4.1 - Media Access Control Flashcards
The _______________ layer (Layer 2 of the OSI Model) is responsible for moving a message from one computer or network device to the next in the overall path from sender to receiver
data link layer
A _______________ determines:
1. Media access
2. Message delineation
3. Error control
data link protocol
Who can transmit at what time
Media access
Where the message begins and ends
Message delineation
How a receiver recognizes and correctes a transmission error
Error control
The data link layer performs two main functions and therefore is often divided into two sublayers:
- Logical Link Control (LLC)
- Media Access Control (MAC)
The data link layer’s connection to the network layer above it
Logical Link Control (LLC)
Responsible for communicating with the network layer software (IP) and for taking the packet, surrounding it with data link PDU, to become a frame
Logical Link Control (LLC)
Controls the physical hardware
Media Access Control (MAC)
This software at the sending device controls how and when the physical layer converts bits into the physical symbols that are sent down the circuit; receiver does the opposite
Media Access Control (MAC)
Refers to the need to control WHEN computers transmit
Media Access Control (MAC)
_____________ becomes important when several computers share the same communication circuit (point-to-point, half-duplex configuration)
Media Access Control (MAC)
- Contention
- Controlled access
Two approaches to media access control
Computers wait until the circuit is free (no other computers are transmitting) and transmit whenever they have data to send
Contention
With _____________, all nodes are operating in half-duplex (two-way traffic, but taking turns) mode, competing for the use of the medium
contention
- Carrier Sense Multiple Access with Collision Detection (CSMA/CD)
- Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA)
Examples of contention
Used on legacy bus-topology Ethernet
CSMA/CD
Used on Wireless LANS
CSMA/CA
One device controls the circuit and determines which clients can transmit at what time
Controlled
Two commonly used controlled access techniques:
- Access request
- Polling
Controlled access is a ____________ type of access — each node has its own time on the medium
deterministic
Controlled access is used on legacy networks such as ____________ and __________
Token Ring… ARCNET
This technique is similar to a situation in which the instructor calls on students who raise their hands
Controlled access
With _______________ technique, client computers that want to send a request to transmit to the device controlling the circuit (e.g., wireless access point)
access request
_______________ grants permission for one computer at a time. All other computers wait until that computer has finished
Controlling device
The process of sending a signal to a client computer that gives it permission to transmit
Polling
The client stores all messages that need to be transmitted
Polling
Periodically, the controlling device (e.g., WAP) ______ the client to see if it has data to send
polls
Types of Polling
- Roll-call polling
- Hub polling (Token Passing)
The controller works consecutively through a list of clients until all are polled
Roll-call polling
This type of polling can be modified to select clients in priority
Roll-call polling
This type of polling involves some waiting time because the controlled has to poll a client and then wait for a response
Roll-call polling
One device starts the poll and passes it to the next computer on the multipoint circuit, which sends its message and passes the poll (or token) to the next
Hub polling (Token Passing)
