# Rutster — Asterisk Capability Checklist

This is the **capability checklist**, not the architecture spine. It walks the Asterisk
subsystem surface as a completeness audit — *"what must a telephony system handle"* — and
assigns every capability a **disposition** in the rutster architecture, with a one-line
rationale. We keep the checklist; we **reject** the Asterisk channel/bridge/dialplan model
as the architecture (see [ADR-0002](adr/0002-north-star-and-fused-core.md)). The crate/service
boundaries fall out of the "Core / Service" rows; the threat model hangs off the "attack
surface" of each row.

Grounded against the Asterisk 22.10.1 tree (~1.18M LOC C/H).

## Disposition legend

| | Disposition | Meaning |
|---|---|---|
| 🦀 | **Core** | In the hardened, memory-safe Rust core. Reserved for the hot media path, call model, and signaling glue — fast, always-present, trusted. |
| 🧩 | **Plugin (WASM)** | Sandboxed extension. Logic that benefits from isolation and third-party extensibility. Cannot crash the core or cross tenant boundaries. |
| ☁️ | **Service** | Independent microservice. Stateful, independently-scaled, or business/billing logic. Talks over API + event bus. |
| 🔌 | **Edge / FFI** | Wrap mature external C (pjproject/spandsp) or front with an SBC. Used where a pure-Rust rewrite is a tar pit. |
| ⛔ | **Drop** | Legacy hardware or dead protocol. Gone. |
| 🔁 | **Replace** | Capability survives but the mechanism is entirely redesigned (no 1:1 mapping). |

## Design rules (the heuristics behind every row)

1. Hot media path & the call model → **Core**. Trusted, fast, always-on. Inside the fused
   per-call vertical.
2. Anything that benefits from isolation or third-party extension → **Plugin** *(now softened —
   WASM demoted out of the core story per [ADR-0002](adr/0002-north-star-and-fused-core.md); the
   agent **tap** is the primary extension point for in-call logic).*
3. Stateful, independently-scaled, or business/billing logic → **Service**. Around the core,
   horizontal platform.
4. Mature C that's a tar pit to rewrite (SIP) → **rent it, don't own it.**
   *[ADR-0007](adr/0007-trunk-rented-transport.md) restores this rule's original instinct for the
   trunk: rutster owns no SIP stack — carrier transport is a rented CPaaS raw-media fork (primary) or
   an out-of-tree SBC (on-prem graduation); ADR-0003's from-scratch Rust trunk SIP is superseded. FFI
   retained only for mature codec/DSP/EQ libraries (libopus, speexdsp, WebRTC APM).*
5. Legacy hardware / dead protocols → **Drop**.
6. Security & multi-tenancy are cross-cutting — never a row, always a property. **Spend / abuse
   control is constitutive**, pulled into the boundary, not externalized.

