Читать книгу Mobile Communications Systems Development - Rajib Taid - Страница 58

In computer network programming, an interface is a logical point, such as a socket where two different applications/systems exchange information and communicate with each other in terms of a protocol data unit (PDU). Similarly, in the case of mobile communications networks also, two different network elements communicate, either signaling or user data, with each other using a set of predefined messages or PDUs. These collective PDUs or messages define the particular logical interface between two network elements.

A logical interface works on top of a particular physical interface. Using a logical interface, network entities exchange both the user data and signaling information in the form of a message or a PDU. For example, consider the GSM A‐bis interface between the BTS and BSC and the A‐interface between the BSC and the MSC. Both of these logical interfaces work on top of the physical E1 interface to transport signaling and user traffic in a GSM network. Typical signaling messages exchanged over the A‐bis interface are radio resources request and allocation to an MS and its release and so on.