CUPS: EPC served À la carte

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4Q 2017 | IN-4862

The evolution of Evolved Packet Core (EPC) has come a long way since its first inception in 2007 by 3GPP, in Release 8, as a simplified, all-IP, flat architecture based core network for LTE system. In release 14, in June 2017, 3GPP provided architectural enhancements by providing a key core network feature in form of Control and User Plane Separation (CUPS) specification for EPC nodes.As IP traffic increased over time, Packet Switching (PS) was introduced as an enhancement to Circuit Switching (CS) to transport data in packets while retaining transport protocol for voice and SMS over CS. With this, the core network evolved into two domains namely, circuit and packet.

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The Evolution of EPC Over Time

NEWS


The evolution of Evolved Packet Core (EPC) has come a long way since its first inception in 2007 by 3GPP, in Release 8, as a simplified, all-IP, flat architecture based core network for LTE system. In release 14, in June 2017, 3GPP provided architectural enhancements by providing a key core network feature in form of Control and User Plane Separation (CUPS) specification for EPC nodes.As IP traffic increased over time, Packet Switching (PS) was introduced as an enhancement to Circuit Switching (CS) to transport data in packets while retaining transport protocol for voice and SMS over CS. With this, the core network evolved into two domains namely, circuit and packet.

With the introduction of EPC for 4G networks in Release 8 by 3GPP, voice, data and SMS was channeled over IP. The motivation was to move to a flat architecture with few nodes to handle traffic, improve performance, and save costs to telcos. EPC now consists of five essential components namely, Serving Gateway (SGW), Packet Data Network Gateway (PGW), Home Subscriber Server (HSS), Mobility Management Entity (MME) and Policy Control and Charging Rules (PCRF). These network elements ensure that all the key requirements of Mobile Broadband (MBB) services i.e., security, mobility and QoS are fully met.

In EPC architecture, gateway nodes serve both User Plane (e.g., routing, tunneling) and Control Plane (e.g. signaling, session management) functionalities whereas MME, HSS and PCRF nodes cater to only CP processes. As network traffic continues to grow and become more heterogeneous with proliferation of smart devices and increasing low latency requirements for on-demand streaming services, it is becoming inevitable to independently scale CP and UP resources to control congestion and provide service differentiation based on latency requirements. This lead to Control and User Plane Separation (CUPS), introduced in 3GPP Release 14, wherein CP and UP functionalities in SGW and PGW are disaggregated.

How Does CUPS Enhance EPC

IMPACT


With CP and UP disaggregated in CUPS, a single user can be provisioned by multiple SGWs to serve different PGWs. This is a fundamental departure from the current EPC wherein one user is always allocated only to one SGW to serve multiple PGWs. Another important feature of disaggregation is that it adds flexibility to allow telcos to place UP functions either close to RAN or keep them centralized with CP functions. This can reduce latency considerably without increasing CP nodes.

With UP/CP functional split, SGW in EPC will be SGW-U and SGW-C and PGW will be PGW-U and PGW-C. Another sub element of EPC called Traffic Detection Function (TDF), that enforces traffic policies based on pre-set or dynamically determined rules by PCRF in real time, will also evolve as TDF-U and TDF-C. Three new interfaces, namely Sxa, Sxb, and Sxc will connect UP and CP functions of SGW, PGW and TDF respectively. EPCs from both pre-and post CUPS architecture are shown below.

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  Smart-Card-Vendor-2016  

The signaling and transfer protocols on the new interfaces will be based on Diameter and GTP respectively while communications among switches will be based on Openflow. CP functions will now process packets from their respective UP counterparts via new interfaces based on UP’s location, capabilities, capacity, and QoS policies. This will enable telcos to seamlessly add UP nodes without making changes to the CP nodes in the network to support any increase in data traffic. This also facilitates dynamic service chaining and network slicing, techniques from NFV/SDN playbook.

Looking Forward to 5G

COMMENTARY


The last decade was entirely focused around Mobile Broadband. However, as innovative technologies like NFV, SDN, Edge and Cloud Computing emerge, networks will also have to evolve to address new use cases for e.g. IoT, AR/VR, Autonomous machines and M2M that designed around these technologies. To that respect, CUPS is definitely a forward-looking step to 5G that is anticipated to encompass these use cases. Recently, SK Telecom and Nokia successfully tested CUPS on a ‘hybrid network architecture’ optimized for transmission of massive data to prove the viability of CUPS to handle copious amounts of data transfer over LTE core network. ABI research believes that more and more telcos will start experimenting CUPS over the next year with their 4G networks over data intensive uses cases for e.g. IoT, automated cars, and high - definition content streaming. While it is still left to be seen how the Next Generation Core (5G Core) network would look like in that if EPC would continue to evolve or a completely new architecture would emerge, CUPS, for now, brings “À La Carte” options for telcos to manage their networks as Distributed and/or Centralized Network Centers.

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