System Overview

System architecture diagram

1xBTS is now organized as explicit network nodes. The default cdma-nib binary can still run the stack together for development, but the architecture treats BTS, BSC, MSC, PCF, PDSN, HLR, SMSC, and the voice gateway as separate ownership domains.

Standards Interfaces

Interface	Nodes	Transport	Purpose
Abis signaling	BTS ↔ BSC	TCP 5604 with F634 framing	BTS/BSC control messages
Abis bearer	BTS ↔ BSC	UDP — BTS-side `17014`, BSC-side `17022`	traffic frames and timing metadata
A1	BSC ↔ MSC	TCP 17013 in the current runtime	IOS call-control seam
A2p	BSC ↔ MSC	per-circuit RTP/UDP	EVRC voice bearer with circuit-specific RTP sessions
A8/A9	BSC ↔ PCF	GRE/IP + UDP/IP target	packet-data radio edge
A10/A11	PCF ↔ PDSN	GRE/IP + UDP/IP target	packet-data core anchor

gRPC is not used for these standards interfaces. It is used for management, diagnostics, web UI, local HLR/SMSC/packet service boundaries, and SIP voice gateway integration.

Current packet-core status: cdma-nib reaches packet data through the packet gRPC service on 127.0.0.1:17021 instead of direct in-process packet service wiring. PCF/PDSN-owned session state and A8/A10 bearer models exist, and cdma-a8 / cdma-a10 include GRE codecs and bearer tables, but there is not yet a UDP socket driver for A8 or A10 and A9/A11 do not cross a standards network boundary.

Node Responsibilities

Node	Owns
BTS	PHY, local MAC/LAC execution, forward/reverse channel processing, paging transmission, RX measurements, radio diagnostics
BSC	radio access state, paging policy, traffic assignment, existing-traffic-channel service negotiation, Abis peer state, A1/A2p/A9 edge behavior, power-control policy
MSC	voice/circuit call policy, A1 state, per-circuit A2p RTP bearer setup, MT/MO call orchestration, preemption, call list management, voice gateway control and media routing, SMS coordination via A1 ADDS
PCF	packet-data radio-edge session state, packet setup timers, A8/A9-facing control behind the `PcfClient` boundary; currently reaches packet service gRPC
PDSN	packet session anchor, PPP/IPCP, mobile IP allocation, TUN/FOU/FOU-TCP transport, A10/A11-facing state, packet gRPC service
HLR	subscriber records, registration bindings, `mobiles_seen` ledger, and HLR gRPC service backed by PostgreSQL
SMSC	SMS submissions, delivery attempts, welcome SMS requests, and SMSC gRPC service backed by PostgreSQL
Voice Gateway	MSC-controlled SIP/RTP interop and EVRC↔G.711 media conversion

Current Deployment

cdma-nib loads per-node configs from config/ and starts the integrated runtime. The checked-in configs wire the BTS and BSC together over localhost Abis TCP/UDP addresses:

cargo run --release -p cdma-nib -- --config-dir config

For split BTS/BSC operation, point bts.json: abis.bind_addr, bsc.json: abis.remote_addr, and the paired bearer addresses at the appropriate hosts.

Unlike BTS/BSC Abis and BSC/MSC A1/A2p, the packet-core split is not a standards network boundary yet. pcf.json points the BSC-side PCF client at the packet gRPC endpoint, while pdsn.json configures the packet gRPC listener and packet transport settings. Real A8/A9/A10/A11 transports remain planned work.

Management Plane

Endpoint	Default	Purpose
Management facade	`127.0.0.1:17016`	facade plus node-scoped BTS/BSC/PCF/PDSN APIs and HLR/SMSC/packet compatibility routes
MSC management	`127.0.0.1:17017`	MSC-owned call actions, call listing, and SMS submission
HLR service	`127.0.0.1:17019`	subscriber and registration storage API
SMSC service	`127.0.0.1:17020`	SMS submission and delivery storage API
Packet service	`127.0.0.1:17021`	packet session service used by PCF/PDSN-facing runtime paths
Voice gateway	`127.0.0.1:17015`	MSC-controlled SIP gateway control/media service
1xbts-web	`http://localhost:3000`	Next.js UI, API routes, SSE streams

The management and service APIs are being split by node. Today the primary facade still serves compatibility APIs for the web UI, while MSC, HLR, SMSC, and packet runtime paths use local gRPC boundaries.