Telephone (cellular mobile telephone network), function, scope - GF82.70-P-0005S: Notes

MODELS 215, 220 with CODE (388) "Portable CTEL" UPCI telephone system

Function of the cellular mobile telephone network

Fig 1: Cellular Mobile Telephone Network Function Diagram

Cellular mobile telephone network, scope

The cellular mobile telephone network is a digital, cellular radio telephone network based on GSM standard (G lobal S ystem M obile). The GSM standard provides the standardization of a cellular mobile telephone system. The goal is to offer a world-wide compatible digital cellular mobile telephone service. The system digitally transmits the switching of calls, the language and the data. Furthermore, additional services are offered such as:

Fee display
conference calls, waiting function
identification of calling party
call relaying
Fax
access to text stations and terminals (ISDN-compatible)

The radio transmission in the cellular mobile telephone network takes place depending on the provider or country in the range of 900 - 1900 MHz between portable CTEL and base transceiver station (BTS) .

Starting at the base transceiver station, all signals are transmitted via cable to the base station controller (BSC) .

With the cellular mobile telephone network, the base transceiver stations are located so as to create a network of the mobile subscribers from the honeycomb-shaped radio frequency cells. Radio frequency cells have to work for a high density of subscribers in densely populated areas, and on the other hand they have to cover large radio frequency ranges in rural areas. Depending on the requests, these radio frequency cells range between 100 m and 40 km.

A feature of the cellular mobile telephone network is the automatic transmission procedure (handover) from one radio frequency cell to the next, without the mobile telephone subscriber noticing anything.

If, during a telephone call, the subscriber leaves the range of reach of a base transceiver station and then moves into the transmission range of the next base transceiver station, the communication can continue without interruption, although the transmitter of the next base transceiver station uses a different frequency.

This transmission procedure takes place within 5 ms to 10 ms.

Transmission problems could occur if the user is located in valleys (dead spot) or in areas with a small number of transmission and reception stations. This can, however, be eliminated by moving to another location.

It is possible to make a telephone call with the own cellular phone and SIM card (S ubscriber I dentity M odule) abroad. The prerequisite is that the particular country offers the GSM standard, that there is a corresponding contract (roaming contract) between the country and the network operator and that the cellular phone is dual-band or tri-band capable according to the different frequencies.

A radio frequency cell is formed by the base transceiver station and is the actual transmitting/receiving terminal. The base transceiver station establishes the connection to the cellular phones, checks the radio transmission and transmits the information via cable to the base station controller.

With the GSM standard, there are 124 or 372 channels for each base transceiver station depending on the frequency.

The base station controller is the control unit of the base transceiver station. The base station controller is switched between the base transceiver stations and the mobile switching center (MSC) . The data for the language and data communication, as well as monitoring and control information is transmitted here. Furthermore, the base station controller is the central control point for the automatic transmission method (handover) from one radio frequency cell to the next.

The cellular mobile switching centers are linked to one another and form the switching system in the mobile telephone networks with GSM standard. The user and visitor data is stored in different databases and directories.

Databases and directories in the mobile switching centers (MSC).

Home location register (HLR)
The following are stored here: subscriber master data such as name, address, telephone number, service features, number of the caller and party being called, information on time, duration, and fees for the call as well as data about the radio cells in which a connection was established or terminated.
Equipment information register (EIR)
The device-specific, electronic identification numbers (IMEI number) of the cellular phones are registered here. The cellular phone transmits this number during log-in. If the cellular phone has been disabled/stolen, network access will be denied if applicable.
Visitor location register (VLR)
The necessary data of a visiting subscriber are stored here for a limited time.
Authentication center (AC)
Here, the access authorization of the mobile subscriber is checked and the corresponding connection is established.

The entirety of the public telephone network is called public switched telephone network (PSTN) .

	Table of contents for function description of the Universal Portable CTEL Interface (UPCI)		GF82.70-P-0996S
	Telephone (cellular mobile telephone network) log-in		GF82.70-P-0005-01S
	Telephone (cellular mobile telephone network) cellular mobile telephone subscribers in the public telephone network		GF82.70-P-0005-02S
	Cellular mobile telephone subscriber (mobile telephone network) to cellular mobile telephone subscriber		GF82.70-P-0005-03S