Section: 19.4.2.6 Serving GPRS Support Node (SGSN) within SGSN pool
Content: A specific SGSN within an operator's network is identified using the RAI FQDN (clause 19.4.2.5) and the Network Resource Identifier (NRI) (see 3GPP TS 23.236[ Intra-domain connection of Radio Access Network (RAN) nodes to multiple Core Network (CN) nodes ]  [23]). Such an identifier can be used by a target MME or SGSN node to connect to the source SGSN node. The SGSN FQDN shall be constructed as: nri-sgsn<NRI>.rac<RAC>.lac<LAC>.rac.epc.mnc<MNC>.mcc<MCC>.3gppnetwork.org <NRI> shall be Hex coded digits representing the NRI code of the SGSN. If there are less than 4 significant digits in < NRI>, one or more "0" digit(s) is/are inserted at the left side to fill the 4 digit coding. Coding for other fields is the same as in Clause 19.4.2.5. When a target MME constructs the FQDN of the source SGSN in the case of SGSN pooling, it should derive the NRI from the 8-bit MME Code received in the GUTI from the UE. However, if the length of the NRI, e.g., X, which is configured in the MME is less than 8 bits, then the MME should use only the most significant X bits of the MME Code as the NRI within the SGSN FQDN. Note: Above subdomain is for release 8 core network nodes to allow DNS records other than A/AAAA records. The subdomain name in Annex C.2 are still used for existing A/AAAA records for pre-Release 8 nodes and are also still used for backward compatibility. .