question into routing in ccnp r&s to mr/keith bogart











hello my sir

 


iam into lecture 22 : tcp overview


 


i cannot understand your explain about window size & maximum segment size 

















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answer from mr/keith bogart



Just like Layer-2 protocols (such as Ethernet) have a maximum size…TCP has a maximum size it must adhere to when creating initial TCP segments.  This maximum size is called the TCP MSS (Maximum Segment Size).  This is something that one TCP system tells another TCP system when the initial TCP 3-way handshake is taking place.  This ensures that one TCP system won’t create a segment that is larger than what the receiver can receive.
 
Imagine if your laptop has multiple, simultaneous TCP sessions running.  Maybe you have five browser tabs open, your email client, and a file transfer window running that is downloading a large file.  Your memory buffers that are receiving all of these TCP segments from multiple sources might start to get overwhelmed and you might not have enough memory to process every TCP segment that is being sent to you.  The TCP sliding window is a mechanism of TCP that allows your laptop to signal to a TCP sender (maybe the application that is downloading a large, TCP file to you) that it should slow down.  The sliding window provides a way for you to tell the sending, “I can only receive 5-TCP segments at-a-time right now…and then you’ll have to pause while I acknowledge them”.  If you have plenty of memory and only a few TCP sessions running on your laptop, your current sliding window might indicate that you can receive up to 10-segments from any sender and then you’ll acknowledge them.  If you start running low on memory, your laptop can lower that sliding window to something less (maybe 3-segments).
 
In this way, the TCP sliding window ensures that no single TCP session will overwhelm your memory buffers forcing data to be discarded.
 
Hope that helps!
Keith
 







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