High-speed circuit switched data (HSCSD) is a feature that enables the co-allocation of multiple full rate traffic channels (TCH/F) of GSM into an HSCSD configuration i.e. many time slots of a frame can be allotted to a single user. The number of time slots bundled together and given to a user depends on the requirement of the user. However, the maximum number of time slots that can be used simultaneously for a single user is 4. Accordingly the resource allocation is flexible which yields different data rates.

The frequency allocation in HSCSD is flexible in nature. The network dynamically assigns resources depending on the end users data transfer needs. Every network operator has it's own strategy for the resource allotment. The provision of the asymmetric air interface connection (means giving variable time slot to different users) allows simple mobile equipment to receive data at higher rates than otherwise would be possible with a symmetric connection.

As shown in Table 1, HSCSD promises a maximum data rate of $14.4 \times 4= 57.6 Kbps.$

Adoption of this new technology has brought many benefits to wireless operators, service providers and end users.

• For operators, migration to HSCSD brought data into the mainstream just by relatively standard software upgrades to Base Station (BS) and Mobile Switching Center (MSC) equipment.
• Service providers will also be able to offer guaranteed quality of service and cost efficient mass-market applications, such as direct IP where users make circuit switched data calls straight into a GSM network router connected to the Internet.
• To the end-user, the value-added service provider or the operator is equivalent to an Internet service provider that offers a fast, secure dial-up Internet protocol service at cheaper mobile-to-mobile rates For end-users, HSCSD enables the roll-out of mainstream high-end segment services that enable faster web browsing, file downloads, mobile video-conference and navigation, telematics and bandwidth secure mobile local area network (LAN) access. End users wanting to use HSCSD have to subscribe to general bearer services. Supplementary services applicable to general bearer services can be used simultaneously with HSCSD.

HSCSD is provided within the existing mobility management. Roaming is also possible. The throughput for an HSCSD connection remains constant for the duration of the call, except for interruption of transmission during handoff. The handoff is simultaneous for all time slots making up an HSCSD connection. Firmware on most current GSM PC cards needs to be upgraded. The reduced Radio link protocol (RLP) layer also means that a stronger signal strength is necessary. Multiple time slot usage is probably only efficiently available in off-peak times, increasing overall off-peak idle capacity usage. HSCSD is not a very feasible solution for bursty data applications.