WARNING: This document has been Deprecated by the XMPP Standards Foundation. Implementation of the protocol described herein is not recommended. Developers desiring similar functionality are advised to implement the protocol that supersedes this one (if any).
An IM user may want to be informed when a contact creates an IM account. If the user knows some information about the contact (e.g., a phone number or email address), the user's service can use that information to place the contact on a "waiting list", then inform the user when the contact creates an IM account. This document defines an extension to XMPP Core  and XMPP IM  that enables such "waiting list" functionality, including the ability to add contacts on other domains if service providers agree to interoperate (e.g., to add a contact who uses a different mobile telephony service provider).
Note: The protocol defined herein is currently in use at several large service providers in Europe. Others are welcome to use the protocol.
A person with whom an IM User seeks to communicate, identified by a URI such as <tel:PhoneNumber> (see RFC 3966 ) or <mailto:EmailAddress> (see RFC 2368 ).
A person who is contracted for services with a ServiceProvider.
Any Customer who has registered for instant messaging services.
Any company that agrees to interoperate using the protocol defined herein.
The unique identifier of an IM User in the XMPP protocol. Outside the context of an IM session, a JID is of the form (<email@example.com> or <domain.tld>) ("bare JID"); within the context of an IM session, a JID is of the form (<firstname.lastname@example.org/resource> or <domain.tld/resource>) ("full JID").
A company that provides telephony or email services to a Customer.
A Uniform Resource Identifier as defined in RFC 3986 . Specific URI schemes that may be useful in this specification include 'tel:', 'mailto:', and 'sip:', but any URI scheme may be used.
A list of Contacts whom an entity (IM User or InteropPartner) is waiting to hear about regarding their status as instant messaging users.
An XMPP service that maintains Waiting lists for IM Users and/or InteropPartners.
An IM User may know a URI for a Contact (e.g., a phone number or email address) but not the Contact's JID. In order to subscribe to the Contact's presence or otherwise communicate with the Contact over an instant messaging system, the IM User first needs to discover the Contact's JID based on a URI for the Contact. However, the Contact may not yet have an IM account. Because the IM User may therefore need to wait until the Contact creates an account, the IM User needs to add the Contact to a WaitingList. The activity flow is as follows:
An IM User should remove a contact from the WaitingList after the IM User Adds Contact to WaitingList use case ends (either successfully or unsuccessfully), and may remove a contact from the WaitingList at any other time.
This section of the document is provided for the sake of domains that implement XMPP as their local protocol; domains that implement another protocol will use their service-specific protocol to complete the user-to-domain interaction.
The WaitingListService SHOULD return detailed information about the service it provides, including the URI schemes it supports (see also the Service Discovery Features section of this document).
Once an IM User has discovered the WaitingListService, the user's client SHOULD request its current Waiting List. This is done by sending an IQ-get to the WaitingListService containing an empty <query/> element qualified by the 'http://jabber.org/protocol/waitinglist' namespace:
Upon request, the WaitingListService MUST return the current WaitingList to the IM User:
Each ItemID MUST be unique within the scope of the client's WaitingList items. The value of the ItemID is an opaque string; an implementation MAY assign semantic meaning to the ItemID (e.g., id="John Smith (mobile)" rather than id="12345"), but such meaning is implementation-specific and outside the scope of the protocol defined herein. The user MAY include a <name/> element containing a natural-language name for the Contact.
The WaitingList MAY contain an item for which a JID has been discovered.
Once an IM User's client has discovered the WaitingListService and requested the user's WaitingList, the user can add Contacts to the WaitingList based on the Contact's URI. (Note: This document uses the example of phone numbers via the 'tel' URI scheme, but the same rules apply to WaitingList items based on email addresses or other URI schemes.)
If the IM User provided a URI whose scheme is not supported, WaitingListService MUST return a <bad-request/> error to the IM User and MUST NOT add the Contact to the WaitingList.
If the IM User included a JID in the request, WaitingListService MUST return a <bad-request/> error to IM User and MUST NOT add the Contact to the WaitingList. (Note: A WaitingListService MUST NOT return a non-XMPP URI to an IM User based on the Contact's JID; see the Security Considerations section of this document.)
If the IM User provided an invalid URI (e.g., a phone number with too many digits or an email address with no '@' character), WaitingListService MUST return a <not-acceptable/> error to the IM User and MUST NOT add the Contact to the WaitingList.
If one of the foregoing errors was generated (all of which have a type of "modify"), IM User SHOULD modify the request and re-submit it.
If none of the "modify" errors was generated, WaitingListService MUST inform the IM User that the request was successfully received, including a unique ID number for the new WaitingList item.
