Transport Layer Services and Protocols
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Questions and Answers

What is the primary purpose of port scanning?

  • To find vulnerabilities and identify running network applications (correct)
  • To improve network speed
  • To establish TCP connections
  • To monitor network traffic

UDP provides reliable transmission through connection establishment.

False (B)

Which port number is primarily used for HTTP traffic on web servers?

80

The most used port scanner that is free and open source is called _____?

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

Match the following transport protocols with their characteristics:

<p>TCP = Connection-oriented with handshaking UDP = Connectionless without handshaking HTTP = Application layer protocol that runs over TCP DNS = Application layer protocol that typically uses UDP</p> Signup and view all the answers

What does TCP do each time it retransmits a segment?

<p>Sets the next timeout interval to twice the previous value (C)</p> Signup and view all the answers

A duplicate ACK indicates that a segment has been lost.

<p>True (A)</p> Signup and view all the answers

What mechanism does TCP use to retransmit a segment upon receiving three duplicate ACKs?

<p>Fast retransmit</p> Signup and view all the answers

To avoid overflowing the connection's receive buffer, TCP provides a __________ service.

<p>flow-control</p> Signup and view all the answers

Which of the following protocols does TCP's error recovery mechanism resemble?

<p>A hybrid of Go-Back-N and Selective Repeat (B)</p> Signup and view all the answers

TCP stores out-of-order segments in the receive buffer until they can be processed.

<p>True (A)</p> Signup and view all the answers

Match the following terms with their definitions:

<p>Duplicate ACK = Reacknowledges a segment already acknowledged Fast retransmit = Resends a missing segment before the timer expires Flow control = Prevents sender from overwhelming the receiver Cumulative acknowledgments = Acknowledgments that indicate receipt of all previous segments</p> Signup and view all the answers

What happens when TCP receives bytes that are correct and in sequence?

<p>They are placed in the receive buffer.</p> Signup and view all the answers

What happens when a sender receives ACK3 in a Go-Back-N protocol?

<p>Packets from 0 to 3 are acknowledged. (C)</p> Signup and view all the answers

In Selective Repeat, the sender retransmits all packets starting from the last acknowledged packet.

<p>False (B)</p> Signup and view all the answers

What type of service does TCP provide?

<p>Full-duplex service</p> Signup and view all the answers

In the TCP connection establishment process, the client sends a special segment first, known as the ______.

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

What distinguishes Selective Repeat from Go-Back-N protocol?

<p>It retransmits only the suspected erroneous packets. (A)</p> Signup and view all the answers

TCP connections are considered point-to-point, allowing multicast connections.

<p>False (B)</p> Signup and view all the answers

What happens during the timeout in a Selective Repeat protocol?

<p>Only the missing packet is resent</p> Signup and view all the answers

In a Go-Back-N protocol, acknowledgements are ______.

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

What is required for two application processes to start sending data via TCP?

<p>A handshake process. (B)</p> Signup and view all the answers

What is the main problem with stop-and-wait protocols in networking?

<p>They require acknowledgment for every packet sent. (C)</p> Signup and view all the answers

What does flow control primarily prevent?

<p>Overflow at the receiver (B)</p> Signup and view all the answers

Flow control and congestion control achieve the same goal.

<p>False (B)</p> Signup and view all the answers

Pipelining allows the sender to send multiple packets without waiting for acknowledgments.

<p>True (A)</p> Signup and view all the answers

Name the two basic approaches toward pipelined error recovery.

<p>Go-Back-N and Selective Repeat</p> Signup and view all the answers

What variable does TCP use to enable flow control?

<p>receive window</p> Signup and view all the answers

The default RcvBuffer size in many systems is typically set to _____ bytes.

<p>4096</p> Signup and view all the answers

In Go-Back-N, the sender is allowed to send up to ______ packets before receiving an acknowledgment.

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

Match the following concepts with their definitions:

<p>Go-Back-N = Sender can send multiple packets but must wait for the first unacknowledged packet. Selective Repeat = Receiver acknowledges individually and can reorder packets. Stop-and-Wait = Sender sends a packet and waits for acknowledgment before sending the next. Pipelining = Technique that allows multiple packets to be in transit at the same time.</p> Signup and view all the answers

Match the following elements of TCP flow control:

<p>RcvBuffer = Size of receive buffer set via socket options rwnd = Receiver's advertised free buffer space LastByteRead = Last byte read by the application LastByteRcvd = Last byte arrived from the network</p> Signup and view all the answers

What happens when a packet is lost in the Go-Back-N protocol?

<p>The receiver discards all packets with sequence numbers greater than the lost packet. (C)</p> Signup and view all the answers

How does sender A manage the amount of unacknowledged data?

