Ch 3 Test

Which of the following best completes this sentence: "In the absence of loss, TCP slow start increases the sending rate ... "

" ... faster than AIMD. In fact, slowstart increases the sending rate exponentially fast per RTT."

Assuming that the congestion window size,cwnd, has not yet reached Wmax, TCP CUBIC will ... (check all that apply)

-... always have a window size, cwnd, and hence a sending rate, higher than that of AIMD (assuming a given window size, Wmax, at which loss would occur). -... increase its sending rate faster than AIMD when cwnd is far away from Wmax, but increase slower than AIMD when cwnd is closer to Wmax

all of the services below that are provided by the TCP protocol

-A congestion control service to ensure that multiple senders do not overload network links -A flow-control service that ensures that a sender will not send at such a high rate so as to overflow receiving host buffers -In-order data delivery -Reliable data delivery -A byte stream abstraction, that does not preserve boundaries between message data sent in different socket send calls at the sender

What are advantages of implementing transport-layer functionality in QUIC at the application layer? Select all that apply.

-QUIC can establish all connection parameters (security, reliability, flow and congestion control)in just one handshake rather than separately in two. -As an application-layer protocol, QUIC can be updated/modified at "app frequency" rather than at the frequency of operating system updates.

UDP header fields. Which of the fields below are in a UDP segment header? [Hint: note the use of the word "header" in this question statement.]

-Source port number -Internet Checksum -Destination Port Number -Length (of UDP header plus payload)

What are advantages of the streams concept in QUIC? Select all that apply.

-Streams allow concurrent retrieval of web objects, while avoiding Head of the Line (HOL) blocking -Since each stream has its own error control, if one stream experiences an error (e.g., lost or damaged segment), the other streams are unaffected

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 implementation at the receiver is simpler -The sender will resend that packet in any case

Which of the following statements about pipelining are true? One or more statements may be true.

-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 -A pipelined sender can have transmitted multiple packets for which the sender has yet to receive an ACK from the receiver

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?

.1

Consider the transport-layer flows interacting at a congested link. In the face of such congestion, what happens at this link to a transport-layer flow that does not cut back on its sending rate?

Nothing different from the other flows crossing the congested link.

A general purpose error message used during connection set up or tear down to let the other side know that an error has occurred, and that the referenced connection should be shut down.

RESET Message

This field contains the number of available bytes in the TCP receiver's buffer.

Receiver advertised window

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

Allows the receiver to eventually receive a packet that was corrupted or lost in an earlier transmission.

Retransmission

A message from client to server initiating a connection request.

SYN message

A message from server to client ACKing receipt of a SYN message and indicating the willingness of the server to establish a TCP connection with the client.

SYNAK message

Allows for duplicate detection at receiver.

Sequence Numbers

This field contains the index in the sender-to-receiver byte stream of the first byte of that data in the payload carried in this segment.

Sequence number

This field contains the port number associated with the sending socket for this TCP segment.

Source port number

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

The currently measured throughput is greater than cwnd/RTTmin

This should never happen.

Where is transport-layer functionality primarily implemented?

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

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

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

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

True or False: with TCP's flow control mechanism, where the receiver tells the sender how much free buffer space it has (and the sender always limits the amount of outstanding, unACKed, in-flight data to less than this amount), it is not possible for the sender to send more data than the receiver has room to buffer.

True

The currently measured throughput is much less that than cwnd/RTTmin

decrease the sending rate

The sender measures RTTs and uses the current RTT measurement to infer the level of congestion.

delay-based

The sender infers segment loss from the absence of an ACK from the receiver.

end-end

The currently measured throughput is equal to or a bit less than than cwnd/RTTmin

increase the sending rate

Bits are set at a congested router in a sender-to-receiver datagram, and bits are in the returned to the sender in a receiver-to sender ACK, to indicate congestion to the sender.

networked-assisted

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

How is the sending rate typically regulated in a TCP implementation?

By keeping a window of size cwnd over the sequence number space, and making sure that no more than cwnd bytes of data are outstanding (i.e, unACKnowledged). The size of cwnd is regulated by AIMD.

This field contains the Internet checksum of the TCP segment and selected fields in the IP datagram header.

Checksum

Used by sender or receiver to detect bits flipped during a packet's transmission.

Checksum

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! The network layer's best effort service doesn't really provide much service at all, does it?

This field contains application data that was written into a socket by the sender of this TCP segment.

Data (or payload)

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!

A message indicating that the sending side is initiating the protocol to terminate a connection.

FIN message

A message sent in response to a request to terminate a connection, ACKing that the side receiving this message is also willing to terminate the connection

FINAK message

Consider TCP use of an exponentially weighted moving average (EWMA) to compute the nth value of the estimated RTT:EstimatedRTTn = (1- a)*EstimatedRTTn-1 + a*SampleRTTnTrue or False: with this EWMA algorithm the value of EstimatedRTTn has no dependence on the earlier sample, SampleRTTn-1

False

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

False

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

This field contains the number of bytes in the TCP header.

Header length field

Lets the sender know that a packet was NOT received correctly at the receiver.

NAK

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

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

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

Lets the sender know that a packet was received correctly at the receiver.

ACK

If set, this segment cumulatively ACKs all data bytes up to, but not including, the byte index in the ACK value field of this segment.

ACK bit

This field contains the index in the byte stream of the next in-order byte expected at the receiver

ACK number field

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