ECE144 Data-Link Layer Chapter 3

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Questions and Answers

What type of communication does the data-link layer primarily handle?

Network-to-network communication

End-to-end communication

Node-to-node communication (correct)

Application-to-application communication

Which sublayer of the data-link layer specifically deals with issues related to broadcast links?

Frame control layer

Media access control (MAC) (correct)

Protocol control sublayer

Data-link control (DLC)

How does framing enhance data transmission at the data-link layer?

By separating messages into distinguishable units (correct)

By compressing data to save space

By adding encryption to packets

By converting messages into a binary format

What type of link dedicates the entire transmission medium to two devices?

Point-to-point link (A) Signup and view all the answers

Which of the following is NOT a component addressed by the data-link control (DLC) sublayer?

Routing (C) Signup and view all the answers

What is a common application of a broadcast link?

Cellular communication (B) Signup and view all the answers

What is a key benefit of dividing messages into smaller frames?

Enhanced flow and error control (B) Signup and view all the answers

Which addresses are added to frames at the data-link layer to facilitate communication?

Source and destination addresses (B) Signup and view all the answers

What is the primary function of Normal response mode (NRM)?

The primary station sends commands while the secondary responds. (C) Signup and view all the answers

In Asynchronous balanced mode (ABM), how do the stations function?

Each station can act as both primary and secondary. (D) Signup and view all the answers

What type of information do Information Frames (I-frames) transport?

User data and control information relating to that data. (B) Signup and view all the answers

What identifies both the beginning and the end of an HDLC frame?

Flag containing the pattern 01111110. (B) Signup and view all the answers

What is the primary purpose of the Control field in HDLC frames?

To indicate the type of frame and its functionality. (A) Signup and view all the answers

The Frame Check Sequence (FCS) in HDLC is used for what purpose?

To enable error detection. (C) Signup and view all the answers

Which statement correctly describes Supervisory frames (S-frames)?

They are only used when piggybacking is unavailable. (B) Signup and view all the answers

How many possible U-frames can be created based on the segmentation defined in the HDLC format?

32 possible U-frames. (D) Signup and view all the answers

What is the primary goal of error detection?

Determine if an error has occurred (A) Signup and view all the answers

Which of the following is a method of error correction?

Forward error correction (D) Signup and view all the answers

Which statement describes the complexity of error correction compared to error detection?

Error correction is more complex than error detection. (B) Signup and view all the answers

What type of information is needed for error correction?

Number and location of corrupted bits (B) Signup and view all the answers

Which of the following best describes High-Level Data-Link Control (HDLC)?

A bit-oriented protocol for point-to-point and multipoint links (A) Signup and view all the answers

In what scenario is forward error correction particularly useful?

For systems with continuous data streams without retransmission (B) Signup and view all the answers

What is a major limitation of error correction techniques?

Their effectiveness significantly decreases with the number of errors. (A) Signup and view all the answers

Which of the following options represents a factor affecting error impact in detection?

Single-bit errors are treated the same as burst errors (A) Signup and view all the answers

What occurs during the Establish State of the PPP protocol?

Options are negotiated between nodes. (C) Signup and view all the answers

Which protocol under Authentication Protocols (AP) provides greater security by keeping the password secret?

Challenge Handshake Authentication Protocol (CHAP) (B) Signup and view all the answers

What is the function of Network Control Protocols (NCPs) in PPP?

They configure the link for network-layer data. (B) Signup and view all the answers

Which state follows the Authenticate State if authentication is not agreed upon?

Network State (D) Signup and view all the answers

What is a key characteristic of Multilink PPP?

Allows a single logical PPP frame to be divided into multiple PPP frames. (C) Signup and view all the answers

What happens during the Terminate State of the PPP protocol?

The connection ends and waits for the carrier signal to drop. (A) Signup and view all the answers

Which option best describes the Link Control Protocol (LCP)?

It establishes, maintains, configures, and terminates links. (B) Signup and view all the answers

Which of the following is NOT a state in the PPP phase transition?

Inactive State (A) Signup and view all the answers

What does variable framing primarily focus on in data communication?

Sequence of bits (B) Signup and view all the answers

In bit-oriented framing, what is the purpose of using a delimiter?

To indicate the start and end of a frame (C) Signup and view all the answers

What problem can the flag pattern 01111110 create in bit-oriented protocols?