<p>By limiting it to the receiver’s rwnd value (D)</p> Signup and view all the answers

Host B uses the LastByteRcvd and LastByteRead to manage flow control.

<p>True (A)</p> Signup and view all the answers

In pipelining, the range of sequence numbers must decrease.

<p>False (B)</p> Signup and view all the answers

What is a consequence of using pipelining in networking?

<p>Increased sequence number range and buffering of multiple packets.</p> Signup and view all the answers

What must Host B do to advertise free buffer space?

<p>Include rwnd value in TCP header</p> Signup and view all the answers

The Go-Back-N protocol allows for the sender's window size to be ______.

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

Flow control is achieved only by the _____ end points.

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

What is the role of many operating systems in relation to the RcvBuffer?

<p>They autoadjust RcvBuffer sizes (A)</p> Signup and view all the answers

What is one key aspect of the Selective Repeat protocol?

<p>It allows the receiver to buffer packets and acknowledge them individually. (A)</p> Signup and view all the answers

Flashcards

Doubling the Timeout Interval

TCP's strategy for handling packet loss by progressively doubling the timeout interval for retransmissions.

Fast Retransmit

A technique where the sender retransmits a missing data segment quickly after noticing three duplicate acknowledgements (ACKs) for the same segment.

Go-Back-N (GBN)

A strategy for handling packet loss by retransmitting all data segments within a window.

Selective Repeat (SR)

A strategy for handling packet loss by retransmitting only the missing packet.

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TCP's Hybrid Error Recovery Mechanism

TCP's error recovery mechanism uses a blend of Go-Back-N and Selective Repeat protocols.

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Flow Control

TCP's mechanism to prevent the sender from overwhelming the receiver's buffer by sending too much data at once.

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Receive Buffer

A temporary storage area where TCP receives and stores data packets before the application processes them.

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Duplicate ACK

An acknowledgment (ACK) that confirms receipt of a segment that has already been acknowledged earlier.

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Cumulative Acknowledgements in Go-Back-N

In Go-Back-N, acknowledging a packet (like ACK3) confirms the successful reception of all packets up to that sequence number (0 to 3), even if individual acknowledgements for earlier packets were not directly received.

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Go-Back-N's Redundant Retransmissions

Go-Back-N retransmits all packets starting from the first missing one, even if subsequent packets are received correctly. This can lead to redundant retransmissions, especially when large window sizes and bandwidth-delay products are involved.

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Selective Repeat: Selective Retransmissions

Selective Repeat protocol addresses the unnecessary retransmissions of Go-Back-N by only retransmitting the specific packet(s) suspected to be lost or corrupted.

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Selective Repeat: Individual Acknowledgements

Selective Repeat employs individual acknowledgements for each packet, allowing the receiver to acknowledge specific packets without confirming the receipt of prior ones.

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Selective Repeat: Sender and Receiver Windows (N)

Both the sender and receiver in a Selective Repeat protocol maintain a window of size N. This enables the transmission and reception of N packets concurrently.

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Selective Repeat: Packet Timers

In Selective Repeat, each packet in the sender's window has a timeout mechanism. When a timeout occurs, only the corresponding packet is resent, avoiding unnecessary retransmission of other packets.

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Selective Repeat: Out-of-Order Packet Buffering

Selective Repeat allows the receiver to buffer out-of-order packets, ensuring that data is delivered in the correct sequence even if packets arrive out of order.

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TCP: Connection-Oriented

TCP (Transmission Control Protocol) is a connection-oriented protocol, meaning that a reliable connection must be established between two application processes before data transmission can commence.

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TCP Connection Establishment: State Variables

During the connection establishment process, both sides of the TCP connection initialize various variables, including window sizes and timeout settings, to manage the flow of data.

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TCP: Full-Duplex Service

A TCP connection allows bi-directional data flow, enabling simultaneous data transfer from both parties in the connection.

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TCP Demultiplexing

A TCP segment arrives and the host uses the destination port number to identify the correct application socket to deliver the data.

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Threaded Server

A single process can have multiple sockets, allowing it to handle connections from various clients simultaneously.

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Port Scanning

Port scanning is the process of checking which network services are running on a target host. It can be used by attackers or system admins to identify vulnerabilities or active applications.

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Web Server and TCP

Web servers use port 80 for HTTP communication. They differentiate clients based on their source IP addresses and port numbers.

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Connectionless UDP

UDP, unlike TCP, doesn't require a connection setup before data transfer. This makes it faster but less reliable. DNS is an example of a protocol using UDP.

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Receive Window (rwnd)

The amount of free space available in the receiver's buffer, advertised to the sender by the receiver.

