Network Protocols & Utilization Concepts
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Questions and Answers

What event triggers a TCP fast retransmit?

  • Triple duplicate ACKs are received. (correct)
  • A timeout occurs.
  • A single duplicate ACK is received.
  • The data packet is acknowledged.

    • Which of the following is a feature of TCP's connection-oriented transport?

  • Flow control (correct)
  • Stateless communication
  • Unreliable data transfer
  • Single traffic flow

    • During the TCP process, what happens when the application processes remove data from the socket buffers?

  • Additional data may be sent without acknowledgment.
  • Network congestion may occur.
  • The data becomes unrecoverable.
  • The flow of data to the buffer may be adjusted. (correct)

    • In the context of reliable data transfer, what is critical for maintaining the integrity of data sent over TCP?

    <p>Implementing flow control measures.</p> Signup and view all the answers

    What role do the ACK packets play in TCP communication?

    <p>They confirm receipt of data.</p> Signup and view all the answers

    What is the formula used to calculate the sender's utilization in a stop-and-wait protocol?

    <p>U = L / (RTT + L / R)</p> Signup and view all the answers

    If the round-trip time (RTT) is 30 ms and the link speed is 1 Gbps, what is the throughput when sending a 1KB packet every 30 ms?

    <p>33 kB/sec</p> Signup and view all the answers

    In pipelined protocols, what must be increased to allow multiple packets to be in-flight?

    <p>Sequence number range</p> Signup and view all the answers

    What effect does three-packet pipelining have on utilization compared to stop-and-wait?

    <p>Increases utilization by a factor of 3</p> Signup and view all the answers

    If the packet length is 8000 bits and the link capacity is 1 Gbps, how long does it take to transmit one packet?

    <p>8 microseconds</p> Signup and view all the answers

    What is the sender's utilization when utilizing RTT = 30 ms and L/R = 0.008?

    <p>0.00027</p> Signup and view all the answers

    Which of the following is NOT a feature of pipelined protocols?

    <p>Increases round-trip time</p> Signup and view all the answers

    Which of the following describes a characteristic of the stop-and-wait protocol?

    <p>Sender waits for an ACK for each packet before sending the next</p> Signup and view all the answers

    What does the acknowledgment number in a TCP segment indicate?

    <p>The sequence number of the next byte expected from the sender</p> Signup and view all the answers

    Which statement accurately describes out-of-order segment handling in TCP?

    <p>TCP implementations may vary in how out-of-order segments are handled</p> Signup and view all the answers

    What is the role of the checksum in a TCP segment?

    <p>To detect errors in the segment</p> Signup and view all the answers

    How does TCP handle a time-out situation?

    <p>It resends the segments that have not been acknowledged</p> Signup and view all the answers

    What does the sequence number in a TCP segment represent?

    <p>The position of the first byte of data in the segment</p> Signup and view all the answers

    In a simple TELNET scenario, what does the sender's segment with Seq=42 and ACK=79 indicate?

    <p>The sender is expecting byte 80 and has sent byte 42</p> Signup and view all the answers

    What does the rwnd field in a TCP segment specify?

    <p>The amount of data that the receiver can accept</p> Signup and view all the answers

    What is the function of the urgent pointer in a TCP segment?

    <p>It points to the end of urgent data within the segment</p> Signup and view all the answers

    What is the fairness goal of TCP when K TCP sessions share the same bottleneck link of bandwidth R?

    <p>Each session should have an average rate of R/K.</p> Signup and view all the answers

    How does TCP achieve fairness among competing sessions during congestion?

    <p>By implementing a multiplicative decrease on throughput and an additive increase.</p> Signup and view all the answers

    What is a common reason multimedia applications prefer using UDP over TCP?

    <p>They do not wish to have their rate throttled by congestion control.</p> Signup and view all the answers

    What mechanism does TCP utilize to address throughput reduction upon experiencing packet loss?

    <p>Decrease the window size by a factor of 2.</p> Signup and view all the answers

    In a scenario with multiple parallel TCP connections, what impact does adding a new application requesting multiple TCP connections have on bandwidth share?

    <p>Each additional connection decreases share for existing connections proportionally.</p> Signup and view all the answers

    What is the primary function of flow control in the transport layer?

    <p>To prevent overwhelming the receiver with too much data.</p> Signup and view all the answers

    What is one of the main principles behind transport layer services?

    <p>Multiplexing and demultiplexing.</p> Signup and view all the answers

    What is one common characteristic of TCP and UDP?

    <p>Both can multiplex multiple connections.</p> Signup and view all the answers

    What is the first state of the client in the TCP 3-way handshake process?

    <p>LISTEN</p> Signup and view all the answers

    What does the ACKnum represent in the TCP 3-way handshake?

    <p>The next expected sequence number</p> Signup and view all the answers

    In which TCP state can a client no longer send data but can still receive data after closing its socket?

    <p>FIN_WAIT_1</p> Signup and view all the answers

    During the TCP closing connection process, what is the appropriate response from the client upon receiving a FIN segment?

    <p>Send an ACK segment</p> Signup and view all the answers

    What condition describes network congestion in TCP terms?

    <p>Too many sources sending too much data too quickly for the network</p> Signup and view all the answers

    What does the FIN bit signify in a TCP segment?

