IDT6.4/3 - Data-Link Layer Overview
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Questions and Answers

What is the primary purpose of the source MAC address field in an Ethernet frame?

  • To identify the originating NIC of the frame. (correct)
  • To identify the type of data being sent.
  • To manage network traffic flow.
  • To store the destination IP address.

    • When a NIC receives an Ethernet frame, it automatically forwards the frame regardless of the destination MAC address.

    False

    What does MAC stand for in the context of network addressing?

    Media Access Control

    A __________ is a one-to-all transmission in network communication.

    <p>broadcast</p> Signup and view all the answers

    Which of the following describes multicast transmissions?

    <p>Sent to multiple devices simultaneously.</p> Signup and view all the answers

    A MAC address is typically 6 bytes or 28 bits in length.

    <p>False</p> Signup and view all the answers

    Match the following types of transmission with their descriptions:

    <p>Unicast = One-to-one transmission Multicast = One-to-many transmission Broadcast = One-to-all transmission</p> Signup and view all the answers

    What method does a Layer 2 switch use to forward packets?

    <p>Based on the MAC address table</p> Signup and view all the answers

    What happens when a packet's destination MAC address cannot be found in the MAC address table?

    <p>The packet is broadcasted to all interfaces in the VLAN except the inbound interface.</p> Signup and view all the answers

    Line discipline in the Data Link layer helps determine which device can send data and when.

    <p>True</p> Signup and view all the answers

    What two methods are used to achieve line discipline?

    <p>ENQ/ACK and Poll/select</p> Signup and view all the answers

    In the Stop-and-wait method, the sender waits for an __________ after every frame it sends.

    <p>acknowledgement</p> Signup and view all the answers

    What does the positive acknowledgement (ACK) indicate in the ENQ/ACK method?

    <p>The receiver is ready to accept the transmission.</p> Signup and view all the answers

    Match the flow control methods with their descriptions:

    <p>Stop-and-wait = Sender waits for an ACK after each frame. Sliding window = Multiple frames are sent before waiting for an ACK.</p> Signup and view all the answers

    Flow control restricts the number of frames a sender can send before an acknowledgement from the receiver.

    <p>True</p> Signup and view all the answers

    What is the main purpose of flow control in the Data Link layer?

    <p>To regulate the amount of data sent by a fast sender to prevent overwhelming a slow receiver.</p> Signup and view all the answers

    What is the primary function of the data-link layer?

    <p>To encapsulate Layer 3 packets into Layer 2 frames</p> Signup and view all the answers

    What is the purpose of error-detecting codes?

    <p>To help detect errors that may occur during transmission</p> Signup and view all the answers

    The data-link layer is responsible for error detection in communications.

    <p>True</p> Signup and view all the answers

    An ARP request is sent only when a device has an entry for the IPv4 address in its ARP table.

    <p>False</p> Signup and view all the answers

    What two sublayers make up the data-link layer and what are their functions?

    <p>Logical Link Control (LLC) and Media Access Control (MAC). LLC adds control information for packet delivery, while MAC controls the hardware for sending and receiving data.</p> Signup and view all the answers

    What is the Frame Check Sequence (FCS) used for?

    <p>To detect errors in a frame</p> Signup and view all the answers

    The data-link layer prepares network data for the ______.

    <p>physical network</p> Signup and view all the answers

    The process of sending multiple frames before needing acknowledgements is known as _____.

    <p>Flow Control</p> Signup and view all the answers

    Which topology refers to the arrangement of network devices?

    <p>Network Topology</p> Signup and view all the answers

    An end device can be classified as a node in a computer network.

    <p>True</p> Signup and view all the answers

    What information is contained in an ARP request?

    <p>Destination MAC and Source MAC address</p> Signup and view all the answers

    Match the following terms with their definitions:

    <p>Flow Control = Sending multiple frames before needing acknowledgements Parity Bit = An additional bit used to detect errors in data ARP = Protocol for resolving IPv4 addresses to MAC addresses Error Detection = Identifying conditions where received information does not match sent information</p> Signup and view all the answers

    What is the purpose of the Start Frame of Preamble in data transmission?

    <p>To synchronize the sending and receiving devices.</p> Signup and view all the answers

    Match the following terms with their descriptions:

    <p>Node = Device that can receive, create, store, or forward data Destination MAC Address = Identifies where the frame needs to go LLC = Adds Layer 2 control information MAC = Controls sending and receiving data on the network medium</p> Signup and view all the answers

    Noise during transmission can change a 0 bit to a 1 bit or vice versa.

    <p>True</p> Signup and view all the answers

    What are the two basic functions of ARP?

    <p>Resolving IPv4 addresses to MAC addresses and maintaining a table of IPv4 to MAC address mappings.</p> Signup and view all the answers

