1. Transmission Control Protocol (TCP) Data Flow
Lesson 14
Transmission Control Protocol (TCP) Data Flow

2. Transmission Control Protocol (TCP) Data Flow
Basic TCP data flow behavior
TCP acknowledgments
TCP send window
TCP receive window
Small segments
Sender-side flow control

3. Basic TCP Data Flow Behavior
Acknowledgments
Sliding send and receive windows
Avoidance of small segments
Sender-side flow control

4. TCP Acknowledgments Delayed acknowledgments
Cumulative for contiguous data
Selective for noncontiguous data

5. TCP Cumulative Acknowledgments
Implied acknowledgment of all bytes from ISN+1 to
Acknowledgment Number-1
. . .
Byte stream
ISN+1
Acknowledgment
Number

6. TCP Selective Acknowledgments
Selective acknowledgment of non-contiguous blocks of received data
Implied acknowledgment of all bytes from ISN+1 to
Acknowledgment Number-1
SACK
block 1
SACK
block 2
ISN+1
Acknowledgment
Number

7. TCP Send Window Window Sent/ACKed Sent/UnACKed Unsent/Inside
Unsent/Outside
ISN+1
Ack-1
SND.NXT
Ack+Window
Ack
SND.NXT -1
Ack+Window-1

8. Sliding the Send Window
Opening
the window
Closing
the window
Sent/ACKed
Sent/unACKed
Unsent/Inside
Unsent/Outside
Window

9. TCP Receive Window Maximum Receive Window Current receive window ISN+1
Rcvd/ACKed/Retr
Rcvd/ACKed/NotRetr
Rcvd/UnACKed
NotRcvd/Inside
NotRcvd/Outside
ISN+1
RCV.USER
Ack-1
RCV.NEXT
Ack+Window
RCV.USER -1
Ack
RCV.NXT-1
Ack+Window-1

10. Sliding the Receive Window
Maximum Receive Window
Shrinking
the window
Closing
the window
Opening
the window
Current receive window
Rcvd/ACKed/Retr
Rcvd/ACKed/NotRetr
Rcvd/unACKed
NotRcv/Inside
NotRecv/Outside

11. Small Segments A TCP segment that is smaller than the MSS
The Nagle algorithm
Small segments are inefficient
TCP can send only a single unacknowledged small segment
Silly window syndrome
A steady pattern of small segments when applications retrieve a single byte at a time

12. Receiver-Side SWS Avoidance
Maximum receive window
Current receive window
Maximum receive window
Current receive window
n bytes
n bytes

13. Sender-Side Flow Control
Sender can overwhelm network using initial advertised receive window
Slow start algorithm
Increases the actual send window for each ACK segment received that acknowledges new data
Congestion avoidance algorithm
Increases the actual send window for each round-trip time

14. Review Basic TCP data flow behavior TCP acknowledgments
TCP send window
TCP receive window
Small segments
Sender-side flow control