Transcript No Slide Title

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/ECEN619/start.php
Research Interests and Projects: URL:http://ece.tamu.edu/~xizhang
Instructor: Professor Xi Zhang
E-mail: [email protected]
Office: WERC 331
ECEN 619, Internet Protocols & Modeling
Prof. Xi Zhang
TCP Closed-loop flow control and “Self-Clocking”
Principle-1
ECEN 619, Internet Protocols & Modeling
Prof. Xi Zhang
TCP Closed-loop flow control and “Self-Clocking”
Principle-2
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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 doesn‘t change as a packet goes
through the network so a packet squeezed into the smaller
long-haul bandwidth must spread out in time.
ECEN 619, Internet Protocols & Modeling
Prof. Xi Zhang
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
receiver’s net packet spacing Pr = Pb.
• If the receiver processing time is the same for all packets,
the spacing between ACKs on the receiver’s net Ar = Pr =
Pb.
ECEN 619, Internet Protocols & Modeling
Prof. Xi Zhang
TCP Closed-loop flow control and “Self-Clocking”
Principle
• If the time slot Pb was big enough for a packet, it’s
big enough for an ACK so the ACK spacing is
preserved along the return path. Thus the ACK
spacing on the sender’s net As= Pb.
• So, if packets after the first burst are sent only in
response to an ACK, the sender’s packet spacing
will be exactly match the packet time on the
slowest link in the path –> “Self-Clocking” is
achieved.
ECEN 619, Internet Protocols & Modeling
Prof. Xi Zhang
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
ECEN 619, Internet Protocols & Modeling
Prof. Xi Zhang
TCP-tahoe Protocol
ECEN 619, Internet Protocols & Modeling
Prof. Xi Zhang
TCP-reno Protocol
ECEN 619, Internet Protocols & Modeling
Prof. Xi Zhang
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Prof. Xi Zhang
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ECEN 619, Internet Protocols & Modeling
Prof. Xi Zhang
TCP protocol control variable
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Bandwidth: m in packets/sec,
Service time: 1/m
Round Trip Time (RTT): T sec
Buffer size: B in packets
Path pipeline capacity:
Wpipe = m*T+B+1
ECEN 619, Internet Protocols & Modeling
Prof. Xi Zhang