Dual Connectivity. • Master eNB (MeNB) is the eNB which terminates at least S1-MME or both S1-MME and S1-U • Secondary eNB (SeNB) is the eNB that is providing additional radio resources. • Master Cell Group is a group of serving cells associated with the MeNB, comprising of the PCell and optionally one or more SCells. • Secondary Cell Group is a group of serving cells associated with the SeNB, comprising of PCell and optionally one or more SCells. • MCG Bearer is a bearer whose radio protocols are only located in the MeNB to use MeNB resources only • SCG Bearer is a bearer whose radio protocols are only located in the SeNB to use SeNB resources. • Split Bearer is a bearer whose radio protocols are located in both the MeNB and the SeNB to use both MeNB and SeNB resources Dual Connectivity Protocol and Network Architecture In Dual Connectivity, the radio protocol architecture that a particular bearer uses depends on how the bearer is setup. Three bearer types exist: MCG bearer, SCG bearer and split bearer. Those three bearer types are depicted on fi gure below. IUUQTXXXUFDIQMBZPODPNEVBMDPOOFDUJWJUZEDEF fi OJUJPOQSPUPDPMBOEOFUXPSLBSDIJUFDUVSFEDBOEDBDPNQBSJTPO ̑(/4"ͰΘΕ͍ͯͳ͍
go through option 3 family, which has sub-options, so called 3, 3a, 3x. The main differences are how to transmit user plane connectivity between Radio Access Network and Core Network. We can find a bunch of explanation on TR 38.801 and TR 38.804. Split bearer concept has been introduced in Dual Connectivity at TS 37.340. For control plane, EPC is going through MeNB to the UE. For user plane, big difference between 3/3x and 3a is X1-U interface between MeNB and SgNB (3/3x) or none (3a). Option 3 is defined to use an MCG split bearer, which would require more process (investment) on the current eNB side. I am not sure how much operators would like to do with this. Option 3a is done to use a perfect Split bearer, which let operators invest on the gNB that they are going to deploy. Then option 3x is combined and modified practically to use an SCG slit bearer, which let operators save budgets on the eNB side and have benefit in utilizing the user plane through both MeNB and SgNB. Here is the summary on option 3 family below based on TR 38.801 and TR 38.804.
Slice suitable for the handling of 5G enhanced Mobile Broadband. URLLC 2 Slice suitable for the handling of ultra- reliable low latency communications. MIoT 3 Slice suitable for the handling of massive IoT. Table 5.15.2.2-1 - Standardised SST values from 3GPP TS 23.501 w /44"*4/44"*ͷू߹Λөͨ͠ͷ w $PO fi HVSFE/44"* ɹ4FSWJOH1-./Ͱαϙʔτ͞ΕΔεϥΠεɻ w3FRVFTUFE/44"* ɹɹ3FHJTUSBUJPOखॱʹ͓͍ͯɺ6&ͷ༻Λ4FSWJOH1-./ʹొ͢ΔͨΊͷεϥΠεɻ w 4VCTDSJCFE4/44"* ɹ6%.Ͱొ͞ΕͨεϥΠεɻ w "MMPXFE/44"* ɹ4FSWJOH1-./͕ొΤϦΞʢ3"ʣͰ6&ʹ༻ΛڐՄ͍ͯ͠ΔεϥΠεɻ w 4/44"*(ແઢΞΫηεͱ($PSFʹ͓͚ΔωοτϫʔΫεϥΠεΛࣝผ͢Δͷ
QoS Flow) ͱɺอূ͞ΕͨϑϩʔϏοτϨʔτΛඞཁͱ͠ͳ͍ QoS Flow (non-GBR QoS Flow) ͷ ྆ํΛαϙʔτɻ QoS FlowɺNG-U (GTP-Uτϯωϧ) Λհͯ͠ΧϓηϧԽϔομʔͰӡΕΔ QoS Flow ID (QFI) ʹΑͬͯ PDU SessionͰࣝผ͞ΕΔɻ (1154/3BOE/(3"/0WFSBMM%FTDSJQUJPO The QoS architecture in NG-RAN, both for NR connected to 5GC and for E-UTRA connected to 5GC, is depicted in the Figure 12-1 and described in the following: • For each UE, 5GC establishes one or more PDU Sessions; • For each UE, the NG-RAN establishes at least one Data Radio Bearers (DRB) together with the PDU Session and additional DRB(s) for QoS fl ow(s) of that PDU session can be subsequently con fi gured (it is up to NG-RAN when to do so); • The NG-RAN maps packets belonging to different PDU sessions to different DRBs; • NAS level packet fi lters in the UE and in the 5GC associate UL and DL packets with QoS Flows; • AS-level mapping rules in the UE and in the NG-RAN associate UL and DL QoS Flows with DRBs. -- IFBEFS 0VUFS*1 IFBEFS &ODBQTVMBUJPO IFBEFS 1%6 IFBEFS 1%6 QBZMPBE *EFOUJ fi FT2P4DMBTT
relationship with the GTP-U tunnel on N3 interface at UPF. • Each QoS fl ow is mapped to a single GTP-U tunnel at N3 interface • gNB may map individual QoS fl ows to one more DRBs • A PDU session may contain multiple QoS fl ows and several DRBs but only a single N3 GTP-U tunnel. • A DRB may transport one or more QoS fl ows. • The QFI that identi fi es the fl ow is carried in an extension header on N3 in the GTP-U protocol, using DL and UL PDU session information frames • The DL and UL PDU session information frame includes a QoS Flow Identi fi er (QFI) fi eld for each packet. • The DL PDU session information frame includes the Re fl ective QoS Indicator (RQI) fi eld to indicate whether the user plane re fl ective QoS is to be activated or not. This is only applicable if re fl ective QoS is activated. IUUQTXXXUFDIQMBZPODPNHOSRPTBSDIJUFDUVSFRPTBUUSJCVUFBOERPT fl PX
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