The following LTE EPC Technology White Paper describes Long-Term Evolution (LTE) and Evolved Packet Core (EPC) and is part five of a 5-part Summary of our 3GPP Core Technologies series. You can also download and print them by clicking below. Contact us for information about our IP Consulting Services, Engineering support, and technology development.
SUMMARY OF 3GPP CORE TECHNOLOGIES
Long-term Evolution (LTE) and Group Communication Services (GCS)
1. Introduction 2. Group Communication Services (GCS) 3. Group Communication Services (GCS) and IP Multimedia core network Subsystem (IMS)
Group Communication Services (GCS) are generally to transmit the same information to a group of people. Services such as public safety services can be mentioned as examples. In 3rd Generation Partnership Project (3GPP), the concept of the GCS was introduced in release 12 by designing the architecture for both Evolved Packet System (EPS) and Multimedia Broadcast, Multicast Services (MBMS) bearer services. The Group Communication Service application server (GCS AS) employs EPS and MBMS bearer services for transmitting downlink signaling and data from the GCS AS to the wireless devices. In the uplink, the wireless devices employ EPS bearer services for signaling and transferring data to the GCS AS.
2. Group Communication Services (GCS)
Figure 1 illustrates the high-level architecture for EPS and MBMS.
The EPS bearer services are implemented by the connection between the GCS-AS and Packet Data Network (PDN) Gateway which resides in PDN Gateway (P-GW) and the connection between the GCS AS and the Policy and Charging Rules Function (PCRF). The Quality of Service (QoS) of the EPS unicast bearer services are adjusted by PCRF with respect to the provided services and the subscription profile of the User Equipment (UE). The GCS-AS determines whether MBMS or unicast should be employed for a given UE.
The MBMS bearer services are implemented by the connection between the GCS-AS and the Broadcast Multicast Service Center (BM-SC). The BM-SC is configured to have a set of functionalities for authorization, authentication, security, scheduling, QoS, and many more for the MBMS bearer services, see 3GPP TS 23.246.
Figure 2 shows the structure of BM-SC according to 3GPP TS 23.246. The functional entities of the BM-SC can be described as:
Membership function which authorizes a UE for MBMS services and may have subscription and charging record. This entity is configurable.
Session and transmission function which schedules session transmission and session retransmission. This functional entity initiates and terminates MBMS bearer resources and provides QoS and MBMS service area to MBMS-GW. Moreover, the session and transmission function authenticates external content provider, performs the header compression, and applies error resilient schemes like Forward Error Correction(FEC) schemes.
Proxy and transport function which may interface to several MBMS-GWs, provides charging records for content provider charging of transmitted data.
Service announcement function provides the UE with media description for MBMS services.
MBMS security function provides integrity and confidentiality of the MBMS data.
The Multicell Coordination Entity (MCE) may reside in the eNodeB (eNB) and determines whether Multicast Broadcast Single Frequency Network (MBSFN) or Single Cell Point to Multipoint (SC-PTM) should be employed for a given group communication.
MBSFN is employed when the services are broadcasted to several cells. Services such as mobile TV benefits from this technology. However, SC-PTM is employed for the scenarios where services are broadcasted and/or multicasted to a limited number of cells and the user of interest changes cells due to its movement. Services such as public safety services or services for vehicle to everything (V2X) benefit from SC-PTM.
3. Group Communication Services (GCS) and IP Multimedia core network Subsystem (IMS)
A group communication service may be based on IP Multimedia core network Subsystem (IMS). In that case, the GCS-AS is an IMS application server and the IMS proxies such as Proxy Call Session Control Function (P-CSCF) and Serving Call Session Control Function (S-CSCF) are also parts of the network architecture.
Figure 2 illustrates the high-level architecture for the case when the GCS utilizes IMS architecture framework. The P-CSCF and S-CSCF are employed to register the UE to the IMS network. That is, a 3rd party registers the UE to the GCS AS. The P-CSCF and S-CSCF are also utilized to setup sessions which may be group communication sessions. They are also employed for standalone messages, which do not require an IMS session. The GC1 reference point in this case is a Session Initiation Protocol (SIP) reference point.
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