Serving applications - Multiple Choices Questions - [CNP3] Computer Networking : Principles, Protocols and Practice

Pregunta 1: The transport services

The services play an important role in computer networks since they define what the user can really expect. Selection all the correct affirmations about the connectionless network service ?

The connectionless network service may deliver the same SDU several times to a given destination.

The connectionless network service can transfer SDUs of limited size

The connectionless network service will never deliver twice the same SDU to a given destination.

The connectionless network service may deliver corrupted SDUs at their destination

The connectionless network service may never deliver some SDUs to their destination.

The connectionless network service can only transfer SDUs of fixed size.

Pregunta 2: The connection-oriented service: user interactions

The connection-oriented service is perhaps the most widely used transport service. The interactions between the user of the service and the underlying protocol can be represented as the exchange of various primitives. Considering the interactions between a user of the connection-oriented transport service and its provider, which of the following affirmations are correct? Select all the correct ones.

To confirm the establishment of a connection, a user responds to a Connect.request primitive by issuing a Connect.response primitive.

A user that has accepted a connection can issue a Data.request immediately after having issued the Connect.response primitive.

A Connect.request primitive is issued by the user to request the establishment of a connection.

A Connect.request primitive issued by a user can be followed by a Disconnect.indication issued by the service provider.

A service provider may issue a Disconnect.indication primitive on an established connection at any time.

A user that has received a Connect.indication primitive can immediately issue Data.request primitives to send data over the connection.

A user that has initiated a connection cannot issue a Data.request before having received a Connect.confirm primitive.

To refuse the establishment of a connection, a user responds to a Connect.indication primitive with a Disconnect.request primitive.

The service provider issues a Connect.indication primitive to indicate that it has received a connection establishment attempt.

A user that has initiated a connection can issue a Data.request after having issued the Connect.request primitive.

Pregunta 3: The connection-oriented transport service

Consider the connection-oriented transport service. Among the following affirmations about this service, select the ones that are correct.

A transport service provider may issue a Data.indication primitive to a user after having received a graceful Disconnect.request from this user.

A transport service provider may itself issue a Disconnect.indication to gracefully terminate a connection.

When a user issues a graceful Disconnect.request, only one direction of transfer is closed.

An abrupt connection release may cause some SDUs to be discarded.

A user may issue a Data.request after having issued a graceful Disconnect.request.

A user may issue a Data.request after having received a graceful Disconnect.indication.

With a message-mode service, each Data.request issued by one user will lead to a Data.indication at the other end.

A transport service provider may issue a Disconnect.indication at any time to terminate a connection.

Pregunta 4: The network layer

Which of the following affirmations correspond to the behaviour of the network layer ? Select all the correct ones.

The network layer always deliver packets in sequence.

The network layer may deliver the same packet several times to a given destination.

The network layer may loose packets.

The network layer may modify the content of packets.

Pregunta 5: Connectionless transport

Which of the following mechanisms are likely to be used inside a protocol that provides the unreliable connectionless transport service running on top of an unreliable connectionless network layer? Select all the applicable mechanisms.

A connection establishment mechanism.

Go-back-n.

A checksum to detect transmission errors.

A CRC to detect transmission errors.

Port numbers to identify the communicating applications.

A retransmission timer to retransmit lost data.

Pregunta 6: The three-way handshake

The three-way handshake allows successfully negotiating the establishment of a transport connection. Among the following time-sequence diagrams, which is the one that corresponds to a valid three-way handshake ?

Pregunta 7: The three-way handshake: possible scenarios

The three-way handshake allows successfully negotiating the establishment of a transport connection. Consider a transport connection that begins which the exchange of two segments as shown in the figure below.

Consider what happens after the exchange of these two segments. Only one of the affirmations below is correct. Which one ?

If Host B does not receive CA(seq=12345,ack=56789) after some time, it will retransmit CA(seq=56789,ack=12345).

If Host A receives again CA(seq=56789,ack=12345), it will discard the duplicate segment.

If Host B receives again CR(seq=12345), it will discard the duplicate segment.

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