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Internet Characteristics

The Internet simply delivers IP packets. However, for various reasons, things can go wrong. For example, if a packet gets corrupted due to (for example) electrical interference then it won't be possible to deliver it. A more common situation is where a router is receiving packets faster than they can be processed, and runs out of memory buffer space to hold the incoming packets. In these situations, packets can be dropped -- discarded by a router. In most cases this happens silently -- all that's observed externally is that the packet never arrives.
 
Two other disasters can befall delivery: a sequence of packets may not arrive in the same order in which they were sent, and a packet can even become duplicated during delivery -- that is, the same packet is received twice.
 
Big Idea #4
these are basic design characteristics of IP -- Internet packet delivery is said to be unreliable.

 
However, note one important fact -- in this context, unreliable doesn't mean "no good", or "poor quality". It simply says that the delivery system may fail to deliver a packet correctly. In fact, most packets do get delivered correctly. This is because the second design concept for the Internet is best effort -- under normal operation, it works. Sections of the network should only exhibit unreliability under abnormally heavy loads.
 
A final design concept, that of connectionless IP packet delivery, will be discussed later.
 
Lecture 2: Internet Overview Copyright © 2005 P.Scott, La Trobe University Bendigo.


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