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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Giordano                   Expires 7 May 2008                   [Page 6]