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Unformatted text preview: circuit versus packet switching, along with organiz ational benefits
and limitations of each. TCP/IP: The Internet’s Secret Sauce
OK, we kno w ho w to read a Web address, we kno w that every device co nnected to the Net needs an
IP address, and we kno w that the DNS can lo o k at a Web address and f ind the IP address o f the
machine that yo u want to co mmunicate with. But ho w do es a Web page, an e-mail, o r an iTunes
do wnlo ad actually get f ro m a remo te co mputer to yo ur deskto p? Fo r o ur next part o f the Internet jo urney, we’ll learn abo ut two additio nal pro to co ls: TCP and IP .
These pro to co ls are o f ten written as TCP / IP and pro no unced by reading all f ive letters in a ro w,
“T-C-P -I-P ” (so metimes they’re also ref erred to as the Internet pro to co l suite). TCP and IP are
built into any device that a user wo uld use to co nnect to the Internet—f ro m handhelds to deskto ps
to superco mputers—and to gether TCP / IP make Internet wo rking happen. Figure 1 2. 4 TCP/IP in Act ion In t his ex amp le, a s erver on t he left s ends a Web p age t o t he us er on t he right . The ap p licat ion (t he Web
s erver) p as s es t he cont ent s of t he p age t o TCP (which is built int o t he s erver’ s op erat ing s ys t em). TCP
s lices t he Web p age int o p acket s . Then IP t akes over, forwarding p acket s from rout er t o rout er acros s
t he Int ernet unt il it arrives at t he us er’ s PC. Packet s s omet imes t ake different rout es , and occas ionally
arrive out of order. TCP running on t he receiving s ys t em on t he right checks t hat all p acket s have
arrived, reques t s t hat damaged or los t p acket s be res ent , p ut s t hem in t he right order, and s ends a
p erfect , ex act cop y of t he Web p age t o your brows er. TCP and IP o perate belo w http and the o ther applicatio n transf er pro to co ls mentio ned earlier.
T CP (t ransmission cont rol prot ocol) wo rks its magic at the start and endpo int o f the trip—o n
bo th yo ur co mputer and o n the destinatio n co mputer yo u’re co mmunicating with. Let...
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This document was uploaded on 01/31/2014.
- Winter '14