Defeating TCP congestion-control mechanisms usually requires explicit cooperation of the sender. However, consider the receiving end of a large data transfer using a TCP modified to ACK packets that have not yet arrived. It may do this either because not all of the data is necessary or because data that is lost can be recovered in a separate transfer later. What effect does this receiver behavior have on the congestion control properties of the session? Can you devise a way to modify TCP to avoid the possibility of senders being taken advantage of in this manner?

Defeating TCP congestion-control mechanisms usually requires explicit cooperation of the sender. However, consider the receiving end of a large data transfer using a TCP modified to ACK packets that have not yet arrived. It may do this either because not all of the data is necessary or because data that is lost can be recovered in a separate transfer later. What effect does this receiver behavior have on the congestion control properties of the session? Can you devise a way to modify TCP to avoid the possibility of senders being taken advantage of in this manner?

Database System Concepts

7th Edition

ISBN:9780078022159

Author:Abraham Silberschatz Professor, Henry F. Korth, S. Sudarshan

Publisher:Abraham Silberschatz Professor, Henry F. Korth, S. Sudarshan

Chapter1: Introduction

Section: Chapter Questions

Problem 1PE

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True or False 1. After fast retransmit is invoked, fast recovery cuts the slow start period in half 2. A host sends a segment with a sequence number 35 and a payload of 5 Bytes. The ACK number in that segment is 40 3. TCP segments can only be lost when router queues overflow. Please explain if possible， Thank you!
Consider a simple protocol for transferring files over a link. After some initial negotiation, A sends data packets of size 1 KB to B; B then replies with an acknowledgment. A always waits for each ACK before sending the next data packet; this is known as stop-and-wait. Packets that are overdue are presumed lost and are retransmitted. (a) In the absence of any packet losses or duplications, explain why it is not necessary to include any "sequence number" data in the packet headers. (b) Suppose that the link can lose occasional packets, but that packets that do arrive always arrive in the order sent. Is a 2-bit sequence number (that is, N mod 4) enough for A and B to detect and resend any lost packets? Is a 1-bit sequence number enough? (c) Now suppose that the link can deliver out of order and that sometimes a packet can be delivered as much as 1 minute after subsequent packets. How does this change the sequence number requirements?
14 The following figure shows a TCP transaction. Assume Host A always has data to send, and each packet has size 20 Bytes. Assume Host A has a sending window of 40 Bytes, that is, it can send two "in-flight” packets maximum. Answer the following questions. A. At the time marked "1", i.e., when the first packet times out, will Host A send any packet? if your answer is no, explain why not; if your answer is yes, how many packets will be sent, what are the sequence numbers of them? B. At the time marked "2", i.e., when the ACK of the 2nd packet is received by Host A, will Host A send any packet? if your answer is no, explain why not; if your answer is yes, how many packets will be sent, what are the sequence numbers of them? Host A Host B Seq=80, 20 bytes of data Seq=100, 20 bytes of data Xª 1 2- timeout
Is it true or false? Consider TCP congestion control. When the timer at the sender ends, the value of ssthresh is reduced to one-half of its previous value.
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