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One of the main responsibilities of ICMP is to report ______. Although technology has produced increasingly reliable transmission media, errors still exist and must be handled. IP is an ______ protocol. This means that error checking and error control are not a concem ofIP JCMP wasdesigned, in part, to compensate for this shortcoming. Howerver, ICMP does not ______ errors, itsimply reports them. Error correction is left to the higher-level protocols. Error messages arealways sent to the original ______ because the only information available in the datagram aboutthe route is the source and destination 1P addresses. ICMP uses the source IP address to send theerror massage to the source of the ______.

A. user
B. destination
C. source
D. Program

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The presentation layer is concerned with the(1) and semantics of the information exchanged between two systems. The processes in two systems are usually exchanginginformation in the form of character(2)numbers, and so on. The information should bechanged to bit (3) before being transmitted. Because different encoding systems, thepresentation layer is responsible for (4)between these different encoding methods. Thepresentation layer at the sender changes the information from its sender-dependent format into acommon format. The presentation layer at the receiving machine changes the common format intoits (5) dependent format. (5)是()

A. receiver
B. user
C. server
D. customer

An internet is a combination of networks connected by (1). When a datagram goes from a source to a (2), it will probably pass many (3) until it reaches the routerattached to the destination network. A router receives a (4)from a network and passes it toanother network. A router is usually attached to several networks. When it receives a packet, towhich network should it pass the packet The decision is based on optimization: Which of theavailable(5) is the optimum pathway (5)是()

A. pathways
B. routers
C. diagrams
D. calls

For(1) service, we need a virtual-circuit subnet. Let us see how that works. The idea behind virtual circuits is to avoid having to choose a new (2) for every packet sent. Instead,when a connection is established, a route from the (3)machine to the destination machine ischosen as part of the connection setup and stored in tables inside the(4)That route is used forall traffic flowing over the connection, exactly the same way that the telephone system works.When the connection is released, the virtual circuit is also terminated. With connection-orientedservice, each packet carries an (5)telling which virtual circuit it belongs to. (5)是()

A. address
B. identifier
C. interface
D. element

Traditional network layer packet forwarding relies on the information provided by network layer (1) protocols, or static routing, to make an independent(2) decisions at each hop within thenetwork. The forwarding (3)is based solely on the destination (4) IP address. All packets for thesame destination follow the same path across the network if no other equal-cost paths exist.Whenever a router has two equal-cost (5)toward a destination, the packets toward the destinationmight take one or both of them, resulting in some degree of load sharing. (4)是()

A. anycast
B. multicast
C. broadcast
D. unicast

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