# Add LinkEdge (latency-free edges) + homogeneous edge enforcement

[GioeleB00]

What’s in this PR

• New schema: LinkEdge

  • Same id|source|target shape as NetworkEdge
  • edge_type = LINK_CONNECTION
  • No latency / dropout_rate

• Edge homogeneity: a topology’s edges must be all NetworkEdge or all
  LinkEdge (no mixing). Enforced in:

  • TopologyGraph typing (list[NetworkEdge] | list[LinkEdge])
  • AsyncFlow.add_edges(...): fixes kind on first call, rejects mixing

• Runtime support:

  • EdgeRuntime: dispatches by type

    • NetworkEdge → current behavior (drop + latency + spike)
    • LinkEdge → immediate delivery (env.timeout(0)), no drop/spike/latency

  • EventInjectionRuntime: if any event targets an edge, the topology must
    be NetworkEdge (clear error if link-only)

  • SimulationRunner: accepts list[NetworkEdge] | list[LinkEdge] and wires
    both transparently

• MMc analyzer: for MMc models, edges must be LinkEdge (network is
  negligible by assumption). Compatibility checks updated accordingly.

• Builder improvements (AsyncFlow):

  • add_edges(*edges): enforces homogeneity; returns self
  • Clearer ValueError messages in build_payload() (aligned with tests)

• Tests:

  • New tests for LinkEdge topologies and mixed-types rejections
  • Runner tests for building edges with LinkEdge
  • Event injection tests asserting link-only topologies reject edge events
  • Updated messages and assertions to match new errors

• Typing & linting: mypy/ruff compliant; ≤88-char lines in tests

Backward compatibility

• Existing simulations using NetworkEdge are unaffected.
• If you previously mixed edge types (unsupported before too), you’ll now get a
  clear error at build time.

Migration notes

• Choose one edge type per topology:

  • Use NetworkEdge when you need latency/drop/spikes.
  • Use LinkEdge when network is negligible (e.g., MMc).

• add_network_spike(...) applies only to NetworkEdge topologies. Using
  it with link-only topologies raises a clear ValueError.

• Builder error messages have been standardized:

  • “The arrivals generator must be instantiated before the simulation”
  • “The client must be instantiated before the simulation”
  • “You must instantiate edges before the simulation.”