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7.3.3 FIXED MOBILE CONVERGENCE ENHANCEMENTS<br />
The Fixed Mobile Convergence (FMC) scenario in 3GPP is part of the Evolved Packet System defined by<br />
3GPP TS 23.402 where it is specified how a non-3GPP system can be connected to a 3GPP EPC<br />
network. The interconnection of a non-3GPP system is based on two scenarios depending on whether<br />
the non-3GPP network is considered a Trusted access network or an Untrusted access network. In 3GPP<br />
specifications, the non-3GPP system can be any technology which is not defined by 3GPP, such as<br />
WLAN, WiMAX, 3GPP2 and xDSL. However in some cases, the access characteristics are taken into<br />
account, while in other cases it is assumed that access network will support some 3GPP specific features.<br />
A simple example is represented by APN and PCO. 3GPP assumes that if supported then the UE has the<br />
same behavior in 3GPP access and in non-3GPP access, otherwise the UE cannot establish a PDN<br />
connection from non-3GPP system, so the user cannot obtain the same services from both networks.<br />
For its nature, the FMC spans several standard organizations. The 3GPP and Broadband Forum (BBF)<br />
started a collaboration and a parallel work for definition of use cases, requirements, architecture and<br />
protocol considering new 3GPP features such as H(e)NBs; Local Internet Protocol Access (LIPA) to<br />
residential/corporate local networks; Selected IP traffic offload (SIPTO) for H(e)NBs; IP Flow Mobility and<br />
seamless WLAN offload (IFOM); and new BBF features as support of IP session, definition of Policy<br />
Framework and Broadband multi-service nodes.<br />
Considering the complexity of the scenario, the work in 3GPP has been divided in three steps: the first<br />
step considers the scenario of a 3GPP UE or a femto connected to the BBF access where the traffic is<br />
always home routed; the second step considers the scenario of traffic offloaded to the broadband access,<br />
(i.e. SIPTO/LIPA and non-seamless WLAN offload); the third scenario considers a more tight convergent<br />
network. The first two steps are commonly identified as interworking scenario. The above work has been<br />
further organized in as a study included in the 3GPP TR 23.839, after the conclusion of each step the<br />
normative specification will be modified accordingly.<br />
The BBF has organized the parallel Fixed Mobile Convergence (FMC) work differently. The 3GPP<br />
interworking use cases and requirements are defined in WT-203; however, some impact is expected on<br />
the WT-134, which defines the use cases, requirements and the information model for the Broadband<br />
Policy Control Framework.<br />
The interworking scenario takes into account the Trusted/Untrusted model and the different mobility<br />
protocols (e.g. DSMIPv6 on s2c, PMIPv6 on s2b, etc) defined in 3GPP TS 23.402, where the generic<br />
non-3GPP access network has been substituted by the BBF access network with its own characteristic.<br />
Figure 7.12 shows the reference architecture for Untrusted scenario with s2c and s2b (for the other<br />
scenario refers to 3GPP TS 23.839 or to WT-203). The key interfaces are the S9* between the PCRF and<br />
the BBF Policy Server and the STa*/Swa between the AAA Servers. The S9* interface represents the<br />
enhancement of 3GPP S9 for supporting the transport of the QoS and Charging information between the<br />
Broadband Policy Framework and the PCC. At current stage of work, BBF and 3GPP agreed that PCRF<br />
sends the 3GPP QoS rules to the BBF Policy Server which performs the mapping to BBF QoS rules.<br />
However, since the BBF is defining the Policy Information Model and the functionalities of the Policy<br />
Framework, many open issues are on the table and further work is required. For example, one of the<br />
main issues is related to the 3GPP UE authentication. The 3GPP specification requires that UE<br />
authentication is EAP-based, but the BBF specification does not support EAP-based authentication for a<br />
single device beyond the Residential Gateway (RG). In order to fulfill such requirement and to enable also<br />
the device authentication for fixed device, BBF has started the definition of the support of EAP for IP<br />
session in WT-146. So, if the 3GPP UE is authenticated when attached to a WLAN both BBF access and<br />
3GPP are aware of the UE identity and the Policy server can start the S9 session towards the PCRF. If<br />
www.4gamericas.org February 2011 Page 69
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