![]() If you don't like reading (like me :), just take 10 minutes (not 10 seconds) and look thorugh each and every part and lines of the picture. If you take a close look at the illustration and just describe it in words, you would get the descrition as follows. ![]() Of those deployment options, refer to Deployment Scenario page and some references linked in the page. It is based on general concept of Option 3, but not showing any specific variation of the option (e.g, plain option 3 or 3a or 3x). NOTE : This illustration is just to give you the big picture of how 4G/5G RAN connected to each other and how they are connected to core network (EPC). Though not shown in this illustration, I would point out that LTE eNB and NR gNB are using their own PHY/MACĪs you see here, in case of data plane both Master Node(LTE) and Secondary Node(gNB) has direct interface with LTE corenetwork(S-GW), but in case of control plane only Master Node(LTE) has direct interface with LTE core network(MME). As you see here, UE is communicating with both LTE eNB and NR gNB in Radio side, but all those communication (signaling and data) are going through LTE core network. Overall RAN architecture of EN-DC can be illustrated as below (this is based on 37.340 - 4.3.1 and 4.3.2). In this configuration, UE get connected to LTE network first and then connected to NR via RRC Connection Reconfigurationįurther details on lower layer process is yet to be studied, but just looking into the conentents of RRCConnectionReconfiguration would give you some general idea about the mechanism. This is about one of NR deployment options where LTE work as a master and NR work as a secondary cell (In 3GPP terms, this is about EN-DC (EUTRA-NR Dual Connectivity) / MR-DC with EPC as described in 37.340). Interworking with LTE - NSA / ENDC in Detail When NR is added to the LTE cell, UE should be able to detect SSB of NR cell and perform RACH procedure to NR.The ratio of the split is configured by RRC Option 2 : Uplink gets split between LTE and NR.Option 1 : All the uplink goes through LTE only.In ENDC, Downlink traffic is always split between LTE and NR, but there is two options for Uplink traffic.In ENDC, Core Network is based on LTE Core, NR just provide additional RAN pipe.ENDC is dominant form of deployment, NEDC is just done in specification, I personally haven't seen any example of real deployment.In NEDC (NR/Eutra Dual Carrier), NR become MCG(Main Cell Group) and Eutra (LTE) become SCG(Secondary Cell Group), meaning that NR is main cell and LTE just work as a secondary cell.In ENDC (Eutra / NR Dual Carrier), Eutra (LTE) become MCG(Main Cell Group) and NR become SCG(Secondary Cell Group), meaning that LTE is main cell and NR just work as a secondary cell.There are two types of LTE - NR interworking : ENDC and NEDC.Interworking with LTE - NSA / ENDC in a Nutshell
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