This document defines the high-level structure of an MTRP frame.

An MTRP frame consists of:

• a protocol header
• a payload
• implementation-local metadata used during processing

Only the serialized protocol header and payload are transmitted on the wire as part of the MTRP frame representation.

The protocol header carries routing-visible and protocol-visible information.

Typical header responsibilities include:

• protocol version identification
• flag signaling
• network identification
• source and destination addressing
• previous-hop identification
• message identification
• hop-limit or TTL behavior

The payload carries protocol-specific or application-specific content.

Examples include:

• control messages
• route advertisements
• application data

Local metadata is used by the router during internal processing and route resolution.

Local metadata is not equivalent to the serialized wire header.

Examples of local metadata include:

• ingress path identifier
• ingress path metric
• resolved egress path identifier
• resolved next-hop identifier
• local delivery behavior flags

On constrained transports, MTRP MAY use a compact on-wire representation.

Compact operation SHOULD preserve core routing semantics while reducing header cost on limited transports.

Compact operation does not remove the requirement for the receiver to correctly determine how the frame is to be interpreted.

A frame MAY be addressed as either:

• unicast, for a specific destination node
• broadcast, for network-wide or local-scope distribution

Broadcast handling and unicast handling MAY differ in forwarding and reliability behavior.

The present documentation does not fully specify:

• fragmentation format
• reliable-delivery extensions
• end-to-end acknowledgment fields
• group-address wire format