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, they were very limited in what they could offer to support the internet on the phone. They employed circuit-switched technologies for voice, SMS and also mobile data. At that time a technology called high-speed circuit-switched-data (HSCSD) in GSM networks could enable maximum downlink speeds of 57.6 kbps. The approach to mobile data in GSM networks changed when packet-switched technology was introduced through General Packet Radio Service – GPRS to offer efficient mobile data services. 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 the use of SGSN and GGSN?
SGSN and GGSN are two essential components of 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), and even though technologies like Circuit-Switched-Data (CSD) and High-Speed CSD could technically enable data, it was not efficient to use dedicated circuits for data services. That is where General Packet Radio Service (GPRS) enhancement came in which was based on the packet-switched technology. As part of that enhancement in the GSM networks (2G), a packet-switched part was introduced into the core network architecture in the form of Serving GPRS Support Node (SGSN) and Gateway GPRS Support Node (GGSN). Later, the UMTS based 3G 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.
What is SGSN and how it works?
SGSN stands for Serving GPRS Support Node, and it 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. The same packet-switched approach was followed by EDGE and UMTS networks also. 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.
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.
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. You can learn more about RAN in our dedicated post here. 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.
What is GGSN and how it works?
GGSN stands for Gateway GPRS Support Node and it is a network component that connects the GSM and UMTS mobile networks 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.
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 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, GGSN is owned and managed by the mobile operators (e.g. Vodafone, T-Mobile etc.), who source this network component from mobile network vendors like Ericsson, Huawei, Nokia etc.
Do we have SGSN and GGSN in 4G LTE?
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. 4G LTE networks can utilise the circuit-switched parts of 2G GSM and 3G UMTS networks to enable services like voice and SMS that require dedicated circuits. 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.
SGSN vs. GGSN – Conclusion
To summarise, SGSN stands for Serving GPRS Support Node and is a network entity that provides the packet-switched capability to mobile networks. 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.
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, or 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 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 product overview and product roadmap.