Internet Engineering Task Force A.Urquizo Internet Draft Cisco Systems Document: draft-urquizo-mgcp-pre-package-00.txt August 2003 Category: Informational The Media Gateway Control Protocol (MGCP) PRE 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. For potential updates to the above required-text see: http://www.ietf.org/ietf/1id-guidelines.txt 1. Abstract This draft presents a package that defines the call processing and signaling requirements to interoperate with Multi-Level Precedence and Preemption (MLPP) capable switching systems when Channel Associated Signalling is used. For comments or additions, please contact the author. 2. Conventions used in this document The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED, "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC-2119 [2]. A. Urquizo Informational - Expires Feb 2004 [Page 1] MGCP PRE Package August 2003 3. Introduction Multi-level Precedence and Preemption (MLPP) service provides authorization and prioritized call handling service as specified in ANSI T1.619 [5] and ITU I.255.3 [6]. The Precedence term refers to the assignment and authorization of a priority level to a call by the Call Agent/Switch for prioritized treatment of MLPP service requests. There are five precedence levels (0-4) where the lowest precedence level 0 is used for normal ROUTINE calls. User invocation of an MLPP request is provided through dedicated dial access codes and selectors in the dial string. The Preemption term refers to the process of replacing a lower precendece call with a higher MLPP precedence call. The resources seized during this process may be used by the new call. Preemption may take one of two forms. First, the called party may be busy with a lower precedence call, which must be preempted in favor of completing the higher precedence call from the calling party. Second, the network resources may be busy with calls some of which are of lower precedence than the call requested by the calling party. One or more of these lower precedence calls SHALL be preempted to complete the higher precedence call. MLPP service applies to a configured domain only. A domain can consists of subscribers, the network and access resources that belong to the domain. The Call Agent is responsible for handling the authorization and precedence assignment and deciding whether a call will be preempted. The purpose of this document is to define a package that supports the signaling required to complete Multi-level Precedence and Preemption transaction in a MLPP capable switching. 4. Package Definition Package Name: PRE Package Version: 0 Package Description: The PRE package groups events and signals that are required for CAS support in a MLPP network. 4.1 Events and Signals This section defines the PRE event package. The terms "signal" and "event" are used to differentiate a command from a Call Agent to a Media Gateway ("signal") from an "event" that is detected by the Media Gateway and then is "Notified" to the Call Agent. A. Urquizo Informational - Expires Feb 2004 [Page 2] MGCP PRE Package August 2003 An ôxö under ôEventö indicates that the Call Agent can request this event. The Media Gateway will notify the Call Agent once the event is detected. Under ôSignalö the following symbols are used to indicate the type of signal applied to the endpoint on command by the Call Agent: - "OO" On/Off signal. The signal is turned on until commanded by the Call Agent to turn it off, and vice versa. - "TO" Timeout signal. The signal lasts for a given duration unless it is superseded by a new signal or terminated on detection of an event. Default time-out values are supplied. A value of zero indicates that the time-out period is infinite. The provisioning process may alter these default values. - "BR" Brief signal. The signal has a short, known duration The table below lists the events and signals defined in this package: ------------------------------------------------------------------ | Code | Description | Event| Signal| Additional Info |------|----------------------------|-----_|-----------------------| | par | Preempt and reserve channel| x | BR | | | | for reuse | | | | | pnr | Preempt and do not reserve | x | BR | | | | channel for reuse | | | | | prt | Precedence ringback tone | | TO |Time-out = 30s | | pt | Preemption tone | | OO |* | ------------------------------------------------------------------ (*) This tone may also be turned off upon a configurable time-out. See definition of Preemption tone. The respective MLPP capable switching system specification should be reviewed for the specific definition of the measured supervisory signals, pnr and par. For instance, GSCR [4] shows the preemption measured supervisory signaling used to initiate preemption and defines proper frequencies for the ringback and preemption tones for the DNS switching system. The preemption supervisory signal selection (par or pnr) is based on the following factors: 1. Circuit Condition (unanswered-onhook/answered-offhook). 