The TTL field was originally designed to hold a time stamp, which was decremented by each visited router. The datagram was ( ) when the value became zero. However, for this scheme, all the machines must have synchronized clocks and must know how long it takes for a datagram to go from one machine to another. Today, this field is used mostly to control the ( ) number of hops (routers) visited by the datagram. When a source host sends the datagram, it ( ) a number in this field. Each router that processes the datagram decrements this number by 1. If this value, after being decremented, is zero, the router discards the datagram.This field is needed because routing tables in the Internet can become corrupted.A datagram may travel between two or more routers for a long time without ever getting depvered to the ( ).This field pmits the ( ) of a datagram.
A.received
B.discarded
C.rejected
D.transferred
問題2選項
A.maximum
B.minimum
C.exact
D.certain
問題3選項
A.controls
B.transmits
C.stores
D.receives
問題4選項
A.switch
B.router
C.source host
D.destination host
問題5選項
A.pfetime
B.moving time
C.receiving time
D.transmitting time