24.3023GPPAccess to the 3GPP Evolved Packet Core (EPC) via non-3GPP access networksRelease 18Stage 3TS
According to 3GPP TS 23.003  the encoding of the Access Network Identity is specified within 3GPP, but the Access Network Identity definition for each non-3GPP access network is under the responsibility of the corresponding standardisation organisation respectively.
If a standardisation organisation for a non-3GPP access network determines they need to define a new Access Network Identity Prefix or additional ANID strings, they can contact the 3GPP TSG-CT WG 1 via a Liaison Statement and indicate the specific values of the Access Network Identity Prefixes or the specific values of, or construction principles for, the additional ANID strings to be specified by 3GPP and give reference to the corresponding specification(s) of the requesting organisation. 3GPP TSG CT WG 1 will then specify the values for the Access Network Identities by updating Table 126.96.36.199 in this specification and inform the requesting standardisation organisation.
Annex C (informative):
Example usage of ANDSF