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Unformatted text preview: ’s say a Web
server wants to send yo u a large Web page. The Web server applicatio n hands the Web page it
wants to send to its o wn versio n o f TCP . TCP then slices up the Web page into smaller chunks o f
data called packet s (or dat agrams). The packets are like little envelo pes co ntaining part o f the
entire transmissio n—they’re labeled with a destinatio n address (where it’s go ing) and a so urce
address (where it came f ro m). No w we’ll leave TCP f o r a seco nd, because TCP o n the Web server
then hands tho se packets o f f to the seco nd half o f o ur dynamic duo , IP . It’s the jo b o f IP (Int ernet prot ocol) to ro ute the packets to their f inal destinatio n, and tho se
packets might have to travel o ver several netwo rks to get to where they’re go ing. The relay wo rk is
do ne via special co mputers called rout ers, and these ro uters speak to each o ther and to o ther
co mputers using IP (since ro uters are co nnected to the Internet, they have IP addresses, to o . So me are even named). Every co mputer o n the Internet is co nnected to a ro uter, and all ro uters are
co nnected to at least o ne (and usually mo re than o ne) o ther ro uter, linking up the netwo rks that
make up the Internet. Ro uters do n’t have perf ect, end-to -end inf o rmatio n o n all po ints in the Internet, but they do talk to
each o ther all the time, so a ro uter has a pretty go o d idea o f where to send a packet to get it clo ser
to where it needs to end up. This chatter between the ro uters also keeps the Internet decentralized
and f ault-to lerant. Even if o ne path o ut o f a ro uter go es do wn (a netwo rking cable gets cut, a ro uter
breaks, the po wer to a ro uter go es o ut), as lo ng as there’s ano ther co nnectio n o ut o f that ro uter,
then yo ur packet will get f o rwarded. Netwo rks f ail, so go o d, f ault-to lerant netwo rk design invo lves
having alternate paths into and o ut o f a netwo rk. Once packets are received by the destinatio n co mputer (yo ur co mputer in o ur example), that
machine’s versio n o f TCP kicks in. TCP checks that it has all the packets, makes sure that no packets
were damaged o r co rrupted, requests replac...
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This document was uploaded on 01/31/2014.
- Winter '14