local exchange (LEX)
The local exchange (OVSt), Local Exchange (LEX), forms the lowest hierarchical level in the long-distance network hierarchy. It is an exchange node of a local network in the public telephone network. Such a node, which forms the end point for the access lines of end users and companies, is connected to the node exch anges(KVSt) located higher up in the hierarchy.
These local exchanges typically supply subscriber lines to an area within a radius of 3 to 5 km. The subscriber lines, the local loop lines, are connected in a star configuration to a distributor in the local exchange. Several local exchanges can be combined to form a local network, which is usually based on political city and municipal boundaries and whose subscribers can be reached under a common local network code (e.g., 0221 for Cologne). In addition, the local exchange supports the long-distance network across local networks with the long-distance exchanges.
The detailed structure of the local network depends on the switching technology used. Whereas in the analog telephone network there is a direct correlation between the local exchange code and the network structure, this is not necessarily the case in digitally operating local networks. Here, the local exchanges form the subscriber exchanges, each of which serves an area and, in contrast to analog local networks, can also extend over different local networks.
The cabling structure from the local exchange to the subscriber
From the local exchange, a main cable, which consists of 400 to 600 copper pairs and can be several kilometers long, goes to the cable branch. From there, it goes via the branch cable, which consists of up to 100 copper twisted pairs, to the terminal, which is installed near the subscriber. It then travels via the terminal line to the subscriber connection box.