2. Intended disposition. Whether circuit will be reused (channel resources are seized to be used on the preempting call) or not. 3. Preempting switch The Call Agent will request the media gateway to send a PNR or PAR signaling to the trunk using the SignalRequest parameter (e.g., S:PRE/pnr or S:PRE/par). The media gateway, based on the trunk state (unanswered/answered state, or the call is originated by this gateway), will send out the correct outpulse as defined in the respective MLPP switching system specifications. For an example see [4], section 6. A. Urquizo Informational - Expires Feb 2004 [Page 3] MGCP PRE Package August 2003 Preemption and Reserve Channel for reuse (par): This event is notified to the Call Agent when a supervisory pulsing is detected in the channel that is to be preempted indicating that the circuit will be reused. GSCR [4] presents a signaling definition for this event. Likewise, when this event is requested by the Call Agent to be signaled, the Media Gateway will outpulse the respective supervisory signal. Preemption and do not reserve channel for reuse (pnr): This event is notified to the Call Agent when a supervisory signal is detected in the channel that is to be preempted indicating that the channel will mot be reserved for reuse. GSCR [4] presents a signaling definition for this event. Likewise, when this event is requested by the Call Agent to be signaled, the Media Gateway will out-pulse the respective supervisory signal. Precedence ringback tone (prt): The precedence ringback tone provides a priority ringback to a user with a precedence level higher than ROUTINE. Refer to the respective switching system specification for the tone characteristics. For instance, [4] defines the prt tone as a dual frequency tone with frequencies at 440Hz and 480Hz. The single tone power level is û 13dBm0 with a composite power level of û16dBm0. The cadence for this on is 1640ms ON and 360ms OFF. Preemption tone (pt): Following the supervisory signal causing a circuit release, the Call Agent SHALL command the media gateway to signal a preemption tone to the calling and called stations. This preemption tone will be played until a disconnect signal is returned or upon a timer expiration. The Call Agent will command to the media gateway when to stop applying the tone to the endpoint. Refer to the respective switching system specification for the tone characteristics. For instance, [4] defines the pt tone as a continuous dual frequency tone with frequencies at 440Hz and 620Hz. The single tone power level is û13dBm0 with a composite power level of û16dBm0. The following example illustrates the encoding of the ôPreemption and Reserve Channel for reuseö event O: PRE/par 5. Acknowledgements Special thanks are due to the reviewers who provided advice in the completion of this document, notably Thiya Ramalingam, Satyam Tyagi, Andrew Foltan, Don Weiner, Pete Babendreier, Gene Keeling, Nate Melhorn, Ted Dennler, Rob Rushton. A. Urquizo Informational - Expires Feb 2004 [Page 4] MGCP PRE Package August 2003 6. References [1] Bradner, S., "The Internet Standards Process -- Revision 3", BCP 9, RFC 2026, October 1996. [2] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997 [3] Andreasen, F., and Foster, B., "Media Gateway Control Protocol 1.0", RFC 3435, January 2003 [4] JIEO Technical Report 8249, ôGeneric Switching Center Requirements (GSCR)ö, March 1997 [5] ôIntegrated Services Digital Network (ISDN)- Multi-Precedence and Preemption (MLPP) Service Capabilityö, ANSI T1.619, 1992 [6] ôIntegrated Services Digital Network (ISDN) General Structure and Service Capabilitiesö, ITU I.255.3, 1990 [7] Foster, B., ôMGCP CAS Packageö, RFC 3064, Feb 2001 7. AuthorÆs Address Alex Urquizo Cisco systems 1414 Massachusetts Ave Boxboro, MA 01719 Phone: +1 978 936 0172 Email: aurquizo@cisco.com 8. Full Copyright Statement Copyright (C) The Internet Society (2003). All Rights Reserved. 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Urquizo Informational - Expires Feb 2004 [Page 5] MGCP PRE Package August 2003 This document and the information contained herein is provided on an "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. A. Urquizo Informational - Expires Feb 2004 [Page 6]