Feat/traffic manager egress#26
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…(P1-P2)
First stage of the high-fidelity Traffic Manager that will replace the
output-only NSQueueingLogicPriRL scheduler. This lands the standalone,
event-driven, thread-free core; it is not yet wired into P4CoreV1model.
P1 - Input-side VOQ + accounting:
* VOQ[in][out][priority], 8 priority levels (7 = highest), N*N*8 queues,
stored flat because TmItem is move-only.
* Finite-buffer accounting: global / per-input / per-VOQ byte counters
with configurable limits (0 = unlimited).
* Admission control with explicit drop reasons (global, input, VOQ full);
egress drop reasons defined for later phases.
* Modular packet-format boundary: carries an opaque move-only TmPayload,
never assumes ns3::Packet (bm::Packet wrapper comes with integration).
* TracedCallbacks (enqueue/dequeue/drop/delays) and cumulative TmStats.
P2 - Fabric scheduler:
* Priority-first maximal matching (one input and one output per round),
behind an overridable DoRunFabricScheduler() so iSLIP / round-robin can
drop in later.
Tests (test/p4-traffic-manager-test-suite.cc, 6 cases, all passing on
ns-3.39): enqueue/dequeue + accounting, priority scheduling, per-input VOQ
isolation, one-in/one-out matching, drop-reason correctness, and delay
measurement in simulated time.
Builds on the standalone VOQ + fabric core (P1-P2). Adds the ns-3
event-driven timing model and the egress side, all thread-free.
P3 - Event-driven fabric loop (opt-in via the "EventDriven" attribute;
default off preserves the manual RunFabricScheduler()/DequeueFromVoq()
API used by the low-level unit tests):
* EnqueueToVoq arms a self-clocking fabric round (Simulator::Schedule).
* Each round applies the scheduler's grants (VOQ -> egress) and re-arms
while demand remains; the fabric is busy for the arbitration delay plus
the transfer time of the largest granted packet (FabricRate).
P4 - Egress side:
* Per-output-port strict-priority queues (8 levels, 7 = highest).
* Serialising egress scheduler: non-preemptive, one packet in service per
port, next packet chosen by strict priority, serialised at PortRate.
* Egress finite-buffer accounting (per-port + per-queue) with
EGRESS_PORT_BUFFER_FULL / EGRESS_QUEUE_FULL drop reasons.
* Byte-neutral VOQ->egress hand-off keeps the global counter consistent
(a packet is counted in global for its whole residence).
* TransmitCallback delivery hook (move-only payload) for wiring to an
ns-3 NetDevice at integration time; egress/total delay traces + stats.
DoDispose cancels pending fabric/egress events.
Adds 3 cases exercising the event-driven path under Simulator::Run,
bringing the suite to 9 (all passing on ns-3.39):
* end-to-end drain: a permutation demand is arbitrated, moved to egress
and serialised to the wire; buffers empty and every packet delivered
via TransmitCallback.
* egress strict priority: a packet in service is not preempted, but the
highest-priority waiting packet goes next (order 2, 7, 5).
* egress overflow: a full egress queue drops with EGRESS_QUEUE_FULL while
the granted-from-VOQ count still advances.
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