Circuit-Switching and Packet-Switching in mobile networks

Circuit-switching and packet-switching techniques have been part of the telecommunication industry for a very long time. The concept of packet-switched telecom networks had been developed even before the first generation (1G) of mobile networks was introduced. However, mobile networks started with circuit-switched techniques in the early 1990s and gradually moved towards packet-switching.

Circuit-Switching is used in 2G and 3G mobile networks for enabling voice calls and text messages through dedicated circuits; Packet-Switching is more efficient and uses shared circuits to enable IP-based mobile data in all mobile networks, and IP voice calls and texts in 4G LTE and 5G NR networks.

When the digital era of mobile communications started with 2G GSM (Global System for Mobile Communications) and D-AMPS (Digital Advanced Mobile Phone System) networks in 1991-92, circuit-switching was the only available communication technique. Packet-Switching was first introduced in the second-generation mobile networks around the year 2000, and it was later also adopted by the third-generation networks. 4G LTE and 5G NR mobile networks rely solely on packet-switching to provide customers with IP-based voice, SMS, and data services. Let us now have a detailed look at the circuit-switching and packet-switching techniques to find out how and why they are used in 2G, 3G, 4G and 5G mobile networks.

Difference between circuit-switching and packet-switching

The term circuit-switching or circuit-switched in mobile communications refers to a traditional switching technique that offers real-time services such as voice in 2G and 3G mobile networks. With the Circuit-Switched (CS) approach, a dedicated radio network resource (timeslot) is assigned to individual mobile users for the entire call duration when a user places a call. The circuit-switched technology is a reliable way to ensure high quality of service (QoS) in voice calls. However, circuit-switching isn’t the most efficient technique as it engages the radio network resources for the entire call duration, even when the user is not communicating. Due to engaging the network resources permanently for the call or session duration, circuit-switching limits the number of simultaneous calls (or sessions) that the network can accommodate at any given time.

On the other hand, Packet-Switching (PS) is a technique that allows mobile networks to transmit and receive data without permanently engaging the radio network resources for each user. PS sends packets of data bursts at different time intervals while sharing the available channel capacity with multiple users. These packets have a ‘header’ with the destination information for each packet and a payload that contains the actual data or information that is being transmitted. The switching nodes use these headers to determine the source and destination of the packets so that the data packets can be directed to the desired subscribers (devices) using the best possible route.

Circuit and packet-switching in 2G and 3G mobile networks

The voice calling and SMS (Short Message Service) services in GSM (2G) and UMTS (3G) networks are based on the circuit-switched technique, whereas the mobile data (internet) services are based on packet-switching. In second-generation (2G) mobile networks, packet-switched technology was introduced in the latter half of the second generation to enable efficient mobile data (internet) services. Before that, GSM networks had a circuit-switched data capability (CSD), which could offer limited mobile internet services to customers over the cellular network. An enhancement to CSD, High-Speed Circuit Switched Data (HSCSD), was introduced in GSM before the introduction of GPRS to improve circuit-switched data speeds.

In 2G GSM networks, packet-switching was added as part of the General Packet Radio Service (GPRS) enhancement, whereas in cdmaOne (IS-95) networks, packet-switching was added as part of the IS-95 B enhancement. GPRS enhancement in GSM networks took place in the early 2000 and led to the introduction of two new core network nodes, GGSN and SGSN. These new nodes (Gateway GPRS Support Node) and Serving GPRS Support Node) were the packet-switched extension in the GSM networks and co-existed alongside the MSC that continued to provide the circuit-switching capability for voice calls and SMS. The 3G UMTS (Universal Mobile Telecommunication System) and 3G CDMA2000 (Code Division Multiple Access – Year 2000) networks followed the same approach and used both circuit-switched (CS) and packet-switched (PS) capabilities.

4G LTE and 5G NR networks only use packet-switching

4G LTE and 5G NR networks do not have any circuit-switched nodes; therefore, they are data-only networks. They use packet-switching for providing voice, text and data services. 4G LTE networks use a technology called Voice over LTE (VoLTE) that utilises the packet-switched part of the network to deliver voice calls and SMS. LTE networks have a 2G/3G circuit-switched fallback (CSFB) that allows them to place any voice calls on 2G/3G networks if the mobile network or user devices do not support the VoLTE capability. 5G networks also have an equivalent technology, Voice over New Radio (VoNR), that follows the same principle as VoLTE to offer voice and text services over the packet-switched part of the network. Whether a mobile network uses VoLTE or VoNR depends on the 5G network deployment type, i.e. non-standalone or standalone. VoLTE and VoNR technologies depend on whether a mobile network uses an LTE core network (EPC) or a 5G core network. I have a dedicated post on standalone and non-standalone 5G networks that can help you understand how these 5G deployments differ and work together.

is packet-switching better than circuit-switching?

The efficient use of radio network resources has been fundamental to the evolution of mobile networks. The multiple access techniques like TDMA, CDMA and OFDMA and modulation schemes like QPSK and QAM have played a vital role in achieving that. When a network is efficient, it can better utilise the resources to extract higher data rates from the available bandwidth, which improves customer data rates. The packet-switching technique makes efficient use of available mobile radio network resources. It doesn’t mean that circuits are not used; they are still used. But rather than being dedicated to individual users, the circuits are shared to serve multiple users simultaneously. When the data payload for an individual has been broken down into smaller chunks of data packets, the packets are marked and sent to the user through the best possible available route.

Conclusion

Circuit-switching and packet-switching are two fundamental communication techniques used by mobile networks to offer voice, SMS and data services to customers. Circuit-Switched is the older of the two techniques used in 2G and 3G networks primarily for making and receiving voice calls and sending & receiving text messages. Packet-Switching is the newer of the two techniques used in 2G and 3G networks for mobile internet and in 4G and 5G networks for all services, including voice, SMS and internet. However, Circuit-Switching engages the network resources for the entire session duration (e.g. voice call), so it isn’t very efficient. On the other hand, Packet-Switching is very efficient as it shares the network resources between multiple users to send and receive the overall data payload in the form of data bursts.

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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