The role of E-CID as a fallback positioning technique is particularly relevant for emergency call locating (it was considered so relevant in 4G that the LTE Positioning Protocol (LPP), unlike RRLP (in 2G networks) and RRC (in 3G networks), supports E-CID).
And, unlike previous protocols, such as RRLP and RRC--which support only control plane positioning--LPP also can be used in user plane positioning [60, 64].
 3GPP, "Location Services (LCS); Mobile Station (MS)--Serving Mobile Location Centre (SMLC) Radio Resource LCS Protocol (RRLP)," 3rd Generation Partnership Project (3GPP) TS 04.31, 2007, http://www.3gpp.org/ftp/Specs/archive/0Thseries/04.31/.
Caption: FIGURE 6: RRLP Assistance Data Delivery Procedure.
Caption: FIGURE 7: RRLP Position Measurement Procedure.