Each Mobile Network Operator providing mobile services has its own Public Land Mobile Network.
Public Land Mobile Networks interconnect with other Public Land Mobile Networks and Public Switched Telephone Networks (PSTN) for telephone communications or with internet service Providers for data and internet access of which links are defined as interconnect links between providers. These links mostly incorporate SDH digital transmission networks via fiber optic on land and digital microwave links.
Access to PLMN services is achieved by means of an air interface involving radio communications between mobile phones or other wireless enabled user equipment and land-based radio transmitters or radio base stations or even fiber optic distributed SDH network between mobile base stations and central stations via SDH equipment (ADMs) with integrated IP network services.