ISE 316 Midterm 2
Why is the UDP header length field needed?
Because the payload section can be of variable length, and this lets UDP know where the segment ends.
In SR, why does the receiver have to acknowledge packets with sequence numbers that are less than (and to the left of) those in its window, which starts at rcv_base.
Because the sender may not have received an ACK for that packet yet.
What are some reasons for not discarding received-but- out-of-sequence packets at the receiver in GBN? Indicate one or more of the following statements that are correct.
Even though that packet will be retransmitted, its next retransmission could be corrupted, so don't discard a perfectly well-received packet, silly!
When computing the Internet checksum for two numbers, a single flipped bit in each of the two numbers will always result in a changed checksum.
False
What is meant by transport-layer demultiplexing?
Receiving a transport-layer segment from the network layer, extracting the payload (data) and delivering the data to the correct socket.
Which of the fields below are in a UDP segment header?
Source Port, Destination Port, Length, and Checksum fields
What is meant by transport-layer multiplexing?
Taking data from one socket (one of possibly many sockets), encapsulating a data chuck with header information - thereby creating a transport layer segment - and eventually passing this segment to the network layer.
Over what set of bytes is the checksum field in the UDP header computed over?
The entire UDP segment, except the checksum field itself, and the IP sender and receive address fields
What are some reasons for discarding received-but- out-of-sequence packets at the receiver in GBN? Indicate one or more of the following statements that are correct.
The sender will resend that packet in any case. The implementation at the receiver is simpler.
What provides host-to-host delivery services?
Transport layer
Where is transport-layer functionality primarily implemented?
Transport layer functions are implemented primarily at the hosts at the "edge" of the network.
When computing the Internet checksum for two numbers, a single flipped bit (i.e., in just one of the two numbers) will always result in a changed checksum. True or false
True
When multiple TCP clients send TCP segments to the same destination port number at a receiving host, those segments (from different senders) will always be directed to the same socket at the receiving host. True or false
false
When multiple UDP clients send UDP segments to the same destination port number at a receiving host, those segments (from different senders) will always be directed to the same socket at the receiving host. True or False
true
What is meant by a cumulative acknowledgment, ACK(n)?
A cumulative ACK(n) acks all packets with a sequence number up to and including n as being received.
What is provided by the TCP protocol?
A flow-control service that ensures that a sender will not send at such a high rate so as to overflow receiving host buffers. Reliable data delivery. A congestion control service to ensure that multiple senders do not overload network links. In-order data delivery A byte stream abstraction, that does not preserve boundaries between message data sent in different socket send calls at the sender.
What is provided by the UDP protocol?
A message abstraction, that preserves boundaries between message data sent in different socket send calls at the sender.
Which of the following statements about pipelining are true? One or more statements may be true.
A pipelined sender can have transmitted multiple packets for which the sender has yet to receive an ACK from the receiver. With a pipelined sender, there may be transmitted packets "in flight" - propagating through the channel - packets that the sender has sent but that the receiver has not yet received.
