Podcast
Questions and Answers
What is the primary function of the Data Link Layer?
What is the primary function of the Data Link Layer?
- To provide routing of packets between networks
- To provide error correction and flow control
- To encapsulate Layer 3 packets into Layer 2 frames (correct)
- To translate domain names to IP addresses
What is the purpose of the Logical Link Control (LLC) sublayer?
What is the purpose of the Logical Link Control (LLC) sublayer?
- To provide media access control
- To perform error detection and correction
- To manage the flow of data between devices
- To communicate between networking software and device hardware (correct)
What is the purpose of the Media Access Control (MAC) sublayer?
What is the purpose of the Media Access Control (MAC) sublayer?
- To de-encapsulate frames to expose encapsulated packets
- To forward frames on the medium of the next network segment
- To re-encapsulate packets into new frames
- To provide media access control and data encapsulation (correct)
What happens to packets as they travel through multiple data link layers and media transitions?
What happens to packets as they travel through multiple data link layers and media transitions?
What organization defines data link layer protocols for LANs and MANs?
What organization defines data link layer protocols for LANs and MANs?
What is the term for the arrangement and relationship of network devices and interconnections?
What is the term for the arrangement and relationship of network devices and interconnections?
What is the purpose of the data link layer in a WAN environment?
What is the purpose of the data link layer in a WAN environment?
What is the term for a communication system that allows data to be transmitted in both directions, but not simultaneously?
What is the term for a communication system that allows data to be transmitted in both directions, but not simultaneously?
What is the primary purpose of a physical topology in network description?
What is the primary purpose of a physical topology in network description?
What is the primary function of the header and trailer in a data link frame?
What is the primary function of the header and trailer in a data link frame?
Which WAN topology is similar to a star topology?
Which WAN topology is similar to a star topology?
What is a characteristic of point-to-point WAN protocols?
What is a characteristic of point-to-point WAN protocols?
What is the main difference between half-duplex and full-duplex communication?
What is the main difference between half-duplex and full-duplex communication?
What type of access control method is used in WLANs and legacy bus topologies with Ethernet hubs?
What type of access control method is used in WLANs and legacy bus topologies with Ethernet hubs?
What is the typical topology used to interconnect end devices on LANs?
What is the typical topology used to interconnect end devices on LANs?
What is the purpose of the frame start and stop fields in a data link frame?
What is the purpose of the frame start and stop fields in a data link frame?
Which of the following is a benefit of a mesh WAN topology?
Which of the following is a benefit of a mesh WAN topology?
What is the main advantage of star and extended star topologies?
What is the main advantage of star and extended star topologies?
What is true about nodes in a point-to-point WAN topology?
What is true about nodes in a point-to-point WAN topology?
What type of WAN protocol is used for point-to-point connections?
What type of WAN protocol is used for point-to-point connections?
What is the purpose of the addressing field in a data link frame?
What is the purpose of the addressing field in a data link frame?
What type of LAN topology is used in Ethernet networks?
What type of LAN topology is used in Ethernet networks?
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Study Notes
Network Topologies
- Star and extended star topologies are easy to install, scalable, and easy to troubleshoot.
Bus and Ring Topologies
- Bus topology: all end systems are chained together and terminated on each end.
- Ring topology: each end system is connected to its respective neighbors to form a ring.
Communication Modes
- Half-duplex communication: only allows one device to send or receive at a time on a shared medium.
- Full-duplex communication: allows both devices to simultaneously transmit and receive on a shared medium.
Access Control Methods
- Contention-based access: CSMA/CD and CSMA/CA.
- Controlled access: used on WLANs and legacy bus topologies with Ethernet hubs.
Data Link Frame
- A data link frame consists of a header, data, and trailer.
- The fields of the header and trailer vary according to the data link layer protocol.
Frame Fields
- Frame Start and Stop: identify the beginning and end of a frame.
- Addressing: indicates source and destination nodes.
- Types: identifies the encapsulated Layer 3 protocol.
- Control: identifies flow control services.
- Data: contains the frame payload.
- Error Detection: used to detect transmission errors.
LAN and WAN Frames
- LAN and WAN frames use different data link layer protocols, such as Ethernet, 802.11 Wireless, Point-to-Point (PPP), High-Level Data Link Control (HDLC), and Frame-Relay.
Layer 2 Addresses
- Also 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.
Data Link Layer
- Responsible for communications between end-device network interface cards.
- Allows upper layer protocols to access the physical layer media and encapsulates Layer 3 packets into Layer 2 frames.
- Performs error detection and rejects corrupt frames.
IEEE 802 LAN/MAN Data Link Sublayers
- Consists of two sublayers: Logical Link Control (LLC) and Media Access Control (MAC).
- LLC sublayer communicates between networking software and device hardware.
- MAC sublayer is responsible for data encapsulation and media access.
Providing Access to Media
- Routers perform four basic Layer 2 functions: accepting a frame, de-encapsulating, re-encapsulating, and forwarding.
Data Link Layer Standards
- Defined by engineering organizations: IEEE, ITU, ISO, and ANSI.
Physical and Logical Topologies
- Physical topology: shows physical connections and interconnections between devices.
- Logical topology: identifies virtual connections between devices using device interfaces and IP addressing schemes.
WAN Topologies
- Point-to-point: a permanent link between two endpoints.
- Hub and spoke: 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.
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