Unknown Message Action
Set this message type to deny.
Many attempts to hack into a carrier network will result in this unknown message type and therefore it is denied for security reasons.
Path Management Messages
| Message Type | Used by | Description |
| Echo Request/Response | GTP-C,
GTP-U, GTP’ |
Echo Request is sent on a path to another GSN to determine if the other node is alive. Echo Response is the reply. |
| Version not Supported | GTP-C,
GTP-U, GTP’ |
There are multiple versions of GTP. Both devices communicating must use the same version of GTP, or this message will be the response. |
| Support Extension Headers
Notification |
Extensions are optional parts that a device can choose to support or not. If a device includes these extensions, it must include headers for the extensions to sure ensure proper formatting. |
Tunnel Management Messages
| Message Type | Used by | Description |
| Create PDP Context Request/ Response | GTP-C | Sent from an SGSN to a GGSN node as part of a GPRS PDP
Context Activation procedure or the Network-Requested PDP Context Activation procedure. A valid request initiates the creation of a tunnel. |
| Update PDP Context Request/ Response | GTP-C | Used when PDP Context information changes, such as when a mobile device changes location. |
| Delete PDP Context Request/ Response | GTP-C | Used to terminate a PDP Context, and confirm the context has been deleted. |
| Create AA PDP Context Request/ Response | GTP-C | Sent as part of the GPRS Anonymous Access PDP Context Activation. It is used to create a tunnel between a context in the SGSN and a context in the GGSN. |
| Message Type | Used by | Description |
| Delete AA PDP Context Request/ Response | GTP-C | Sent as part of the GPRS PDP Anonymous Access Context
Deactivation procedure to deactivate an activated PDP Context. It contains Cause and Private Extension Information Elements |
| Error Indication | GTP-U | Sent to the GGSN when a tunnel PDU is received for the following conditions:
— No PDP context exists — PDP context is inactive — No MM context exists — GGSN deletes its PDP context when the message is received. |
| PDU Notification Request/
Response/ Reject Request/ Reject Response |
GTP-C | When receiving a Tunneled PDU (T-PDU), the GGSN checks if a PDP context is established for the given PDP address. If no PDP context has been established, the GGSN may initiate the Network-requested PDP Context Activation procedure by sending a PDU Notification Request to the SGSN.
Reject Request – Sent when the PDP context requested by the GGSN cannot be established. |
Location Management Messages
| Message Type | Used By | Description |
| Send Routing Information for GPRS Request/ Response | GTP-C | Sent by the GGSN to obtain location information for the MS.
This message type contains the IMSI of the MS and Private Extension. |
| Failure Report Request/ Response | GTP-C | Sent by the GGSN to the HLR when a PDU reject message is received.
The GGSN requests the HLR to set the flag and add the GGSN to the list of nodes to report to when activity from the subscriber that owns the PDP address is detected. The message contains the subscriber IMSI and Private Extension |
| Note MS GPRS Present Request/ Response | GTP-C | When the HLR receives a message from a mobile with MDFG
set, it clears the MDFG and sends the Note MS Present message to all GGSN’s in the subscriber’s list. This message type contains subscriber IMSI, GSN Address and Private Extension |
Configuring message type filtering in FortiOS Carrier
Mobility Management Messages
| Message Type | Used By | Description |
| Identification
Request/Response |
GTP-C | Sent by the new SGSN to the old SGSN to request the IMSI for a MS when a GPRS Attach is done with a P-TMSI and the MS has changed SGSNs since the GPRS Detach was done. |
| SGSN context Request/ Response/ Acknowledge | GTP-C | Sent by the new SGSN to the old SGSN to request the MM and PDP Contexts for the MS. |
| Forward Relocation Request/
Response/ Complete/ Complete Acknowledge |
GTP-C | Indicates mobile activation/deactivation within a Routing Area. This prevents paging of a mobile that is not active (visited VLR rejects calls from the HLR or applies Call Forwarding). Note that the mobile station does not maintain an attach/detach state.
SRNS contexts contain for each concerned RAB the sequence numbers of the GTP-PDUs next to be transmitted in uplink and downlink directions. |
| Relocation Cancel Request/ Response | GTP-C | Send to cancel the relocation of a connection. |
| Forward SRNS Context/ Context Acknowledge | GTP-C | This procedure may be used to trigger the transfer of SRNS contexts from RNC to CN (PS domain) in case of inter system forward handover. |
| RAN Information Relay | GTP-C | Forward the Routing Area Network (RAN) information.
A Routing Area (RA) is a subset of a GSM Location Area (LA). A RA is served by only one SGSN. Ensures that regular radio contact is maintained by the mobile |
MBMS messages
| Message Type | Used By | Description |
| MBMS Notification Request/
Response/ Reject Request/ Reject Response |
GTP-C | Notification of the radio access devices. |
| Create MBMS Context Request/ Response | GTP-C | Request to create an active MBMS context. The context will be pending until the response is received.
Once active, the MBMS context allows the MS to receive data from a specific MBMS source |
| Message Type | Used By | Description |
| Update MBMS Context Request/ Response | GTP-C | |
| Delete MBMS Context Request/ Response | GTP-C | Request to deactivate the MBMS context. When the response is received, the MBMS context will be inactive. |
GTP-U and Charging Management Messages
| Message Type | Used By | Description |
| G-PDU | GTP-C, GTP-U | GPRS Packet data unit delivery message. |
| Node Alive Request/Response | GTP-C, GTP-U | Used to inform rest of network when a node starts service. |
| Redirection
Request/Response |
GTP-C, GTP-U | Used to divert the flow of CDRs from the CDFs to another CGF when the sender is being removed, or they are used when the CGF has lost its connection to a downstream system. |
| Data Record Transfer Request/Response | GTP-C, GTP-U | Used to reliably transport CDRs from the point of generation (SGSN/GGSN) to non-volatile storage in the CGF |
IMSI on carrier networks
GTP identity filtering
FortiOS Carrier supports a number of filtering methods based on subscriber identity such as APN filtering, IMSI filtering, and advanced filtering.
This section includes:
IMSI on carrier networks
Other identity and location based information elements
Configuring APN filtering in FortiOS Carrier
Configuring IMSI filtering in FortiOS Carrier
Configuring advanced filtering in FortiOS Carrier
IMSI on carrier networks
The International Mobile Subscriber Identity (IMSI) number is central to identifying users on a carrier network. It is a unique number that is assigned to a cell phone or mobile device to identify it on the GMS or UTMS network.
Typical the IMSI number is stored on the SIM card of the mobile device and is sent to the network as required.
An IMSI number is 15 digits long, and includes the Mobile Country Code (MCC), Mobile Network Code (MNC), and Mobile Station Identification Number (MSIN).