The telephone system is a circuit-switched network. For much of the history of the system, when you placed (26)* U. I$ ~7 c( C* G
a call, you were renting a pair of copper wires that ran continuously from your telephone to the other party’s phone. You had excluding use of those wires during the (27)0 y- V3 z* P2 P
call; when you hung up, they were rented to someone else. Today the transaction is more complicated. ( your call may well possess a fiber-optic cable or a satellite with hundreds of other calls), but more conceptually the system (28)$ v2 l0 }/ z, w& S+ W
still works the same way. When you dial the phone, you get a private connection of one other party. This is an alternative network architecture called (29)
9 d' [ A7 D: [7 X9 N. P7 Y" K packet switching, in which all stations are always connected to the network, but they receive only the messages addressed to them. It is as if your telephone was always tuned in to (30)& w: {' d4 b1 m6 p& p
thousands of conversations going on the wire, but you (31)
" P+ j: r3 Q- t6 b4 X heard only the occasional word intended to you. Most (32)
5 j9 N' S: N( v( p, J; x8 E5 n computer networks employ packet switching, because it is more efficient than circuit switching when traffic is heavy. It seems reasonable the existing packet-switched (33)/ D8 J# J2 c8 T7 D3 ~. X8 K8 k) o
network will grow, and new one may be created; they could (34)# P$ W: T: o X3 Z
well absorb traffic that would otherwise go to the telephone system and thereby reduce the need for telephone numbers. (35)
; D& G3 t/ ?: H! g* o 答案:
! O- U! c* d7 E6 i; ` 26.much改为most
8 |. W5 j5 | ]; B6 T: H: o 27.excluding改为exclusive# \7 m5 q6 F- ~0 }# {" y
28.more
1 ?$ `/ T' X+ U# ~. s+ c: g 29.This改为There
) `* b0 }3 p/ T* a& v' [ 30.was改为were
+ Z+ S# Q" l7 S1 i 31.going后加by, K9 F, q6 H) L& x' K) t
32.to改为for/ T0 @) N# Y# v. H! Y$ a
33.reasonable后加that0 D, g/ b$ u ]/ E
34.one改为ones5 k6 Y* _- A. t" }) o: |# K9 T3 n
35.need改为demand |
发表于 2012-8-14 11:54:21