---

## 1. Signaling & channel drivers (`channels/`, `res/res_pjsip*`)

| Asterisk subsystem | Module(s) | Disp. | Rationale |
|---|---|---|---|
| SIP signaling (trunk) | `chan_pjsip` + `res_pjsip*` (48 mods) | 🔌 Rented / out-of-tree | **Re-decided ([ADR-0007](adr/0007-trunk-rented-transport.md), supersedes ADR-0003):** rutster owns **no SIP stack.** PSTN audio arrives as a media-leg ingress from a rented CPaaS raw-media fork (Twilio Media Streams / Telnyx — primary), or an out-of-tree SBC (Kamailio/FreeSWITCH/drachtio + rtpengine) when media must stay on-prem. rutster parses no SIP → SIP is removed from the attack surface entirely, not rewritten. The from-scratch Rust trunk SIP of ADR-0003 was the highest-cost / lowest-differentiation square on the board, with no production-hardened Rust SIP stack to stand on. |
| ↳ outbound registration (to carriers) | `res_pjsip_outbound_registration` | 🔌 Rented / out-of-tree | Handled by the rented transport or the out-of-tree SBC ([ADR-0007](adr/0007-trunk-rented-transport.md)), not by rutster — the provider/SBC owns register-to-carrier. |
| ↳ **inbound endpoint registration (desk/soft phones)** | `res_pjsip_registrar` | ⛔ **Deferred — community edge** | **Split from trunk.** An inbound endpoint server re-imports the *unbounded device interop tail* — it fails all three FOB tests ([ADR-0008](adr/0008-fob-and-green-zone.md)), so it's **green-zone, out-of-tree, never first-party** ([ADR-0007](adr/0007-trunk-rented-transport.md)): Polycom/Yealink/Zoiper `REGISTER`, BLF/MWI, DTMF variants, per-device NAT/provisioning. In an SSO/browser-agent UX, the desk-phone demographic has collapsed. Out-of-tree SBC-style adapter (fronting the public API / B2B-SIP) for anyone who needs it — **outside the trust boundary**, so its tail can't compromise the wedge. See [ADR-0006](adr/0006-ingress-posture.md). |
| ↳ SDP / media negotiation | `res_pjsip_session`, `_sdp_rtp` | 🦀 Core | Offer/answer drives the media plane directly. |
| ↳ auth | `res_pjsip_outbound_authenticator_digest`, etc. | 🦀 Core | Digest + token auth, deny-by-default, rate-limited. Security-critical. |
| ↳ NAT / ICE / rtcp | `res_pjsip_nat`, `res_rtp_asterisk` ICE | 🦀 Core | ICE/STUN/TURN via `str0m`/`webrtc-rs`. |
| ↳ pub/sub (presence, MWI, BLF) | `res_pjsip_pubsub`, `_exten_state`, `_mwi` | 🦀 Core + ☁️ | Signaling in core; presence/MWI state aggregation as a service. |
| ↳ T.38 fax | `res_pjsip_t38` | ☁️ Service | Isolate fax entirely (see §5). |
| WebRTC signaling (agent ingress) | `chan_websocket`, `res_http_websocket` | 🦀 Core | **First-party human-participant ingress** ([ADR-0006](adr/0006-ingress-posture.md)). The browser is the softphone: SSO in, one peer-connection, DTLS-SRTP + ICE handled by the browser, zero device-provisioning tail. Also the modern hosted UX and the escalation path (rung 2): agent clicks *take this call* → WebRTC leg + audiohook/barge handoff. WSS + DTLS-SRTP via the media stack. |
| External media | `chan_audiosocket` | 🦀 Core | Modern, relevant pattern (stream media to an external process); keep as a media tap/source API. |
| Local console audio | `chan_console` | 🧩 Plugin | Dev/testing convenience; not core. |
| RTP-only pseudo-channel | `chan_rtp`, `chan_bridge_media` | 🦀 Core | Media-plane primitives. |
| IAX2 | `chan_iax2` | ⛔ Drop | Dead inter-Asterisk protocol. SIP trunks instead. |
| TDM / analog / ISDN | `chan_dahdi`, `sig_analog`, `sig_pri`, `sig_ss7` | ⛔ Drop | No hardware era. PSTN via SIP trunk / SBC. |
| H.323 | `addons/chan_ooh323` | ⛔ Drop | Dead protocol. |
| SCCP / Skinny, MGCP | (Skinny/MGCP) | ⛔ Drop | Dead protocols. |
| Unistim | `chan_unistim` | ⛔ Drop | Dead vendor protocol. |
| XMPP / Jingle | `chan_motif`, `res_xmpp` | ⛔ Drop | Dead path. |

