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C network

The C-network was a mobile communications network that, like the A-network and the B-network, operated in analog mode, but with digital signaling for circuit-switched dial-up connections. The C-network was the first cellular network in Germany, which began regular operation in 1981 and was used primarily for voice transmissions. The C-Netz was limited to national coverage and was built up nationwide in Germany. The radio cells of this network covered a large area; integration of small cell networks took place in 1988. The large radio cells of a fixed radio station had a range of 15 km to 20 km; that of the small radio cells was 2 km to 3 km.

The development of the C-Net

The C-network was built up nationwide in Germany and had about 200 radio base stations for large cells when it was completed.

Cellular cells of the C-Net

Cellular cells of the C-Net

The C-Net operated in the UHF range at 450 MHz and had transparent duplex channels for voice and data. Originally, 222 duplex channels were available for voice transmission in the frequency range between 451.30 MHz and 455.74 MHz and between 461.30 MHz and 465.74 MHz with a channel spacing of 20 kHz. The spacing of the duplex channels was 10 MHz. The frequency bands were later expanded to 287 channels, and 10-kHz offset channels and 12.5-kHz offset channels were also added to improve utilization of the radio frequency range.

Frequency bands in the C-network

Frequency bands in the C-network

As with the classic telephone network, the transmission bandwidth was between 300 Hz and 3.4 kHz. In addition, the C-Net had an automatic handover, i.e., a handover of the connection when a mobile station moves from the coverage area of one base station to that of the next. Its use was essentially limited to voice transmission.

Data transmission in the C-network

Data transmission was limited in quality and hardly produced satisfactory results. In addition, data transmission required special modems with a V.24/ V.28 interface to the PC and a special TAE adapter for the familiar a/b telephone interface. The data rate was 2.4 kbit/s.

Architecture of the C-Net

Architecture of the C-Net

In order to enable the subscriber to use the C-Net regardless of the terminal device, the C-Net worked with a subscriber authorization card(BK) the size of a credit card. The subscriber-relevant data was stored on this card. There were four different authorization cards: the A card with a magnetic strip and without a chip, the B card as a chip card with a magnetic strip, the C card as a magnetic card and the D card as a smart card without a magnetic strip. The cards differed in terms of security requirements, usage and access options, with restrictions on national long-distance calls and international calls. In terms of services, the C network knew call forwarding and voice storage in addition to handover.

The C-Net reached its final stage of development at the end of the 1990s. Due to the development and construction of modern GSM networks, the C-Net could not meet the increasing requirements and was shut down at the end of the century.

Informations:
Englisch: C network
Updated at: 10.02.2019
#Words: 492
Links: network, mobile communications, analog, mode, digital
Translations: DE
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