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uMesh - Network Layer

Addressing, discovery, routing, multi-hop forwarding

Overview

The network layer provides:

  • node addressing (NET_ID + NODE_ID)
  • join/assign/leave discovery
  • multi-hop packet forwarding
  • two routing modes: distance-vector and gradient

Addressing

NET_ID (8-bit) identifies the mesh network. NODE_ID (8-bit) identifies a node inside the network.

Reserved node IDs:

  • 0x00 broadcast
  • 0x01 coordinator
  • 0xFE unassigned

Roles

  • UMESH_ROLE_COORDINATOR
  • UMESH_ROLE_ROUTER
  • UMESH_ROLE_END_NODE
  • UMESH_ROLE_AUTO (auto election)

Routing Modes

UMESH_ROUTING_DISTANCE_VECTOR (default):

  • route table per destination
  • good for smaller networks and bidirectional traffic
  • practical range: up to ~10 nodes

UMESH_ROUTING_GRADIENT:

  • each node tracks only one value: hop distance to coordinator
  • packets to coordinator move uphill through neighbors with lower distance
  • good for many-to-one sensor collection
  • practical range: 10-100+ nodes

Gradient beacon propagation

  1. Coordinator sends UMESH_CMD_GRADIENT_BEACON with payload {distance=0}.
  2. Node receiving beacon with distance D computes candidate D+1.
  3. If candidate improves local distance, node stores it and rebroadcasts with random jitter 50-200 ms.
  4. If candidate is equal/worse, node updates neighbor info but does not rebroadcast.
  5. Propagation depth is capped by UMESH_MAX_HOP_COUNT.

Gradient forwarding

When routing mode is gradient and destination is coordinator:

  1. choose neighbor with neighbor_distance < my_distance
  2. prefer lowest neighbor distance
  3. if tie, prefer better RSSI
  4. if none exists, return UMESH_ERR_NOT_ROUTABLE

Discovery commands

  • UMESH_CMD_JOIN (0x50)
  • UMESH_CMD_ASSIGN (0x51)
  • UMESH_CMD_LEAVE (0x52)
  • UMESH_CMD_DISCOVER (0x53)
  • UMESH_CMD_ROUTE_UPDATE (0x54)
  • UMESH_CMD_NODE_JOINED (0x55)
  • UMESH_CMD_NODE_LEFT (0x56)
  • UMESH_CMD_ELECTION (0x57)
  • UMESH_CMD_ELECTION_RESULT (0x58)
  • UMESH_CMD_GRADIENT_BEACON (0x59)
  • UMESH_CMD_GRADIENT_UPDATE (0x5A)
  • UMESH_CMD_POWER_BEACON (0x5B)

Timers

  • UMESH_ROUTE_UPDATE_MS = 30000
  • UMESH_NODE_TIMEOUT_MS = 90000
  • UMESH_DISCOVER_TIMEOUT_MS = 2000
  • UMESH_ELECTION_TIMEOUT_MS = 1000
  • UMESH_GRADIENT_BEACON_MS = 30000
  • UMESH_NEIGHBOR_TIMEOUT_MS = 30000