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+Network Working Group                                          B. Foster
+Request for Comments: 3992                                  F. Andreasen
+Category: Informational                                    Cisco Systems
+                                                           February 2005
+
+
+                 Media Gateway Control Protocol (MGCP)
+                  Lockstep State Reporting Mechanism
+
+Status of This Memo
+
+   This memo provides information for the Internet community.  It does
+   not specify an Internet standard of any kind.  Distribution of this
+   memo is unlimited.
+
+Copyright Notice
+
+   Copyright (C) The Internet Society (2005).
+
+IESG Note
+
+   This document is being published for the information of the
+   community.  It describes a non-IETF protocol that is currently being
+   deployed in a number of products.  Implementers should be aware of
+   RFC 3015, which was developed in the IETF Megaco Working Group and
+   the ITU-T SG16, and which is considered the standards-based
+   (including reviewed security considerations) way to meet the needs
+   that MGCP was designed to address by the IETF and the ITU-T.
+
+Abstract
+
+   A Media Gateway Control Protocol (MGCP) endpoint that has encountered
+   an adverse failure condition (such as being involved in a transient
+   call when a Call Agent failover occurred) could be left in a lockstep
+   state whereby events are quarantined but not notified.  The MGCP
+   package described in this document provides a mechanism for reporting
+   these situations so that the new Call Agent can take the necessary
+   fault recovery procedures.
+
+1.  Introduction
+
+   In the Media Gateway Control Protocol (MGCP) [2], when an endpoint
+   operating in "step" mode generates a Notify, it will enter the
+   notification state, where it waits for a response to the Notify.
+   Furthermore, the endpoint must wait for a new NotificationRequest
+   before it can resume event processing.  As long as the endpoint is
+   waiting for this NotificationRequest, we say that it is in the
+   lockstep state.
+
+
+
+Foster & Andreasen           Informational                      [Page 1]
+
+RFC 3992        MGCP Lockstep State Reporting Mechanism    February 2005
+
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+   An endpoint that is in the lockstep state cannot perform any event
+   processing and therefore also cannot generate a new Notify.
+   Endpoints should only be in the lockstep state for a very short time.
+   However, in adverse conditions, an endpoint could potentially end in
+   the lockstep state without the Call Agent realizing it.  Clearly,
+   this could have very negative consequences in terms of the service
+   provided.
+
+   The Lockstep package defined in this document defines extensions to
+   the EndpointConfiguration and RestartInProgress commands that allow a
+   Call Agent to request an endpoint to inform it when the endpoint is
+   in the lockstep state for a specified period of time.
+
+1.1.  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 BCP 14, RFC 2119 [1].
+
+2.  Lockstep Package
+
+   Package Name: LCK
+   Version: 0
+
+   Package Description: The purpose of this package is to provide a
+   mechanism for reporting a condition in which an endpoint has been in
+   the "lockstep state" for a specified period of time.
+
+   There are two aspects of this package:
+
+      *  The ability for a Call Agent to request endpoints to report if
+         they are in lockstep state for a specified period of time.
+         This is done with the EndpointConfiguration command, as
+         described in section 2.1.
+
+      *  The reporting mechanism itself, which is done with a new
+         "lockstep" RestartMethod for the RSIP command as described in
+         section 2.2.
+
+2.1.  Request to Report Lockstep State
+
+   The new "LCK/LST" EndpointConfiguration parameter is used by the Call
+   Agent to request the reporting of "lockstep" state.  It uses the
+   following ABNF:
+
+      "LCK/LST:" 0*WSP LSTIME
+
+      LSTIME = 1*(4DIGIT)
+
+
+
+Foster & Andreasen           Informational                      [Page 2]
+
+RFC 3992        MGCP Lockstep State Reporting Mechanism    February 2005
+
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+   where LSTIME is expressed in seconds, with a value ranging from 0 to
+   9999.  A value greater than 2*T-HIST (refer to [2]) is RECOMMENDED.
+
+   LSTIME is the amount of time the endpoint is in the lockstep state
+   before reporting.  The timer starts when the endpoint enters the
+   lockstep state and is canceled if the endpoint leaves the lockstep
+   state before the timeout occurs.  The value provided remains in
+   effect until explicitly changed (or a restart occurs).  If the
+   endpoint is already in the lockstep state when a non-zero timer value
+   is provided, the lockstep timer is simply started with the value
+   provided; any existing lockstep timer is cancelled.  The value zero
+   is used to turn off reporting.
+
+   This parameter can be audited by using the AuditEndpoint command.
+   The value returned is the last configured value, or the value zero
+   when no value was configured.
+
+2.2.  Lockstep Restart Method
+
+   A new "lockstep" restart method is defined in the "LCK" package.  A
+   RestartInProgress (RSIP) will be sent with this RestartMethod if the
+   endpoint has been configured with a non-zero value for LSTIME and
+   that timer has expired.  Note that once the lockstep timer has been
+   set, it can fire only once per Notify command; however it is possible
+   to set the timer more than once while an endpoint is in lockstep
+   state (and hence rearm it for that particular Notify).  The syntax of
+   the restart method is as per [2]:
+
+      "RM" ":" 0*(WSP) "LCK/lockstep"
+
+   RestartDelay (see [2]) is not used with the "lockstep" RestartMethod.
+   Also, the "lockstep" RestartMethod does not define a service-state,
+   and thus it will never be returned when auditing the RestartMethod.
+
+3.  IANA Considerations
+
+   The MGCP package title "Lockstep" with the name "LCK" and version
+   number zero has been registered with IANA as indicated in Appendix
+   C.1 in [2].
+
+4.  Security Considerations
+
+   Section 5 of the base MGCP specification [2] discusses security
+   requirements for the base MGCP protocol that apply equally to the
+   package defined in this document.  Use of a security Protocol such as
+   IPsec (RFC 2401, RFC 2406) that provides per message authentication
+   and integrity services is required to ensure that requests and
+   responses are obtained from authenticated sources and that messages
+
+
+
+Foster & Andreasen           Informational                      [Page 3]
+
+RFC 3992        MGCP Lockstep State Reporting Mechanism    February 2005
+
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+   have not been modified.  Without these services, gateways and Call
+   Agents are open to attacks.
+
+5.  Normative References
+
+   [1]  Bradner, S., "Key words for use in RFCs to Indicate Requirement
+        Levels", BCP 14, RFC 2119, March 1997.
+
+   [2]  Andreasen, F. and B. Foster, "Media Gateway Control Protocol
+        (MGCP) Version 1.0", RFC 3435, January 2003.
+
+Authors' Addresses
+
+   Bill Foster
+
+   Phone: +1 250 758 9418
+   EMail: bfoster@cisco.com
+
+
+   Flemming Andreasen
+   Cisco Systems
+   499 Thornall Street, 8th Floor
+   Edison, NJ 08837
+
+   EMail: fandreas@cisco.com
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+Foster & Andreasen           Informational                      [Page 4]
+
+RFC 3992        MGCP Lockstep State Reporting Mechanism    February 2005
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+Full Copyright Statement
+
+   Copyright (C) The Internet Society (2005).
+
+   This document is subject to the rights, licenses and restrictions
+   contained in BCP 78, and at www.rfc-editor.org, and except as set
+   forth therein, the authors retain all their rights.
+
+   This document and the information contained herein are provided on an
+   "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
+   OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
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+
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+
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+Acknowledgement
+
+   Funding for the RFC Editor function is currently provided by the
+   Internet Society.
+
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+Foster & Andreasen           Informational                      [Page 5]
+