SGSN and GGSN are two terminologies that started their journey in the late 1990s when General Packet Radio Service (GPRS) was introduced. SGSN and GGSN are two core network nodes that have been part of mobile communications since then.
GGSN (Gateway GPRS Support Node) and SGSN (Serving GPRS Support Node) are two core network nodes in 2G GSM and 3G UMTS networks that enable packet-switched mobile internet. GGSN and SGSN were added to GSM networks as part of the GPRS enhancement, and they are used by both GSM and 3G UMTS networks.
When we use our smartphones today for 4G and 5G services, we take the high-speed internet on our phones for granted. However, when the most widely deployed 2G GSM networks were launched in the early 1990s, they were limited in what they could offer to support the internet on the phone. GSM networks originally employed circuit-switched technologies for voice, SMS and mobile data. At that time, High-Speed Circuit-Switched-Data (HSCSD) technology could enable maximum downlink speeds of 57.6 kbps in the GSM networks through traditional circuit-switching. The approach for offering mobile data changed in the GSM networks when a highly efficient technology General Packet Radio Service (GPRS) was introduced based on packet-switching. With GPRS, two new network nodes, SGSN and GGSN, were added to the GSM network architecture. These nodes still exist in the 2G GSM and 3G UMTS networks, and every time we see the E symbol or the H/H+ symbol on our mobile phones, we are connected to these nodes to access the internet through our phones.
What is SGSN – Serving GPRS Support Node?
SGSN stands for Serving GPRS Support Node, and it is an essential core network node in GPRS networks that enables packet-switched mobile data (internet) in 2G GSM and 3G UMTS networks. SGSN works with GGSN and is responsible for mobility management, billing, and the management of data sessions.
SGSN is an essential network entity in GPRS (General Packet Radio Service), EDGE (Enhanced Data for Global Evolution) and 3G UMTS networks. SGSN (together with GGSN) was added to introduce the packet-switched technology within 2G GSM networks. In the overall 2G /3G mobile core network, SGSN can be seen as the “packet-switched” version of the MSC. So, just like the MSC utilises its circuit-switched capabilities to facilitate voice services, SGSN uses its packet-switched capabilities to facilitate data services. In the network architecture, SGSN sits between Radio Access Network (RAN) and Gateway GPRS Support Node (GGSN). It communicates with mobile phones through RAN and communicates with external networks through GGSN. That way, it allows our mobile phones to be able to connect to external networks.
What is GGSN – Gateway GPRS Support Node?
GGSN stands for Gateway GPRS Support Node and it is a network node that connects SGSN (Serving GPRS Support Node) to external data networks such as the internet and X.25 for enabling packet-switched mobile data (internet) in 2G GSM and 3G UMTS networks. GGSN is part of the mobile core network.
GGSN is a network component that works closely with SGSN (Serving GPRS Support Node) and connects the core network in 2G GSM and 3G UMTS to external packet networks. The word ‘packet’ is important in this context because GGSN is all about packet-switched networks that enable mobile data. GGSN was added to the mobile core network as a gateway to connect the GPRS network to the external data world. From a network architecture point of view, GGSN is situated between the Serving GPRS Support Node (SGSN) and the external data networks such as the internet and X.25 networks.
What are SGSN and GGSN used for?
SGSN and GGSN are used for connecting our cell phones to mobile internet through GPRS, EDGE, HSPA and HSPA+ technologies in 2G GSM and 3G UMTS networks. SGSN is the main node that performs packet-switching functions, whereas GGSN is more of a router that connects SGSN to the external data networks.
SGSN and GGSN are two essential nodes within the GSM and UMTS mobile core networks. These nodes allow us to access external networks such as the internet through our mobile phones when we are on 2G or 3G networks. The core network is central to the overall mobile network because it allows the subscribers of a mobile operator to access all the services that they are entitled to. The original GSM networks were mainly designed to support voice calls and SMS (text messages). Even though technologies like Circuit-Switched-Data (CSD) and High-Speed Circuit-Switched Data (HSCSD) could technically enable data, it was not the best use of network resources by engaging dedicated circuits for data sessions. That is where the General Packet Radio Service (GPRS) enhancement came in with its packet-based approach. As part of the GPRS enhancement, a packet-switched part was introduced into the core network architecture of GSM by adding two new nodes. These nodes are called the Serving GPRS Support Node (SGSN) and Gateway GPRS Support Node (GGSN). Later, the 3G UMTS networks also followed the same approach and continued with separate circuit-switched and packet-switched network entities that included SGSN and GGSN. 4G LTE networks, however, use a more advanced mobile core network called the EPC or Evolved Packet Core.
How does SGSN work?
SGSN is responsible for the two-way communication of data packets with information content (e.g. WhatsApp message) between the mobile phone user and the destination network in the geographical area it serves. SGSN connects to external networks through GGSN and to the user through RNC and NodeB.