False flags in data frames (B) Signup and view all the answers

What defines a single-bit error in data transmission?

A single bit being corrupted (B) Signup and view all the answers

Which of the following is NOT a common technique for error detection?

Retransmission techniques (C) Signup and view all the answers

What does error control primarily facilitate in data-link communication?

Recovering lost or damaged frames (C) Signup and view all the answers

What is the role of bit stuffing in data framing?

To prevent flag patterns from appearing in data (A) Signup and view all the answers

Which type of error refers to multiple bits being altered in a single transmission?

Burst error (B) Signup and view all the answers

Study Notes

Data-Link Layer Overview

Node-to-node communication occurs at the data-link layer, contrasting with end-to-end communication in higher layers.
Data units must traverse multiple networks (LANs and WANs) and are facilitated by routers.
Nodes consist of end hosts and routers, while links connect these nodes.

Link Types

Data-link layer manages the utilization of transmission mediums (cable, air).
Point-to-point links dedicate resources to two devices; broadcast links share resources among multiple devices.
Traditional home phones exemplify point-to-point links, while cellular networks illustrate broadcast links.

Sublayers of Data-Link Layer

Divided into two sublayers:
- Data-Link Control (DLC): Addresses issues for both point-to-point and broadcast links.
- Media Access Control (MAC): Specifically manages issues for broadcast links.

Framing

Bits are packed into frames for distinction; analogous to postal systems.
Each frame includes sender and destination addresses for effective communication.
Messages are broken into smaller frames which improves flow and error control.
Frames can be fixed or variable in size, and may utilize different framing protocols:
- Character-oriented Framing: Traditional approach, but limited by character encoding issues.
- Bit-oriented Framing: Uses bits for data representation and requires delimiters to separate frames.

Bit Stuffing

Employed to prevent flag patterns (0 1 1 1 1 1 1 0) from appearing in data.
If five consecutive 1 bits are detected, an extra 0 is inserted, which is later removed by the receiver.

Error Control

Incorporates error detection and correction strategies while addressing data loss and integrity during transmission.
Two error types:
- Single-bit Error: Occurs in a single bit.
- Burst Error: Involves multiple bits.
Error Detection Techniques include:
- Exact-code coding, parity checking, and redundancy methods (Checksum, VRC, LRC, CRC).

Error Correction

More complex than detection; focuses on identifying and correcting erroneous data.
Two primary methods:
- Retransmission: Involves sending data again after detection of errors.
- Forward Error Correction: Uses techniques like Hamming codes to correct errors without retransmission.

High-Level Data-Link Control (HDLC)

A bit-oriented protocol used for communication on point-to-point and multipoint links.
Defined transfer modes:
- Normal Response Mode (NRM): Unbalanced configuration, primary node initiates communication.
- Asynchronous Balanced Mode (ABM): Balanced configuration, each node can act as primary or secondary.

HDLC Frame Types

Information Frames (I-frames): Carry user data and control info.
Supervisory Frames (S-frames): Convey control info without user data.
Unnumbered Frames (U-frames): Manage session and control information.

HDLC Frame Structure

Flag: Synchronization pattern that indicates frame boundaries.
Address: Identifies secondary station's address.
Control: Bytes for flow and error control; varies based on frame type.
Information: Contains user data; length can vary.
Frame Check Sequence (FCS): Error detection field using CRC.

Point-to-Point Protocol (PPP)

Extends HDLC for point-to-point communication; facilitates link establishment and data transfer with various protocol layers.
State Phases of PPP include:
- Dead State
- Establish State
- Authenticate State
- Open State
- Terminate State

PPP Protocols

Link Control Protocol (LCP): Configures and maintains the connection; negotiates options.
Authentication Protocols (APs): Verify user identity through methods like PAP and CHAP.
Network Control Protocols (NCPs): Configure links for multiple network-layer protocols.

Multilink PPP

Allows logical frames to be distributed across multiple physical channels, enhancing link efficiency.
Sequence numbering in PPP frames indicates the position of fragments within logical frames.

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Explore the fundamentals of the Data-Link Layer in this quiz. Dive into key concepts such as framing, error control, and protocols that facilitate node-to-node communication. Perfect for students of Data Communications in course ECE144.