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20
Chapter 1
Internetworking
machine waits for an acknowledgment for each data segment it transmits
before transmitting another. If you've configured a window size of 3, it's
allowed to transmit three data segments before an acknowledgment is
received. In our simplified example, both the sending and receiving machines
are workstations. Reality is rarely that simple, and most often acknowledg-
ments and packets will commingle as they travel over the network and pass
through routers. Routing definitely complicates things, but no worries,
you'll learn about applied routing in Chapter 5.
F I G U R E 1 . 7
Windowing
If a TCP session is set up with a window size of 2 bytes, and during the transfer
stage of the session the window size changes from 2 bytes to 3 bytes, the
sending host must then transmit 3 bytes before waiting for an acknowledg-
ment instead of the 2 bytes originally set up in the virtual circuit.
Acknowledgments
Reliable data delivery ensures the integrity of a stream of data sent from one
machine to the other through a fully functional data link. It guarantees that
the data won't be duplicated or lost. This is achieved through something
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