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Unformatted text preview: that applicatio ns such as Internet
pho ne calls (ref erred to as Vo IP , o r voice over Int ernet prot ocol) are beco ming mo re
reliable. That do esn’t just mean that Skype beco mes a mo re viable alternative f o r co nsumer
landline and mo bile pho ne calls; it’s also go o d news f o r many businesses, go vernments, and
no npro f its. Many large o rganizatio ns maintain two netwo rks—o ne f o r data and ano ther f o r P OTS (plain
o ld telepho ne service). Maintaining two netwo rks is expensive, and while co nventio nal pho ne
calls are usually o f a higher quality than their Internet co unterparts, P OTS equipment is also
inef f icient. Old pho ne systems use a techno lo gy called circuit sw itching. A “circuit” is a
dedicated co nnectio n between two entities. When yo u have a P OTS pho ne call, a circuit is
o pen, dedicating a specif ic amo unt o f capacity between yo u and the party o n the o ther end.
Yo u’re using that “circuit” regardless o f whether yo u’re talking. P ause between wo rds o r put
so meo ne o n ho ld, and the circuit is still in use. Anyo ne who has ever tried to make a pho ne call
at a busy time (say, early mo rning o n Mo ther’s Day o r at midnight o n New Year’s Eve) and
received an “all circuits are busy” reco rding has experienced co ngestio n o n an inef f icient
circuit-switched pho ne netwo rk. But unlike circuit-switched co unterparts, Internet netwo rks are packet-switched netwo rks,
which can be mo re ef f icient. Since we can slice co nversatio ns up into packets, we can squeeze
them into smaller spaces. If there are pauses in a co nversatio n o r so meo ne’s o n ho ld,
applicatio ns do n’t ho ld up the netwo rk. And that creates an o ppo rtunity to use the netwo rk’s
available capacity f o r o ther users. The trade-o f f is o ne that swaps circuit switching’s quality o f
service (Qo S) with packet switching’s ef f iciency and co st savings. Try to have a Vo IP call when
there’s to o much traf f ic...
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- Winter '14