Table 4 List of the reference points and network elements of the 3GPP reference model for MTC communications (taken from [45, 51–53]). The acronyms of network elements are given in Table 1
From: Mobile M2M communication architectures, upcoming challenges, applications, and future directions
| Descriptions | |
|---|---|
| Reference points | |
| Tsms | It enables the communication between an entity lying outside the 3GPP network and |
| MTC using SMS | |
| Tsp | It connects MTC-IWF to SCSs to provide several functionalities |
| such as device triggering | |
| T4 | It performs SME tasks, e.g., connects MTC-IWF to the HPLMN domain. |
| T4 also supports device triggering functionlities | |
| T5a | It enables communication between MTC-IWF and serving SGSN |
| T5b | It establishes the communication path between MTC-IWF and serving MME |
| T5c | It creates the communication link between MTC-IWF and serving MSC |
| S6m | It performs subscription and MTC-related information tasks by establishing |
| the communication path between MTC-IWF to HSS/HLR | |
| S6n | It also performs subscription and MTC-related information tasks by establishing |
| communication link between MTC-AAA and HSS/HLR and supports | |
| interrogation of HSS/HLR | |
| Network elements | |
| MTC-IWF | One of the instances of MTC-IWF exists in HPLMN to support indirect and hybrid models |
| Receives trigger request of an MTC device from SCS | |
| Reporting and updating SCS about the acceptance or rejection of the device trigger request | |
| HSS/HLR | It determines whether an SCS is allowed to send a trigger to a particular MTC |
| It also performs mapping tasks between IMSI and external identifier(s) | |
| GGSN/P-GW | It enquires an MTC AAA server for regenerating external identifier(s) |
| SGSN/MME/MSC | Accepting an MTC device trigger from MTC-IWF |
| It confines the device trigger information in NAS messages sent to MTC | |
| It accepts a device trigger acknowledgement from the triggering MTC | |
| It reports to the MTC-IWF about the device trigger delivery success/failure status | |
| It also delivers SGSN/MME congestion/load information to MTC-IWF | |
| SMS-SC | It delivers the routing information from MTC-IWF to SMS-GMSC |
| MTC AAA | It uses standard procedures such as RADIUS to identify the destination external AAA server |
| SCEF | It performs several tasks such as device authentication and profile management |
| It makes external entities capable to discover various service capabilities |