Module 6: Data Link Layer Flashcards
What are the two sublayers of the Data Link Layer and what are their functions?
The two sublayers of the Data Link Layer are the Logical Link Control (LLC) and the Media Access Control (MAC). The LLC is responsible for error control, flow control, and framing, while the MAC is responsible for controlling how devices access the network media and how data is transmitted over the media. Together, these sublayers perform error detection and reject corrupt frames to ensure reliable data transmission between network devices.
What are the functions of the Logical Link Control (LLC) and Media Access Control (MAC) sublayers in the Data Link Layer?
The Logical Link Control (LLC) sublayer in the Data Link Layer serves as a bridge between the networking software at the upper layers and the device hardware at the lower layers. It communicates with the upper layers to ensure reliable data transmission and provides flow control, error control, and framing.
Media Access Control (MAC) sublayer is responsible for data encapsulation and media access control. It determines how data is transmitted over the media and how devices access the network media. Together, the LLC and MAC sublayers ensure error-free and efficient data transmission between network devices.
What are the four basic Layer 2 functions performed by a router?
A router performs the following four basic Layer 2 functions:
1 Accepts a frame from the network medium.
2 De-encapsulates the frame to expose the encapsulated packet.
3 Re-encapsulates the packet into a new frame.
4 Forwards the new frame on the medium of the next network segment.
The router receives a frame from the network medium, removes the header and trailer added by the previous device to expose the packet, adds a new header and trailer for the next segment, and forwards the new frame to the next network segment.
What is the difference between physical and logical topology
The physical topology refers to the physical layout of devices and their interconnections.
Logical topology refers to the way devices communicate over a network using virtual connections and IP addressing schemes.
The physical topology shows the physical arrangement of devices and their interconnections, including cables, connectors, and other physical components.
The logical topology identifies the virtual connections between devices, including the path that data takes from one device to another.
What is the most common WAN topology?
The most common WAN topology is the point-to-point topology, which consists of a permanent link between two endpoints.
How does the hub and spoke WAN topology work?
The hub and spoke WAN topology is similar to a star topology, where a central site (the hub) interconnects branch sites (the spokes) through point-to-point links.
What is the mesh WAN topology known for providing?
The mesh WAN topology is known for providing high availability, as every end system is connected to every other end system.
Do nodes in a point-to-point WAN topology share the media with other hosts?
No, nodes in a point-to-point WAN topology may not share the media with other hosts.
Where is half-duplex communication commonly used?
Half-duplex communication is commonly used on WLANs (Wireless Local Area Networks) and legacy bus topology with Ethernet hubs.
What is half-duplex communication?
Half-duplex communication allows one device to send or receive at a time on a shared medium.
What is full-duplex communication?
Full-duplex communication allows both devices to simultaneously transmit and receive on a shared medium.
In what mode do Ethernet switches operate?
Ethernet switches operate in full-duplex mode, allowing both devices to transmit and receive simultaneously without any collisions.
What is the difference between CSMA/CD and CSMA/CA, and on what types of networks are they commonly used?
CSMA/CD stands for carrier sense multiple access with collision detection and is used on legacy bus-topology Ethernet networks. CSMA/CA stands for carrier sense multiple access with collision avoidance and is used on wireless LANs. The key difference between the two is that CSMA/CD detects collisions that occur when two nodes transmit simultaneously and takes steps to resolve them, while CSMA/CA attempts to avoid collisions in the first place by having nodes wait for a brief time before transmitting to ensure the medium is free of other transmissions.
How does CSMA/CD manage collisions?
CSMA/CD uses a collision detection process to govern when a device can send and what happens if multiple devices send at the same time. If a collision is detected, CSMA/CD initiates a backoff algorithm to ensure that the devices wait a random amount of time before retransmitting to avoid further collisions.
What are the three steps of the CSMA/CD collision detection process?
The three steps of the CSMA/CD collision detection process are:
Devices transmitting simultaneously will result in a signal collision on the shared media.
Devices detect the collision.
Devices wait a random period of time and retransmit data.
