High Speed Circuit Switched Data

High Speed ​​Circuit Switched Data ( HSCSD), German as fast circuit-switched data transmission, is an extension of the GSM cellular standards CSD to achieve faster data transfer. By combining multiple data channels theoretical data transfer speeds up to about 115.2 kbit / s (= 8 × 14.4 kbit / s ) can be achieved.

Technically, it is a grouping of several adjacent time slots to a logical connection. In GSM eight time slots are transmitted delayed depending on frequency. Theoretically all eight radio slots of a compound to be assigned. However, this would only be using two antennas ( send) and downlink one for uplink ( received data ). In the usual one antenna, the phone switches to the transmit pulse to reception and need to aim at a certain time to adapt. In fact, as only a maximum of four channel slots can be used, with a pitch of 2:2, 3:1 or 4:1 for the downlink: uplink stands for election. They then act as a multiplier of the basic data rate of each slot of 9.6 kbit / s and 14.4 kbit / s, with a practical maximum of 4 × 14.4 to 57.6 kbit / s

HSCSD allows transparent and non- transparent data transmission. In the transparent transmission, error monitoring the application is left. This allows for a uniform data stream, which is necessary for real-time applications (such as video broadcasts). Small defects in the image are not so disturbing, thereby HSCSD is better suited for this type of application as GPRS. In the non-transparent data transmission, the network takes on the error correction. This is used when surfing and e-mailing.

Practical Application

Not every GSM network operator offered the channel bonding on by HSCSD. In Germany it is only Vodafone (and only in contract rates, not at CallYa ), because E-Plus HSCSD has shut down on 1 August 2010. Vodafone allowed per channel, a transmission rate of 14.4 kbit / s

Since Only terminals are available on the German market, which dominate total of four channels that arise in practice two variants:

  • The bundling of two channels for uplink and downlink results in each direction 28.8 kbit / s Vodafone only allows this 2:2 bundling with the ISDN interface, eg analog or digital protocol V.34 V.110 protocol, which then s must be set to 38.6 kbit / s.
  • When bundling of three to one channel are 43.2 kbit / s and 14.4 kbit / s. This speed is only offered by E-Plus, but requires the ISDN interface to fully utilize the digital V.120 protocol. The analog protocol limited to 33.6 kbit / s This offer is, as I said above, omitted.

If the unit is moved, in a HSCSD handover the bundle can often not be accepted, and the connection falls back to CSD with only one channel.

Future

HSCSD will lose the benefit of the packet-oriented transmission GPRS / EDGE and UMTS / HSDPA in importance. UMTS, it is possible to construct compounds CSD (64 kbit / s) so that appropriate treatments can be used custom-designed in UMTS networks pass.

Since 2006 the number of devices available on the market decreases, support HSCSD. 2010 is further greatly diminished the importance of HSCSD favor of packet-oriented transmission. Some industrial applications (eg: telemetry ) still work with this type of transmission.

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