3. PDU Definitions

This chapter defines the structure and semantics of the Protocol Data Units (PDUs) used in XSCP. Each PDU is designed to be parsed with minimal overhead, adhering to strict size constraints and a predictable field-based layout.

PDU Categories

XSCP classifies communication into three distinct types:

  1. Request: A message sent from a client to a server requiring a mandatory response.
  2. Response: A mandatory reply to a Request.
  3. Notification: An asynchronous, one-way message that does not require a reply.

Size Constraints (Network Budget)

To ensure compatibility with low-memory devices and maintain high performance, XSCP enforces strict byte limits:

  • Requests & Notifications: Maximum of 512 bytes.
  • Responses: Maximum of 38 bytes (designed for status codes and brief metadata).