H.450 - Wikipedia

International Telecommunication Union standards

H.450 refers to a set of standards created by the International Telecommunication Union (ITU) to define several Supplementary Services of the packet based telecommunication protocol known as H.323.[1] It parallels another set of standards known as QSIG which define similar services for ISDN based networks.

Standards

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• H.450.1, Supplementary Services Framework[2]

The general mechanism for delivering supplementary services is explained in this paper. Supplementary services messages are exchanged by means of ROSE (Remote Operations Service Extension).

• H.450.2, Call Transfer Supplementary Service[3]

E.g. explains how a party-B can turn an active call between party-A and party-B into a call between party-A and a new party-C.

• H.450.3, Call Diversion Supplementary Service

E.g. explains how an IP phone can activate a diversion to e.g. a cell phone. E.g. explains how an IP phone can interrogate whether it has any active diversion.

• H.450.4, Call Hold Supplementary Service

E.g. explains how a call can be put on hold and be fed with a music on hold.

• H.450.5, Call Park and Pickup Supplementary Service

Think of big warehouse, where a call is coming in at the front-desk for Mrs. Smith. The front-desk parks the call and broadcasts via the intercom: "Mrs. Smith, please 223". Mrs. Smith proceeds soon after to the next wall phone, dials 223 and gets the call.

• H.450.6, Call Waiting Supplementary Service

Explains how to signal a second call to an IP phone already engaged in an active call.

• H.450.7, Message Waiting Indication Supplementary Service

Explains elements related to voicebox systems and how these can be implemented by means of H.323.

• H.450.8, Name Identification Supplementary Service

Explains how names are displayed or how to intentionally call incognito.

• H.450.9, Call Completion Supplementary Service

Explains how to schedule an automatic call-back request in case of a remote party being busy in a call or being absent for a while and becoming available later on.

• H.450.10, Call Offer Supplementary Service

A variation of Call Waiting. Also known as "Camp-On".

• H.450.11, Call Intrusion Supplementary Service

Explains how e.g. the secretary of a CEO can intentionally and legally intrude into a call of her boss, in order to communicate urgent information.

• H.450.12, Common Information Additional Network Feature for H.323

A means to communicate additional miscellaneous information between endpoints. E.g. whether certain features are available, and/or allowed.

References

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1. ^ Swale, Richard (2001-12-17). Voice Over IP (Internet Protocol). London: IET. p. 254. ISBN 978-0-85296-024-0.
2. ^ "H.450.1 Generic functional protocol for the support of supplementary services in ITU-T H.323 systems". ITU. Retrieved 2025-07-24.
3. ^ "H.450.2 Call transfer supplementary service for ITU-T H.323 systems". ITU. 2014-05-15. Retrieved 2025-07-24.