terminal problem

A

When a two wireless terminals are unaware of each other and so they xmit causing collision

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4
Q

True/False - Every port of a router constitutes a separate network

A

True

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5
Q

True/False - Even though a L2 switch and an Access Point are layer 2, the AP is not transparent. The wireless client needs to know the ID of the AP

A

True

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6
Q

What wireless channels do not overlap

A

1, 6, 11

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7
Q

Describe the AP passive scanning process

A
  • Periodically the AP broadcasts a beacon frame
  • A host sends a association request frame to AP
  • AP sends a association response frame to host
  • Authentication and DHCP may be performed
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8
Q

Describe the AP active scanning process

A
  • The host broadcasts a probe request frame
  • AP sends a probe response frame
  • Host sends association request frame to selected AP
  • AP sends an association response frame to Host
  • Authentication and DHCP may be performed
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9
Q

True/False - In ethernet no ack is used. For wi-fi an ack is used.

A

True

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10
Q

True/False - In wifi back to back frames are not allowed, there must be interframe spacing (IFS)

A

True

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11
Q

Describe 802.11 CSMA/CA

A
  • Station has a frame to send, start sensing the medium
  • If medium free for DIFS, start sending
  • If medium is busy wait for DIFS + random back-off
  • If medium becomes busy during back-off pause the back off timer, resume backoff when medium idle
  • Start sending
  • When rx gets frame, wait sifs then send ack
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12
Q

Describe 802.11 CSMA/CA w/ RTS/CTS

A
  • Station has a frame to send, start sensing the medium
  • If medium is free for DIFS, send RTS with reservation for amount of time needed
  • When Rx gets RTS, wait SIFS and send CTS
  • Station waits SIFS and starts sending data
  • After getting data Rx waits SIFS and sends ACK
  • Other stations go to sleep when they hear the CTS
  • After other stations wake up they sense the medium, if idle for DIFS + contention window they start the process
  • If a station cant hear RTS (hidden terminal) and sends RTS concurrently there will be collision. The stations will know collision occured bc they never got a CTS
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13
Q

True/False - Physical sensing is the process of the radio actively measuring the strength of signals on the channel

A

True

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14
Q

True/False - In virtual sending the xmiter doesnt have a frame to send but they are hearing others xmitting.

A

True

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15
Q

Describe the exposed terminal problem

A

When a terminal goes to sleep erroneously after hearing a RTS from another station but could have transmitted to a different AP in a non-interfering physical area.

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16
Q

True/False - In 802.11, The access point is transparent to the router but not to the host

A

True

17
Q
A
18
Q
A