GGSN and SGSN are two essential parts of the mobile core network in GPRS-based mobile networks i.e. GSM (2G) and UMTS (3G). The mobile core network is very central to the overall mobile network because it allows the subscribers of a mobile operator to use all the services that they are entitled to. The original GSM networks were mainly designed to offer voice calls and SMS (text messages), and the mobile core network in the GSM architecture was called Network Switching System (NSS). The original GSM networks only had the circuit-switched part that consisted of dedicated circuits for voice calls and text messages. Those networks could also offer limited data sessions (mobile internet) but the circuit-switched technique did not prove to be very efficient for data services.
So, that is where the 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. The 4G LTE networks, however, use a more advanced mobile core network called the EPC or Evolved Packet Core. We would recommend ‘EPC and 4G Packet Networks’ as a technical reference on EPC. You can find this book on Amazon’s website here and on Amazon UK’s website here. If you need to brush up on your understanding of GPRS and EDGE, check out our dedicated post on that topic by clicking here.
What is GGSN?
GGSN stands for Gateway GPRS Support Node and it is a network component that connects the GSM and UMTS mobile networks to the external packet networks such as the internet. The word ‘packet’ is very important in this context because GGSN is all about packet-switched networks that enable mobile data. GGSN is responsible for tasks related to the mobile internet (data) in those networks that employ GPRS and inter-related technologies. As the GPRS technology is relevant only for GSM and UMTS networks, the GGSN component is part of only those 2G and 3G networks that are based on GSM and UMTS technologies respectively. For clarity, as part of GSM, we mean both GPRS and EDGE networks.
Historically speaking, the packet-based mobile data was introduced in GSM networks through GPRS technology. GGSN was therefore 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. More information on the mobile core network in our post here.
The 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. You can see the high-level network architecture of the WCDMA based-UMTS networks in the diagram below to see where GGSN fits in. If you are interested in the design aspects of WCDMA networks, we recommend reading ‘WCDMA Design Handbook’ on Amazon’s website here or Amazon UK’s website here.
Just 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.
What is SGSN?
SGSN stands for Serving GPRS Support Node, and it is an essential network component in the GPRS-based 2G and 3G networks. As mentioned earlier, GPRS was an enhancement made to the GSM networks to introduce packet-based mobile data. SGSN (together with GGSN) was then added, as a key packet-switched network entity in the GSM networks. The same approach was followed by the EDGE and UMTS networks also. SGSN provides the packet-switched capability to mobile networks for enabling mobile data services i.e. mobile internet. The packets of data with information content (e.g. results from 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. Have a look at this post for more information on packet-switching and circuit-switching.
In the overall 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. This way, it allows mobile phones to be able to connect with 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 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 to the mobile phone user. You can learn more about RAN in our dedicated post here.
Have a look at the following diagrams to see how SGSN and GGSN fit in the 2G, 3G and 4G networks. What you see below are the combinations of 2G & 3G and 3G & 4G networks.
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 over to the external data network. On the way back, everything is reversed.
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