Internet DRAFT - draft-giordano-cli-forward-in-call-trx
draft-giordano-cli-forward-in-call-trx
Internet-Draft Daniele Giordano
4 November 2007
Expires: 7 May 2008
CLI forwarding method during call transfer
draft-giordano-cli-forward-in-call-trx-01
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Copyright Notice
Copyright (C) The IETF Trust (2007).
Abstract
Many telephony services are IP based and they can use various
signaling protocols like H.323, SIP, MGCP, MEGACO and vendor
proprietary protocols. This document describe a method to identify
and to change the Calling Line Identification (or CLI) field during
call forwarding. This method is voice over ip protocol independent.
This method can be apply to all voice over ip protocols.
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Table of Contents
1. Conventions Used In This Document . . . . . . . . . . . . . . . 3
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Implementation and Operations . . . . . . . . . . . . . . . . 3
4. Consideration about well known services . . . . . . . . . . . . 4
5. Security Considerations . . . . . . . . . . . . . . . . . . . . 5
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5
7. Normative References . . . . . . . . . . . . . . . . . . . . . 5
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 6
Intellectual Property and Copyright Statements . . . . . . . . . . 6
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1. Conventions Used In This Document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
2. Introduction
In POTS/PSTN networks the CLI (Calling Line Identification) is a base
information about the billing telephone number from which calls are
originated. CLI can be managed to obtain various services: CLI
presentation or CLIP, CLI restriction or CLIR, CLI stripping, CLI
screening and other well known services.
These cases are implemented in IP based telephony network or voice
over IP network.
But, What happens during call forwarding?
In traditional telephony, two calling line ids are sent along with
the outgoing call.
It doesn't happen in the current IP implementations.
There is a need for a mechanism to identify the originating party and
to send the appropriate CLI.
3. Implementation and Operations
When a call is forwarded (unconditionally, on busy and not answered)
we MUST identify three parties: the calling party A, the called
transferor party B and the transferred party C.
call flow
A ----------> B ---------> C
During call setup A sends its CLI to B.
B can send both CLI, its own and CLI of A.
CLI of A SHOULD be called original-CLI; CLI of B SHOULD be called
transferor-CLI.
What happens to CLI in this scenario?
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We MUST identify two cases:
1) CLI pass through: the transferred party C MUST receive the
original-CLI
A ----------> B ---------> C
|____________CLI___________|
2) CLI override: the transferred party C MUST receive the
transferor-CLI
A ----------> B ---------> C
|_____CLI____|
Who set the forwarding MUST select a CLI forwarding method. In this
way the appropriate caller line id can be sent during call setup.
This implementation would be protocol independent. All signaling
protocols describe how to write CLI information in own signaling
message.
4. Consideration about well known services
This draft doesn't influence the correct working of well known
services like CLI Presentation or CLI Restriction. Their working is
described in all signaling voice protocols.
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5. Security Considerations
This document is not directly concerned with security.
However, implementing this feature you can obtain more control over
call routing and more information in the call report.
6. IANA Considerations
None.
7. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
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Author's Address
Giordano Daniele
Email: d.giordano@fastpiu.it
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