Packet Core Evolution From 2G/3G Toward 4G

Most mobile operators have witnessed huge changes in the telecommunications markets, and voice services have been neglected as operators set their sights on more profitable data services. Voice services will probably be superseded by another telecom service in the near future. The development of mobile broadband, wide deployment of 3G networks, and popularity of 3.5G networks are driving this transformation. End users want permanent connection, higher bandwidth, faster access, seamless mobility, and lower prices. These will be realized as 4G LTE matures.

Although LTE and EPC can support both voice and data, there are problems with reusing existing 2G and 3G networks and having these networks coexist with 4G networks. Operators have to consider technologies, market, cost, and engineering issues, and their ultimate goal is to build an independent, efficient LTE and EPC network.

Evolution Analysis

2G/3G PS and 4G EPC are defined differently in 3GPP. In the 2G and 3G eras, a core network is divided into CS and PS domains that provide voice and data services, respectively. In a 2G network, the control and user planes are combined in order to achieve a download rate of up to 460 kbps. Since the 3G era, the control plane has been gradually split from the user plane in order to make a flat network in which direct tunnels can be deployed. With HSDPA, a download rate of more than 10 Mbps can be achieved. Now in the 4G era, the CS domain is gone, and EPC can provide all telecom services with an optimum download rate of more than 100 Mbps and support both 3GPP and non-3GPP access.

LTE networks will have the following impact on 2G/3G networks:

●    An independent NE will have to carry two to five million users.

●    As data throughput at the interface increases from 1 Gbps to 10 Gbps, adjacent switches, routers, and firewalls of the GPRS network will need to be upgraded to support 10 GE.

●    With an increase in user numbers and smart terminals, and with frequent handover from 2G/3G to LTE, network signaling storms should be avoided.

In the early stage of LTE deployment, an existing core network should be upgraded to an EPC, or a new EPC should be constructed. In the broadband data service stage, the EPC should guarantee continuity of data services coming out of the new LTE network. The cost of maintaining multiple networks should also be reduced as much as possible. Once LTE/EPC has been put into service, operators should introduce voice services, QoS guarantee, and service control for LTE users and consider reconstructing or swapping over their old networks.

According to the 3GPP standard, the overall goal of LTE/EPC is to increase data rate, decrease latency, and optimize packet transmission. Another goal at the EPC side of a core network is support for different wireless access technologies, including traditional GSM/UMTS access and non-3GPP access (such as WiFi). This helps create a seamless experience for users moving between different access networks.

The following need to be ensured when smoothly evolving from 2G/3G to 4G networks:

●    improved voice QoS, which helps operators cement their market position

●    large-capacity intelligent network with DPI technology

●    target network that supports flexible policy charging control (PCC)

●    network convergence that supports 2G, 3G and 4G networks and can save investment and opex

●    support for more internet services and improved service management and control 

●    future-proof networks that can easily be expanded and upgraded.

Implementation Mode

There are two ways to introduce an EPC: upgrade the existing PS domain or build a new EPC that can be incorporated into existing PS services at a later stage.

In order to upgrade a traditional PS to make it serve as an EPC, the traditional GSN needs to support LTE access and provide a large space for LTE services. All-IP networking should also be supported. This implementation mode requires low initial investment but high maintenance cost and may affect existing services.

A new EPC needs to have large capacity for LTE access, all-IP networking, and 2G/3G access. With this implementation mode, initial investment is high but maintenance cost is low, and the new EPC network does not affect existing services.

No matter which mode an operator adopts, the core network will become a converged SGSN/MME or GGSN/SGW/PGW network that supports 2G, 3G, and 4G access.

Target Network

In a converged core network solution, a core network in the PS domain contains an intelligent mobile access controller (MAC), which converges SGSN and MME, and a converged gateway (GW), which converges GGSN, PWG, and SGW (Fig. 1). The two nodes split the control plane from the user plane in order to simplify the network and enable a high degree of NE integration.

MAC is an NE at the control plane and is responsible for controlling the access and mobility of 2G, 3G, and LTE users. The converged GW is responsible for packet transmission at the user plane and guarantees that there is only one node in the core network that processes the user plane of every access type. This ensures that the core network can be further flattened to lower opex, save backbone transmission bandwidth, and provide better QoS and lower latency for users.

In the EPC, a user data convergence (UDC) solution is a data-management layer in the network architecture that converges data and guarantees data consistency. This helps lower TCO. The UDC solution supports convergence of applications such as GSM HLR, UMTS HLR, CDMA HLRe, FNR, MNP, EIR, IMS HSS, and EPC HSS. UDC also enables

●    sharing of unified user information. This helps in the unified control and management of UMTS/CDMA/LTE/IMS user data.

●    service integration, such as automatic roaming between UMTS and CDMA networks, binding of a terminal and its SIM card, sharing of user state between HLR and HSS, and simplifying MNP process.

●    providing a unified data management platform for MTOs. This helps implement region-based management.

As more and more multimode terminals appear in the market and users demand seamless roaming, the number of users in a 2G/3G network or an LTE network may change dynamically, even if the total user base of an operator remains unchanged. For this reason, in a network architecture where 2G/3G network is separated from LTE, each network needs the maximum capacity, and the cost of meeting the need for seamless roaming is higher. A converged core network solution promises maximum capacity at low cost by sharing software and hardware between 2G/3G and LTE networks. As 2G/3G users become LTE users, 2G/3G operational costs will gradually be reduced. When all 2G/3G users become LTE users, the converged core network will completely change its role as a real EPC.

EPS networks are becoming more sophisticated as more and more LTE terminals are released. Smooth network upgrade can save operator investment and bring about better user experience.