---

## 2. Media plane (`main/rtp_engine.c`, `res_rtp_asterisk`, `bridges/`, `main/dsp.c`)

| Asterisk subsystem | Module(s) | Disp. | Rationale |
|---|---|---|---|
| RTP / RTCP engine | `rtp_engine.c`, `res_rtp_asterisk` | 🦀 Core | **Crown jewel.** Built on `str0m`/`webrtc-rs`, sans-IO, dedicated timing (not the shared tokio pool). |
| SRTP / DTLS | `res_srtp` | 🦀 Core | Mandatory-by-default encryption. |
| Bridging framework | `main/bridge.c` | 🦀 Core | The 2-party + N-party call topology engine. |
| ↳ softmix conference mixer | `bridges/bridge_softmix` | 🦀 Core | N-party mixing on the hot path. |
| ↳ simple / native-RTP bridge | `bridge_simple`, `bridge_native_rtp` | 🦀 Core | Direct media flow (re-INVITE peers together) when no mixing needed. |
| ↳ holding bridge | `bridge_holding` | 🦀 Core | Parking/hold media state. |
| ↳ native DAHDI bridge | `bridge_native_dahdi` | ⛔ Drop | Hardware. |
| DSP (DTMF/MF detect, silence, tone) | `main/dsp.c` | 🦀 Core | Media-plane primitive; exposed to plugins as events. |
| Echo cancellation | (hardware / sw) | 🔌 Edge/FFI | No mature pure-Rust EC; FFI speexdsp / WebRTC APM. |
| Audio hooks (tap/inject/volume) | `main/audiohook.c` | 🦀 Core | Primitive behind recording, ChanSpy, whisper/barge. |
| Music on hold | `res_musiconhold` | 🦀 Core | Just a media source; small, keep in core (asset from object storage). |
| Jitter buffer | `func_jitterbuffer`, abstract jb | 🦀 Core | Quality-critical; part of the RTP path. |

---

## 3. Call model & PBX core (`main/`)

| Asterisk subsystem | Module(s) | Disp. | Rationale |
|---|---|---|---|
| Channel abstraction | `main/channel.c` (`ast_channel`) | 🦀 Core | The unifying "leg" object (signaling + media state). Reimagined as a `Channel`/leg. |
| PBX / dialplan engine | `main/pbx.c` | 🔁 Replace | → declarative routing (data) + event-driven apps. No `extensions.conf`. |
| Call features (transfer/park/pickup) | `res_features`, `res_parking` | 🦀 Core | Call-control primitives, exposed via the API. |
| Scheduler / taskprocessor / threadpool | `main/sched.c`, `taskprocessor.c`, `threadpool.c` | 🦀 Core | tokio for control; dedicated timing threads + timer wheel for the 20ms media loop. |
| Internal message bus (Stasis) | `main/stasis*.c` | 🔁 Replace | In-core dispatcher for intra-core; external event bus (NATS/Kafka) for cross-service. |
| Module loader | `main/loader.c` | 🔁 Replace | → WASM host + service registry. No in-process `.so`. |
| ACL / named ACL | `main/acl.c`, `res_named_acl` | 🦀 Core | Security primitive; policy-driven. |
| astdb (internal KV) | `main/db.c` | 🔁 Replace | → state store (**Valkey** KV, [ADR-0005](adr/0005-event-bus.md)). |

---

## 4. Dialplan & programmability (`pbx/`, `res_agi`, `res_ari`, `manager`)

| Asterisk subsystem | Module(s) | Disp. | Rationale |
|---|---|---|---|
| `extensions.conf` dialplan | `pbx_config` | 🔁 Replace | Declarative routing as data (GitOps) for the 90% case. |
| AEL / Lua dialplan | `pbx_ael`, `pbx_lua` | ⛔ Drop | Replaced by WASM call-flow + routing config. |
| Realtime dialplan | `pbx_realtime` | 🔁 Replace | Routing in the config/state layer. |
| Call files / spool | `pbx_spool` | 🔁 Replace | → originate via API. |
| Macro / Gosub / Stack | `app_stack`, `app_macro` | 🔁 Replace | → WASM call-flow logic. |
| AGI / FastAGI | `res_agi` | 🔁 Replace | → WASM plugins + gRPC. Same "external program controls a call," sandboxed and typed. |
| ARI (REST + stasis apps) | `res_ari*`, `res_stasis*` | 🦀 Core | **Becomes THE API** — the control-plane resource model. `api-docs/*.json` is the reusable spec. |
| AMI (manager) | `main/manager*.c` | 🔁 Replace | Drop the plaintext TCP protocol → mTLS gRPC + RBAC + audit log. |
| CLI | `main/cli.c` | 🔁 Replace | Thin CLI that's an API client, not an in-process console. |
| DUNDi (distributed routing) | `pbx_dundi` | ⛔ Drop | Dead/niche. |
| ENUM lookup | `func_enum` | 🧩 Plugin | Routing-time lookup; pluggable. |

