Transport Layer Knowledge Checks

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

TRUE

True or 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

What is meant by transport-layer demultiplexing? A. 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. B. Taking data from multiple sockets, all associated with the same destination IP address, adding destination port numbers to each piece of data, and then concatenating these to form a transport-layer segment, and eventually passing this segment to the network layer. C. Receiving a transport-layer segment from the network layer, extracting the payload, determining the destination IP address for the data, and then passing the segment and the IP address back down to the network layer. D. Receiving a transport-layer segment from the network layer, extracting the payload (data) and delivering the data to the correct socket.

D. Receiving a transport-layer segment from the network layer, extracting the payload (data) and delivering the data to the correct socket.

Compute the Internet checksum value for these two 16-bit words: 11110101 11010011 10110011 01000100

01010110 11100111

Which services below are provided by the TCP protocol. 1. Reliable data delivery. 2. A guarantee on the minimum amount of throughput that will be provided between sender and receiver. 3. A message abstraction, that preserves boundaries between message data sent in different socket send calls at the sender. 4. A congestion control service to ensure that multiple senders do not overload network links. 5. A byte stream abstraction, that does not preserve boundaries between message data sent in different socket send calls at the sender. 6. A flow-control service that ensures that a sender will not send at such a high rate so as to overflow receiving host buffers. 7. In-order data delivery 8. A guarantee on the maximum amount of time needed to deliver data from sender to receiver.

1. Reliable data delivery. 4. A congestion control service 5. A byte stream abstraction 6. A flow-control service 7. In-order data delivery

Compute the Internet checksum value for these two 16-bit words: 01000001 11000100 00100000 00101011

10011110 00010000

Which services below are provided by the UDP protocol. 1. Reliable data delivery. 2. A congestion control service to ensure that multiple senders do not overload network links. 3. A guarantee on the maximum amount of time needed to deliver data from sender to receiver. 4. A message abstraction, that preserves boundaries between message data sent in different socket send calls at the sender. 5. A flow-control service that ensures that a sender will not send at such a high rate so as to overflow receiving host buffers. 6. A guarantee on the minimum amount of throughput that will be provided between sender and receiver. 7. A byte stream abstraction, that does not preserve boundaries between message data sent in different socket send calls at the sender. 8. In-order data delivery

4. A message abstraction

UDP header fields. Which of the fields below are in a UDP segment header? A. Upper layer protocol B. Destination port number C. Sequence number D. Length (of UDP header plus payload) E. Source port number F. Source IP address G. Internet checksum H. Data (payload)

B. Destination port number D. Length (of UDP header plus payload) E. Source port number G. Internet checksum

Over what set of bytes is the checksum field in the UDP header computed over? A. Just the UDP header but not the payload. B. The entire UDP segment, except the checksum field itself, and the IP sender and receive address fields C. The entire UDP segment, except the checksum field itself.

B. The entire UDP segment, except the checksum field itself, and the IP sender and receive address fields

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.

What is meant by transport-layer multiplexing? A. Taking data from multiple sockets, all associated with the same destination IP address, adding destination port numbers to each piece of data, and then concatenating these to form a transport-layer segment, and eventually passing this segment to the network layer. B. Receiving a transport-layer segment from the network layer, extracting the payload (data) and delivering the data to the correct socket. C. 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. D. Receiving a transport-layer segment from the network layer, extracting the payload, determining the destination IP address for the data, and then passing the segment and the IP address back down to the network layer.

C. 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.

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 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

True or False: The network layer's best-effort delivery service means that IP makes its "best effort" to deliver segments between communicating hosts, but it makes no guarantees. In particular, it does not guarantee segment delivery, it does not guarantee orderly delivery of segments, and it does not guarantee the integrity of the data in the segments.

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

True or False: On the sending side, the UDP sender will take each application-layer chunk of data written into a UDP socket and send it in a distinct UDP datagram. And then on the receiving side, UDP will deliver a segment's payload into the appropriate socket, preserving the application-defined message boundary.

TRUE

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

Where is transport-layer functionality primarily implemented? A. Transport layer functions are implemented primarily at the hosts at the "edge" of the network. B. Transport layer functions are implemented primarily at the routers and switches in the network. C. Transport layer functions are implemented primarily at each end of a physical link connecting one host/router/switch to another one host/router/switch.

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