Mod 6 - Data Link Layer Flashcards
What is the purpose of the Datalink layer?
The Datalink layer is responsible for communication between end-point NICs. It allows upper layers to access physical layer media and encapsulates Layer 3 packets into Layer 2 Frames. It also performs error detection and rejects corrupt frames.
What two sublayers does the Data link layer consists of?
Logical Link Control and Media Access Control
What is the purpose of the LLC (logical link control) sublayer?
The LLC sublayer communicates between the networking software at the upper layers and the device hardware at the lower layers.
What is the purpose of the MAC (media access control) sublayer?
The MAC sublayer is responsible for data encapsulation and media access control.
What 4 basic Layer 2 functions does a router perform when packets are exchanged between nodes?
- Accepts a frame from the network medium.
- De-encapsulates the frame to expose the encapsulated packet.
- Re-encapsulates the packet into a new frame.
- Forwards the new frame on the medium of the next network segment.
What are four engineering org. that have defined protocols?
- IEEE
- ITU
- ISO
- ANSI
What does topology mean?
Topology is the arrangement and relationship of the network devices and the interconnections between them.
What does physical topology show?
Physical topology shows the physical connections and how devices are interconnected.
What does logical topology show?
Logical topology shows the virtual connections between devices using device interfaces and IP addressing schemes.
What are the three common WAN topologies?
- Point-to-point: the simplest and most common WAN topology. Consists of a permanent link between two endpoints.
- Hub and spoke: similar to a star topology where a central site interconnects sites though point-to-point links.
- Mesh: provides high availability but requires every end system to be connected to every other end system.
What are the common LAN topologies?
Usually through star or extended star topology, but early ethernet and legacy token ring used bus or ring.
What does half-duplex mean?
Half-duplex communication only allows one device to send or receive at a time on a shared medium. Used on WLANs and legacy bus topologies with Ethernet hubs.
What does full-duplex mean?
Full-duplex communication allows both devices to simultaneously transmit and receive on a shared medium. Ethernet switches operate in full-duplex mode.
What are two access control methods?
Contention-based access and controlled access.
What is contention-based access?
All nodes are operating in half-duplex, and are competing for use of the medium. Ex.: Carrier sense multiple access with collision detection (CSMA/CD) as used on legacy bus-topology ethernet, and carrier sense multiple access with collision avoidance (CSMA/CS) as used on WLANs.
