Switch (PacketSwitch)

PacketSwitch (src/switches/switch.rs) is a demultiplexing switch model:

• It does not implement queueing or link serialization.
• It forwards packets to the correct next hop using a per-flow forwarding table.

Forwarding tables

Each switch maintains:

• fib: HashMap<flow_id, next_id> for forward (data) traffic
• r_fib: HashMap<flow_id, prev_id> for reverse traffic (TCP ACKs and control packets)

These tables are installed after flow paths are computed in Topology::route_flows (src/topos/topo.rs).

Output ports

PacketSwitch.outputs maps a destination ID to an Output<Packet>:

• destination IDs can be neighboring switch IDs or endpoint IDs (source/sink actors),
• the topology builder ensures IDs don’t collide by starting endpoint IDs after the switch ID range.

Packet classification

packet_received distinguishes:

• Data packets: ack.is_none() and control.is_none() → forward via fib[flow_id]
• Reverse/control traffic: ACKs or control packets → forward via r_fib[flow_id]

This split keeps “reverse-path” semantics explicit without building a second network.

Time handling

Switches maintain a local time: f64 and update it from packet.time. In test builds (--features test), switches also assert that packet.time matches the simulation engine clock (cx.time()).