    <p>Connection termination request</p> Signup and view all the answers

    Which state indicates that the server has received the client's SYN segment and is ready to send a SYNACK?

    <p>SYN RCVD</p> Signup and view all the answers

    What happens in the last state during a TCP connection closure for both client and server?

    <p>CLOSED</p> Signup and view all the answers

    Which segment structure elements are essential for reliable data transfer in TCP?

    <p>Sequence number and acknowledgment number</p> Signup and view all the answers

    What is the purpose of the TIMED_WAIT state in TCP?

    <p>To handle potential delayed segments</p> Signup and view all the answers

    Study Notes

    Delay and Utilization

    • An 8000 bit packet takes 8 microseconds to be transmitted over a 10^9 bits/sec link.
    • Sender utilization, the fraction of time a sender is busy sending is calculated as the packet size divided by the sum of round trip time and the time to transmit the packet.
    • With a round trip time of 30 milliseconds and 1KB packets every 30 milliseconds, throughput is 33kB/sec over a 1Gbps link.
    • Network protocols restrict the usage of physical resources.

    Stop-and-Wait Operation

    • The sender waits for an acknowledgment from the receiver before sending the next packet.
    • Sender utilization in Stop-and-Wait is calculated as the packet size divided by the sum of round trip time and the time to transmit the packet, which is identical to the calculation for the initial delay example.

    Pipelined Protocols

    • Pipelined protocols allow multiple packets to be in transit at the same time.
    • To support pipelining, the range of sequence numbers must be increased and buffering must be implemented at both the sender or the receiver.
    • Pipelining increases the utilization of the network, for example 3-packet pipelining increases utilization by a factor of 3.

    TCP Segment Structure

    • TCP uses sequence numbers and acknowledgments to track the flow of data.
    • Sequence numbers indicate the byte stream number of the first byte in a segment's data.
    • Acknowledgments include the sequence number of the next byte expected from the other side and it serves as a cumulative acknowledgment.
    • TCP specifies the window size, which indicates the amount of data the receiver is willing to accept.
    • The receiver handles out-of-order segments by buffering them until the missing segments arrive.

    TCP Round Trip Time and Timeout

    • TCP uses round trip time (RTT) to track the time it takes for a packet to be transmitted and its acknowledgment to be received.

    TCP Fast Retransmit

    • TCP can retransmit a packet quickly if it receives three duplicate acknowledgments indicating that the packet has been lost.
    • When a packet is retransmitted, a timeout is triggered.

    Principles of Congestion Control

    • Congestion occurs when too many sources send too much data too quickly for the network to handle.
    • Congestion control aims to prevent congestion by dynamically adjusting the rate at which data is sent through the network.

    TCP Fairness

    • TCP aims for fairness by ensuring that each TCP connection sharing a bottleneck link receives approximately the same bandwidth.
    • TCP uses additive increase multiplicative decrease (AIMD) to achieve fair bandwidth allocation among competing connections.
    • Additive increase allows the throughput to increase linearly when there is no congestion.
    • Multiplicative decrease reduces the throughput proportionally when congestion is detected.

    TCP Flow Control

    • TCP flow control regulates the rate at which a sender transmits data to the receiver.
    • TCP uses a window mechanism to control the amount of data that can be sent at any time, ensuring the receiver's buffer does not become overwhelmed.

    TCP 3-Way Handshake

    • TCP establishes a connection using a 3-way handshake.
    • The client initiates by sending a SYN (synchronization) packet to the server.
    • The server responds with a SYN-ACK (synchronization-acknowledgment) packet.
    • The client acknowledges the SYN-ACK with an ACK packet, completing the connection establishment.

    TCP Closing a Connection

    • Closing a connection occurs in a 4-way handshake.
    • Both the client and server indicate their intention to close the connection by sending a FIN (finish) packet.
    • The other party acknowledges the FIN with an ACK packet.
    • The closing process concludes when both parties have received the FIN and ACK packets.

    Principles of Congestion Control

    • Congestion occurs when the network is overloaded with data.
    • Congestion control reduces the amount of data in the network to avoid congestion collapse, and maximize throughput.

    TCP Congestion Control

    • TCP uses various mechanisms to control congestion through the network including slow start, congestion avoidance, fast retransmit, and fast recovery.

    Fairness and UDP/TCP

    • UDP applications do not use congestion control and therefore can suffer from high packet loss.
    • Applications using UDP often send at a constant rate, tolerating packet loss for real-time streaming.
    • Applications can open multiple TCP connections in parallel, leading to potential unfairness and bandwidth allocation issues.

    Chapter 3: Summary

    • The transport layer is responsible for providing services on top of the network layer.
    • The transport layer handles multiplexing, demultiplexing, reliable data transfer, flow control, and congestion control.
    • The transport layer is implemented in the Internet by two primary protocols: UDP (User Datagram Protocol) and TCP (Transmission Control Protocol).
    • The transport layer is responsible for transmitting data through the network core, while the application layer handles the applications.

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    Related Documents

    Chapter 3 Transport Layer PDF

    Description

    Explore the fundamentals of network protocols including delay and utilization calculations. Understand how stop-and-wait operations and pipelined protocols affect packet transmission and overall throughput. This quiz covers essential concepts and calculations relevant to networking.

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