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Questions and Answers
Match the following terms with their descriptions in the context of packet transmission:
ACK = Acknowledgment from the receiver NAK = Negative acknowledgment from the receiver Checksum = Data integrity verification method Sequence Number = Unique identifier for each packet
Match the scenarios with the corresponding actions taken by the sender:
If ACK/NAK is corrupted = Sender retransmits the packet If not sure what happened = Sender waits for a response If duplicate packet needs to be sent = Sender adds a sequence number If receiving an ACK = Sender can send the next packet
Match the sender and receiver responsibilities:
Sender = Waits for ACK or NAK from the receiver Receiver = Delivers data to the application layer
Match the terms related to packet transmission mechanisms:
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Match the types of acknowledgements with their purposes:
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Match the reliable data transfer protocols with their characteristics:
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Match the types of errors with their recovery mechanisms:
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Match the terms with their correct explanations in data transfer protocols:
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Match the terms related to TCP with their meanings:
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Match the pipelined protocols with their characteristics:
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Match the roles of sender and receiver in Go-back-N protocol:
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Match the following transport-layer services with their descriptions:
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Match the following TCP concepts with their details:
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Match the following networking topics with their importance level:
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Match the following terms in networking with their definitions:
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Match the following concepts with their transport layer categories:
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Match the following principles of reliable data transfer with their attributes:
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Match the following types of transport with their characteristics:
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Match the following components of connection-oriented transport with their functions:
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Study Notes
Reliable Data Transfer - RDT2.1
- Problem: RDT1.0 assumes a perfect channel. RDT2.0 introduces a channel with bit errors.
- Solution: Checksums detect errors, but a mechanism is needed for the receiver to inform the sender about problems.
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Methods:
- ACK (Acknowledgement): The receiver confirms successful packet reception.
- NAK (Negative Acknowledgement): The receiver indicates a packet error.
- Sender: The sender retransmits a packet if it receives a NAK.
- Receiver: The receiver sends an ACK if the packet is received correctly and a NAK if there’s an error.
RDT2.1 - Sender FSM
- Initial State: The sender starts with a sequence number of 0.
- Event 1: When rdt_send is called, the sender creates a packet with data and a checksum.
- Action 1: The packet is sent using udt_send.
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Event 2: When an ACK or NAK arrives:
- If corrupt, the sender retransmits.
- If it's an ACK for sequence number 0, the sender moves to state 1.
- Event 3: When rdt_send is called again, the sender creates a packet with data and a checksum.
- Action 3: The packet is sent using udt_send and the sender moves to state 1.
RDT2.1 - Receiver FSM
- Initial State: The receiver is expecting a packet with sequence number 0.
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Event 1: When a packet arrives:
- If corrupted or doesn’t have the correct sequence number, send a NAK.
- If the packet is valid and has sequence number 0, extract the data and deliver it. Send an ACK for sequence number 0.
- Event 2: When the receiver receives an ACK for sequence number 0, it moves to the state where it is expecting sequence number 1.
Handling Duplicate Packets
- Solution: The sender adds a sequence number to each packet.
- Receiver: The receiver discards duplicate packets.
RDT2.1 - Discussion
- Sender: Adds a sequence number to packets.
- Receiver: Checks the sequence number to identify duplicate packets.
Pipelined Protocols
- Go-Back-N: Allows multiple unacknowledged packets to be in transit. The receiver only sends cumulative ACKs (acknowledging all packets up to a certain sequence number).
- Selective Repeat: Allows multiple unacknowledged packets to be in transit. The receiver sends an individual ACK for each packet.
Go-Back-N
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Sender:
- Uses a k-bit sequence number in the packet header.
- Maintains a "window" of up to N unacknowledged packets.
- Sends packets in sequence.
- If the timer for the oldest unacknowledged packet expires, retransmit all unacknowledged packets.
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Receiver:
- Only accepts packets in sequence.
- Sends cumulative ACKs.
- Discards out-of-order packets.
Selective Repeat
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Sender:
- Maintains a timer for each unacknowledged packet.
- If the timer expires, retransmit only the corresponding packet.
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Receiver:
- Can buffer out-of-order packets.
- Sends individual ACKs for each packet.
TCP Congestion Control
- Problem: Sending too many packets can overwhelm the network and cause congestion.
- Goal: Optimize the sending rate to avoid congestion.
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Mechanism:
- Congestion Window (cwnd): Limits the amount of data the sender can send at a time.
- Slow Start: Initially starts with a small cwnd and increases it exponentially until a loss event.
- Congestion Avoidance (CA): Increases the cwnd linearly after a loss event.
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Loss Detection:
- Timeout: A packet hasn't been acknowledged within a certain timeframe.
- 3 Duplicate ACKs: Indicates packet loss.
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Reaction to Loss:
- Timeout: cwnd is set to 1.
- 3 Duplicate ACKs: cwnd is cut in half.
- AIMD (Additive Increase Multiplicative Decrease): Progressively probes for available bandwidth and adjusts the cwnd accordingly.
- TCP Reno: A specific implementation of congestion control that uses 3 duplicate ACKs to detect loss.
TCP - Switching from Slow Start to CA
- Condition: When cwnd reaches half its value before the timeout occurred.
- Reason: Indicates that the network can handle a larger amount of data.
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Description
Explore the fundamentals of Reliable Data Transfer (RDT) 2.1, which addresses bit errors in communication channels. This quiz covers the concepts of acknowledgments (ACK) and negative acknowledgments (NAK), detailing how senders and receivers manage packet transmission and error correction. Test your understanding of sender and receiver mechanics in reliable data protocols.