Understanding GTPv2
The GPRS tunneling protocol (GTP) establishes a GTP tunnel between a Serving GPRS Support Node (SGSN) and a Gateway GPRS Support Node (GGSN) for individual Mobile Stations (MS). In previous releases, only GTP version 0 (GTPv0) and GTP version 1 (GTPv1) were deployed. GTP version 2 (GTPv2) is implemented in the Junos operating system (Junos OS) Release 11.4.
GTPv2 is part of Long Term Evolution (LTE), a fourth generation (4G) wireless broadband technology developed by Third-Generation Partnership Project (3GPP). 3GPP is the standard body for developing GPRS standards. LTE is designed to increase the capacity and speed of mobile telephone networks. GTPv2 is a protocol designed for LTE networks. An LTE network comprises network elements, LTE interfaces, and protocols.
GTPv0 and GTPv1 are implemented using SGSNs and GGSNs. However, in GTPv2, the traditional SGSNs and GGSNs are replaced by three logical nodes—a serving gateway (SGW), a packet data network gateway (PGW), and a mobility management entity (MME).
Figure 1 shows the following LTE interfaces where SRX Series devices are deployed in the public land mobile network (PLMN).
Figure 1: LTE Interfaces
- S5—This interface connects an SGW and a PGW. It provides user plane tunneling and tunnel management capability between the SGW and the PGW. It is also used for SGW relocation that happens because of user equipment mobility or SGW connection to a non-collocated PGW. The S5 interface is equivalent to the Gn interface in a Third Generation (3G) mobile network.
- S8—This interface connects an SGW in a visited PLMN (VPLM) and a PGW in a home PLMN (HPLMN). S8 is the inter-PLMN variant of S5. The S8 interface is equivalent to the Gp interface in a 3G mobile network.
- S4—This interface connects an S4 SGSN and an SGW. It provides related control and mobility support between GPRS core network and 3GPP Anchor function. It also provides user plane tunneling if direct tunneling is not established. The S4 interface does not have any equivalent interface in the 3G mobile network, because it provides interoperability between 3G and 4G networks.
