Section: 4.3.20 Relaying function 4.3.20.1 General
Content: The relaying function enables an operator to improve and extend the coverage area by having a Relay Node (RN) wirelessly connected to an eNodeB serving the RN, called Donor eNodeB (DeNB), via a modified version of the E-UTRA radio interface called the Un interface as specified in TS 36.300[ Evolved Universal Terrestrial Radio Access (E-UTRA) and Evolved Universal Terrestrial Radio Access Network (E-UTRAN); Overall description; Stage 2 ]  [5]. The relaying function and use of RN/DeNB entities in a network is transparent to the operations of the UEs connected to it and associated core network entities (e.g. MME, S/P-GW, PCRF etc.) for the UEs. The relaying architecture is shown in figure 4.3.20.1-1. Figure 4.3.20.1-1: Relaying Architecture NOTE 1: Impact to core network elements from the introduction of RNs and DeNB is minimized by reusing the existing nodes and protocols when interacting with the core network. NOTE 2: Functions of the MME for the RN and MME for the UE may be collocated in a single MME. The RN supports the eNodeB functionality like termination of the radio protocols of the E-UTRA radio interface and the S1 and X2 interfaces. The RN also supports a subset of the UE functionality and protocols to wirelessly connect to the DeNB. In addition to supporting eNodeB functionality, the DeNB also embeds and provides the S-GW/P-GW-like functions needed for the RN operation. This includes creating a session for the RN and managing EPS bearers for the RN as shown in clause 4.3.20.3, as well as terminating the S1-AP and S11 interfaces towards the MME serving the RN. Due to the proxy functionality, the DeNB appears as an MME (for S1), an eNodeB (for X2) and an S-GW to the RN. The RN and DeNB also perform mapping of signalling and data packets onto EPS bearers that are setup for the RN. The mapping is based on existing QoS mechanisms defined for the UE and the P-GW and are described in TS 36.300[ Evolved Universal Terrestrial Radio Access (E-UTRA) and Evolved Universal Terrestrial Radio Access Network (E-UTRAN); Overall description; Stage 2 ]  [5].