Читать книгу Mobile Communications Systems Development - Rajib Taid - Страница 59

One of the most commonly used physical interfaces is the E1, which is defined under the standard G.703 of ITU‐T [12]. An E1 physical interface is not only used in the mobile communications system but also used in other systems to carry voice, data, and so on. For example, E1 physical interface is used between the GSM Base Station Controller (BSC) and Base Transceiver Station (BTS); GSM BSC, and Mobile Switching Center (MSC), or between the MSC and Serving GPRS Support Node (SGSN) for the Gs interface. An E1 physical interface has two pair/four wire cables for both Receive (RX) and Transmit (TX) purposes. The total bandwidth supported by the E1 interface is the 2 Mbps that is divided into 32 timeslots of 64 kbps each. Each 64 kbps timeslot is again divided into four sub‐timeslots. A sub‐timeslot can be allocated to a GSM voice call or General Packet Radio Service (GPRS) data communication purpose. Figure 3.1 illustrates the configuration and usages of an E1 physical interface to carry signaling as well as user traffic. Using an E1 interface, several transceivers (TRXs), along with their signaling channels, of a BTS can be configured.

Figure 3.1 Illustration: physical E1 interface configuration for GSM A‐bis interface.