Chapter 4 FortiOS Carrier : ­­­­Overview of FortiOS Carrier features : GTP basic concepts : Parts of a GTPv1 network
  
Parts of a GTPv1 network
A sample GTP network consists of the end handset sender, the sender’s mobile station, the carrier’s network including the SGSN and GGSN, the receiver's mobile station, and the receiver handset.
When a handset moves from one mobile station and SGSN to another, the handset’s connection to the Internet is preserved because the tunnel the handset has to the Internet using GTP tracks the user’s location and information. For example, the handset could move from one cell to another, or between countries.
The parts of a GPRS network can be separated into the following groups according to the roles of the devices:
Radio access to the GPRS network is accomplished by mobile phones and mobile stations (MS). See “Radio access”.
Transport the GPRS packets across the GPRS network is accomplished by SGSNs and GGSNs, both local and remote, by delivering packets to the external services. See “Transport”.
Billing and records are handled by CDF, CFR, HLR, and VLR devices. See “Billing and records”.
GPRS networks also rely on access points and PDP contexts as central parts of the communication structure. These are not actual devices, but they are still critical .
For more information on APN, see “Access Point Number (APN)”. For more information on PDP Context, see “PDP Context”.
These devices, their roles, neighboring devices, the interfaces and protocols they use are outlined in the following table. These devices and their connections can be viewed in the “Packet flow through the GPRS network”.
Figure 144: Carrier network showing the interfaces used (GTPv1)
 
Table 33: Devices on a GTPv1 network
Device role
Neighboring Devices
Interfaces used
Protocols used
Mobile Users
Mobile Stations (MS)
Radio Access Technology (RAT)
 
Mobile Stations (MS)
Mobile Users, SGSN
Gb
IP, Frame Relay
SGSN (local)
MS, SGSN (local or remote), GGSN (local and remote), CDR, CFR, HLR, VLR
Ga, Gb, Gn, Gp, Gz
IP, Frame Relay, GTP, GTP’
SGSN (remote)
SGSN (local)
Gn
GTP
GGSN (local)
SGSN (local or remote), GGSN (local and remote), CDR, CFR, HLR, VLR
Ga, Gi, Gn, Gp, Gz
IP, GTP, GTP’
GGSN (remote)
SGSN (local), WAP gateway, Internet, other external services
Gi, Gp
IP, GTPv1
CDR, CFR
SGSN (local), GGSN (local)
Ga, Gz
GTP’
HLR, VLR
SGSN (local), GGSN (local)
Ga, Gz
GTP’