COT 4600 Operating Systems Fall 2009. Dan C. Marinescu Office: HEC 439 B Office hours: Tu-Th 3:00-4:00 PM. Lecture 27. Schedule Tuesday November 24 - Project phase 4 and HW 6 are due Tuesday December 1st -Research projects instead of final exam presentation
COT 4600 Operating Systems Fall 2009
Dan C. Marinescu
Office: HEC 439 B
Office hours: Tu-Th 3:00-4:00 PM
Tuesday November 24 - Project phase 4 and HW 6 are due
Tuesday December 1st -Research projects instead of final exam presentation
Thursday December 3rd - Class review
More on Scheduling
Network properties - (Chapter 7) - available online from the publisher of the textbook
Data Link Layer
Transport protocols; end-to-end problems
level, but the situation is very different.
ESTABLISHED FIN_WAIT_1FIN_WAIT_2 TIME_WAITCLOSED
Reason: the local side of the connection sent an ACK segment in response to a FIN segment but does not know if the ACK segment reached the other side. The other side may have retransmitted the FIN that might arrive late and be acted upon by a new reincarnation of the connection.
NextByteExpectedLastByteRcvd + 1
LastByteSent - LastByteAckedAdvertisedWindow
EffectiveWindow = AdvertisedWindow –
(LastByteSent - LastByteAcked)
LastByteWritten - LastByteAckedMaxSendBuffer
(LastByteWritten - LastByteAcked) + y > MaxSendBuffer
Time Until Wrap Around
Delay x Bandwidth Product
Diff = SampleRTT - EstimatedRTT
EstimatedRTT = EstimatedRTT + (dx)
Deviation = Deviation + d(|Diff|- Deviation)
Datagram (no state) | Virtual Circuit (hard state) |Flows (soft state)
Flow à a sequence of packets between a source/destination pair following the same route through the network. Established explicitly or implicitly.
Soft state à cannot explicitly be created and removed by signaling
MaxWin = MIN(CongestionWindow, AdvertisedWindow)
EffWin = MaxWin - (LastByteSent - LastByteAcked)
Additive Increase/Multiplicative Decrease
has in transit every RTT.
(increment by 1 packet for each ACK)
in one blast.
Linear growth till about 0.4 sec. Then packets get lost and the window ramps up. A timeout occurs at 2 sec. Then the window size becomes about half of what it was before 17 kB versus 34, and increases linearly towards that value…..
Why packets get lost: assume that the network would only support 20 packets from this source. When they get to the destination and ACKs are sent, the window size is doubled to 40. Obviously the other half is lost.