Topic 5 Flashcards
What is the purpose of the Data Link Layer?
Prepares network data for the physical network and is responsible for network interface card (NIC) to NIC communications.
List the functions of the Data Link sublayers.
- Accepts Layer 3 packets and encapsulates them into Layer 2 frames.
- Controls how data is placed and received on the media.
- Exchanges frames between endpoints over the network media.
- Receives encapsulated Layer 3 packets, and directs them to the proper upper-layer protocol.
- Performs error detection and rejects any corrupt frame.
What are the functions of the LLC Sublayer?
- Communicates between the networking software at the upper layers and the device hardware at the lower layers.
- Places information in the frame to identify which network layer protocol is used for the frame.
What are the functions of the MAC Sublayer?
Implemented in hardware and is responsible for data encapsulation and media access control.
List the four functions performed by a router at each hop along the data path.
- 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.
Describe briefly the three common physical 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 branch sites through point-to-point links.
- Mesh - provides high availability but requires every end system to be connected to every other end system.
What is Half Duplex?
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 is Full Duplex?
Allows devices to send and receive simultaneously on a shared medium.
Used by Ethernet switches.
What are the two contention-based access methods?
- Carrier sense multiple access with collision detection (CSMA/CD) - used on legacy bus-topology Ethernet.
- Carrier sense multiple access with collision avoidance (CSMA/CA) - used on Wireless LANs.
What are two characteristics of CSMA/CD?
- Used by legacy Ethernet LANs.
- Operates in half-duplex mode.
Uses a collision detection process to control when a device can send and what happens if multiple devices send at the same time.
What are two characteristics of CSMA/CA?
- Used by IEEE 802.11 WLANs.
- Operates in half-duplex mode.
Uses a collision avoidance process to govern when a device can send and what happens if multiple devices send at the same time.
What are the functions of Frame Start and Stop?
Identifies beginning and end of frame.
What is the function of Addressing in a Data Link Frame?
Indicates source and destination nodes.
What is the function of Error Detection in a Data Link Frame?
Used to determine transmission errors.
What are the four characteristics of Layer 2 address?
- Referred to as a physical address.
- Contained in the frame header.
- Used only for local delivery of a frame on the link.
- Updated by each device that forwards the frame.
What is Half Duplex?
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 is Full Duplex?
Allows devices to send and receive simultaneously on a shared medium.
Used by Ethernet switches.
What are the two contention-based access methods?
- Carrier sense multiple access with collision detection (CSMA/CD) - used on legacy bus-topology Ethernet.
- Carrier sense multiple access with collision avoidance (CSMA/CA) - used on Wireless LANs.
What are two characteristics of CSMA/CD?
- Used by legacy Ethernet LANs.
- Operates in half-duplex mode.
Uses a collision detection process to control when a device can send and what happens if multiple devices send at the same time.
What are two characteristics of CSMA/CA?
- Used by IEEE 802.11 WLANs.
- Operates in half-duplex mode.
Uses a collision avoidance process to govern when a device can send and what happens if multiple devices send at the same time.
What are the functions of Frame Start and Stop?
Identifies beginning and end of frame.
What is the function of Addressing in a Data Link Frame?
Indicates source and destination nodes.
What is the function of Error Detection in a Data Link Frame?
Used to determine transmission errors.
What are the four characteristics of Layer 2 address?
- Referred to as a physical address.
- Contained in the frame header.
- Used only for local delivery of a frame on the link.
- Updated by each device that forwards the frame.
What are the two factors that determine the data link protocol used?
The logical topology and physical media.
Give three examples of data link protocols used in LANs and WANs.
- 802.3 Ethernet.
- 802.11 Wireless LAN (WLAN).
- Frame-Relay (FR).
