====== 8. Transport Model ======

===== 8.1 Purpose =====

This document defines how MTRP interacts with underlying transports.

===== 8.2 Transport Abstraction =====

MTRP is transport-agnostic at the routing layer.

A registered transport is represented as a path. Each path provides the routing layer with the information necessary to send, receive, and characterize traffic over that transport.

===== 8.3 Path Properties =====

A path SHOULD provide:

  * transport instance binding
  * transport mode
  * maximum frame length
  * maximum payload length
  * path metric
  * transport state

===== 8.4 Multiple Paths =====

A node MAY register multiple paths simultaneously.

The routing layer MAY use those paths independently or comparatively during send-time route resolution.

===== 8.5 Transport Modes =====

Transport modes allow the routing layer to distinguish between different operational capabilities.

Examples include:

  * full-capability operation
  * constrained operation
  * inactive or unavailable operation

A node role and a transport role are distinct concepts.

A node MAY participate as a fully capable router while one of its registered transports operates under constrained rules.

===== 8.6 Metric Contribution =====

Each path contributes a local metric.

When routes are relayed, the effective metric of the learned route SHOULD reflect additive hop cost.

===== 8.7 Transport Diversity =====

The transport abstraction is intended to support heterogeneous links.

Examples of intended or existing transport families include:

  * ESP-NOW v1
  * ESP-NOW v2
  * NRF24-class links
  * serial transports
  * future Wi-Fi or Bluetooth-capable transports

===== 8.8 Current Boundaries =====

The transport model does not yet fully define:

  * cross-transport fragmentation behavior
  * transport-specific reliability semantics
  * transport-aware end-to-end acknowledgment behavior
  * formal bridge-policy coordination