Section: 13.5 Public Service Identity (PSI)
Content: The public service identity shall take the form of either a SIP URI (see IETF RFC 3261 [26]) or a Tel URI (see IETF RFC 3966 [45]). A public service identity identifies a service, or a specific resource created for a service on an application server. The domain part is pre-defined by the IMS operators and the IMS system provides the flexibility to dynamically create the user part of the PSIs. The PSIs are stored in the HSS either as a distinct PSI or as a wildcarded PSI. A distinct PSI contains the PSI that is used in routing , whilst a wildcarded PSI represents a collection of PSIs. Wildcarded PSIs enable optimisation of the operation and maintenance of the nodes. A wildcarded PSI consists of a delimited regular expression located either in the userinfo portion of the SIP URI or in the telephone-subscriber portion of the Tel URI. The regular expression in the wildcarded PSI shall take the form of Extended Regular Expressions (ERE) as defined in chapter 9 in IEEE 1003.1-2004 Part 1 [60]. The delimiter shall be the exclamation mark character ("!"). If more than two exclamation mark characters are present in the userinfo portion or telephone-subscriber portion of a wildcarded PSI then the outside pair of exclamation mark characters is regarded as the pair of delimiters (i.e. no exclamation mark characters are allowed to be present in the fixed parts of the userinfo portion or telephone-subscriber portion). When stored in the HSS, the wildcarded PSI shall include the delimiter character to indicate the extent of the part of the PSI that is wildcarded. It is used to separate the regular expression from the fixed part of the wildcarded PSI. Example: The following PSI could be stored in the HSS - "sip:chatlist!.*!@example.com". When used on an interface, the exclamation mark characters within a PSI shall not be interpreted as delimiter.. Example: The following PSIs communicated in interface messages to the HSS will match to the wildcarded PSI of "sip:chatlist!.*!@example.com" stored in the HSS: sip:chatlist1@example.com sip:chatlist2@example.com sip:chatlist42@example.com sip:chatlistAbC@example.com sip:chatlist!1@example.com Note that sip:chatlist1@example.com and sip:chatlist!1@example.com are regarded different specific PSIs, both matching the wildcarded PSI sip:chatlist!.*!@example.com. When used by an application server to identify a specific resource (e.g. a chat session) over Inter Operator Network to Network Interface (II-NNI), the PSI should be a SIP URI without including a port number. NOTE: Based on local configuration policy, a PSI can be routed over Inter Operator Network to Network Interface (II-NNI). Details of this routing are operator specific and out of scope of this specification.