SGSN provides the packet-switched capability to GSM and UMTS networks to enable mobile data (mobile internet). The packets of data with information content (e.g. results from a Google search) can be sent and received by the mobile phones operating in a given geographical area covered by a serving SGSN. The SGSN is responsible for mobility management, billing, and the management of data sessions.
When SGSN receives data (with information content) from mobile phone users, it passes that on to GGSN. GGSN converts that data into a suitable protocol format (e.g. IP) before sending it over to the destination external network. On the way back, the process is reversed. So, the data is received from the external network in the format of that network and then converted by GGSN into a protocol format that mobile phones can understand before finally sending it to the mobile phone user. Have a look at the following network diagram to see how SGSN fits within the 2G / 3G network architecture.
If some of the network entities above are unclear to you, you can check out our Mobile Networks Made Easy to get some guidance.
How does GGSN work?
GGSN acts as a router that sits between SGSN and external data networks (e.g. internet) to enable two-way communication. It receives data packets from a mobile user through SGSN and converts them into the format required by the destination network (e.g. IP). On the way back, the process is reversed.
GGSN receives data from a mobile user via the SGSN, converts the data into the protocol format that the destination requires (e.g. IP format for the internet) and sends that on to the destination data network (e.g. internet). On the way back, everything is reversed, so it receives data from the external network in the protocol format of the external network, which is then sent to the serving SGSN in the protocol format of the destination. The serving SGSN here means the SGSN that is serving the end-user (destination). For the external networks, GGSN is just a router interfacing the mobile packet-switched network (GPRS/EDGE/UMTS) and the external data networks. Have a look at the high-level network architecture of the UMTS networks in the diagram above to see where GGSN fits in.
Like the other key parts of the mobile core network, SGSN and GGSN are owned and managed by the mobile operators (e.g. Vodafone, T-Mobile etc.), who procure this network component from mobile network vendors like Ericsson, Huawei, Nokia etc.
Do we have SGSN and GGSN in 4G LTE networks?
4G LTE networks do not have SGSN and GGSN, but they use equivalent network nodes that offer the packet-switching capability in 4G. LTE networks are fully packet-switched and use Serving Gateway (S-GW) as the equivalent of SGSN and Packet Data Network Gateway (PDN-GW) as the equivalent of GGSN.
SGSN and GGSN network nodes only exist in GPRS, EDGE and UMTS networks. The 4G LTE mobile core network, Evolved Packet Core (EPC), consists of different network entities that perform the packet-switched tasks. The equivalent of SGSN in LTE is Serving Gateway (S-GW), as shown in the network diagram below. The equivalent of GGSN in LTE is Packet Data Network Gateway (PDN-GW). 4G LTE networks only use packet-switched technology which is why you cannot see the circuit-switched representation in the 4G LTE network architecture below. 4G LTE networks however have a circuit-switch fallback option that utilises the 2G GSM and 3G UMTS networks to facilitate circuit-based voice calls and SMS. Since the future of voice and SMS is all data, LTE networks have a capability called Voice over LTE (VoLTE) that allows packet-switched LTE networks to enable IP based voice calls and SMS. 5G networks have an equivalent technology, Voice over New Radio (VoNR) that enables voice calls and SMS through the 5G core network.
SGSN vs GGSN – Conclusion
SGSN and GGSN are the mobile core network nodes within 2G GSM and 3G UMTS networks that enable packet-switched mobile data. SGSN stands for Serving GPRS Support Node and is a network entity that provides the packet-switched capability. GGSN stands for Gateway GPRS Support Node and is a gateway situated between SGSN and external data networks. GGSN receives data from a mobile user via SGSN, converts that into a suitable protocol format (e.g. IP) and sends it over to the external data network. On the way back, everything is reversed. Before the introduction of SGSN and GGSN, GSM mobile networks only had the circuit-switching capability, which enabled voice calls, text messages and limited circuit-switched data (CSD). SGSN and GGSN were added to the mobile core network architecture to support General Packet Radio Service (GPRS) for offering packet-switched mobile data services. The circuit-switching capability in GSM networks is provided by the MSC (Mobile Switching Centre), whereas the packet-switching function is handled by SGSN (Serving GPRS Support Node). The EDGE enhancement (Enhanced Data rates for Global Evolution) in GSM makes use of the same network nodes for mobile data services. The 3G UMTS networks and the HSPA (High-Speed Packet Access) enhancements also rely on SGSN and GGSN for all things mobile data. 4G LTE networks are fully packet-switched and do not have a circuit-switched part. LTE networks have a different architecture and use Serving Gateway (S-GW) and Packet Data Network Gateway (PDN-GW) for packet-switching.
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 extra support, especially when preparing for a new job, studying a new topic, or 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.
