Using fiber optic cable, optical communications have enabled telecommunication （93） to be made over much greater distances and （94）much lower levels of（95）in the transmission medium and possibly most important of all, optical fiber communications have enabled much higher data rates to be accommodated

As a result of these advantages, optical fiber communication systems are widely employed for applications （96）major telecommunications backbone （97） to Ethernet systems, broadband distribution, and general data networking.

【An overall cellular network contains a number of different elements from the base transceiver station (BTS) itself with its antenna back through a base station controller (BSC), and a mobile switching centre (MSC) to the location registers (HLR and VLR) and the link to the public switched telephone network (PSTN). Of the units within the cellular network, the BTS provides the direct communication with the mobile phones. There may be a small number of base stations then linked to a base station controller. This unit acts as a small centre to route calls to the required base station, and it also makes some decisions about which of the base station is best suited to a particular call. The links between the BTS and the BSC may use either land lines of even microwave links. Often the BTS antenna towers also support a small microwave dish antenna used for the link to the BSC. The BSC is often co-located with a BTS. The BSC interfaces with the mobile switching centre. This makes more widespr

电信职业道德与电信法律（）

电信经营者经营活动的基本原则是（）。

为提高物理线路的使用效率，电信网的传输系统通常都采用多路复用技术，如PSTN网络和GSM网络的局间中继线路传输均采用（）复用技术。