---

## 5. Applications (`apps/`) — the contact-center domain

> **Scope lift** ([vision-revision](superpowers/specs/2026-06-26-vision-revision-design.md) §4): the
> contact-center capabilities Asterisk kept as apps are **rutster's core domain**, not peripheral.
> This is the difference between "Asterisk successor" and "AI-era contact-center engine." Every row
> here is load-bearing for the wedge (the thing LiveKit will never ship).

| Asterisk app | Module | Disp. | Rationale |
|---|---|---|---|
| Dial / originate | `app_dial`, `app_originate` | 🦀 Core | Core call origination, exposed via the API. |
| Queues / ACD | `app_queue` | ☁️ Service (**domain core**) | Stateful, independently scaled. **First-class** — ACD is the beating heart of a contact center, not a peripheral app. The AI self-serve + human-escalation loop (capability ladder) is an ACD-shaped problem. |
| Voicemail | `app_voicemail` | ☁️ Service | Stateful storage + business logic; isolate it. |
| Conferencing | `app_confbridge` | 🦀 Core + ☁️ | Mixing in core (softmix); orchestration/features as a service. |
| MeetMe | `app_meetme` | ⛔ Drop | DAHDI-timing legacy; ConfBridge supersedes. |
| Recording | `app_mixmonitor`, `app_monitor` | 🦀 Core + ☁️ | Audiohook tap in core; storage/lifecycle as a recording service (object-storage-backed, retention policy, tenant-scoped — **durable, not on the bus**). |
| ChanSpy / whisper / barge | `app_chanspy` | 🦀 Core | Audiohook primitive; gated by RBAC. **The escalation primitive** (rung 2). |
| Answering-machine detect | `app_amd` | 🦀 Core + 🧩 | DSP primitive in core; policy/thresholds as a plugin. |
| IVR primitives (playback/read/say) | `app_playback`, `app_read`, `app_sayunixtime`, `app_directory` | 🦀 Core | Media primitives (play/collect-digits/say) exposed via the API/tap. The IVR *flow* dissolves into the agent; these are the primitives left over. |
| Echo / test | `app_echo`, `app_milliwatt` | 🦀 Core | Trivial diagnostics. |
| FollowMe | `app_followme` | 🧩 Plugin | Routing policy → plugin/service. |
| Speech recognition | `app_speech_utils`, `res_speech` | ☁️ Service | Modern ASR is external; expose as a service integration. |
| Fax | `res_fax`, `res_fax_spandsp` (T.38) | ☁️ Service (FFI) | Niche, isolate fully; spandsp via FFI. Optional. |
| **Supervisor / agent-state** | (scattered manager/AMI surfaces) | ☁️ Service (**domain core**) | **First-class.** Agent presence, state, real-time monitoring, coaching/whisper — the contact-center operator surface. Pure API client (the dashboard). |
| **Dialer (predictive/progressive)** | (custom/`app_dial`-derived) | ☁️ Service (**domain core**) | **First-class.** Outbound campaign dialing with pacing — where the in-boundary spend/abuse gate (§10) *bites hardest*; structurally co-located. |

---

## 6. Telephony features / subscriptions

| Asterisk subsystem | Module(s) | Disp. | Rationale |
|---|---|---|---|
| Presence / BLF | `res_pjsip_pubsub`, `res_pjsip_exten_state` | 🦀 Core + ☁️ | Signaling in core; state aggregation service. |
| MWI (message-waiting) | `res_mwi_external`, `app_voicemail` MWI | ☁️ Service | Tied to the voicemail service. |
| STIR/SHAKEN (attestation) | `res_stir_shaken` | ☁️ Service | **Keep — modern, anti-robocall/fraud.** Core to the security story. |
| Call recording lifecycle | `app_mixmonitor` + storage | ☁️ Service | Object-storage backed, retention policy, tenant-scoped. |
| CDR (call detail records) | `cdr/`, `cdr_*` | ☁️ Service | Event stream → billing/analytics pipeline. |
| CEL (channel event logging) | `cel/`, `cel_*` | ☁️ Service | Folded into the unified event bus + analytics. |

