YateUCN, the EPC cloud

The YateUCN is an LTE EPC that unifies all the functions of a conventional LTE core network into a single server. A single YateUCN unit combines the MME, SGW, PGW, PCEF and PCRF functions. A pool of YateUCN servers provide seamless horizontal redundancy, scalability and load balancing in the LTE core network. The YateUCN also replaces the latest core network approaches to design and management, such as network function virtualization (NFV) that virtualizes the functions of the network’s nodes in software or software-defined networking (SDN) that splits the control plane from the user plane.

A conventional LTE core network has many components and each requires a back-up node for redundancy. To ensure load balancing, operators need to deploy load balancers and external servers, which only add to the complexity count.

The YateUCN servers that form the EPC cloud have a many-to-many relationship with the eNodeBs, are equal at application lever, and eliminate the single point of failure between the RAN and the core network. All these characteristics allow for horizontal redundancy, load balancing, easy management and an overall simplicity within the network.


Redundant EPC

In conventional LTE networks, all core network components (MME, SGW, PGW, PCEF, PCRF) need to be duplicated to ensure redundancy and synchronization in case of failure. With a YateUCN-based core network, operators add extra servers to the existing pool to increase the network’s overall capacity.

To achieve redundancy, subscribers get assigned to random servers from the YateUCN pool. If a YateUCN fails, all the devices served by that unit are automatically re-assigned to other available YateUCN servers, as seen in the diagram.yucn_redund_epc_2015-11-18_version1.3

LTE core network cloud

A cluster of YateUCN servers act as an LTE core network cloud, providing all the EPC services: mobility, authentication, quality of service, routing upload and download IP packets, IP address allocation and more. Mobile operators eliminate the occurrence of a single point of failure between the RAN and the core network because YateUCN servers are equal at application level, and have a many-to-many relationship with the eNodeBs.

By removing the single point of failure possibility, mobile carriers can build scalable and considerably leaner core networks, while also providing load balancing for enhanced flexibility.

Each YateUCN core network server is implemented in off-the-shelf servers commodity software (Linux), offering a shorter lead time, more servicing options and faster replacement time.

Integration in existing LTE networks

The entire LTE EPC layer is implemented in a single YateUCN unit, meaning that it replaces the MME, the SGW, the PGW, the PCEF and the PCRF units of conventional networks.

The YateUCN is compatible with any generic LTE RAN and core network component. It supports the S1-AP and GTP interfaces between its MME and SGW functions and the eNodeBs. The YateUCN uses Diameter (S6a) to connect to an existing generic Home Subscriber Server (HSS). The unified server can connect to external PGW and SGW via the S5/S8 interface. To link to an existing IMS, to the Internet or to an MMS service, the YateUCN uses the SGi interface. Finally, to interrogate an external Equipment Identity Register (EIR) about blacklisted IMEIs, the YateUCN uses S13 over Diameter.

Additionally, the YateUCN also implements the IMS functions necessary for deploying VoLTE, but this will be detailed in a future article. In the meantime, previous blog posts have detailed the YateUCN’s VoLTE call with an iPhone 6 or how the YateUCN handles SRVCC.

A few final words

A unified core network server that delivers redundancy, scalability, load balancing and flexibility allows mobile operators to tap new core network equipment innovations and reduce their CAPEX. Easily integrated in an existing LTE network, the YateUCN makes it possible for mobile carriers to optimize their networks and replace solutions typically characteristic to the recent mobile LTE deployments, such as NFV or SDN.

YateUCN – the redundant MSC/VLR

Traditionally, the redundancy of the Mobile Switching Center / Visitor Location Register (MSC/VLR) is obtained through redundant dedicated hardware and software. The problem lies in the Abis + A interfaces (BSSAP protocol) which do not allow a base station to move easily to another MSC/VLR. To overcome this problem, we decided to use the SIP protocol (with enhanced features for GSM operations), which allows a YateBTS SatSite base station to move to another YateUCN (MSC/VLR) automatically and quickly.

Redundant GSM MSC/VLR

In a GSM network deployed with YateBTS-based SatSite base stations and YateUCN core network servers, each subscriber is randomly assigned to a YateUCN from a pool of core network servers. Operators can increase the redundancy of the pool by simply adding additional YateUCN servers for excess capacity in case a unit malfunctions. Therefore, handsets connected to a single SatSite can be served by multiple identical YateUCNs, while, at the same time, a single YateUCN serves multiple SatSite units. If a YateUCN server fails, all the mobile devices served by it are automatically moved to the other available YateUCN servers. When the subscriber is registered to the new YateUCN, its location is updated in the HLR.

In short, YateUCN and the GSM YateBTS SatSite base stations form a many-to-many relationship, and this was made possible though a number of characteristics.

