Page 184 - DCAP207_NETWORKS_DCAP406_COMPUTER_NETWORKS

Unit 11: Transport Layer

Notes
Figure 11.9: Window Management in TCP

0-4K
Application Empty
2K write 2K SEQ=0

2K
ACK=2048
Left
Application
3K write
2K SEQ=2048
Full
Sender is
blocked Applications Read 2K
ACK=4096 WIN=0 2K
ACK=4096 WIN=0 Left
Sender may
send up to 2K
1K SEQ=4096 1K 2K

Buffer
Receiver
Sender

The TCP buffer on the receiving side is full and the sending host knows this because the window
size is set to zero. The process reads one byte. TCP forwards a window update of one. The
sending host acknowledges and sends one byte. The buffer becomes full so the receiving host
acknowledges the byte and sets the window size to zero.

Figure 11.10: Silly Window Syndrome

Receiving Host buffer is full

Application reads 1 byte

Space for one more byte

Header Window update segment sent

New byte arrives
Header 1

Receiving Host buffer is full

Byte

TCP Congestion Control

All Internet TCP algorithms are based on time-outs that are mostly caused by congestion due to
network and receiving host capacity. The missing packets due to noise on the transmission lines

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