What is the difference between HSCSD and GPRS?

HSCSD-High Speed Circuit Switched Data and GPRS-General Packet Radio Service are second-generation network enhancements made to the most widely deployed 2nd generation standard GSM. GSM, which stands for Global System for Mobile Communications, is a second-generation network technology that started its journey in the early 1990s. The second generation of mobile networks primarily enabled voice calls and text messaging service, SMS, based on conventional circuit-switched technology. Circuit-switched technology is where a dedicated circuit is required in the mobile network to establish a connection.

HSCSD (High-Speed Circuit Switched Data) was a mobile data service in GSM networks that offered peak data rates of up to 64 kbps through circuit-switching; GPRS (General Packet Radio Service) is a packet-switched mobile data service in GSM networks that offers maximum speeds of up to 171.2 kbps.

HSCSD enables circuit-switched data in GSM

When the second generation of mobile networks was launched, the key services customers could get were voice calling and text messaging. The mobile users could use their GSM phones to call landline numbers and other cell phone numbers locally and internationally. That was possible through the PSTN connectivity (Public Switched Telephone Network) in the GSM networks. In addition, another network entity SMSC (Short Message Service Centre), enabled users to send and receive text messages. HSCSD or High-Speed Circuit-Switched Data was an enhancement that was added to the GSM networks later. As the name suggests, HSCSD worked on the existing circuit-switched technology, which was a quick win for mobile operators. HSCSD could be introduced in the GSM networks with minor modifications to the existing network architecture. However, the mobile phones needed a multi-slot capability to allow GSM phones to establish a connection through multiple timeslots instead of a single timeslot. GSM networks use a combination of FDMA (Frequency Divison Multiple Access) and TDMA (Time Division Multiple Access). A frequency channel called an ARFCN (Absolute Radio Frequency Channel Number) is split into eight (8) TDMA timeslots and is assigned to individual mobile users. Regular voice calls on a mobile phone can be established on a single timeslot at any given time. A single timeslot for mobile data services (internet) could enable up to 14.4 kbps after the HSCSD enhancement. Theoretically, that means 14.4 kbps x 8 timeslots = 115.2 kbps. But due to network limitations, HSCSD could only enable a maximum throughput of up to 64 kbps.

GPRS enables packet-switched data in GSM

The HSCSD enhancement was a quick win for mobile operators in terms of the network deployment because it required minimal modifications to the existing circuit-switched part of the network. But from an operational perspective, it was not efficient as it needed mobile phones to stay connected to the network for the entire duration of the data session. Engaging network resources for the whole data session was operationally expensive, and since the charging was linked to the connection duration, the solution was not ideal for customers. Therefore, a paradigm shift was required, which led to the introduction of the packet-switched technology, GPRS. GPRS-General Packet Radio Service still exists today (2021) and is aligned with the bursty nature of internet services. With internet services, users download and upload but can also be idle, i.e. neither downloading/uploading at a given time. GPRS was able to support this bursty use pattern, and it did not require the permanent engagement of network resources for the entire duration of a data session. Charging also followed the same principle and was based on the amount of transmitted data instead of the connection duration. The maximum throughput of GPRS with all eight timeslots (channels) is 171.2 kbps. GPRS required changes to the network architecture and introduced some modifications in the core network in the form of Serving GPRS Support Node (SGSN) and Gateway GPRS Support Node (GGSN).

Conclusion

HSCSD and GPRS are network enhancements made to the second-generation GSM networks to enable mobile internet services. HSCSD stands for High-Speed Circuit Switched Data, and it was a data service that used the circuit-switched part of a mobile network to allow a maximum data rate of up to 64 kbps. GPRS stands for General Packet Radio Service, and it is a data service that uses the packet-switched part of a mobile network to enable maximum data rates of up to 171.2 kbps.

Here are some helpful downloads

Thank you for reading this post, I hope it helped you in developing a better understanding of cellular networks. Sometimes, we need some extra support, especially when preparing for a new job, studying a new topic, or maybe just buying a new phone. Whatever you are trying to do, here are some downloads that can help you:

Students & fresh graduates: If you are just starting, the complexity of the cellular industry can be a bit overwhelming. But don’t worry, I have created this FREE ebook so you can familiarise yourself with the basics like 3G, 4G etc. As a next step, check out the latest edition of the same ebook with more details on 4G & 5G networks with diagrams. You can then read Mobile Networks Made Easy, which explains the network nodes, e.g., BTS, MSC, GGSN etc.

Professionals: If you are an experienced professional but new to mobile communications, it may seem hard to compete with someone who has a decade of experience in the cellular industry. But not everyone who works in this industry is always up to date on the bigger picture and the challenges considering how quickly the industry evolves. The bigger picture comes from experience, which is why I’ve carefully put together a few slides to get you started in no time. So if you work in sales, marketing, product, project or any other area of business where you need a high-level view, Introduction to Mobile Communications can give you a quick start. Also, here are some templates to help you prepare your own slides on the product overview and product roadmap.

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