Circuit Switched Data

HSCSDCSDHigh-Speed Circuit-Switched DataGSM CSDcircuit-switched datacircuit-switched transportmobile data telephony
In communications, Circuit Switched Data (CSD) is the original form of data transmission developed for the time-division multiple access (TDMA)-based mobile phone systems like Global System for Mobile Communications (GSM).wikipedia
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Enhanced Data Rates for GSM Evolution

EDGEEGPRSGSM EDGE
After 2010 many telecommunication carriers dropped support for CSD, and CSD has been superseded by GPRS and EDGE (E-GPRS). HSCSD is also an option in Enhanced Data Rates for GSM Evolution (EDGE) and Universal Mobile Telecommunications System (UMTS) systems where packet data transmission rates are much higher.
It also enhances the circuit data mode called HSCSD, increasing the data rate of this service.

General Packet Radio Service

GPRSGSM GPRS(E)GPRS
After 2010 many telecommunication carriers dropped support for CSD, and CSD has been superseded by GPRS and EDGE (E-GPRS).
In addition to GPRS, there are two other GSM technologies which deliver data services: circuit-switched data (CSD) and high-speed circuit-switched data (HSCSD).

GSM

Global System for Mobile CommunicationsGSM networkGSM (850/900/1800/1900)
In communications, Circuit Switched Data (CSD) is the original form of data transmission developed for the time-division multiple access (TDMA)-based mobile phone systems like Global System for Mobile Communications (GSM).
This expanded over time to include data communications, first by circuit-switched transport, then by packet data transport via General Packet Radio Service (GPRS), and Enhanced Data Rates for GSM Evolution (EDGE).

UMTS

WCDMAW-CDMATD-SCDMA
HSCSD is also an option in Enhanced Data Rates for GSM Evolution (EDGE) and Universal Mobile Telecommunications System (UMTS) systems where packet data transmission rates are much higher.
These speeds are significantly faster than the 9.6 kbit/s of a single GSM error-corrected circuit switched data channel, multiple 9.6 kbit/s channels in High-Speed Circuit-Switched Data (HSCSD) and 14.4 kbit/s for CDMAOne channels.

Network switching subsystem

HLRHome Location RegisterMobile Switching Center
CSD uses a single radio time slot to deliver 9.6 kbit/s data transmission to the GSM network switching subsystem where it could be connected through the equivalent of a normal modem to the Public Switched Telephone Network (PSTN), allowing direct calls to any dial-up service.
The NSS originally consisted of the circuit-switched core network, used for traditional GSM services such as voice calls, SMS, and circuit switched data calls.

Circuit switching

circuit switchedcircuit-switchedcircuit-switched network
Channel allocation is done in circuit-switched mode, as with CSD.

Data

statistical datascientific datadatum
In communications, Circuit Switched Data (CSD) is the original form of data transmission developed for the time-division multiple access (TDMA)-based mobile phone systems like Global System for Mobile Communications (GSM).

Mobile phone

cell phonemobile phonesmobile
In communications, Circuit Switched Data (CSD) is the original form of data transmission developed for the time-division multiple access (TDMA)-based mobile phone systems like Global System for Mobile Communications (GSM).

Time-division multiplexing

TDMtime division multiplexingtime slot
CSD uses a single radio time slot to deliver 9.6 kbit/s data transmission to the GSM network switching subsystem where it could be connected through the equivalent of a normal modem to the Public Switched Telephone Network (PSTN), allowing direct calls to any dial-up service.

Data-rate units

Mbit/skbit/sGbit/s
CSD uses a single radio time slot to deliver 9.6 kbit/s data transmission to the GSM network switching subsystem where it could be connected through the equivalent of a normal modem to the Public Switched Telephone Network (PSTN), allowing direct calls to any dial-up service.

Modem

modemsdial-up modem56k modem
CSD uses a single radio time slot to deliver 9.6 kbit/s data transmission to the GSM network switching subsystem where it could be connected through the equivalent of a normal modem to the Public Switched Telephone Network (PSTN), allowing direct calls to any dial-up service.

Public switched telephone network

PSTNpublic telephone networktelephone network
CSD uses a single radio time slot to deliver 9.6 kbit/s data transmission to the GSM network switching subsystem where it could be connected through the equivalent of a normal modem to the Public Switched Telephone Network (PSTN), allowing direct calls to any dial-up service.

Dial-up Internet access

dial-updialupdial-up access
CSD uses a single radio time slot to deliver 9.6 kbit/s data transmission to the GSM network switching subsystem where it could be connected through the equivalent of a normal modem to the Public Switched Telephone Network (PSTN), allowing direct calls to any dial-up service.

CdmaOne

IS-95CDMA2G:''' cdmaOne
For backwards compatibility, the IS-95 standard also supports CDMA Circuit Switched Data. With the evolution of CDMA to CDMA2000 and 1xRTT, the use of IS-95 CDMA Circuit Switched Data declined in favour of the faster data transmission speeds available with the newer technologies.

Code-division multiple access

CDMAcode division multiple accessCDMA-450
However, unlike TDMA, there are no time slots, and all CDMA radios can be active all the time to deliver up to 14.4 kbit/s data transmission speeds.

CDMA2000

CDMA1xRTTCDMA 2000
With the evolution of CDMA to CDMA2000 and 1xRTT, the use of IS-95 CDMA Circuit Switched Data declined in favour of the faster data transmission speeds available with the newer technologies.

Data compression

compressionvideo compressioncompressed
At the same time, the speech-oriented audio compression used in GSM actually meant that data rates using a traditional modem connected to the phone would have been even lower than with older analog systems.

Telephone call

callphone callphone calls
A CSD call functions in a very similar way to a normal voice call in a GSM network.

Base station

base stationsWireless base stationradio base station
A single dedicated radio time slot is allocated between the phone and the base station.

Transcoding

transcodetranscodertranscodes
A dedicated "sub-time slot" (16 kbit/s) is allocated from the base station to the transcoder, and finally, another time slot (64 kbit/s) is allocated from the transcoder to the Mobile Switching Centre (MSC).

Mobile switching centre server

mobile switching center servermobile switching centersMobile Switching Centre
A dedicated "sub-time slot" (16 kbit/s) is allocated from the base station to the transcoder, and finally, another time slot (64 kbit/s) is allocated from the transcoder to the Mobile Switching Centre (MSC).

Analog signal

analoganalogueanalogue signal
At the same time, the speech-oriented audio compression used in GSM actually meant that data rates using a traditional modem connected to the phone would have been even lower than with older analog systems. At the MSC, it is possible to use a modem to convert to an "analog" signal, though this will typically actually be encoded as a digital pulse-code modulation (PCM) signal when sent from the MSC.

Pulse-code modulation

PCMLPCMLinear PCM
At the MSC, it is possible to use a modem to convert to an "analog" signal, though this will typically actually be encoded as a digital pulse-code modulation (PCM) signal when sent from the MSC.

Integrated Services Digital Network

ISDN ISDNISDN30
It is also possible to directly use the digital signal as an Integrated Services Digital Network (ISDN) data signal and feed it into the equivalent of a remote access server.