---

## 7. Codecs & formats (`codecs/`, `formats/`)

| Codec / format | Module | Disp. | Rationale |
|---|---|---|---|
| G.711 a-law / µ-law | `codec_alaw`, `codec_ulaw`, `codec_a_mu` | 🦀 Core | Trivial, ubiquitous. Native Rust. |
| G.722 (HD) | `codec_g722` | 🦀 Core | Common wideband. Native Rust. |
| Opus | (external `codec_opus`) | 🦀 Core (FFI) | WebRTC default; libopus via FFI. |
| Sample-rate resample | `codec_resample` | 🦀 Core | Needed for any transcoding/mixing. |
| GSM | `codec_gsm` | 🧩 Plugin (FFI) | Optional; FFI libgsm. |
| G.726 / G.729 | `codec_g726` / (external) | 🧩 Plugin (FFI) | Optional; G.729 now patent-free. |
| Speex / iLBC / LPC10 / ADPCM / codec2 | `codec_speex`, `codec_ilbc`, … | ⛔ Drop | Obsolete; drop or community plugin. |
| Hardware transcode | `codec_dahdi` | ⛔ Drop | Hardware. |
| File formats (wav/sln/ogg-opus) | `format_wav`, `format_sln`, … | 🦀 Core | Small set for prompts/recordings in core; rest as plugins. |
| Legacy file formats (gsm/g729/g726 files) | `format_*` | 🧩 Plugin | Optional. |

---

## 8. Config, state & data (`res_config_*`, `res_sorcery*`)

| Asterisk subsystem | Module(s) | Disp. | Rationale |
|---|---|---|---|
| `.conf` files | `main/config.c` | 🔁 Replace | Config-as-data (declarative, validated, GitOps). |
| Sorcery (object config abstraction) | `res_sorcery*` | 🔁 Replace | Typed config + state-store layer. |
| Realtime backends (ODBC/PgSQL/SQLite/cURL/LDAP) | `res_config_*` | 🔁 Replace | One config/state service with pluggable backends. |
| HTTP media cache | `res_http_media_cache` | 🦀 Core | Prompt/asset fetch → object storage + cache. |
| Security event logging | `res_security_log` | 🦀 Core | Structured audit log; security-critical. |

---

## 9. Management & APIs

| Asterisk surface | Module(s) | Disp. | Rationale |
|---|---|---|---|
| ARI (REST resource model + event WS) | `res_ari*` | 🦀 Core | The control-plane API. Reuse the resource model. |
| AMI (plaintext TCP admin) | `manager*.c` | 🔁 Replace | → mTLS gRPC + RBAC + audit. No plaintext admin channel. |
| HTTP server | `res_http*` | 🦀 Core | TLS-only; axum/hyper. |
| CLI | `cli.c` | 🔁 Replace | API-client CLI. |

---

## 10. New subsystems (no Asterisk equivalent)

These are the "modern" deltas — load-bearing, not optional polish.

| Subsystem | Disp. | Purpose |
|---|---|---|
| WASM plugin host | 🧩 **Demoted (candidate)** | **Out of the core story** ([ADR-0002](adr/0002-north-star-and-fused-core.md)). The agent **tap** is the extension point for in-call logic; ops-simplicity wants one binary. Softly retained as a *candidate* mechanism for community call-flow/routing plugins — undecided vs. webhooks/scripting. |
| Multi-tenancy / isolation | 🦀 Core | Per-tenant keys, quotas, media separation, RBAC. |
| Toll-fraud / spend / abuse engine | 🦀 Core (**promoted**) | **Constitutive, not a service** ([ADR-0002](adr/0002-north-star-and-fused-core.md), re-scoped by [ADR-0009](adr/0009-spend-gate-honest-rescope.md)). Spend caps, pacing caps, deny-by-default routing, rate limits, pattern detection — **co-located with the tap + the provider call-control client inside the boundary**: the brain never holds provider credentials, the gate is unskippable on everything rutster mediates (which is everything the brain can do), and pacing/playout are enforced over media the core terminates ([ADR-0007](adr/0007-trunk-rented-transport.md)). Not a physical wire monopoly — deployments pair it with provider-side caps. This is what makes the boundary *auditable* on spend. |
| Secrets / KMS | 🦀 Core | Vault/KMS integration; no plaintext credentials in config. |
| Observability (OTel) | 🦀 Core | Distributed traces that follow a single call across services. |
| Event bus | ☁️ Service | **Valkey** ([ADR-0005](adr/0005-event-bus.md)): streams + consumer groups (CDR/CEL/analytics), pub/sub (presence/MWI/BLF), KV (state store). Pluggable to NATS later at a config seam. The 20ms media loop never rides the bus. |
| SBOM / supply chain | — | cargo-deny, SBOM generation, reproducible builds. |
| Fuzzing harness | — | Continuous fuzzing of every wire parser (SIP/SDP/RTP). |