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Receive Buffer Size Adjustment

The process of adjusting the receiver's buffer size to accommodate varying data arrival rates. This can be done manually by setting socket options or automatically by the operating system.

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Unacknowledged Data (In-flight Data)

Data that has been sent by the sender but not yet acknowledged by the receiver. This data is 'in flight' between the sender and receiver.

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Congestion Control

A process that manages the flow of data to avoid overwhelming the network. This involves preventing network congestion by regulating the data transmission rate.

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LastByteRead

The number of the last byte in the data stream that has been read by the application.

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LastByteRcvd

The number of the last byte that has arrived from the network and been placed in the receiver's buffer.

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LastByteRcvd - LastByteRead

The difference between the last byte received (LastByteRcvd) and the last byte read (LastByteRead). This represents the amount of data in the receiver's buffer that is waiting to be processed by the application.

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Sender's Data Limits

The sender limits the amount of unacknowledged data in flight to respect the receiver's window size, preventing buffer overflow.

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Pipelining

A method of data transmission where the sender can send multiple packets without waiting for acknowledgements for each packet, creating a pipeline of packets in transit.

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Reliable Data Transfer Protocol (rdt3.0)

A reliable data transmission protocol that addresses packet loss and corruption by using acknowledgements (ACKs) to confirm packet receipt.

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Sender Window Size

The maximum number of unacknowledged packets that a sender can send before waiting for an acknowledgment.

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Packet Dropping

A situation where a packet is lost or corrupted in transit and the receiver discards all subsequent packets in the sequence.

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Timeout

The sender's action of waiting for a specific amount of time to receive an acknowledgement for a transmitted packet.

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Retransmission Delay

The time it takes for a sender to retransmit packets when a timeout occurs or a packet is lost.

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Pipelined Error Recovery

A protocol that allows the sender to send multiple packets without waiting for acknowledgements, increasing network efficiency.

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Packet Ordering

The process of ensuring that data packets arrive in the correct order at the receiver, even if the sender transmits them out of order.

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Study Notes

Transport Layer Services

  • A transport-layer protocol enables logical communication between application processes on different hosts.
  • Applications use this for message exchange, unaffected by underlying infrastructure details.
  • Transport protocols reside in end systems, not routers.

Transport Layer Segments

  • Transport layer takes application messages, breaks them into smaller segments, and adds headers.
  • These segments are then passed to the network layer.

Relationship Between Transport and Network Layers

  • Transport layer provides logical communication between processes.
  • Network layer provides logical communication between hosts.

Transport Layer Protocols in the Internet

  • UDP (User Datagram Protocol) is unreliable and connectionless.
  • TCP (Transmission Control Protocol) is reliable and connection-oriented.

Multiplexing and Demultiplexing

  • Multiplexing gathers data from different sockets and encapsulates them into segments.
  • Demultiplexing delivers data segments to the appropriate sockets on the destination host.
  • Sockets have unique identifiers, and segments have source and destination port fields for delivery.
  • Well-known port numbers are reserved for specific applications (e.g., HTTP).

Reliable Data Transfer

  • Reliable data transfer ensures data transmission without corruption or loss, and in the correct order.
  • Protocols can include mechanisms like acknowledgments and retransmissions.
  • ARQ (Automatic Repeat reQuest) protocols are used for reliable transfer.

UDP Segment Structure

  • UDP segments have four fields: source port, destination port, length, and checksum.

UDP Checksum

  • Used for error detection during transmission.

TCP Connection-Oriented Transport

  • TCP connection establishment uses a three-way handshake.
  • TCP sockets, identified by four-tuples (source IP, source port, destination IP, destination port).
  • TCP provides flow control to prevent buffer overflow.

TCP Segment Structure

  • TCP segments use sequence numbers and acknowledgment numbers for reliable data transfer.
  • Include source port, destination port, sequence number, acknowledgment number, and header length fields as well as options (variable length).

TCP Retransmission Scenarios

  • Lost ACKs, premature timeouts, etc., can lead to retransmissions.

TCP Connection Management

  • TCP uses a three-way handshake for connection initiation.
  • The process includes SYN, SYN-ACK, and ACK segments.
  • TCP connection closing uses a four-way handshake.

TCP Congestion Control

  • Mechanism to manage network congestion by controlling the sender's transmission rate.
  • Includes slow start, congestion avoidance, and fast recovery strategies.
  • The congestion window size (cwnd) controls the rate of transmission.

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Related Documents

Transport Layer, PDF

Description

This quiz covers the fundamental concepts of transport layer services, including segmentation, multiplexing, and the relationship between transport and network layers. It also explores key transport protocols like TCP and UDP, focusing on their characteristics and functionalities in the Internet. Test your understanding of how these protocols enable communication between applications.

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