Unified 4G LTE core

image revealing the EPC based on YateUCN and how it simplify the network

The YateUCNTM is a unified core network server intended for GSM, LTE, and VoLTE deployments. It can be used to build new networks or upgrade existing ones to LTE.

For LTE, the YateUCN is a software implementation of the EPC and IMS layer, based on Yate telephony application. The YateUCNTM is implemented on a commodity Intel server, reducing drastically the network equipment requirements.

As an EPC, the YateUCN performs the following functions:

Mobility management (MME):
handles subscriber authentication (with any HSS/HLR, such as the YateHSS/HLR), inter-MME mobility and handover over S1 interface. The MME function in YateUCN handles UE connection to the network. It is responsible for subscriber authentication and uses S6a interface (Diameter) to connect to the operator’s HSS database. The MME is also in charge of mobility management, allowing UEs continuous connectivity and active sessions as they move through the network. The MME uses S1-AP interface to manage inter-MME handover, making YateUCN fully compatible with any eNodeB used by the operator.

Traffic management (S-GW/P-GW):
assigns default and dedicated bearers, establishes IP session, routes data packets
through the network. The S-GW function allows the YateUCN to manage data traffic routing over S1-U interface, ensuring communication between the eNodeB and the P-GW, which establishes and maintains the IP session. The P-GW interconnects with the operator’s charging function over Diameter and Radius interfaces, enabling AAA management for wireless access.

Policy management (PCRF):
defines policy and charging rules, assigns and manages QoS for each session. The PCRF in the YateUCN maintains QoS levels and charging policies, enabling mobile operators to control bandwidth usage while their subscribers are roaming. The Policy and Control Enforcement Function, PCEF, performs policy enforcement and service data flow detection, making sure the data flow through from the P-GW is accessible.

The YateUCN supports both Diameter and SS7 protocols and implements the Interworking Function to allow inter-operability with legacy networks. Since the functionality of GSM/GPRS networks is included in the YateUCN, continuity with the legacy CS network is achieved without upgrades to existing networks. This results in major cost savings associated with PS-CS networks interworking.

For VoLTE deployments, the YateUCN integrates the P-CSCF (Proxy-Call Session Control Function), a combined I-CSCF (Interrogating CSCF) + S-CSCF (Serving CSCF), an IWF (Interworking Function), and a BGW (Bridge Gateway).

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Distributed EPC

image showing a conventional EPC and how is harder to manage due network complexity

Many virtualized EPCs today combine several network functions onto one component (typically the P-GW-S-GW or the MME-SGSN), but the equipment is purpose-built.

Using dedicated hardware means that the functions can’t be changed and different hardware needs to be supplied for different functions or different technologies.

Separate nodes for different functions require back-up for each component, which adds up to equipment costs.

For VoLTE, the implementation of the IMS requires updates to the legacy 2G/3G networks, in order for subscribers to be handed over for voice services.