Physical Layer, Data Link Layer Protocols

Flashcards reviewing key concepts from lecture notes on Physical and Data Link Layers.

What are the three primary digital-to-digital conversion techniques, and what is the purpose of each?

The three main techniques are line coding, block coding, and scrambling. Each serves to convert digital data into a format suitable for transmission over a physical channel.

What is the fundamental purpose of line coding in digital communication systems?

Line coding is essential for converting digital data into digital signals to ensure compatibility with the transmission medium and facilitate accurate data transfer.

Define what constitutes a 'data element' in the context of digital data transmission.

A data element is the smallest, indivisible unit that represents a piece of information, serving as the fundamental building block for data transmission.

What is a 'signal element,' and how does it relate to data transmission?

A signal element is the shortest unit of a digital signal, representing a single instance of the signal's state (e.g., voltage level) used to convey data elements.

Define 'Data Rate' and specify the unit in which it is typically measured.

Data Rate is the measure of how many data elements (bits) are transmitted per second, quantified in bits per second (bps), indicating the speed of data transfer.

What does 'Signal Rate' signify, and what unit is used to quantify it?

Signal Rate refers to the number of signal elements (or symbols) sent per second, measured in baud, reflecting the actual rate of signal changes on the transmission medium.

What potential issues can arise from the presence of DC components in signal transmission, and how might they impact signal integrity?

DC components in signal transmission can lead to very low frequencies within the signal spectrum, potentially causing interference and degrading signal quality, thus affecting data integrity.

Explain the concept of 'Self-Synchronization' and its importance in digital communication.

Self-Synchronization is the process of ensuring that the receiver's bit intervals are precisely aligned with the sender's bit intervals, crucial for accurate data decoding and reliable communication.

List the primary line coding schemes used in digital communication.

The main line coding schemes include Unipolar, Polar, Bipolar, Multilevel, and Multitransition, each employing unique methods to represent digital data as signals.

Describe the characteristics of Unipolar NRZ and discuss its drawbacks.

Unipolar NRZ represents all signal levels on one side of the time axis, making it a simple but costly scheme due to its inefficiency and DC component issues.

What is the key distinction between NRZ-L and NRZ-I line coding schemes?

NRZ-L uses voltage levels to represent bit values, while NRZ-I uses the presence or absence of a voltage inversion to represent bit values.

Describe the Polar RZ scheme, noting its advantages and disadvantages.

Polar RZ uses three values—positive, negative, and zero—reducing the DC component issue but increasing the required bandwidth.

Explain how Manchester Encoding achieves synchronization.

Manchester Encoding combines RZ (transition at the middle of the bit) and NRZ-L to provide inherent synchronization capabilities.

How does Differential Manchester Encoding differ from Manchester Encoding in terms of synchronization and bit value representation?

Differential Manchester Encoding combines RZ (transition at the middle of the bit) and NRZ-I for synchronization, where the presence or absence of a transition at the beginning of the bit determines the bit value.

Describe Bipolar schemes and provide examples of common Bipolar schemes.

Bipolar schemes use three levels: positive, zero, and negative, with examples including AMI and Pseudoternary, offering a balanced signal with reduced DC component.

What are the two main analog-to-digital conversion techniques?

The two primary analog-to-digital conversion techniques include Pulse Code Modulation (PCM) and Delta Modulation, each serving to convert analog signals into digital format.

List the three essential components of a PCM encoder.

A PCM encoder consists of sampling, quantizing, and encoding stages, each playing a critical role in converting analog signals to digital.

State the Nyquist theorem and explain its significance.

The Nyquist theorem states that the sampling rate must be at least twice the highest frequency component of the signal to accurately reconstruct the original signal.

What is 'Quantization' in the context of analog-to-digital conversion?

Quantization involves mapping a continuous range of analog signal amplitudes to a set of fixed, predefined levels, which depends on the range of the amplitudes of the analog signal.

How does Delta Modulation simplify the process compared to PCM?

Delta Modulation simplifies PCM by focusing on transmitting the difference between successive samples rather than the absolute value of each sample.

Name the two fundamental modes of data transmission.

The two primary transmission modes are Parallel Transmission and Serial Transmission, each offering different approaches to data communication.

List the three subclasses of serial transmission.

The three subclasses of serial transmission are Asynchronous, Synchronous, and Isochronous, each characterized by different timing mechanisms.

Describe the process of Asynchronous transmission.

Asynchronous transmission involves sending each byte with a start bit (0) at the beginning and one or more stop bits (1s) at the end, allowing irregular timing intervals.

Explain Synchronous transmission and its requirements.

Synchronous transmission sends bits continuously without start or stop bits or gaps, requiring precise clock synchronization between sender and receiver.

What is Isochronous transmission, and why is it essential for certain applications?

Isochronous transmission ensures that the entire stream of bits is synchronized, and data arrives at a fixed rate, crucial for real-time applications.

Outline the primary responsibilities of the data link layer in network communication.

The data link layer is responsible for moving frames from one hop (node) to the next, handling framing, physical addressing, flow control, and error control.

What are the two primary functions of the data link layer?

The two main functions of the data link layer are Data Link Control (DLC) and Media Access Control (MAC), each managing different aspects of data transmission.

Define 'framing' in the context of data transmission.

Framing is the process of organizing bits into structured frames, enabling each frame to be distinguished from another for efficient data transmission.

Name the common approaches used in framing.

The common framing approaches include Bit-Oriented Framing, Byte-Oriented Framing, and Clock-Based Framing, each using different methods to delineate frame boundaries.

