Chapter 11: Flow Control – can occur at layer 2 (data link) and at layer 4 (transport) You saw the need in the most recent assignment. Data packets can be damaged, but it’s not only data that can be changed. If the sequence number is changed how do you know what packet was damaged? What if the acknowledgment is damaged?
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Chapter 11: Flow Control – can occur at layer 2 (data link) and at layer 4 (transport) You saw the need in the most recent assignment. Data packets.
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Chapter 11: Flow Control – can occur at layer 2 (data link) and at layer 4 (transport)
You saw the need in the most recent assignment. Data packets can be damaged, but it’s not only data
that can be changed. If the sequence number is changed how do you know
what packet was damaged? What if the acknowledgment is damaged?
What if a data packet is lost? What if an acknowledgment is lost? How many data packets can we acknowledge with
one acknowledgment packet? Book does some calculation of bit rates; you can
skip that stuff. We’ll focus on the protocols. Main thing is that the download speed is a function
of not only the raw bit rate, but the flow control protocol used.
Recall the layering of protocols Frame – layer 2 unit of transmission Packet – layer 3 unit of transmission Text uses layer 2 context for flow control, but it
does occur at layer 4 (TCP) as well
2.4
Figure 2.4 An exchange using the OSI model
Byte oriented Frame interpreted as a sequence of bytes Each byte means something Old protocol typical of transferring text files Flags (e.g. 01111110) delimit start and end of
frame
What if flag was part of the data (non-text files)?
Bit oriented More typical of streaming, binary files, graphics,
etc Frame interpreted as a bit stream Start and end of frame marked with a
flag=01111110
Again, what if flag is part of the data? Stuff a bogus 0 after 5 consecutive 1s.
Flow control
Flow control refers to a set of procedures used to restrict the amount of datathat the sender can send before
waiting for acknowledgment.
11.10
Figure 11.5 Taxonomy of protocols discussed in this chapter