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TCP congestion avoidance flow

We have already seen that TCP connection starts up in slow start mode, geometrically increasing the congestion window (cwnd) until it crosses the slow start threshold (ssthresh). Once cwnd is greater that ssthresh, TCP enters the congestion avoidance mode of operation. In this mode, the primary objective is to maintain high throughput without causing congestion. If TCP detects segment loss, it assumes that congestion has been detected over the internet. As a corrective action, TCP reduces its data flow rate by reducing cwnd. After reducing cwnd, TCP goes back to slow start.

We examine congestion avoidance in detail. We examine in detail how TCP reacts to the loss of a segment. The changes to the congestion window and the transition into slow start are covered in detail.

TCP congestion avoidance sequence diagram


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LTE Downlink Frame Structure

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This article will explain the downlink frame structure. For the beginners, there is always a confusion about the frame structure, the physical channels etc, so to make their job easy, I am writing this article.

To start with, what does the downlink frame structure consists of? The answer is simple, it contains the downlink channels and signals. Refer article LTE Physical Downlink Channels for more details. The LTE frame is nothing but a imaginary grid of time vs frequency , where there are placeholders for different channels and signals, for Eg: the dowlink control channels are always restricted to first 3 symbols or less, of the subframe. The frame structure changes depending on the cyclic prefix type, bandwidth and duplexing modes.

Currently let us focus on a 10MHz, FDD, Normal CP type downlink frame structure, with following configuration,

  • Subframe number –…
  • Duplexing mode – FDD
  • System bandwidth – 10Mhz
  • Number…

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