What is HSCSD?

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High-speed circuit-switched data, or HSCSD, is the next generation of circuit-switched data available for GSM mobile phone systems. HSCSD allows wireless data to be transmitted at a rate of 57.6 kilobits per second. HSCSD is currently available in more than 25 countries and is especially popular in Europe. HSCSD first became popular at the beginning of the 21st Century, starting to appear in many European countries around the year 2000.

HSCSD is a standard that uses multiple time slots to send data at the same time, thus increasing transmission capacity. The more time slots that are used, the faster the transmission rate can be. These slots usually support a bandwidth of anywhere between 9.6 kilobits and 14.4 kilobits. HSCSD can use a maximum of four slots at a time, thus the 57.6 kilobits of total transmission rate.

HSCSD can be used only for data transfer applications, not voice. Due to the fact that voice transmissions always take precedence over data, there may be times when an HSCSD connection does not work as it should, because more slots are needed for voice applications. HSCSD has the advantage over some other types of protocols on GSM phones because it has a dedicated circuit-switched channel which makes its transfers more reliable. This can be especially helpful for time sensitive transfers such as video. HSCSD also receives less interference from outside sources as compared to other protocols, making both voice and data sessions of higher quality.

However, some other protocols, such as general packet radio service (GPRS) are actually more popular over GSM networks. This is mainly a cost factor. GPRS is much more efficient than HSCSD and therefore is used more frequently by companies building infrastructure and services. Thus, GPRS has a greater market saturation than does HSCSD based on this cost factor alone.

Most mobile phone companies always try to maintain a market edge. Using a higher-priced phone service does not keep a company competitive, simply because those charges must be passed to the customer. The customer is going to consider each service and make a determination based not only on quality, but on price, with price often being a deciding factor. This explains why HSCSD is not as common as other protocols.

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HSCSD (High Speed Circuit Switched Data) is a specification for data transfer over GSM networks. HSCSD utilizes up to four 9.6Kb or 14.4Kb time slots, for a total bandwidth of 38.4Kb or 57.6Kb.
14.4Kb time slots are only available on GSM networks that operate at 1,800MHz. 900Mhz GSM networks are limited to 9.6Kb time slots. Therefore, HSCSD is limited to 38.4Kbps on 900Mhz GSM networks. HSCSD can nly achieve 57.6Kbps on 1,800Mhz GSM networks.
The History of HSCSD

HSCSD was an enhancement to to earlier CSD (Circuit Switched Data) standard.
EDGE (Enhanced Data-Rates for GSM Evolution) enabled GSM networks are able to implement ECSD (Enhanced Circuit Switched Data), an enhanced version of HSCSD. ECSD increases the bandwidth of each timeslot to 48Kb and allows the use of eight timeslots, which gives a total transmission speed of 384Kbps.



Both HSCSD/ECSD and GPRS are likely to eventually be phased out in favor of UMTS, which is a packet switched technology with speeds up to 2Mbps.

HSCSD vs. GPRS

HSCSD has an advantage over GPRS in that HSCSD supports guaranteed quality of service because of the dedicated circuit-switched communinations channel. This makes HSCSD a better protocol for timing-sensitive applications such as image or video transfer.
GPRS has the advantage over HSCSD for most data transfer because HSCSD, which is circuit-switched, is less bandwidth efficient with expensive wireless links than GPRS, which is packet-switched.
Due to this, HSCSD is not as widespread as GPRS. HSCSD is, however, currently available in over 27 countries.