What does the agreed accelerated plan for 5G standardization by 3GPP mean for core network evolution?

3GPP agreed an accelerated plan for 5G deployment in the RAN plenary meeting at Dubrovnik, Croatia between 6th and 9th March, 2017. The agreed plan is documented in RP-170741.zip. Stage 3 completion of non stand alone (NSA) mode 5G NR connecting to EPC will be done by Dec 2017 and the ASN.1 completion will be by March 2018 making the standards in a state for 5G-NR to be deployed by end of 2018.

What does this imply for the core network evolution and deployment for 5G?

• By 2018, 5G will be deployed as a non standalone radio enhancement, acting as a secondary cell to E-UTRAN eNBs as specified under option 3 of TR 38.801 under section 7.2 (given below)

• As the purpose of this accelerated time plan is to deploy high bandwidth services (for eMBB) by 2018, using option 3 implies that all 5G traffic from the 5G gNB has to be backhauled to eNB and the S1-U link from eNB to EPC shall have a huge backhaul capacity.
• Though with option 3A, this need to backhaul 5G traffic via eNB is not there, option 3A implies SCG bearer solution is deployed with dual connectivity, which means the core network has to create multiple bearers, with the eNB (acting as MeNB) moving the high bandwidth service bearers towards the gNB. For internet traffic, typically we dont see multiple bearers created. So practically speaking, its hard to see option 3A kind of deployment being used for increased bandwidth and capacity for internet services. Option 3A would rather be used for specialised services that would require multiple bearers (e.g RCS, low latency edge hosted services).
• If option 3 is used for capacity enhancement for internet traffic, then a huge investment in increasing the capacity of the S1U backhaul needs to be done.
• This increased investment in backhaul towards the EPC would make the operators run 5G services using EPC for a longer duration (to justify the investment). 
• Deployment of nexgen core (NG Core) would be rather slow.
• In the meantime, one might see 3GPP working in future to define more of the services of NG Core in EPC also - so that roll out of 5G services can happen with EPC itself. Already control user plane separation (CUPS) is supported in EPC. This would enable hosting the user plane node closer to RAN for edge hosted services. eDECOR allows support for basic network slicing in EPC. All these indicate a potentially longer run for EPC (atleast for few more years) before NG core deployments happen.