Describe the 'bit stuffing' technique and its purpose.

Bit stuffing involves adding an extra 0 whenever five consecutive 1s are encountered in the data to prevent confusion with flag patterns.

What is 'byte stuffing,' and why is it used?

Byte stuffing involves adding an extra byte (escape character) whenever a flag or escape character appears in the text to avoid misinterpretation.

Explain the concept of 'physical layer coding violations' in framing.

Physical layer coding violations use specific signal patterns (combinations of high-high and low-low) that are not used for data to mark frame boundaries.

What are the two main categories of errors that can occur during data transmission?

The two primary types of errors in data transmission are single-bit errors and burst errors, each affecting data integrity differently.

What is the purpose of adding redundant bits to data before transmission?

Redundant bits are added to data to enable the detection and/or correction of errors that may occur during data transmission.

Describe the process of Block Coding, including the roles of datawords and redundant bits.

In Block Coding, the message is divided into blocks of k bits (datawords), and r redundant bits are added to each block to create codewords of length n = k + r for error detection or correction.

Define 'Hamming distance' and explain its significance in error detection and correction.

Hamming distance is the measure of the number of bit positions in which two codewords differ, used to assess the error-detecting and error-correcting capabilities of a code.

List common error detection techniques used in data transmission.

Error detection techniques include Parity Checker, CRC (Cyclic Redundancy Check), and Checksum, each employing different algorithms to identify errors in transmitted data.

Explain how the Parity Checker works to detect errors.

The Parity Checker adds an extra bit to the data to ensure that the number of 1s is either even or odd, allowing detection of single-bit errors.

How does a two-dimensional parity checker enhance error detection capabilities?

A two-dimensional parity checker organizes the dataword in a table to detect up to three-bit errors by checking parity along both rows and columns.

On what mathematical concept is Cyclic Redundancy Check (CRC) based?

Cyclic Redundancy Check (CRC) is based on the concept of binary division, where the transmitted data is divided by a generator polynomial to produce a remainder used for error detection.

What is the divisor in a cyclic code commonly called?

The divisor in a cyclic code is referred to as the Generator polynomial or simply the generator, used to calculate the CRC remainder.

Describe the error checking process performed at the receiver side in CRC.

At the receiver side in CRC, the received codeword is divided by the same generator polynomial; if the remainder is all zeros, the message is accepted; otherwise, it is discarded.

Explain how checksum is calculated and used for error detection.

Checksum works by adding each data word to a running total, computing a checksum value that is then transmitted along with the data for error detection.

How does the Internet Checksum specifically operate?

Internet Checksum divides the message into 16-bit words, sums them using 1s complement arithmetic, and then complements the result to produce the checksum.

Define 'Flow control' and explain its importance in data transmission.

Flow control is a set of procedures used to manage the amount of data a sender can transmit before receiving acknowledgment, preventing receiver overload.

Mention types of major flow control protocols for dealing with errors and loss.

Protocols include those for noiseless channels (Simplest, Stop-and-Wait) and noisy channels (Stop-and-Wait ARQ, Go-Back-N ARQ, Selective Repeat ARQ), each designed for different channel conditions.

Describe the operation of the Stop-and-Wait Protocol.

The Stop-and-Wait Protocol involves the sender transmitting one frame and waiting for acknowledgment before sending the next, ensuring reliable but slow data transfer.

Why is error correction essential in Stop-and-Wait ARQ, and how is it implemented?

Error correction in Stop-and-Wait ARQ is crucial and is achieved by retaining a copy of each sent frame and retransmitting if acknowledgment is not received within a specified timeout period.

What is 'piggybacking,' and how does it enhance protocol efficiency?

Piggybacking is a technique that improves the efficiency of bidirectional protocols by appending acknowledgments to outgoing data frames.

What is Data Link Layer divided into?

From the data link layer, two sublayers with different functionality-oriented are: the upper sublayer which is responsible for data link control and the lower sublayer which is responsible for resolving access to the shared media.

Describe taxonomy of multiple-access protocols.

Multiple-access protocols can be classified into FDMA, TDMA, CDMA, CSMA, CSMA/CD, and CSMA/CA, each providing different mechanisms for sharing a communication channel.

In Random access protocols, Why station uses a procedure defined by the protocol?

In random access protocols, stations use a procedure defined by the protocol to determine whether to transmit data, aiming to minimize collisions in shared media.

List Random access Protocols.

Random access Protocols include ALOHA, Carrier Sense Multiple Access (CSMA), Carrier Sense Multiple Access with Collision Detection (CSMA/CD), and Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA).

How pure ALOHA protocol works?

Pure ALOHA allows each station to transmit a frame whenever it has data to send, increasing the risk of collisions between frames from different stations.

How does slotted ALOHA works

Slotted ALOHA divides time into discrete slots and requires stations to transmit only at the beginning of a time slot, reducing collision probability compared to pure ALOHA.

What is Carrier Sense Multiple Access (CSMA) and how does it works?

CSMA requires each station to listen to the medium before transmitting, following the principle of 'sense before transmit' to avoid collisions.

What are the three persistence methods of CSMA?

The three persistence methods in CSMA are 1-persistent, Nonpersistent, and P-persistent, each defining how a station reacts upon sensing a busy medium.

How does CSMA/CD works?

CSMA/CD enhances CSMA by allowing stations to detect collisions during transmission and cease transmitting to reduce channel wastage, following a random backoff period before retransmission.

How does CSMA/CA works?

CSMA/