Networking Flow Control

General Idea

• Don’t send more packets than receiver can process
• Receiver gives sender feedback

Stop and Wait

• A FSM
• At most one packet inflight at any time
• Sender sends one packet
• Receiver sends acknowledgment packet when it receives data
• On receiving acknowledgment, sender sends new data
• On timeout, sender resends current data
• Have trouble when ACK Delay, need to use 1-bit counter to detect duplicates

Sliding Window Algorithm

• Idea: allow multiple packets, referred to as the window, to be sent without waiting for an acknowledgment (ACK) for each packet.
• TCP flow control and the sliding window - IBM Documentation
• Used in TCP
• Types
  • Stop-and-wait: The simplest sliding window protocol, where the sender sends one packet and waits for the receiver’s acknowledgment before sending the next packet.
  • Go-Back-N: The sender can send multiple packets without waiting for acknowledgments, but has to retransmit all packets from the last unacknowledged one if an error occurs.
  • Selective Repeat: The sender can send multiple packets without waiting for acknowledgments, but only has to retransmit the packets that were lost or corrupted.
  • Sliding-window Network Coding: A variation of Network Coding that improves the throughput of TCP on wireless networks by encoding packets at intermediate nodes and decoding them at the destination.