---

## Phasing → the thin-slice first proof + capability ladder

The old Phase 0–4 capability-rolldown is **replaced** (see [vision-revision §10–11](superpowers/specs/2026-06-26-vision-revision-design.md)) by a **brutally thin vertical slice** that proves the *combination* (the wedge) first, then a **capability ladder** that grows the contact center feature by feature. The spearhead proves the hardest, most-differentiating part before trunk integration piles on.

### The thin-slice first proof (spearhead)

1. **WebRTC media loopback** — terminate RTP/SRTP, echo audio to a browser. Proves the media core.
2. **Add the tap** — route audio to an external echo process and back. Proves the tap interface.
3. **Swap echo for the brain** — ideally a single speech-to-speech API (e.g. OpenAI Realtime) to collapse STT+LLM+TTS into one integration. Proves agent integration.
4. **Add barge-in** — VAD-driven playout kill. Proves the reflex.
   - **4½ — Benchmark + simulation harness** ([ADR-0010](adr/0010-spearhead-benchmark-sim-harness.md)):
     synthetic-caller ingress drives p50/p99 mouth-to-ear + barge-in kill-time under concurrent
     load, CI-regressed. Proves the reflex *measurably*; seeds `rutster-sim`.
5. **Add a real phone number via rented transport** — a CPaaS raw-media fork (e.g. Twilio Media Streams) lands a PSTN call on the reflex loop; no first-party SIP ([ADR-0007](adr/0007-trunk-rented-transport.md)).
6. **Add the spend cap** — hard-stop at threshold. Proves the boundary.

Steps 1–4 *are* the reflex loop. Keep the dev loop on WebRTC ingress until step 5.
Post-review re-sequencing ([ADR-0010](adr/0010-spearhead-benchmark-sim-harness.md)): after
step 4½, **rung-2 escalation is pulled forward ahead of steps 5–6**.

### The capability ladder (the grand vision, incrementally)

| Rung | Capability | Reuses |
|---|---|---|
| 1 | **Self-serve** — AI answers, contains the call | the thin-slice first proof |
| 2 | **Escalation** — human agent barges in / takes over when AI breaks down | the audiohook/barge primitive (§5) |
| 3 | **Measurement** — containment rate, where/why AI failed | CDR + analytics on calls *you own* |
| 4 | **Self-improvement** — every takeover → auto-labeled training data → loop | rungs 1–3 compounding |

## Open decisions

- ~~**SIP:** FFI pjproject vs. SBC front vs. pure-Rust.~~ ~~Decided — ADR-0003: Rust-native trunk SIP.~~ **Re-decided — [ADR-0007](adr/0007-trunk-rented-transport.md):** rutster owns no SIP stack; the trunk is rented transport (CPaaS raw-media fork) or an out-of-tree SBC.
- ~~**License**~~ **Decided — ADR-0004:** GPL-3.0-or-later.
- ~~**Event bus:** NATS vs. Kafka vs. Redis Streams.~~ **Decided — ADR-0005:** Valkey.
- ~~**Ingress:** WebRTC vs. inbound SIP endpoint.~~ **Decided — ADR-0006:** WebRTC-first; SIP endpoint deferred.
- **WASM runtime** — `wasmtime` component model, *if* WASM is retained at all (demoted to candidate per [ADR-0002](adr/0002-north-star-and-fused-core.md)). Uncoupled from the critical path.
- **Plugin mechanism** — WASM vs. webhooks vs. scripting for community call-flow/routing extensions. Deferred.
- **Agent-tap protocol** — presumptively WSS + core-as-client + clean PCM + core-authoritative playout (see ARCHITECTURE.md, "Agent tap"). To harden against the thin-slice first proof, *not* a decided ADR yet.