HSCSD

High-Speed Circuit-Switched Data (HSCSD), nyaéta standar atawa téknologi nu mangrupa paningkatan tina standar Circuit Switched Data, mékanisme pangiriman data dina sistem telepon mobil nu leuwih tiheula. Laju pangiriman datana opat kali leuwih gancang batan GSM, kalayan laju data nepi ka 38.4 Kbps.

Saru jeung CSD, alokasi kanal dina HSCSD digawekeun dina jero modeu circuit switched. Bédana jeung CSD ngan dina kamampuh pikeun ngagunakeun padika-padika pangkodeuan (coding) nu béda-béda sarta / atawa multi time slot pikeun ngaronjatkeun throughput data.

Inovasi séjenna dina HSCSD nyaéta padika koréksi kasalahan nu béda-béda bisa dipaké pikeun pangiriman data. Koréksi kasalahan orisinil nu digunakeun dina GSM mah dirarancang dina kaayaan kawatesna wengkuan GSM. Hal ieu boga harti yén sabagian gedé kapasitas pangiriman GSM dieusian ku kodeu koréksi kasalahan. Sedengkeun HSCSD nyadiakeun tingkat koréksi kasalahan nu béda-béda nu bisa digunakeun gumantung kana kualitas tumbu radiona. Hartina, dina kaayaan nu pangalusna, laju 14.4 kbit/s bisa dihontal ku HSCSD ngaliwatan sahiji time slot nu mana dina CSD mah ngan mampuh mawa 9.6 kbit/s, pikeun ngaronjatkeun troughput saloba 50%.

Inovasi lianna dina HSCSD nyaéta kamampuh pikeun ngagunakeun multi time slot dina waktu nu bareng. Ku cara ngagunakeun salobana opat (4) time slot, HSCSD bisa ngaronjatkeun laju pangiriman maksimum nepi ka 57.6 kbit/s (4 kali 14.4 kbit/s), sarta, sanajan dina kaayaan radio nu goréng nu merlukeun koréksi kasalahan undakan nu leuwih luhur, masih bisa nawarkeun paningkatan laju opat kali dibandingkeun CSD (38.4 kbit/s vs 9.6 kbit/s). Ku cara ngagabungkeun nepi ka 8 time slot GSM, kapasitas bisa dironjatkeun nepi ka 115 kbit/s.

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HSCSD requires the time slots being used to be fully reserved to a single user. It is possible that either at the beginning of the call, or at some point during a call, it will not be possible for the user's full request to be satisfied since the network is often configured so that normal voice calls take precedence over additional time slots for HSCSD users.

The user is typically charged for HSCSD at a rate higher than a normal phone call (e.g., by the number of time slots allocated) for the total period of time that the user has a connection active. This makes HSCSD relatively expensive in many GSM networks and is one of the réasons that packet-switched GPRS, which typically has lower pricing (based on amount of data transferred rather than the duration of the connection), has become more common than HSCSD.

Apart from the fact that the full allocated bandwidth of the connection is available to the HSCSD user, HSCSD also has an advantage in GSM systems in terms of lower average radio interface latency than GPRS. This is because the user of a HSCSD connection does not have to wait for permission from the network to send a packet.

HSCSD is also an option in EDGE and UMTS systems where packet data transmission rates are much higher. In the UMTS system the advantages of HSCSD over packet data are even lower since the UMTS radio interface has been specifically designed to support high bandwidth, low latency packet connections. This méans that the primary réason to use HSCSD in this environment would be access to legacy dial up systems.

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