Data Communication Protocols

Questions and Answers

What is the primary characteristic of Normal Response Mode (NRM)?

Both stations can send and receive commands.

Both stations share a balanced configuration.

Only the primary station sends commands, while the secondary responds. (correct)

It is limited to point-to-point links only.

In Asynchronous Balanced Mode (ABM), how do the stations interact?

Each station can function as both primary and secondary peers. (correct)

One station transmits data while the other receives.

It is exclusively used for multipoint links.

The primary station controls communication at all times.

What is the purpose of Information Frames (I-frames) in HDLC?

To manage error detection using CRC.

To provide session management protocols.

To transport user data and control information. (correct)

To control the acknowledgment process alone.

Which of the following frame types is used solely for control information when piggybacking is not possible?

S-frames Signup and view all the answers

What is contained in the Frame Check Sequence (FCS) field?

Error-detection information using a CRC. Signup and view all the answers

How is the Control field utilized in I-frames?

It indicates sequence numbers and acknowledgment processes. Signup and view all the answers

What does the first bit of the Control field in an I-frame signify?

It indicates the type of the frame. Signup and view all the answers

What unique feature distinguishes U-frames in HDLC?

They contain two segments with a prefix and a suffix code. Signup and view all the answers

What does the code '00' indicate in the S-frame type definitions?

Acknowledges safe receipt of frame Signup and view all the answers

Which of the following statements about PPP is true?

PPP lacks flow control Signup and view all the answers

What aspect of PPP does the escape byte 01111101 relate to?

Flag identification Signup and view all the answers

Which service is NOT offered by PPP?

Flow control Signup and view all the answers

What is the maximum payload size in PPP frames?

1500 bytes Signup and view all the answers

Which control value is used in the PPP frame format?

00000011 Signup and view all the answers

What is indicated by the code '11' in S-frame types?

Selective reject option Signup and view all the answers

What is the purpose of the FCS in a PPP frame?

Error detection Signup and view all the answers

What occurs during the Authenticate State in the PPP process?

If authentication fails, it moves to network state. Signup and view all the answers

Which protocol is primarily responsible for establishing, maintaining, and terminating PPP links?

Link Control Protocol (LCP) Signup and view all the answers

In the Multilink PPP, what is the purpose of sequence numbers in the PPP frames?

To indicate the position of each fragment within the logical frame. Signup and view all the answers

Which of the following best describes the Challenge Handshake Authentication Protocol (CHAP)?

A three-way handshaking protocol that enhances security. Signup and view all the answers

Which of the following statements is true regarding Password Authentication Protocol (PAP)?

It is a simple two-step authentication procedure. Signup and view all the answers

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

To configure the link for network-layer data. Signup and view all the answers

What marks the transition from the Open State to the Terminate State in the PPP phases?

Waiting for the carrier signal to drop. Signup and view all the answers

During which state in PPP does actual data transfer occur?

Open State Signup and view all the answers

What is the main issue with character-oriented protocols in data communications?

They use 8-bit characters that conflict with Unicode systems. Signup and view all the answers

What is the purpose of the 8-bit pattern flag in bit-oriented framing?

To define the start and end of a frame. Signup and view all the answers

What is the function of bit stuffing in framing protocols?

To avoid flag patterns appearing in the data. Signup and view all the answers

What is the main characteristic of fixed-size framing?

The size of the frames itself is used as a delimiter. Signup and view all the answers

Which of the following best describes the character-oriented framing approach?

Frames begin and end with a flag composed of 8 bits. Signup and view all the answers

Which type of error control primarily focuses on error detection and retransmission?

Data-link layer error control. Signup and view all the answers

In error detection, what is the ultimate goal of the technique used?

To avoid undetected errors from impacting data integrity. Signup and view all the answers

What is the purpose of byte stuffing in variable-size framing?

To differentiate between flag characters and data characters. Signup and view all the answers

What happens to a bit if a sequence of one 0 followed by five 1s is encountered in bit stuffing?

An extra 0 bit is added. Signup and view all the answers

What marks the presence of an ESC (escape character) in data?

Another ESC being added before it. Signup and view all the answers

Which of the following best describes a single-bit error?

Only one bit in the data has flipped. Signup and view all the answers

Why was byte stuffing introduced in character-oriented framing?

To avoid confusion between control signals and actual data. Signup and view all the answers

What potential problem does variable-size framing face when transmitting mixed data types?

The flag pattern can appear in the data, causing frame misinterpretation. Signup and view all the answers

What does error detection not accomplish when monitoring received data?

