GGSN
The Gateway GPRS Support Node (GGSN) connects the GPRS network on one side via the SGSN to outside networks such as the Internet. These outside networks are called packet data networks (PDNs). The GGSN acts as an edge router between the two different networks — the GGSN forwards incoming packets from the external PDN to the addressed SGSN and the GGSN also forwards outgoing packets to the external PDN. the GGSN also converts the packets from the GPRS packets with SGSN to the external packets, such as IP or X.25.
SGSN
The Serving GPRS Support Node (SGSN) connects the GPRS network to GTPv1 compatible mobile stations, and mobile units (such as UTRAN and ETRAN) on one side and to the gateway node (GGSN), which leads to external networks, on the other side. Each SGSN has a geographical area, and mobile phones in that area connect to the GPRS network through this SGSN. The SGSN also maintains a location register that contains customer’s location and user profiles until they connect through a different SGSN at which time the customer information is moved to the new SGSN. This information is used for packet routing and transfer, mobility management also known as location management, logical link management, and authentication and billing functions.
GTPv2
GTPv2, defined in 3GPP TS 29.274, is dramatically differnet from GTPv1, defined in 3GPP TS 29.060. Where in GTPv1 the tunnel is between the SGSN and the GGSN, in GTPv2 The SGSN is between the MME and the LTE Serving Gateway (S-GW), beyond which is the PDN gateway (P-GW). Even tunnel management messages have changed significantly.
Network diagram for GTPv2
Device roles on a GTPv2 network
| Device role | Neighboring Devices | Interfaces used | Protocols used |
|
Mobile Users |
Mobile Stations (MS) |
Radio Access Tech- nology (RAT) |
— |
|
GTPv1 Mobile Sta- tions (MS) |
Mobile Users, SGSN |
Gb |
IP, Frame Relay |
|
GTPv2 Mobile Sta- tions (MS) |
Mobile Users, MME |
??? |
IP, Frame Relay |
|
SGSN (local) |
GTPv1 MS, SGSN, S-GW |
??? |
IP, Frame Relay, GTPv1, GTP’ |
|
S-GW |
SGSN, MME, P-GW |
??? |
IP, GTPv2, GTP’ |
|
P-GW |
S-GW, Internet, other exter services |
nal ??? |
IP, GTPv2 |
|
GTPv2–C |
GTPv2-C is the control layer messaging for GTPv2. It is used by LTE mobile stations, SGSN units for backwards compatibility, and SGWs that are the gateway to other networks. The messaging is very different from GTPv1. GTPv2-C is required to communicate with the Mobility Management Entity (MME) to create, change and delete EPS bearers when handover events happen, and to create Forwarding tunnels. The protocol is also used to communicate with the Serving Gateway (SGW) which has the S-GW and PDN-GW interfaces, and the Serving GPRS Support Node (SGSN).