Four times faster than GSM, with a transfer rate of up to This speed makes it comparable to many fixed-line telecommunications networks and will allow users to access the Internet and other datacom services via a GSM network. In a GSM network single slots are allocated to each user, which has a standard data transfer rate of 9. In HSCSD, users are allocated multiple slots so that the transmission speed can be drastically increased, with some service providers offering rates of up to This enables internet access at the same speed of many dial-up modem services across fixed line networks.
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Technical[ edit ] CSD uses a single radio time slot to deliver 9. Prior to CSD, data transmission over mobile phone systems was done by using a modem, either built into the phone or attached to it. Such systems were limited by the quality of the audio signal to 2. 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. A single dedicated radio time slot is allocated between the phone and the base station.
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. 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.
Channel allocation is done in circuit-switched mode, as with CSD. This contrasts with the more widely adopted GPRS. Higher speeds are achieved as a result of superior coding methods, and the ability to use multiple time slots to increase data throughput.
It requires the time slots being used to be fully reserved to a single user. A transfer rate of up to The original error correction used in GSM was designed to work at the limits of coverage and in the worst case that GSM will handle. This means that a large part of the GSM transmission capacity is taken up with error correction codes.
HSCSD provides different levels of possible error correction which can be used according to the quality of the radio link. This means that in the best conditions This is because the user of an HSCSD connection does not have to wait for permission from the network to send a packet. This means that the primary reason to use HSCSD in this environment would be access to legacy dial up systems.
High-Speed Circuit-Switched Data
Circuit Switched Data