  • The GSM YateBTS SatSite implements all the functions of a conventional Base Station Controller (BSC).
  • The A interface (between the BSC and the MSC/VLR) was replaced with SIP (between YateBTS and YateUCN), making it possible to quickly re-associate handsets with different YateUCN servers.
  • All YateUCN servers are identical units that support many core network functions. Operators will only have to duplicate one component, as opposed to multiple in conventional networks.
  • YateUCN is implemented in commodity hardware (off-the-shelf servers) and software (Linux), delivering a shorter lead time, more servicing options and faster replacement time.

The diagram below illustrates the technology perfectly.


Integration in an LTE core network

The SatSite and the YateUCN components are easy to integrate into existing LTE networks because 2G services are delivered in SIP. These GSM services are integrated into a 4G network by employing the same GTP and IMS interfaces that are typically used in conventional EPC/IMS core networks.

YateUCN implements the same SIP switch to both provide GSM services and connect to an existing IMS network. Thus, with both the SIP-powered RAN and core network products, operators’ migration from GSM to LTE turns into a much simpler process.

Integration in a GSM core network

As an MSC/VLR, YateUCN performs all the functions of other MSC/VLRs: mobility, authentication, speech call and SMS routing. The server supports authentication of handsets using the SIM/USIM (EAP-SIM/EAP-AKA) and SIP AKAv1-MD5 algorithms.

YateUCN can connect to any standard HLR via the SS7 MAP protocol, and to other MSCs and GMSCs through the MAP-E protocol, allowing it to be in any conventional GSM network.

A few final words

YateUCN brings something new to GSM equipment: affordable redundancy, scalability, and uncomplicated management into a single core network server. It is easy to integrate to existing GSM and LTE networks and can be easily upgraded with new features within the same hardware and allows operators a seamless network extension.

YateUCN – the solution for MVNO networks

With mobile consumers’ expectations on the rise, new business models proliferate. Mobile Virtual Network Operator solutions must differentiate to stay competitive and maximize their offerings.

MVNOs wishing to offer subscribers high quality voice and/or data services can use YateUCN as a GMSC (voice), a GGSN (GPRS), or a PGW (LTE data).

YateUCN supports billing integration through CAMEL, RADIUS, and Diameter.

YateUCN, the unified core network for GSM/GPRS and LTE is a software implementation of the functions and protocols from the 2G and 4G LTE core layers on a commodity server. For GSM and GPRS, YateUCN performs the functions of the MSC, VLR, SGSN, GMSC, and GGSN. From 4G LTE, it acts as an MME, SGW, PGW, and PCRF.

YateUCN can be used to operate either all of these functions (for MNOs) or one specific function (for MVNOs). Each case scenario is presented below.


  • YateUCN for voice (GMSC)

The GMSC (Gateway Mobile Switching Center) functionality serves to locate the subscriber’s HLR (Home Location Register) in a mobile-terminated call, and then to route the call. Based on the information from the originating MSC, YateUCN uses the HLR to find the MSC of the called subscriber; with the number assigned by the HLR, the GMSC then forwards the call to the destination MSC. As a GMSC, YateUCN also provides CAMEL support.

  • YateUCN for data (GGSN and PGW in a single component)

In 2G networks, YateUCN as a GGSN (Gateway GPRS Support Node) is responsible for establishing and maintaining the user’s IP session and for storing billing information. It routes the IP packets to the SGSN in the MNO network over GTP-C. Establishing the data session in the YateUCN core network is independent of the radio network and is performed by the same component which can act either as a GGSN or as a PGW. If a session is initiated in GPRS, the GGSN (YateUCN) will connect to the SGSN over GTP-C v1.

In an LTE network, YateUCN can act as a PGW (PDN Gateway) to assign the IP address to the UE. YateUCN only communicates with the SGW in the operator’s network (over the S8 interface) and supports both Diameter and RADIUS to connect to the charging function in the network. If the session is started in LTE, YateUCN will act as a PGW and will connect to the SGW over GTP-C v2. It is also possible for a session to be started in LTE and continued in a 2G or 3G network.

  • YateUCN for billing integration

YateUCN connects to any billing system used by the MVNO, for both voice and data sessions management. It supports the Diameter Ro interface for prepaid services and the Rf interface for postpaid billing. For real-time credit control over SIP, YateUCN implements the Diameter Credit-Control Application (RFC 4006) to connect to the MVNO’s Charging Server.

  • YateUCN for SIP users

YateUCN also offers support for PC2Call registered users.

The unified core network, YateUCN, provides a profitable and flexible solution for the different requirements of emerging MVNOs. Detailed information about how YateUCN works in 2G and 4G networks is available here.