1. 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:
Research Interests and Projects: URL:
Instructor: Professor Xi Zhang
Office: WERC 331
ECEN 619, Internet Protocols & Modeling
Prof. Xi Zhang

2. TCP Closed-loop flow control and “Self-Clocking” Principle-1
ECEN 619, Internet Protocols & Modeling
Prof. Xi Zhang

3. 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 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

4. 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

5. 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

6. 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

7. TCP-tahoe Protocol ECEN 619, Internet Protocols & Modeling
Prof. Xi Zhang

8. TCP-reno Protocol ECEN 619, Internet Protocols & Modeling
Prof. Xi Zhang

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ECEN 619, Internet Protocols & Modeling
Prof. Xi Zhang

20. 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 = m*T+B+1
ECEN 619, Internet Protocols & Modeling
Prof. Xi Zhang