Introduction to EPC Primer
EPC is the main component of the System Architecture Evolution architecture (SAE). It provides an efficient, scalable, flat, and an all IP network infrastructure for datacom network operators. Users attached to an LTE network use the EPC backbone network to access external data networks (identified via APNs). EPC was first introduced by 3GPP in Release 8 of the standard. While moving from circuit switched to packet switched technology, EPC offers an attractive solution for operators migrating from traditional GSM/GPRS to an all IP network of the future where a number of network services use the same backbone to offer services to the end user (including voice, commonly known as VoLTE.
Convergence is the future
In traditional GSM, the architecture relies on circuit-switching (CS). This means that circuits are established between the calling and called parties throughout the telecommunication network (radio, the core network of the mobile operator, fixed network). This circuit-switching mode can be seen as an evolution of the “two cans and a string”. In GSM, all services are transported over circuit-switches telephony principally, but short messages (SMS) and some data are also seen.
In GPRS, packet-switching (PS) is added to the circuit-switching. With this technology, data is transported in packets without the establishment of dedicated circuits. This offers more flexibility and efficiency. In GPRS, the circuits still transport voice and SMS (in most cases). Therefore, the core network is composed of two domains: circuit and packet.
In UMTS (3G), this dual-domain concept is kept on the core network side. Some network elements have evolved but the concept remains very similar.
When designing the evolution of the 3G system, the 3GPP community decided to use IP (Internet Protocol) as the key protocol to transport all services. It was therefore agreed that the EPC would not have a circuit-switched domain anymore and that the EPC should be an evolution of the packet-switched architecture used in GPRS/UMTS.
This decision had consequences on the architecture itself but also on the way that the services were provided. Traditional use of circuits to carry voice and short messages needed to be replaced by IP-based solutions in the long term.
The Basic EPC Architecture
EPC is an all IP network. It doesn’t support traditional circuit-switched connections. Services which heavily relied on CS technology earlier (legacy voice), are now adapted to use the IP technology so that the same EPC backbone could be used for them as well. However, real-time traffic has a very strict throughput and latency requirements as compared to non-real-time traffic. So, efficient service differentiation techniques had also to be devised. All of these requirements led to a completely new data network architecture design, which:
- was flat and convergent
- had separate control and user plane data path
- supported “always on” network connectivity paradigm
- could realize end-to-end QoS management based on network traffic type
- and have lots and lots of performance improvements over GPRS (To be continued…)
Author: Vinit Shandilya
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