Internet Engineering Task Force Martin Wakley Internet Draft Tania Sassenberg Document: draft-wakley-mgcp-extalpkg-00.txt Nortel Networks Category: Informational December 2001 MGCP Extended Analog Line Package Status of this Memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026 [1]. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. 1. Abstract This document provides proposed definitions for a supplemental package for MGCP. This package addresses support of functionality for standard and enhanced telephony services delivered over analogue line terminations, specifically line/tip & ring polarity reversal. The package is defined with the intention of adding further line supervision signals at a later date. 2. 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]. 3. Document Organization The subsequent text in this document is organized into the following major sections: * Introduction * Description of the Extended Analog Line Supervision Package * Use Cases, Example Call Flows * References * Author's address Wakley Informational - Expires July 2002 [Page 1] MGCP Extended Analog Line Package December 2001 4. Introduction The Basic MGCP Line Package defined in RFC2705 [3] supports basic telephony services, using on-hook and off-hook events and ringing signals. Some telephony services delivered over analog line terminations have additional supervisory signalling requirements that are not met by this package. The package defined in this document is intended to meet the needs of the following supervisory signalling functions: Line Reversal û Line reversal consists of reversing the polarity of the tip/ring leads (GND becomes û48V and û48V switches to GND). There are two ways in which line reversal is often used: 1. Line reversal on seizure û This is used to prevent a glare condition when a call is originating from a line at the same time that a call is terminating to the line. The line reversal signal is applied on seizure to the terminating/ called party followed by ringing and maintained until the line is answered. Once reversal has been applied the line cannot attempt a simultaneous origination. 2. Line reversal on answer û In this case line reversal will be applied to the originating party to control electronic equipment such as coin phones or answering machines. The line reversal signal acts as a stimulus to the equipment to perform specific actions such as dropping coins or activating the answering machine. 5. Extended Analog Line Supervision Package PackageID: XL Version: 1 This package is a new MGCP package. In it's first version, only one new signal is defined: Line Reversal. Signals MUST always be prefixed with the "XL" package name. 5.1 Properties None. 5.2 Events None. 5.3 Signals Line Reversal SignalID: XL/rev Wakley Informational - Expires July 2002 [Page 2] MGCP Extended Analog Line Package December 2001 This signal activates or switches off line reversal on an endpoint (line). The gateway shall reverse the polarity of the tip and ring wires for that line (or return it to normal), immediately after the signal is received (whatever call processing state the line is currently in). Signal Type: OnOff (+) or (-) 5.4 Statistics None. 5.5 Procedures A specific line reversal signal is needed in order for the call agent to have full control of the line polarity states. This enables the call agent to control both line reversal on answer and line reversal on seizure using one MGCP signal. This approach maps well to the legacy method of setting/resetting a data flag to indicate line reversal state. Media gateways can then provide both support for the full control of line reversal using the new XL/rev signal and support direct supervision signals such as 'lsa' (line-side answer), which will typically involve a line-reversal being applied by the media gateway. In the latter case, the implementation of the supervision is left to the media gateway (so it could be provisioned based on market/country for instance). The new signal provides a method for the call agent to have full control over the line reversal state. 6. Use Cases, Example Call Flows 6.1 Line Reversal 6.1.1 Line Reversal on Seizure The call agent seizes the terminating line by applying the line reversal signal: RQNT 311 aaln/1@mg23.whatever.net MGCP 1.0 X: 880 S: XL/rev(+) The endpoint confirms: 200 311 OK Now the call agent can apply ringing: RQNT 312 aaln/1@mg23.whatever.net MGCP 1.0 X: 881 S: L/rg R: L/hd(N) Q: loop Wakley Informational - Expires July 2002 [Page 3] MGCP Extended Analog Line Package December 2001 The endpoint confirms: 200 312 OK When the line answers a call: NTFY 3132 aaln/1@mg23.whatever.net MGCP 1.0 X: 4564 O: L/hd The call agent then instructs the gateway to switch off line reversal: RQNT 313 aaln/1@mg23.whatever.net MGCP 1.0 X: 882 S: XL/rev(-) The endpoint confirms: 200 313 OK 6.1.2 Line Reversal on Answer The called party has answered, so the call agent sends the line reversal signal to the originating party: RQNT 322 aaln/1@mg23.whatever.net MGCP 1.0 X: 867 S: XL/rev(+) The endpoint confirms: 200 322 OK Later, the call agent instructs the gateway to switch off line reversal: RQNT 329 aaln/1@mg23.whatever.net MGCP 1.0 X: 868 S: XL/rev(-) The endpoint confirms: 200 329 OK 6.3 Audit Endpoint The state of On/Off signals is an auditable property. If the Audit Endpoint command asks for currently applied signal requests, the endpoint MUST return a list of the On/Off signals that are currently "on" for the endpoint (with or without parameters). The Call Agent audits the endpoint: AUEP 361 aaln/1@mg23.whatever.net MGCP 1.0 F: S The response indicates that line reversal signal is on: 200 361 OK S: XL/rev(+) Wakley Informational - Expires July 2002 [Page 4] MGCP Extended Analog Line Package December 2001 7. Formal Syntax Not applicable. 8. Security Considerations Not applicable. 9. Terms Ring & Tip: The two copper wires that make up a standard analogue telephone line. Also sometimes referred to as the A & B wires. When line reversal is not active, the tip or A wire has a voltage of 0v or GND, whilst the ring or B wire has a voltage of û48v. 10. Other Documents of Interest Internet Draft draft-taylor-megaco-enhalpkgs-00.txt [4] describes an Extended Analog Line Supervision package for H.248/MEGACO. This defines signals for Line-side Answer Supervision and Network Disconnect. These signals have not been included in this XL package definition as they is already included ('lsa' and 'osi') in the MGCP Basic Line Package defined in Internet Draft draft-foster-mcgp-basic- packages-02.txt [5]. 11. Acknowledgement Thanks goes to Bill Foster for his guidance, comments and general input to this document. 12. References 1 Bradner, S., "The Internet Standards Process -- Revision 3", BCP 9, RFC 2026, October 1996. 2 RFC 2119 Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997 3 Arango, Dugan, Elliot, Huitema, Pickett, Foster, Andreasen, Media Gateway Control Protocol (MGCP) Version 1.0bis, Work in Progress, draft-andreasen-mgcp-rfc2705bis-01.txt, Internet Engineering Task Force, May 2001 4 Taylor, Brown, CopperCom, Nortel Networks, Megaco/H.248 Enhanced Analog Line Packages, Work in Progress, draft-taylor-megaco- enhalpkgs-00.txt, Internet Engineering Task Force, April 2001 Wakley Informational - Expires July 2002 [Page 5] MGCP Extended Analog Line Package December 2001 5 Arango, Dugan, Elliot, Huitema, Pickett, Foster, Andreasen, Basic MGCP Packages, Work in Progress, draft-foster-mgcp-basic- packages-02.txt, Internet Engineering Task Force, August 2001 13. Author's Addresses Martin Wakley Nortel Networks Concorde Road Norreys Drive Maidenhead Berkshire, UK Phone: +44 (0) 1628 431579 SL6 2RP. Email: mwakley@nortelnetworks.com Tania Sassenberg Phone: (919) 991-2341 Email: tanisas@nortelnetworks.com Wakley Informational - Expires July 2002 [Page 6]