5g NR MBS architecture introduction

5G NR MBS System architecture

2022 year 6 month ,3GPP R17 Version freeze . among , Added NR MBS(Multicast/Broadcast Service) characteristic . from TS 23.247 The support described in NR MBS You can see the system architecture diagram of , Compared with the existing 5G System architecture , Four new and MBS Related ne , namely MB-UPF(Multicast/Broadcast User Plane Function),MB-SMF(Multicast/Broadcast Session Management Function),MBSTF(Multicast/Broadcast Service Transport Function),MBSF(Multicast/Broadcast Service Function).

 

5G NR MBS Protocol stack architecture

stay TS 38.300 5G NR MBS in , layer 2 The architecture of the protocol stack is shown in the following figure . In the aspect of wireless bearer, it is used to MBS Wireless bearer for , namely MRB(MBS Radio Bearer). In the aspect of logical channel, a new MCCH(MBS Control Channel) and MTCH(MBS Traffic Channel). In terms of transmission channel and physical channel , Then no relevant channel is added . be-all MBS Both the service and the terminal unicast service are provided by DL-SCH bearing .

 

5G NR MBS newly added RNTI

Because there is no new physical channel and transmission channel , For that need MBS Add corresponding RNTI Used to distinguish between unicast and MBS, namely G-RNTI(Group RNTI)、G-CS-RNTI(Group Configured Scheduling RNTI) and MCCH-RNTI(MBS Control Channel RNTI). When MBS In business , The network can PTP(Point To Point) The way (C-RNTI) Send the data to the terminal , It can also be done through PTM(Point To MultiPoint) The way (G-RNTI) Send the data to the terminal .

RNTI	Usage	Transport Channel	Logical Channel
G-CS-RNTI	Configured scheduled multicast transmission (activation, reactivation and retransmission)	DL-SCH	MTCH
G-RNTI	Dynamically scheduled MBS PTM transmission	DL-SCH	MTCH
MCCH-RNTI	Dynamically scheduled MCCH signalling and MCCH change notification	DL-SCH	MCCH

Reference resources ：

1、TR 21.917

2、TR 38.300

3、TR 38.321

4、TR 23.247