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Appendix A. Code Skeleton

A.1. Overview​

Appendix A provides a code skeleton for NTPv4 implementation in C-like pseudocode. These code fragments demonstrate implementation methods for NTP algorithms and data structures, helping implementers understand the protocol's core logic.

Note: The code skeleton is for illustration purposes only. Actual implementations may require adjustments based on specific platforms and requirements.

A.2. Main Components​

A.2.1. Data Structures​

  • System variables structure
  • Peer/association variables structure
  • Packet header structure
  • Clock filter structure

A.2.2. Core Algorithms​

  • Clock filter (clock_filter): Select most reliable time samples
  • Selection algorithm (clock_select): Identify truechimers and falsetickers
  • Cluster algorithm (cluster): Refine candidates statistically
  • Combine algorithm (combine): Calculate weighted average offset
  • Clock discipline (clock_discipline): Adjust system clock

A.2.3. Protocol Processing​

  • Receive (receive): Process inbound NTP packets
  • Transmit (transmit): Construct and send NTP packets
  • Fast transmit (fast_xmit): Stateless server response
  • Packet (packet): Validate and process packet contents

A.2.4. Time Management​

  • Clock adjust (clock_adjust): Adjust system clock every second
  • Poll process (poll): Manage periodic packet exchange
  • Association management (mobilize/clear): Create and destroy associations

A.3. Implementation Considerations​

Precision: Use 64-bit fixed-point or floating-point arithmetic. Handle timestamp wraparound correctly. Maintain sufficient precision for microsecond-level synchronization.

Performance: Minimize cryptographic operations. Efficient packet processing. Optimized algorithm implementation.

Robustness: Complete error checking. Defense against malicious or misconfigured peers. Graceful degradation.

A.4. Usage Guide​

The code skeleton provides a starting point for implementing NTPv4. Implementers should adjust data types for target platform, add error handling and logging, implement security mechanisms, optimize performance-critical paths, and add configuration interfaces.

A.5. Reference​

Complete code skeleton in RFC 5905 Appendix A. Implementers should carefully read code comments to understand function purposes and parameter requirements.

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