1xBTS

1xBTS is an open-source implementation of a CDMA2000 1x cellular network stack, developed in Rust. It provides a complete system from the radio frequency interface through to the network core, enabling the setup and management of a full cellular network. The platform is designed to cover the entire cellular stack, including radio access, switching, subscriber management, messaging, and packet data services.

25 MHz channel. It supports pilot, sync, paging, and traffic channels, utilizing Walsh code spreading and Viterbi decoding, with closed-loop power control at 800 Hz to maintain signal quality. The base station (BTS) handles the physical radio layer, passing decoded frames to the base station controller (BSC) via an internal Abis interface. The BSC manages channel assignment, radio configurations, and state machines for moving phones from idle to active, forming the radio access network.

At the core network level, the mobile switching center (MSC) manages call origination and termination, audio routing, and integration with SIP trunks for both inbound and outbound calls. Voice is carried as EVRC over the A2p interface, with transcoding or passthrough as needed. The home location register (HLR) tracks network subscribers, storing each device's IMSI, registration state, and history. Paging for incoming calls or messages is managed through this subscriber database, which uses PostgreSQL for storage.

The SMS center (SMSC) supports end-to-end messaging, delivering messages as data bursts over the traffic channel. Messages are tracked for delivery state, and the system includes features like automatic welcome SMS on first registration, forwarding for mobile-to-mobile messages, and delayed delivery for offline recipients. An optional MMS profile adds embedded Mbuni MMSC and WAP Push delivery, with captive DNS redirection for carrier-specific MMS hostnames. Packet data services are provided using Service Option 33, with RLP framing, PPP negotiation, and optional F-SCH downlink acceleration. The platform supports IP transport via TUN or FOU interfaces.

Provisioning features include over-the-air updates via the 228 dial code, allowing the network to read or modify handset identity, dialed number, operator banner, MMS URL, and roaming list. A PRL editor enables uploading or creating preferred roaming lists and pushing them to devices. 1xBTS is available under an open-source license, making it accessible for those interested in building or experimenting with CDMA2000 1x networks.