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Unformatted text preview: ement packets (if needed), and then puts the packets in the co rrect o rder, passing a perf ect co py o f yo ur transmissio n to the pro gram yo u’re co mmunicating with (an e-mail server, Web server, etc.). This pro gressio n—applicatio n at the so urce to TCP at the so urce (slice up the data being sent), to IP (f o r f o rwarding amo ng ro uters), to TCP at the destinatio n (put the transmissio n back to gether and make sure it’s perf ect), to applicatio n at the destinatio n—takes place in bo th directio ns, starting at the server f o r messages co ming to yo u, and starting o n yo ur co mputer when yo u’re sending messages to ano ther co mputer. UDP: TCP’s Faster, Less Reliable Sibling TCP is a perf ectio nist and that’s what yo u want f o r Web transmissio ns, e-mail, and applicatio n do wnlo ads. But so metimes we’re willing to sacrif ice perf ectio n f o r speed. Yo u’d make this sacrif ice f o r streaming media applicatio ns like Windo ws Media P layer, Real P layer, Internet vo ice chat, and video co nf erencing. Having to wait to make sure each packet is perf ectly sent wo uld o therwise lead to awkward pauses that interrupt real-time listening. It’d be better to just grab the packets as they co me and play them, even if they have mino r erro rs. P ackets are small eno ugh that if o ne packet do esn’t arrive, yo u can igno re it and mo ve o n to the next witho ut to o much quality disruptio n. A pro to co l called UDP (user dat agram prot ocol) do es exactly this, wo rking as a TCP stand-in when yo u’ve go t the need f o r speed, and are willing to sacrif ice quality. If yo u’ve ever watched a Web video o r had a Web-based pho ne call and the quality go t sketchy, it’s pro bably because there were packet pro blems, but UDP kept o n chugging, making the “get it f ast” instead o f “get it perf ect” trade-o f f . VoIP: When Phone Calls Are Just Another Internet Application The increasing speed and reliability o f the Internet means...
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This document was uploaded on 01/31/2014.

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