> For the complete documentation index, see [llms.txt](https://gsm.learn-telecom.com/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://gsm.learn-telecom.com/architecture.md).

# Architecture

- [GSM Radio Stack](https://gsm.learn-telecom.com/architecture/gsm-radio-stack.md)
- [Layer 1 - Radio](https://gsm.learn-telecom.com/architecture/gsm-radio-stack/layer-1-radio.md)
- [Layer 2 - LAP-Dm](https://gsm.learn-telecom.com/architecture/gsm-radio-stack/layer-2-lap-dm.md)
- [Layer 3 − GSM signalling](https://gsm.learn-telecom.com/architecture/gsm-radio-stack/layer-3-gsm-signalling.md)
- [MS - Mobile Station](https://gsm.learn-telecom.com/architecture/ms-mobile-station.md)
- [ME - Mobile Equipment](https://gsm.learn-telecom.com/architecture/ms-mobile-station/me-mobile-equipment.md)
- [Baseband](https://gsm.learn-telecom.com/architecture/ms-mobile-station/me-mobile-equipment/baseband.md)
- [SIM Card - Subscriber Identity Module](https://gsm.learn-telecom.com/architecture/ms-mobile-station/sim-card-subscriber-identity-module.md)
- [BSS - Base Station Subsystem](https://gsm.learn-telecom.com/architecture/bss-base-station-subsystem.md)
- [BTS - Base Transceiver Station](https://gsm.learn-telecom.com/architecture/bss-base-station-subsystem/bts-base-transceiver-station.md)
- [BSC - Base Station Controller](https://gsm.learn-telecom.com/architecture/bss-base-station-subsystem/bsc-base-station-controller.md)
- [NSS - Network Switching Subsystem](https://gsm.learn-telecom.com/architecture/nss-network-switching-subsystem.md)
- [MSC - Mobile Switching Center](https://gsm.learn-telecom.com/architecture/nss-network-switching-subsystem/msc-mobile-switching-center.md)
- [HLR - Home Location Register](https://gsm.learn-telecom.com/architecture/nss-network-switching-subsystem/hlr-home-location-register.md)
- [VLR - Visitor Location Register](https://gsm.learn-telecom.com/architecture/nss-network-switching-subsystem/vlr-visitor-location-register.md)
- [AuC - Authentication Center](https://gsm.learn-telecom.com/architecture/nss-network-switching-subsystem/auc-authentication-center.md)
- [EIR - Equipment Identity Register](https://gsm.learn-telecom.com/architecture/nss-network-switching-subsystem/eir-equipment-identity-register.md)
- [VMS - Voice Mail Subsystem](https://gsm.learn-telecom.com/architecture/nss-network-switching-subsystem/vms-voice-mail-subsystem.md)
- [IWF - Interworking Function](https://gsm.learn-telecom.com/architecture/nss-network-switching-subsystem/iwf-interworking-function.md)
- [OSS - Operation Support Subsystem](https://gsm.learn-telecom.com/architecture/oss-operation-support-subsystem.md)
- [OMC - Operation and Maintence Center](https://gsm.learn-telecom.com/architecture/oss-operation-support-subsystem/omc-operation-and-maintence-center.md)
- [NMC - Network Managment Center](https://gsm.learn-telecom.com/architecture/oss-operation-support-subsystem/nmc-network-managment-center.md)
- [ABC - Administration & Billing Center](https://gsm.learn-telecom.com/architecture/abc-administration-and-billing-center.md)