My Little White Lie About Acknowledgments

My Little White Lie About Acknowledgments

Okay, let me confess something to you: TCP error recovery and acknowledgements do not work exactly like I showed in Figures 9-7 and 9-8. I purposefully simplified the earlier descriptions to get through some of the detail. Now that you've read most of this chapter about TCP, let me clear something up about TCP error recovery.

note I could've placed the upcoming details a little earlier in this chapter, but experience from teaching these concepts tells me that it's good to get a little of the concept, and then the rest, so here it goes!

The TCP sequence number and acknowledgement number fields do not number the segments; they identify the first byte in the data portion of the segment. For instance, if a PC sent a segment, and each segment had just 1 byte in it, then sequence numbers and acknowledgements would work just like you read about earlier in this chapter. However, in the example shown in Figure 9-8, all the segments have 1000 bytes in them. So, Figure 9-9 shows the correct sequence and acknowledgement fields.