/*! This file is auto-generated */ .wp-block-button__link{color:#fff;background-color:#32373c;border-radius:9999px;box-shadow:none;text-decoration:none;padding:calc(.667em + 2px) calc(1.333em + 2px);font-size:1.125em}.wp-block-file__button{background:#32373c;color:#fff;text-decoration:none} Problem 22 Consider an ARQ protocol that us... [FREE SOLUTION] | 91影视

91影视

Log out

Learning Materials

Features

Discover

Chapter 2: Problem 22

Consider an ARQ protocol that uses only negative acknowledgments (NAKs), but no positive acknowledgments (ACKs). Describe what timeouts would need to be scheduled. Explain why an ACK-based protocol is usually preferred to a NAK- based protocol.

Short Answer

Expert verified
Timeouts are scheduled to detect lost packets and depend on RTT. ACK-based protocols are preferred due to their explicit confirmations, improving reliability and efficiency.

Step by step solution

01

- Understanding ARQ Protocols

An Automatic Repeat reQuest (ARQ) protocol is used for error control in data transmission. It ensures that the sender and receiver can communicate reliably even with occasional lost or corrupted packets.
02

- Explaining NAK-based ARQ

In a NAK-based ARQ protocol, the receiver sends a negative acknowledgment (NAK) when it detects an error or a missing packet. This requests the sender to retransmit the erroneous or missing packet.
03

- Scheduling Timeouts

Timeouts are needed to detect lost packets. If the sender does not receive a NAK within a certain time period, it assumes the packet has been received successfully. Scheduling a timeout for the retransmission depends on the network's round-trip time (RTT) and the expected processing delays.
04

- Timeout Calculation

Calculate the timeout interval using RTT estimation. For instance, timeout can be set to a default of two to three times the average RTT to ensure that any packet loss can be detected within a reasonable timeframe.
05

- Comparing ACK-based Protocols

In ACK-based protocols, the receiver sends positive acknowledgments for received packets. The sender will retransmit a packet if it does not receive an ACK within the timeout period. ACK-based protocols are preferred because they explicitly confirm successful receipt, making the detection of lost packets simpler and more reliable.
06

- Conclusion

While NAK-based protocols rely on detecting errors or losses to trigger retransmissions, ACK-based protocols continuously affirm the successful receipt, reducing ambiguity. Thus, ACK-based protocols can enhance reliability and efficiency in communications.

Unlock Step-by-Step Solutions & Ace Your Exams!

  • Full Textbook Solutions

    Get detailed explanations and key concepts

  • Unlimited Al creation

    Al flashcards, explanations, exams and more...

  • Ads-free access

    To over 500 millions flashcards

  • Money-back guarantee

    We refund you if you fail your exam.

Over 30 million students worldwide already upgrade their learning with 91影视!

Key Concepts

These are the key concepts you need to understand to accurately answer the question.

NAK-based ARQ
Automatic Repeat reQuest (ARQ) protocols are vital in error control for data transmission. One type of ARQ protocol is the NAK-based ARQ. In this approach, the receiver sends a Negative Acknowledgment (NAK) whenever it detects an error or finds a missing packet. The NAK essentially tells the sender to retransmit the specific packet that had issues. This mechanism is reactive since retransmissions only happen after detecting a problem.
Using NAKs helps to control the data flow and ensures that even if a packet gets lost or corrupted, the communication remains intact by requesting a correction.
ACK-based ARQ
Another common ARQ protocol is the ACK-based ARQ. In this method, the receiver sends a Positive Acknowledgment (ACK) after successfully receiving and processing a packet. If the sender does not receive an ACK within a predetermined timeout period, it assumes the packet was lost and retransmits the packet.
ACK-based ARQ provides several benefits over NAK-based ARQ:
  • Guarantees confirmation for each packet received, reducing uncertainty.
  • Improves overall reliability of the data transmission process.
  • Helps quickly detect and correct errors.
This proactive confirmation method often leads to more efficient and reliable data communications.
Timeout Scheduling
Timeout scheduling is crucial for ensuring both NAK-based and ACK-based ARQ protocols function effectively. Timeouts help in detecting lost packets. Here's how you can approach it:
  • Estimate the network's Round-Trip Time (RTT). RTT is the time it takes for a signal to travel from the sender to the receiver and back again.
  • Set your timeout intervals based on this RTT to detect and correct packet loss efficiently.
For example, you might set a timeout to two to three times the average RTT. This approach provides a buffer to account for slight variations in network delays, ensuring timely detection of lost packets without causing unnecessary retransmissions.
Effective timeout scheduling enhances communication reliability, whether using NAK-based or ACK-based ARQ protocols.

One App. One Place for Learning.

All the tools & learning materials you need for study success - in one app.

Get started for free

Most popular questions from this chapter

Assume that a SONET receiver resynchronizes its clock whenever a 1 bit appears; otherwise, the receiver samples the signal in the middle of what it believes is the bit's time slot. (a) What relative accuracy of the sender's and receiver's clocks is required in order to receive correctly 480 bytes (one ATM AAL. 5 cell's worth) in a row? (b) Consider a forwarding station A on a SONET STS-1 line, receiving frames from the downstream end \(B\) and retransmitting them upstream. What relative accuracy of A's and B's clocks is required to keep A from accumulating more than one extra frame per minute?

Suppose we want to transmit the message 1011001001001011 and protect it from errors using the CRC-8 polynomial \(x^{8}+x^{2}+x^{1}+1\). (a) Use polynomial long division to determine the message that should be transmitted. (b) Suppose the leftmost bit of the message is inverted due to noise on the transmission link. What is the result of the receiver's CRC calculation? How does the receiver know that an error has occurred?

Suppose \(A, B\), and \(C\) all make their first carrier sense, as part of an attempt to transmit, while a fourth station D is transmitting. Draw a timeline showing one possible sequence of transmissions, attempts, collisions, and exponential backoff choices. Your timeline should also meet the following criteria: (i) initial transmission attempts should be in the order \(A, B, C\), but successful transmissions should be in the order \(\mathrm{C}, \mathrm{B}, \mathrm{A}\), and (ii) there should be at least four collisions.

Consider an ARQ algorithm running over a \(20-\mathrm{km}\) point-to-point fiber link. (a) Compute the propagation delay for this link, assuming that the speed of light is \(2 \times 10^{8} \mathrm{~m} / \mathrm{s}\) in the fiber. (b) Suggest a suitable timeout value for the ARQ algorithm to use. (c) Why might it still be possible for the ARQ algorithm to time out and retransmit a frame, given this timeout value?

Suppose that we attempt to run the sliding window algorithm with SWS = RWS = 3 and with MaxSeqNum \(=5 .\) The Nth packet DATA[ \(N]\) thus actually contains \(N\) mod 5 in its sequence number field. Give an example in which the algorithm becomes confused; that is, a scenario in which the receiver expects DATA[5] and accepts DATA[0]-which has the same transmitted sequence number-in its stead. No packets may arrive out of order. Note this implies MaxSeqNum \(\geq 6\) is necessary as well as sufficient.
See all solutions

Recommended explanations on Computer Science Textbooks

Algorithms in Computer Science

Read Explanation

Problem Solving Techniques

Read Explanation

Cloud Services

Read Explanation

Computer Systems

Read Explanation

Functional Programming

Read Explanation

Computer Organisation and Architecture

Read Explanation
View all explanations

What do you think about this solution?

We value your feedback to improve our textbook solutions.

Study anywhere. Anytime. Across all devices.