LTE Advanced Pro

8LLC Service – Group Communications

8.1. Introduction

The group communication service (GCS) provides a fast and efficient mechanism for distributing the same content to multiple users in a controlled manner.

The eMBMS (evolved Multimedia Broadcast/Multicast Service) network completes the 4G mobile network architecture by introducing:

• – a transport architecture allowing the transmission, for the downstream direction, of IP packets in a multicast bearer;
• – a service architecture comprising two domains:
  • - the security domain ensuring the mutual authentication and the key establishment;
  • - the application domain ensuring the description and the structuring of the data.

Two functions determine the transmission mode on the radio interface:

• – the MBSFN (MBMS over Single-Frequency Network) function makes it possible to broadcast the same IP packet from several synchronized eNB entities in the physical multicast channel (PMCH), whose transmission characteristics are identical for all mobiles participating at the MBMS session and for a set of cells. The MBSFN function uses the broadcast transmission mode;
• – the SC-PTM (Single-Cell Point-To-Multipoint) function makes it possible to broadcast the same IP packet from a single eNB entity, in the physical downlink shared channel (PDSCH), whose transmission characteristics are specifically defined for each mobile participating at the MBMS session. The SC-PTM function uses the unicast transmission mode.

8.2. Transport architecture