High-Speed Circuit-Switched Data
Encyclopedia
High-speed circuit-switched data (HSCSD), is an enhancement to Circuit Switched Data
(CSD), the original data transmission mechanism of the GSM mobile phone
system, four times faster than GSM, with data rates up to 38.4 kbit/s.
Channel allocation is done in circuit-switched
mode, as with CSD. Higher speeds are achieved as a result of superior coding methods, and the ability to use multiple time slots to increase data throughput.
The other innovation in HSCSD is the ability to use multiple time slots at the same time. Using the maximum of four time slots, this can provide an increase in maximum transfer rate of up to 57.6 kbit/s (i.e., 4 × 14.4 kbit/s) and, even in bad radio conditions where a higher level of error correction needs to be used, can still provide a four times speed increase over CSD (38.4 kbit/s versus 9.6 kbit/s). By combining up to eight GSM time slots the capacity can be increased to 115 kbit/s.
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 to allow normal voice calls to 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 reasons that packet-switched general packet radio service (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 an HSCSD connection does not have to wait for permission from the network to send a packet.
HSCSD is also an option in enhanced data rates for GSM evolution
(EDGE) and universal mobile telephone system
(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 means that the primary reason to use HSCSD in this environment would be access to legacy dial up systems.
Circuit Switched Data
Circuit Switched Data is the original form of data transmission developed for the time division multiple access -based mobile phone systems like Global System for Mobile Communications...
(CSD), the original data transmission mechanism of the GSM mobile phone
Mobile phone
A mobile phone is a device which can make and receive telephone calls over a radio link whilst moving around a wide geographic area. It does so by connecting to a cellular network provided by a mobile network operator...
system, four times faster than GSM, with data rates up to 38.4 kbit/s.
Channel allocation is done in circuit-switched
Circuit switching
Circuit switching is a methodology of implementing a telecommunications network in which two network nodes establish a dedicated communications channel through the network before the nodes may communicate. The circuit guarantees the full bandwidth of the channel and remains connected for the...
mode, as with CSD. Higher speeds are achieved as a result of superior coding methods, and the ability to use multiple time slots to increase data throughput.
Description
One innovation in HSCSD is to allow different error correction methods to be used for data transfer. 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 14.4 kbit/s can be put through a single time slot that under CSD would only carry 9.6 kbit/s, for a 50% improvement in throughput.The other innovation in HSCSD is the ability to use multiple time slots at the same time. Using the maximum of four time slots, this can provide an increase in maximum transfer rate of up to 57.6 kbit/s (i.e., 4 × 14.4 kbit/s) and, even in bad radio conditions where a higher level of error correction needs to be used, can still provide a four times speed increase over CSD (38.4 kbit/s versus 9.6 kbit/s). By combining up to eight GSM time slots the capacity can be increased to 115 kbit/s.
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 to allow normal voice calls to 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 reasons that packet-switched general packet radio service (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 an HSCSD connection does not have to wait for permission from the network to send a packet.
HSCSD is also an option in enhanced data rates for GSM evolution
Enhanced Data Rates for GSM Evolution
Enhanced Data rates for GSM Evolution is a digital mobile phone technology that allows improved data transmission rates as a backward-compatible extension of GSM...
(EDGE) and universal mobile telephone system
Universal Mobile Telecommunications System
Universal Mobile Telecommunications System is a third generation mobile cellular technology for networks based on the GSM standard. Developed by the 3GPP , UMTS is a component of the International Telecommunications Union IMT-2000 standard set and compares with the CDMA2000 standard set for...
(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 means that the primary reason to use HSCSD in this environment would be access to legacy dial up systems.
See also
- Circuit-switched dataCircuit Switched DataCircuit Switched Data is the original form of data transmission developed for the time division multiple access -based mobile phone systems like Global System for Mobile Communications...
(CSD) - Global system for mobile communicationsGlobal System for Mobile CommunicationsGSM , is a standard set developed by the European Telecommunications Standards Institute to describe technologies for second generation digital cellular networks...
(GSM) - General packet radio serviceGeneral Packet Radio ServiceGeneral packet radio service is a packet oriented mobile data service on the 2G and 3G cellular communication system's global system for mobile communications . GPRS was originally standardized by European Telecommunications Standards Institute in response to the earlier CDPD and i-mode...
(GPRS) - Mobile phoneMobile phoneA mobile phone is a device which can make and receive telephone calls over a radio link whilst moving around a wide geographic area. It does so by connecting to a cellular network provided by a mobile network operator...
- Time division multiple accessTime division multiple accessTime division multiple access is a channel access method for shared medium networks. It allows several users to share the same frequency channel by dividing the signal into different time slots. The users transmit in rapid succession, one after the other, each using its own time slot. This...
(TDMA) - List of device bandwidths