490 study exam 3

Stop-and-wait: channel utilization. Suppose a packet is 10K bits long, the channel transmission rate connecting a sender and receiver is 10 Mbps, and the round-trip propagation delay is 10 ms. What is the maximum channel utilization of a stop-and-wait protocol for this channel?

0.1

UDP header fields

1. Internet checksum 2. Source port number 3. Destination port number 4. Length (of UDP header plus payload)

Transport layer services using TCP. Check all of the services below that are provided by the TCP protocol.

1. Reliable data delivery. 2. In-order data delivery 3. A congestion control service 4.A flow-control service 5.A byte stream abstraction

Transport-layer demultiplexing. 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.

Transport-layer multiplexing. 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.

Internet checksum and UDP. 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

Location of transport-layer functionality. Where is transport-layer functionality primarily implemented?

Transport layer functions are implemented primarily at the hosts at the "edge" of the network.

Does UDP preserve application-layer message boundaries?

True

True or False: It is possible for two TCP segments with source port 80 to be sent by the sending host to different clients.

True

True or False: It is possible for two UDP segments to be sent from the same socket with source port 5723 at a server to two different clients.

True

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

Transport-layer functionality. True or False: The transport layer provides for host-to-host delivery service?

true

Packet buffering in Go-Back-N. (Discarding)

1. The sender will resend that packet in any case. 2. The implementation at the receiver is simpler.

UDP segment length field. 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.

Packet buffering in Go-Back-N (Not Discarding)

Even though that packet will be retransmitted, its next retransmission could be corrupted, so don't discard a perfectly well-received packet, silly!

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.

False

Network-layer functionality. The transport layer sits on top of the network layer, and provides its services using the services provided to it by the network layer. Thus it's important that we know what is meant by the network layer's "best effort" delivery service. True or False:

Correct!

True or False: 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

True or False: 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

Channel utilization with pipelining (more). Suppose a packet is 10K bits long, the channel transmission rate connecting a sender and receiver is 10 Mbps, and the round-trip propagation delay is 10 ms. How many packets can the sender transmit before it starts receiving acknowledgments back?

10

Transport-layer services using UDP. Check all of the services below that are provided by the UDP protocol.

A message abstraction, that preserves boundaries between message data sent in different socket send calls at the sender.

Channel utilization with pipelining. Suppose a packet is 10K bits long, the channel transmission rate connecting a sender and receiver is 10 Mbps, and the round-trip propagation delay is 10 ms. What is the channel utilization of a pipelined protocol with an arbitrarily high level of pipelining for this channel?

1.0

Cumulative ACK. 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.