    Study Notes

    IDT6.4/3 - Data-Link Layer

    • The data link layer prepares network data for the physical network.
    • It sits between the network layer and the physical layer in the OSI model.
    • It enables upper layers to access the media, which the upper layer isn't aware of.
    • It accepts Layer 3 packets (e.g., IPv4 or IPv6) and encapsulates them into Layer 2 frames.
    • It controls how data is placed and received on the media, including the transmission and receipt of frames between endpoints.
    • The data link layer directs encapsulated Layer 3 packets to the appropriate upper-layer protocol.
    • It detects and rejects corrupt frames.
    • A PDU (protocol data unit) at the data link layer is called a frame.
    • A node is a device on a network.
    • The media are the physical means used to carry data signals.
    • A network is two or more devices connected to a common medium.
    • The Data Link layer is responsible for communications between end-device network interface cards.
    • The layer allows upper-layer protocols to access physical-layer media.
    • It encapsulates Layer 3 packets (IPv4 and IPv6) into Layer 2 frames.
    • It performs error detection and rejects corrupt frames.
    • Frame: A PDU (Protocol Data Unit) at the Data Link layer
    • Node: A device on a network
    • Media: The physical means used to carry data signals
    • Network: Two or more devices connected to a common medium
    • Logical Link Control (LLC): Communicates between network software and device hardware at upper and lower layers.
    • Media Access Control (MAC): Responsible for data encapsulation and media access control. IEEE 802.3 (Ethernet), 802.11 (Wireless LAN), 802.15 (Wireless PAN).
    • Data link layer protocols are defined by engineering organizations (IEEE, ITU, ISO, ANSI) for protocols such as Ethernet, WLAN, and Wireless PAN.

    Data Link Frame - Frame Fields

    • Frame has three parts: Header, Data, Trailer.
    • Fields in the header and trailer vary according to data-link layer protocol.
    • Amount of control information in the frame varies based on access control and logical topology.
    • Frame Start and Stop: Identifies beginning and end of the frame.
    • Addressing: Identifies source and destination nodes.
    • Type: Identifies encapsulated Layer 3 protocol.
    • Control: Identifies flow control services.
    • Data: Contains the frame payload.
    • Error Detection: Used for determining transmission errors/corruptions.

    Start Frame of Preamble

    • The Start of Frame fields are used for synchronization between sending and receiving devices.
    • The first few bytes tell receivers to get ready to receive a new frame.

    Addressing

    • Destination MAC Address Field: Identifies where the frame needs to go.
    • Source MAC Address Field: Identifies the originating NIC or interface of the frame.

    Ethernet MAC Addresses

    • A device sending a message will include Source MAC address and Destination MAC address in the Ethernet Header.
    • When a NIC receives a frame, it checks the destination MAC address against its own physical MAC address in RAM.
    • If there is a match, the frame is passed up OSI layers for de-encapsulation; otherwise, the frame is discarded.
    • Ethernet NICs accept frames if the destination MAC is broadcast or multicast.
    • Unicast: Frame is sent to a single destination MAC address.
    • Multicast: A single stream of frames is sent to multiple devices.
    • Broadcast: A one-to-all transmission to all devices on the network.

    MAC Address Table

    • MAC Address Table determines where to forward data on a LAN.
    • It maps each switch port to the MAC address of the device connected.
    • This optimizes traffic forwarding, only forwarding to the port associated with the destination MAC address.

    Switch Learning and Forwarding

    • Every frame entering the switch is checked for new source MAC address information.
    • If the source MAC address is not in the switch's table, it is added, and the incoming port is associated with the MAC address.
    • If the address exists on the table, on a different port, the switch treats it as a new entry.
    • Entries are removed from the table after 5 minutes by default.

    Packet Forwarding

    • The device uses the MAC address table to forward packets.
    • In unicast mode, the switch forwards the packet to the interface matching the destination MAC address.
    • Broadcast mode: The packet is sent out all ports (except the incoming port) to all devices on the LAN..

    Sending the Frame to the Default Gateway

    • The devices in the network will use switches to forward the data or frame to the default gateway when the destination is outside the local network.
    • The default gateway is typically a router.
    • When a device needs to send data to another network, it sends the frame to the default gateway, which then forwards the frame to the appropriate destination.
    • Line discipline: Determines who should send data.
    • Flow Control: Regulates the amount of data sent to prevent overwhelming a slow receiver.
    • Error Control: Detects and corrects errors during transmission.

    Line Discipline

    • Line Discipline is a functionality of the Data Link layer that coordinates link systems and determines which device can send data and when.
    • Methods include ENQ/ACK (enquiry/acknowledgement) and poll/select.
    • Using ENQ/ACK, the transmitter sends an ENQ to the receiver requesting permission to send data.
    • If the receiver is ready, it responds with an ACK, allowing the transmitter to send data.
    • If the receiver isn't ready, it sends a NACK, and the transmitter waits and retries.
    • Following an error, the transmission will be restarted.

    Flow Control

    • Flow control regulates the amount of data sent to prevent a fast sender from overwhelming a slow receiver.
    • Methods include Stop-and-Wait, which sends one frame at a time and waits for acknowledgement. Sliding window, which sends multiple frames and tracks the unacknowledged frames.

    Error Detection

    • Errors occur when receiver and sender data don't match.
    • Noise in transmission can modify the binary bits ('0' to '1' or '1' to '0') during transmission.
    • Error detecting codes, including parity bits and frame check sequences (FCS) are used to detect errors in the transmitted message/frame.

    ARP (Address Resolution Protocol)

    • ARP is used to determine the MAC address of a device given its IP address on the same local network.
    • ARP provides two basic functions: (1) Resolving IPv4 addresses to MAC addresses; and (2) Maintaining a table of IPv4 to MAC address mappings.
    • ARP request: Sent when a device needs a MAC address, and doesn't have one in its table.
    • The request is encapsulated in an Ethernet frame with a broadcast destination MAC address to all devices on the local network, requesting the requested MAC address.
    • The device having the requested IP address responds with its MAC address, updating the sending device's ARP table.

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    IDT6.4/3 Data-Link Layer PDF

    Description

    This quiz covers the essential functions and purposes of the Data Link layer in the OSI model. It examines how Layer 2 frames encapsulate Layer 3 packets and the role of the Data Link layer in ensuring reliable communication between network devices. Test your knowledge on the mechanics of data transmission and frame handling.

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