802 Layer 2 Flashcards
(30 cards)
when two or more devices attempt to transmit data simultaneously and two packets crash into each other
Collision
In 802.3 networks this is used to detect that a collision has occurred
Carrier Sense Multiple Access with Collision Detection(CSMA/CD)
In 802.11 networks there is no way to detect if a collision happens, so we focus on avoiding collisions;
provides half duplex access to multiple devices;
Listens and attempts to send your data when no other device is transmitting;
Asks whether there are any other devices transmitting on my network;
What do wireless devices use to attempt to prevent collisions?
the sending device might just transmit the data, or it might request to send(RTS), and wait on a clear to send(CTS) before transmitting data. Either way the receiving device will acknowledge that they received the data or it will be sent again
Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA)
provides half duplex access to multiple devices;
Listens and attempts to send your data when no other device is transmitting;
In a wired environment its sensing a voltage level going through the wire;
When a collision happens a jam signal is sent to alert all other devices;
This causes all devices to stop transmitting for a specified amount of time to let the collision clear, and network traffic returns to normal
Carrier Sense Multiple Access with Collision Detection(CSMA/CD)
exist to allow multiple users to send data across a shared medium;
each user is assigned a code to identify its data
CDMA Code Division Multiple Access
exist to allow multiple users to send data across a shared medium;
each user gets a specific time slot to send data
TDMA Time Division Multiple Access
The device that has data to send
Source Address(SA)
The device that is transmitting the data
Transmitter Address(TA)
The device that receives the transmission
Receiver Address(RA)
The device that the data is being sent to
Destination Address(DA)
The source address can be the same as the transmitter address if the two end devices are on the same ___.
BSS
If the two devices are connected to separate AP’s of an ESS then all four addresses will be _____.
different
What OSI layer is the wireless address at?
Data Link Layer (Layer 2)
will help you know who/what device you are looking at, if it’s connected to a specific wireless network and possibly what data they are sending;
indicate if traffic is going out to the DS, or inbound from the DS
WIFI Frame Structure
Facilitate devices to join or leave an AP -Management Frames
Control of the wireless channel space/assist with data delivery-Control Frames
Carry the data across the network- Data Frames
High throughput and experimental WIFI standards, not normal use
Extension Frames
Contains all pertinent information for a device to connect to a network, and is transmitted by the AP at a regular(configurable) interval;
SSID, Supported Rates, IBSS Parameter Set, and other modulation Info; Broadcast frame- as it needs to go to any and all devices that may want to connect (ff:ff:ff:ff:ff:ff);
disabled in hidden networks
beacon
Transmitted by a client using the default broadcast address (ff:ff:ff:ff:ff:ff), to figure out
probe request
AP sends the requested information back to the client
Probe response
Verifies who the client is and if they are capable of connecting to the network(What standards the AP can use, and if the client has the correct encryption key)
authentication
Client sends what standards it can use/AP sends response to allow or deny
Association Request/Response
move between AP’s due to better signal strength
Reassociation Request/Response
reset the state of a client machine;
client dissociated
deauthentication
terminate the clients association;
Client powers off, Client has failed authentication , load balancing, inactivity, entering a state of maintenance;
No reply
Disassociation
RTS - Request-to-Send (optional to minimize collisions)
CTS - Clear-to-Send (optional to minimize collisions)
ACK - Acknowledges that a data frame was received(happens for every data frame).
Block ACK Request - The transmitting device requests the receiving device to only acknowledge a block of data, instead of after each frame.
Block ACK - The receiving device will acknowledge yes or no, based on if it has the capability/permission to do this (not all devices can)
control frame
