Lectures notes for 2010 - KTH
Lectures notes for 2010 - KTH Lectures notes for 2010 - KTH
TCP Performance TCP’s path MTU discovery: • use min(MTU of outgoing interface, MSS announced by other end) • use per-route saved MTU • once an initial segment size is chosen - all packets have don’t fragment bit set • if you get an ICMP “Can’t fragment” message - recompute Path MTU. • periodically check for possibility of using a larger MTU (RFC 1191 recommends 10 minute intervals) Maguire TCP header continued 5: 34 of 77 maguire@kth.se 2010.03.21 Internetworking/Internetteknik
Long Fat Pipes Networks with large bandwidth-delay products are called Long Fat Networks (LFNs) - pronounced “elefants”. TCP running over a LFN is a Long Fat Pipe. • Window Scale option - to avoid 16 bit window size limit • Timestamp option - putting a time stamp in each segment allows better computation of RTT • Protection Against Wrapped Sequence Numbers (PAWS) - with large windows you could have sequence number wrap around and not know which instance of a given sequence number is the correct one; solved by using timestamps (which must simply be monotonic) • T/TCP - TCP extension for Transactions; to avoid the three way handshake on connection setup and shorten the TIME_WAIT state. (for details of T/TCP see Stevens, Vol.3) Maguire TCP header continued 5: 35 of 77 maguire@kth.se 2010.03.21 Internetworking/Internetteknik
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- Page 313 and 314: TCP header continued Reliability is
- Page 315 and 316: time client SYN, seq=x SYN, seq=y,
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- Page 353 and 354: Decrease in total time to produce a
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TCP Per<strong>for</strong>mance<br />
TCP’s path MTU discovery:<br />
• use min(MTU of outgoing interface, MSS announced by other end)<br />
• use per-route saved MTU<br />
• once an initial segment size is chosen - all packets have don’t fragment<br />
bit set<br />
• if you get an ICMP “Can’t fragment” message - recompute Path MTU.<br />
• periodically check <strong>for</strong> possibility of using a larger MTU (RFC 1191<br />
recommends 10 minute intervals)<br />
Maguire TCP header continued 5: 34 of 77<br />
maguire@kth.se <strong>2010</strong>.03.21 Internetworking/Internetteknik
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