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So basically the transport control 
protocol has a responsibility of 

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compensating for the imperfections of the 
IP layer. 

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Data can arrive not out of order, it can 
arrive not at all and so the TCP layer 

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marks the data in a way, and stores the 
data in the source computers until it is 

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acknowledged by the destination 
computers. 

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And so TCP buffers this information, and 
the buffers are kept on the edge, and 

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this allows the internet, to grow in 
wonderful ways.{COUGH} So, this results 

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in a layer, that really provides us what 
seems to be an end to end connection. 

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So we can send data in one end, a stream 
of data, just send it in, just roll it 

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in, and out comes a stream of data. 
It comes out in the same order, it comes 

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out reliably, and we can stop thinking 
about it. 

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And again, the whole goal of this layered 
architecture is so that we can pretend 

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that the complexity inside this box is 
simple. 

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So it's not simple inside. 
But we, the applications, we're going to 

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make use of this transport layer and 
pretend it's simple. 

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00:01:18,672 --> 00:01:22,260
Okay? 
And so we just, I put in H. 

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And a H comes out and I put in an E and 
an E comes out and I put in an L and an L 

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comes out, an O comes out, and it's 
hundreds of thousands of engineers and 

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billions of dollars of research that 
makes it work, but it just is simple. 

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It's been oversimplified. 
So now we've talked about the link layer, 

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the IP layer, and the transport layer. 
And up next, we're going to talk about 

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what we do once we have reliable pipes 
connecting one application to another.