Determine which bit is erroneous. Signup and view all the answers

What components are included in a character-oriented frame?

Header, trailer, and data section. Signup and view all the answers

What is a potential limitation of the character-oriented framing approach?

It is incompatible with modern data types. Signup and view all the answers

Study Notes

Framing in Networking

Fixed-size framing
- Utilizes size as a delimiter, eliminating the need for boundary definition.
- Example: ATM WAN employs fixed-size frames known as cells.
Variable-size framing
- Common in local-area networks.
- Requires methods to mark frame beginnings and endings.
- Traditionally uses two approaches: character-oriented and bit-oriented.

Character-oriented Framing

Operates with 8-bit characters, typically from ASCII coding.
Frames begin and end with an 8-bit flag, ensuring clear frame separation.
Components of a frame include:
- Header: Contains source and destination addresses, control information.
- Trailer: Includes error detection bits.
Designed for text data exchange; now also supports diverse information types.
Issues arise with patterns in data resembling flag patterns; leads to confusion about frame boundaries.

Byte Stuffing Technique

Introduced to address ambiguity between flag characters and data.
Adds an escape byte (ESC) before a character that matches the flag pattern.
If an ESC appears in the data, another ESC precedes it to clarify that it’s data, not a flag.

Bit-oriented Framing

Handles a sequence of bits instead of fixed-width characters, accommodating various data types (text, graphic, audio).
Requires a delimiter for frame separation; commonly uses an 8-bit flag pattern.
Faces similar problems as character-oriented framing; introduces bit stuffing to maintain frame integrity.
In bit stuffing, an extra 0 is added after encountering 0 followed by five consecutive 1s to prevent flag appearance in data.

Error Control in Data-Link Layer

Encompasses both error detection and correction.
Allows receivers to notify senders about lost or damaged frames for retransmission.
Types of errors include single-bit errors and burst errors.

Error Detection Techniques

Involves monitoring data to identify transmission errors.
Does not pinpoint specific erroneous bits; focuses on preventing undetected errors.
Common techniques include exact-code coding, parity checks, normal response mode (NRM), and asynchronous balanced mode (ABM).

HDLC (High-Level Data Link Control)

Defines three frame types:
- Information Frames (I-frames): Transport user data and control info.
- Supervisory Frames (S-frames): Transport only control information.
- Unnumbered Frames (U-frames): Manage session and control information.
Frame structure includes:
- Flag: Synch pattern for frame identification.
- Address: Secondary station address.
- Control: Used for flow and error management.
- Information: User data from network layer.
- Frame Check Sequence (FCS): Error detection field utilizing CRC.

HDLC Frame Control

Frames vary by type, identified by bit patterns (e.g., I-frame starts with 0, S-frame starts with 10).
S-frames feature acknowledgment codes for frame transmission statuses.

Point-to-Point Protocol (PPP)

Widely used for point-to-point access, especially for ISP connectivity.
Services Provided:
- Defines frame format, negotiates link establishment.
- Supports multipoint authentication.
Limitations:
- Lacks flow control, sophisticated error handling, and does not guarantee frame sequencing.

PPP Frame Structure

Flag: Singular byte with pattern 01111110 indicating frame boundaries.
Address: Fixed broadcast address.
Control: Constant value mimicking U-frames in HDLC.
Protocol: Indicates the content type within data field.
Payload: User data, max length of 1500 bytes.
FCS: Standard CRC for error detection.

Byte Stuffing and Transition Phases in PPP

Escape byte added whenever flag-like patterns appear in data.
Transition Phases:
- Dead State: No active carriers.
- Establish State: Connection setup and option negotiation.
- Authenticate State: Authentication verification process.
- Open State: Active data transfer with packet exchange.
- Terminate State: Connection closure, returning to dead state.

Multiplexing in PPP

Uses protocols such as Link Control Protocol (LCP) and Network Control Protocols (NCPs) to manage connections.
Authentication Protocols:
- Password Authentication Protocol (PAP): Basic two-step authentication.
- Challenge Handshake Authentication Protocol (CHAP): More secure three-step process to verify user identity.

Multilink PPP

Allows logical PPP frames to split into multiple actual frames across several channels.
Facilitates efficient data transmission by adding sequence numbers to fragments for proper reassembly.

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Description

This quiz covers key aspects of data communication protocols, focusing on the acknowledgment and negative acknowledgment systems. You'll explore different types of S-frames and their functionalities in managing data transmission and congestion control. Test your knowledge of these essential concepts and codes used in data communication.