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rfc:rfc3992

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

 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

 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

 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

Foster & Andreasen Informational [Page 4] RFC 3992 MGCP Lockstep State Reporting Mechanism February 2005

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.
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 INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
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Acknowledgement

 Funding for the RFC Editor function is currently provided by the
 Internet Society.

Foster & Andreasen Informational [Page 5]

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