[e2e] TCP fragmentation and reassembly

[Joe Touch]

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Lloyd Wood wrote:
> On Mon, 5 Dec 2005, Joe Touch wrote:
> 
> 
>>It's useful to keep in mind that TCP is a byte-stream protocol; there
>>are no segment boundaries preserved between application and transport layer:
> 
> 
> (cough) urgent pointer (cough).

You can set the URG; you can know that at most one URG will be inside
each segment, you can't know where TCP will break the data around the
URG pointers. Also, when the URG pointers are overwritten, only the last
one will count. And the sender app doesn't know when an URG is received,
so there's no way to ensure you're not overwriting an URG.

As a result, you can correlate writes to segment size only in the
degenerate case:
	- open a connection
	- write one byte
	- close that connection

Joe
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