An Independent Review of SAE (System Architecture Evolution, aka 4G Core or Evolved Packet System (EPS)): A view on the emerging core network

This article follows on from a previous article that reviewed LTE (Long Term Evolution, also know as 4G).  Several people asked why I had not included a fuller discussion on the 4G core in that article.  It is because LTE is an access technology; my focus of the article was on the access where there is a lot of hype at the moment.  However, to support LTE a new core is required, as specified by the SAE (System Architecture Evolution).

In the standards community the names have now become E-UTRAN (Enhanced UMTS Terrestrial Radio Access Network) for LTE, and EPS (Evolved Packet System) for SAE.  Think of the SAE as a pure IP core without RNCs (Radio Network Controller) or SGSNs (Serving GPRS Support Node).  So in principle an operator would need to run two core networks to support the existing 3G network and the new 4G network.  Given the slight benefits of LTE compared to HSPA+, as discussed in a previous article, this would appear to be a significant barrier for LTE adoption.

However, the NEPs (Network Equipment Providers) are providing a range of solutions that enable the existing 3G core to evolve towards the SAE vision such as:

  • One Tunnel, moving the SGSN into the control plane;
  • Direct Tunnel, moving the SGSN and RNC into the control plane; and
  • Internet HSPA: control-plane SGSN and RNC is integrated into the NodeB.

The 3GPP core market is roughly $1B in size, and the top three suppliers in this market are: Ericsson (34%), NSN (33%), Huawei (15%).  Who unsurprisingly are the three players behind the three different solutions that evolve the core towards the SAE vision.  Given we’re likely to see the number of mobile broadband customers worldwide explode to over 1B over the next 4 years, mobile core costs could potential to explode as well.  Hence the immediate focus on moving the RNC and SGSN out of the data path and into the control plane, to better manage broadband growth.

Specifically the motivations for this early transition are:

  • Lower cost/bit – depending on the architecture it has the potential to reduce equipment costs by 80%;
  • Preparation for 4G – in other words avoid a dual core situation which would delay operators buying LTE BSRs (Base Station Routers).  Note the base stations are where NEPs make their money, so they’re keen to remove any barriers; and
  • Ease of integration of non-3GPP access (i.e. network convergence, avoiding multiple cores and service platforms).

Hopefully this sets out why we’ll likely see the ‘4G core’ happen before the ‘4G access.’