Q::26.Error control is needed at the transport layer because of potential error occurring ..............
(A) from transmission line noise
(B) in router
(C) from out of sequence delivery
(D) from packet losses
Answer:
Explanation:
TCP is a reliable transport layer protocol. This means that an application program that delivers a stream of data to TCP relies on TCP to deliver the entire stream to the application program on the other end in order, without error, and without any part lost or duplicated. TCP provides reliability using error control. Error control includes mechanisms for detecting corrupted segments, lost segments, out-of-order segments, and duplicated segments. Error control also includes a mechanism for correcting errors after they are detected. Error detection and correction in TCP is achieved through the use of three simple tools: checksum, acknowledgment, and time-out.
Q::27. Making sure that all the data packets of a message are delivered to the destination is ................ control.
(A) Error (B) Loss
(C) Sequence (D) Duplication
Answer: A
Q::28. Which transport class should be used with a perfect network layer?
(A) TP0 and TP2 (B) TP1 and TP3
(C) TP0, TP1, TP3 (D) TP0, TP1, TP2, TP3, TP4
Answer: A
Q::29. Which transport class should be used with residual-error network layer?
(A) TP0, TP2 (B) TP1, TP3
(C) TP1, TP3, TP4 (D) TP0, TP1, TP2, TP3, TP4
Answer: B
Q::30. Virtual circuit is associated with a ..................... service.
(A) Connectionless (B) Error-free
(C) Segmentation (D) Connection-oriented
Answer: D
Explanation:
A virtual-circuit network is a cross between a circuit-switched network and a datagram network. It
has some characteristics of both.
(a)As in a circuit-switched network, there are setup and teardown phases in addition to the data transfer phase.
(b) Resources can be allocated during the setup phase, as in a circuit-switched network,
or on demand, as in a datagram network.
(c) As in a datagram network, data are packetized and each packet carries an address in
the header. However, the address in the header has local jurisdiction (it defines what
should be the next switch and the channel on which the packet is being canied), not
end-to-end jurisdiction.
(d) As in a circuit-switched network, all packets follow the same path established during
the connection.
(e) A virtual-circuit network is normally implemented in the data link layer, while a
circuit-switched network is implemented in the physical layer and a datagram network
in the network layer. But this may change in the future.
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