ECEN 619-600

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ECEN 619-600 Internet Protocols and Modeling

• Course Materials Papers, Reference Texts
  Bertsekas/Gallager, Stuber, Stallings, etc
• Lecture notes and Paper Reading Lists available
  on-line TBA
• Class Website http//ece.tamu.edu/xizhang/ECEN61
  9/start.php
• Research Interests and Projects
  URLhttp//ece.tamu.edu/xizhang
• Instructor Professor Xi Zhang
• E-mail xizhang_at_ece.tamu.edu
• Office WERC 331

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TCP Closed-loop flow control and Self-Clocking
Principle-1
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TCP Closed-loop flow control and Self-Clocking
Principle-2

• Sender sends packets back-to-back to receiver
• The vertical line is bandwidth
• The horizontal line is time
• Each of shaded box is a packet
• Bandwidth Time Bits, and so the area of each
  box is the packet size.
• The number of bits doesnt change as a packet
  goes through the network so a packet squeezed
  into the smaller long-haul bandwidth must spread
  out in time.

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TCP Closed-loop flow control and Self-Clocking
Principle-3

• The time Pb represents the minimum packet spacing
  on the slowest link in the path (the bottleneck).
• As the packets leave the bottleneck for the
  destination net, nothing changes the inter packet
  interval so on the receivers net packet spacing
  Pr Pb.
• If the receiver processing time is the same for
  all packets, the spacing between ACKs on the
  receivers net Ar Pr Pb.

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TCP Closed-loop flow control and Self-Clocking
Principle

• If the time slot Pb was big enough for a packet,
  its big enough for an ACK so the ACK spacing is
  preserved along the return path. Thus the ACK
  spacing on the senders net As Pb.
• So, if packets after the first burst are sent
  only in response to an ACK, the senders packet
  spacing will be exactly match the packet time on
  the slowest link in the path gt Self-Clocking
  is achieved.

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Two versions of TCP Protocols

• TCP-tahoe (Jacobson, 1988)
• Time-out based protocol - use timeout to detect
  packet loss and congestions
• TCP-reno (Jacobson, 1990)
• Triple-ACK and time-out based - Use
  triple-duplicate ACK to same sequence number and
  timeouts to detect packet loss and congestions
• Use fast retransmissions and fast recovery
• Skip Slow Start phase

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TCP-tahoe Protocol
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TCP-reno Protocol
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TCP protocol control variable

• Bandwidth m in packets/sec,
• Service time 1/m
• Round Trip Time (RTT) T sec
• Buffer size B in packets
• Path pipeline capacity
• Wpipe mTB1