An Overview Of Round Trip Time Computer Science Essay


This essay has been submitted by a student. This is not an example of the work written by our professional essay writers.

RTT: Round-Trip Time can also be called as round-trip delay. It is to calculate how much time required for sending a packet or signal pulse from one source to a specific destination and comes back to the same specific source. RTT is one of the several factors that affecting latency and the time between the request for data and also the complete return or display of that data. RTT can range between a few milliseconds under some ideal conditions to several seconds between points under adverse conditions.

Estimated RTT plus can be defined as "safety margin". It is the estimated value of RTT that is based on the combination of current RTT and the past RTT.

EstimatedRTT = (1- a)*EstimatedRTT + a*SampleRTT

Large variation in Estimated RTT means larger safety margin. To calculate the DevRTT we need to estimate how much Sample RTT deviates from Estimated RTT i.e.,

DevRTT = (1-b)*DevRTT +b*|SampleRTT-EstimatedRTT|

(typically, b = 0.25)

A premature retransmission timeout occurs if there is no packet or signal loss or if the lost packet or signal can be captured by fast retransmission mechanism. With contrast, over estimation of RTT will lead to late retransmission timeout, in that case, if there is a loss and which cannot be captured by the fast retransmission mechanism. Therefore, it is crucial to have a Retransmission Timeout (RTO) value for TCP performance which is an equilibrium point in balancing between both the above cases.

Note: RTO must be smaller than RTT.

Following are the few algorithms which help in setting the retransmission timeout

Ludwig and Katz propose the Eifel algorithm to eliminate the unnecessary retransmissions that can result from a spurious retransmission timeout.

Gurtov and Ludwig present an enhanced version of the Eifel algorithm and show its performance benefits on paths with a high bandwidth-delay product.

Ekstrand Ludwig proposes a new algorithm for calculating the RTO, named the Peak-Hopper-RTO (PH-RTO), which improves upon the performance of TCP in high loss environments.

RFC 3649 proposes modification of TCP congestion control that adapts the increase strategy and makes it more aggressive for high bandwidth links (i.e. for large window sizes)

In order to set the ACK timer we need to know how large the ACK timeout value should be. It can be too short or too long.

Too short --> premature timeout --> extra retransmission

Too long --> slow reaction to loos --> poor performance

for this we need to have the timer longer than RTT, for this we need to estimate RTT by measuring the time from a segment transmission until the receipt of ACK which is nothing but Sample RTT. For this we need to ignore retransmissions and measure only one segment's RTT at a time. By doing so, the sample RTT will vary and we can compute an average RTT based on the several recent RTT samples.

Timeout = Estimated RTT + 4*DevRTT

The probability of premature retransmission timeout is

P1 = P[RTO < RTT]

    ((1-p) W + (1-(1-p) W) (1-3/W) )

˜ P[RTO < RTT] (1-3/W 2)

˜ P[RTO < RTT]

The throughput degradation due to this event is:

L1 = WlogW.

During the slow start ph.ase we can observe, TCP sends at most W packets. We obtain that the expected output degradation result to premature retransmission timeout is:

P1.L1 = P[RTO&lt;RTT].WlogW.

According to the given data maximum RTT is 291, the probability of premature timeout will occur on Segment 17.

Writing Services

Essay Writing

Find out how the very best essay writing service can help you accomplish more and achieve higher marks today.

Assignment Writing Service

From complicated assignments to tricky tasks, our experts can tackle virtually any question thrown at them.

Dissertation Writing Service

A dissertation (also known as a thesis or research project) is probably the most important piece of work for any student! From full dissertations to individual chapters, we’re on hand to support you.

Coursework Writing Service

Our expert qualified writers can help you get your coursework right first time, every time.

Dissertation Proposal Service

The first step to completing a dissertation is to create a proposal that talks about what you wish to do. Our experts can design suitable methodologies - perfect to help you get started with a dissertation.

Report Writing

Reports for any audience. Perfectly structured, professionally written, and tailored to suit your exact requirements.

Essay Skeleton Answer Service

If you’re just looking for some help to get started on an essay, our outline service provides you with a perfect essay plan.

Marking & Proofreading Service

Not sure if your work is hitting the mark? Struggling to get feedback from your lecturer? Our premium marking service was created just for you - get the feedback you deserve now.

Exam Revision

Exams can be one of the most stressful experiences you’ll ever have! Revision is key, and we’re here to help. With custom created revision notes and exam answers, you’ll never feel underprepared again.