If none of the "modify" errors was generated and WaitingListService knows Contact JID when the IQ result is returned to the user (e.g., because Contact is served by ServiceProvider), WaitingListService MAY include the WaitingList item in the IQ result: 
If none of the "modify" errors was generated and WaitingListService does not know Contact JID when the IQ result is returned to the user, it needs to contact InteropPartners in order to determine if the Contact is associated with one of the InteropPartners. Thus before it returns the Contact JID to the IM User, it needs to wait for the one of the InteropPartners to return Contact JID or for all of the InteropPartners to return errors.
If all of the InteropPartners return an error of type "cancel" (typically <item-not-found/> and/or <not-authorized/>) to WaitingListService, WaitingListService MUST return an <item-not-found/> error (or local equivalent) to the IM User (and IM User SHOULD complete IM User Removes Contact from WaitingList use case).
If the connection to at least one of the InteropPartners times out (a <remote-server-timeout/> error), WaitingListService MUST return an IQ-result as described above (indicating that the request was received) and resend the request to the InteropPartners that timed out. If connections continue to time out (over some configurable time period and for some configurable number of retries), WaitingListService SHOULD then return a <remote-server-timeout/> error to IM User via a "JID push" message as shown below.
If WaitingListService knows Contact JID (or learns Contact JID from InteropPartner), it MUST inform IM User through a "JID push" message, which consists of a message stanza that contains a <waitlist/> element qualified by the 'http://jabber.org/protocol/waitinglist' namespace:
Note: The JID push uses an XMPP <message/> stanza because the WaitingListService has no knowledge of the user's presence and therefore cannot assume that an <iq/> stanza will be received by the user at a specific resource.
If WaitingListService learns that Contact's URI is not handled by any InteropPartner, it MUST inform IM User through a "JID push" message:
If WaitingListService previously recorded request, WaitingListService removes request from list and returns result to IM User.
If WaitingListService did not previously record this request, WaitingListService MUST return an <item-not-found/> error to the IM User.
5.2 WaitingListService Interaction With InteropPartners¶
This section of the document describes the inter-domain protocol for communication between WaitingListServices. The protocol defined in this section MUST be implemented by ServiceProviders.
A ServiceProvider's WaitingListService MUST be configured with a "whitelist" of InteropPartner's WaitingListServices with which it communicates. Therefore service discovery SHOULD NOT be necessary. However, if necessary it MAY use either the Agent Information protocol or the Service Discovery protocol as described in the following examples.
Note: The InteropPartner's WaitingListService is not required to be hosted by InteropPartner, and could be hosted by a third party (e.g., a neutral phone number translation service). In this case, InteropPartner would simply advertise 'waitlist.third-party.com' as its WaitingListService.
5.2.1 ServiceProvider's WaitingListService Retrieves Current WaitingList¶
5.2.2 ServiceProvider's WaitingListService Adds Contact to WaitingList¶
Once a ServiceProvider's WaitingListService has discovered the InteropPartner's WaitingListService and requested its WaitingList, the ServiceProvider's WaitingListService can add items to its WaitingList based on URI.
If InteropPartner refuses to provide service to ServiceProvider, it MUST return a <not-authorized/> error to the ServiceProvider:
If Contact's URI is not associated with a person served by this InteropPartner, the InteropPartner MUST return an <item-not-found/> error to the ServiceProvider.
If ServiceProvider's WaitingListService receives <not-authorized/> and/or <item-not-found/> errors from all InteropPartners, it returns a <item-not-found/> error to IM User:
If Contact's URI is associated with a person served by this InteropPartner, InteropPartner MUST return acknowledgement of the WaitingList addition to the ServiceProvider's WaitingListService.
If Contact is an IM User served by InteropPartner, InteropPartner's WaitingListService pushes Contact's JID to ServiceProvider's WaitingListService.
After receiving acknowledgement (but not before), InteropPartner's WaitingListService MUST remove that item from the WaitingList for the ServiceProvider's WaitingListService.
5.2.3 ServiceProvider's WaitingListService Removes Contact from WaitingList¶
If item exists on WaitingList, InteropPartner's WaitingListService removes item from list and returns result to ServiceProvider's WaitingListService.
If item does not exist on WaitingList, InteropPartner's WaitingListService MUST return an <item-not-found/> error to the ServiceProvider's WaitingListService.
Protocols and mechanisms for inviting a Contact to register as an IM User are out of scope for this document and shall be determined by each InteropPartner individually.
A ServiceProvider's WaitingListService MUST record which of its IM Users have requested the JID associated with Contact's URI, and an InteropPartner's WaitingListService MUST record that Service Provider's WaitingListService (not User) has requested JID associated with Contact's URI. Therefore when Contact registers, InteropPartner's WaitingListService informs its local users as well as ServiceProvider's WaitingListService, and ServiceProvider's WaitingListService informs its local users.
The InteropPartner's WaitingListService is not required to be hosted by InteropPartner, and could be hosted by a third party (e.g., a neutral phone number translation service). In this case, InteropPartner would simply advertise 'waitlist.third-party.com' as its WaitingListService.
