EPC: A new core network for the new LTE radio technology

Many new transmission facilities to the cellular towers are visible part of the LTE structure.


The second, invisible to the public, is equally important part: The technology and infrastructure with which these new LTE transmission facilities are operated and controlled, the so-called core network, changes radically. This core network for LTE (Engineered packet-based core network) and Evolved Packet Core Evolved Packet or designated system. It basically works like the normal Internet, the technical term for this technology is an IP-based network or English an all-IP network. But what does that mean and how this network is different from a GSM network or a UMTS network, so what is the new in it?

GSM, UMTS and LTE networks: the differences

Put simply, the current mobile phone networks were completely fixed, or in large part on voice telephony. The GSM network, the second generation of mobile phone was originally designed as a pure network; other functions such as SMS and data transmission were then gradually it. The UMTS network calls and sending large amounts of data as equal functions together. The core network is divided into a part of UMTS, which provided fixed channels for the transmission of telephone calls (circuit switched) and one of the different data sets – like the Internet – transported.

The LTE network has – like the Internet – the absolute data priority. Telephoning is thus only one of many sub-functions of data transmission. A development is reconstructed, which is advanced in the fixed network have further calls is no longer handled through a separate channel, but runs as a Voice over IP over the Internet.

Which then affects the manner in which the LTE core network works: It is anything from one terminal to the other terminal to the Internet technology – are transmitted – the Internet Protocol, or IP. Technically speaking, it is an IP-based network or an all-IP network.

This fundamental change in the net makes the data transmission speed – both for downloading and sending, as well as in the reaction times. The Australian IT specialist Stuart Corner says: It is not primarily be the new LTE data radio technology, which allows high speed jumps, but most of all the new core network.

Signaling data: By registering for the bill

The new network is allocated differently: Over a part of running the so-called signaling data – for example, the registration of the participant in the network, its verification and identification, the location of their mobile device – the other part of the so-called user data – ie services that he accepts the scheme as phone or mobile Internet.

Among the parts that manage the signaling data and edit include Management Mobility Entity, short MME (Management of the mobile units), the Home Subscriber Server, short HSS (Subscriber Server) and the Policy and Charging Rules Function, briefly PCRF (fees office).

Logs in the MME to the mobile device, and then is forwarded to a location which the services – manages – ie the data transmissions. The MME also retrieves the information about the customer at HSS – because they are deposited there, in the GSM and UMTS networks had this customer database the name of Home Location Register (HLR). The PCRF can – depending on the rate – to specific data flows from that terminal or declines; it calculates how much the service costs at the rate reserved by the customer and shall issue an invoice.

User data: designing services funneled through the net

The services themselves are carried out in the so-called SAE gateway. The acronym stands for System Architecture Evolution Gateway – and said in German as the main interface for the network. This gateway consists of two areas: First, since the serving gateway is – short SGW in German about services portal. There the user’s terminal is managed by the application at the MME continues. It remains registered so when the user switches between two cell towers or when switching from LTE to a different wireless technology. It takes the data packets received by the user sends – for example by surfing – and forwards it to the exit.

The output is referred to as PDN Gateway, which is German for Public Data Network Gateway as portal to the public networks. And that is its function: Here the data to other networks – other mobile networks, Internet – forwarded and received the input data for the terminal of customers and forwarded.


LTE Networks: The Architecture

The architecture of LTE networks is given the technical term System Architecture Evolution or the corresponding abbreviations SAE.


It is compared to previous wireless networks and provides a simpler structure to process with greater amounts of data. Thereby it provides a faster response time of the entire network. The new architecture is also the seamless mobility between LTE and other wireless technologies such as GPRS or WiMAX. Finally, the new architecture could transform the wireless network to an all-IP network. This means the data packets are sent to the wireless network in the Internet-standard. In order for mobile devices, IP-based services such as IPTV, online games, or data transfer from the Internet, but also Internet telephony is optimized.

EUTRAN: The wireless network

As with any wireless network even in the LTE, radio network consists of individual cells. The device of the user need the radio signals from the base station, from there to the base station – in LTE it is called eNodeB. Transmission tower and base station form a cell.

In LTE radio network, several adjacent radio cells are combined to form a group, which are known as the Tracking Area. The entire radio part, that all radio cells and tracking areas of an operator is taken together, the technical English with E  UTRAN or EUTRAN called. The term EUTRAN is from the initials of Evolved Universal Terrestrial Radio Access Network formed. This part of the network is also referred to as air interface.

EPC: The core network

The user’s data are going to the core network Of the air interface for LTE, which in technical English Evolved Packet Core ( EPC is called). The Evolved Packet Core consists of three components:

The first is the MME. This abbreviation stands for Mobility Management Entity. An MME manages multiple tracking areas. The MME is the most important control element in the EPC; it is only responsible for control signals. The MME is responsible for the mobility management, which means that they registered and be identified by the exact location of the user, which is a terminal in the LTE network. In the MME, it’s possible to notify the user to speak with his terminal.

The MME also organizes the recognition of the user, or finds his admission. Detection of the user accesses the MME to a database, in which the participants are recorded, this means in English technical HSS (Home Scriber server). His profile is stored in the MME. the MME sets the key, after the data is encrypted and sends it to the base station – or the eNodeB – which performs the encryption. When the terminal is turned on, the MME calls him an SGW.

This SGW (short for English Service Gateway) is the second component of an LTE network. The service gateway remains the focal point for the user’s device when it switches between two LTE transmission towers or when the LTE network must switch to UMTS or GSM network. The SGW is a switching station – it switches the users coming from or addressed to him data to the correct address.

By the user sent or addressed to him, data runs over the third component: the Public Data Network Gateway (symbol: PGW, meant: Interface for public data networks). The PGW is as it were a terminal, where the user’s data from the network of the mobile operator forwarded to other networks or in the data arriving from other networks for him, ready to collect.

The terminal of a user is able to communicate with a plurality of PDN-GW – if it is responsive simultaneously different networks. The PDN gateway also sends data to a computing unit, which is outside of the core network, the PCRF (Policy and Charging Rules Function).

The user directory and the accounting office

This brings us to the two parts of which are outside of the core network, however, associated with this are: the Home Server Scriber, short HSS are the user data, including a profile stored. He is like a complete list of all customers of a mobile operator. Here, for example, the identification number (IMSI) of the mobile subscriber is stored or which services are allowed for him. There will also be stored at which the MME device was last logged.

The accounting and control station is finally in the part that policy and charging rules function (PCRF) is called. It’s noted that the types of data that arrive in the PGW can be used by the customer, and if so, under which tariff they fall. Using this information the bill then finally can create.