Editing Telecommunications in Russia (section)

===Public switched telephone network===
Russian [[public switched telephone network]] (PSTN) has specific features. The lowest part of this model is example of the local network in the middle and large cities. The central office (CO) is connected to the tandem exchange (TE). In some cases, COs are connected by the directly{{Clarify|date=March 2019}}. Such possibility is shown by the dotted lines for three COs connected to the TEIII. COs may be directly connected with the toll exchange. This option is shown by the dotted line for the COII1. Automatic Branch Exchange (PABX) is served by the nearest CO. All TEs are forming the meshed network. Up to the 1990s, TE was independent element of the local network. Operators did not use the equipment combined functions Tandem and Toll Exchanges. So, TE provided connections between COs of the local network, and access to the toll exchange. A function of the toll exchange is to establish connections for the long-distance and international calls. Last type of calls is served by the Gateway (GW). Processing of the local calls is performed by the COs and TEs. If a subscriber dials digit "8" (prefix of the long-distance connection in the national PSTN) all further processing of the call is a function of a toll exchange. The [[Telephone numbers in Russia|numbering plan for the cellular networks]] based on the Area Code (three digits) and number of mobile terminal (seven digits). In this case, the Area Code defines the concrete cellular network.<ref>Research Institute of Telecommunications, St. Petersburg, Russia</ref>