Section: 8.62 Fully qualified PDN Connection Set Identifier (FQ-CSID)
Content: A fully qualified PDN Connection Set Identifier (FQ-CSID) identifies a set of PDN connections belonging to an arbitrary number of UEs on a MME, SGW, TWAN, ePDG or PGW. The FQ-CSID is used on S5, S8, S2a, S2b and S11 interfaces. The size of CSID is two octets. The FQ-CSID is coded as follows: Figure 8.62-1: FQ-CSID Where Node-ID Type values are: 0 indicates that Node-ID is a global unicast IPv4 address and p = 9. 1 indicates that Node-ID is a global unicast IPv6 address and p = 21. 2 indicates that Node-ID is a 4 octets long field with a 32 bit value stored in network order, and p= 9. The coding of the field is specified below: - Most significant 20 bits are the binary encoded value of (MCC * 1000 + MNC). - Least significant 12 bits is a 12 bit integer assigned by an operator to an MME, SGW, TWAN, ePDG or PGW. Other values of Node-ID Type are reserved. Values of Number of CSID other than 1 are only employed in the Delete PDN Connection Set Request. The node that creates the FQ-CSID, (i.e. MME for MME FQ-CSID, SGW for SGW FQ-CSID, TWAN for TWAN FQ-CSID, ePDG for ePDG FQ-CSID and PGW for PGW FQ-CSID), is responsible for making sure the Node-ID is globally unique and the CSID value is unique within that node. When a FQ-CSID is stored by a receiving node, it is stored on a PDN basis even for messages impacting only one bearer (i.e. Create Bearer Request). See 3GPP TS 23.007[ Restoration procedures ]  [17] for further details on the CSID and what specific requirements are placed on the PGW, TWAN, ePDG, SGW and MME.