Once an IM User learns a Contact's JID, the IM User MAY send a normal subscription request to the Contact, setting the "to" address to Contact's JID. This interaction is defined in the base XMPP specifications and is out of scope for this document.
For historical reasons, implementations MUST support the older Agent Information protocol (XEP-0094) and SHOULD support Service Discovery (XEP-0030). Note well that the Agent Information protocol will eventually be deprecated in favor of Service Discovery.
An IM User's client receives WaitingList information either through a "JID push" message (received from WaitingListService at any time) or in the IQ result received after requesting the WaitingList (since one or more of the WaitingList items may contain a JID). (The same rule applies to a ServiceProvider's WaitingListService that receives an IQ set from an InteropPartner's WaitingListService.)
When an IM User logs in, the user's client SHOULD request the current WaitingList.
Although the examples in this document show the hostname of the WaitingListService as 'waitlist.third-party.com' (etc.), this is for convenience only; the hostname MAY be any valid DNS hostname.
When sending JID pushes, an implementation MAY specify a message type of 'headline', which in some deployments will prevent such messages from being stored offline for later delivery.
It can happen that WaitingListService does not receive a reply from InteropPartner within a certain amount of time or the connection to InteropPartner times out. Because such behavior is often transient, WaitingListService MAY attempt to reconnect and then resend the request (although any retry logic to handle these cases is a matter of implementation). However, WaitingListService SHOULD NOT return an <item-not-found/> error to IM User unless it knows definitively that the Contact's InteropPartner is permanently unavailable, since returning an <item-not-found/> error in response to temporary connection timeouts is likely to be misleading.
A ServiceProvider's WaitingListService MUST be configured with a "whitelist" of InteropPartners with which it communicates. The WaitingListService SHOULD NOT communicate with any InteropPartners that are not on the whitelist.
Requesting JIDs via WaitingLists is not bidirectional; i.e., a service MUST NOT allow an IM User to discover a Contact's non-XMPP URI based on the Contact's JID.
A service MAY require a Contact to approve the disclosure of the Contact's JID, either as a global preference or for each request; however, this is a local policy matter.
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The Extensible Messaging and Presence Protocol (XMPP) is defined in the XMPP Core (RFC 6120) and XMPP IM (RFC 6121) specifications contributed by the XMPP Standards Foundation to the Internet Standards Process, which is managed by the Internet Engineering Task Force in accordance with RFC 2026. Any protocol defined in this document has been developed outside the Internet Standards Process and is to be understood as an extension to XMPP rather than as an evolution, development, or modification of XMPP itself.
The following requirements keywords as used in this document are to be interpreted as described in RFC 2119: "MUST", "SHALL", "REQUIRED"; "MUST NOT", "SHALL NOT"; "SHOULD", "RECOMMENDED"; "SHOULD NOT", "NOT RECOMMENDED"; "MAY", "OPTIONAL".
9. Even if WaitingListService returns Contact JID in the IQ-result, it MUST also send a "JID push" message.
10. When waiting list information is included in a message stanza, the root element for the 'http://jabber.org/protocol/waitinglist' namespace is <waitlist/> rather than <query/> (as used within IQ stanzas). This disparity is historical and tracks the protocol syntax that was most widely implemented, as defined in version 0.4 of this specification. In the interest of interoperability, the IQ usage was changed back to <query/> in version 1.1 of this specification. If this document were not historical, the root element usage would be harmonized to use only the <waitlist/> element.
11. The Internet Assigned Numbers Authority (IANA) is the central coordinator for the assignment of unique parameter values for Internet protocols, such as port numbers and URI schemes. For further information, see <http://www.iana.org/>.
12. The XMPP Registrar maintains a list of reserved protocol namespaces as well as registries of parameters used in the context of XMPP extension protocols approved by the XMPP Standards Foundation. For further information, see <https://xmpp.org/registrar/>.
Clarified alternate flow for main use case; corrected order of errors and JID pushes; specified that item removal is always the responsibility of the IM user; removed remote-server-not-found example (use item-not-found instead).
Changed document type to Informational; corrected Remote Server Error example to use <remote-server-not-found/> rather than <service-unavailable/>; added service discovery identity to XMPP Registrar Considerations; corrected text regarding registration of service discovery features; corrected some small errors in the text, examples, and schema.
Added alternate flow for situation in which Contact URI is not handled by any InteropPartner; changed headline message type for JID pushes from SHOULD to MAY; clarified semantics of item ID; added name child of item; corrected and updated the XML schema; updated examples to use XMPP error conditions.
Changed client-server push mechanism to use <message/> rather than <iq/>, since client may not be online; allowed IQ result to include waitlist information if known; added more detailed disco#info lookup to support discovery of URI types supported.
Refactored protocol to use IQ sets that are "pushed" to the component or client (similar to XMPP rosters); added service discovery and agents support; made text more generic; simplified error handling; change name to "Waiting Lists".