802 Layer 2 Flashcards
____ allows multiple users access to the same medium
____ uses collision avoidance to minimize data loss in transmissions
Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA)
- each user is assigned a code to identify its data
CDMA Code Division Multiple Access
- each user gets a specific time slot to send data
TDMA - Time Division Multiple Access
used in ethernet connections between devices
CSMA/CD - Carrier Sense Multiple Access with Collision Detection
used in 802.11 wireless LANs
CSMA/CA - Carrier Sense Multiple Access with Collision Avoidance
Listening to ensure the channel is idle, it will send its data, then wait for a response from the destination device with an acknowledgment If the acknowledgment is NOT received it will send the data again.
Collision Avoidance (CA) protocol
sending a REQUEST-TO-SEND message, an access point will respond with a CLEAR-TO-SEND message
RTS/CTS
Device scans (passive OR active) for SSID to use
APs transmit beacon frames
Step 1 : Discovery
response from the AP/router with a success or failure message.
request is sent from the mobile device that contains the station ID
Open system
requests “shared key”
AP sends challenge phrase
Station encrypts challenge phrase
AP decrypts and verifies original text
Shared Key Authentication : Wired Equivalent Privacy (WEP)
There are three frame types:
Management
Control Frames
Data
constantly broadcasted signal from a WAP announcing itself to clients, and broadcasts its parameters (SSID, Supported data rate, RF channel number used, etc)
Beacon
Used by clients to obtain information from an AP. This can be directed to a SSID or to any AP available (null probe request), happens constantly with clients
Probe Request
Used by AP to send info about its parameters (same info found in Beacon)
Probe Response
used in the process to gain access to a network
Authentication
once authenticated, a client can request association to an SSID
Association Request
sent by an AP to accept or deny association
Association Response
actual data being sent
Data
used to prioritize data ie-streaming data
QoS Data
used by client to inform an AP of a change in clients status/power save mode
Null Data
Wireless capability gives us the ability to convert 1s and 0s into radio waves, and convert radio waves back into 1s and 0s. (T/F)
True
CSMA/CA is a protocol that operates in which layer of the OSI model?
Layer 2- Data Link Layer
Which technologies, which allow multiple users to send data across a shared medium, do not use Collision Detection or Collision Avoidance?
CDMA
TDMA
Wireless networks often use a Collision Avoidance (CA) protocol. Where a device will wait a random amount of time, before attempting to send data again, if it recognizes the medium as being busy.
True
