Internet Engineering Task Force                             B. Foster
Internet Draft                                           F. Andreasen
Document: <draft-foster-mgcp-lockstep-01.txt>           Cisco Systems
Category: Informational                                     July 2003

     Media Gateway Control Protocol (MGCP) Lockstep State Reporting

Status of this Document

  This document is an Internet-Draft and is in full conformance with
  all provisions of Section 10 of RFC2026

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  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 such that 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.

Conventions used in this document

  The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
  document are to be interpreted as described in RFC-2119 [1].

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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.

  An endpoint that is in lockstep state cannot perform any event
  processing and hence can also not generate any new Notifys.
  Endpoints should only be in lockstep state for a very short time,
  however in case of 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 if the endpoint is in
  the lockstep state for a specified period of time.

2.0. 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. 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 "lstime" EndpointConfiguration parameter is used by the Call
  Agent to request the reporting of "lockstep" state.  It uses the
  following ABNF:


     LSTIME = 1*(4DIGIT)

  where LSTIME is expressed in seconds, with a value ranging from 0 to
  999. A value greater than 2*T-HIST (refer to [2]) is RECOMMENDED.

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  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 cancelled if the endpoint leaves the lockstep
  state before the timeout occurs.  The value zero is used to turn off

  This parameter can be audited using the AuditEndpoint command.

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.  The syntax of the restart method is as per

     "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 hence it will never be returned when auditing the RestartMethod.

3.0. IANA Considerations

  The MGCP package title "Lockstep" with the name "LCK" and version
  number zero should be registered with IANA as indicated in Appendix
  C.1 in [2].

4.0. Security Considerations

  Section 5 of the base MGCP specification [2] discusses security
  requirements for the base MGCP protocol, which 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 in order to ensure that requests
  and responses are obtained from authenticated sources and that
  messages have not been modified.  Without such services, gateways and
  Call Agents are open to attacks.

5.0. Normative References

 [1]  Bradner, S., "Key words for use in RFCs to Indicate Requirement
      Levels", BCP 14, RFC 2119, March 1997.
 [2]  F. Andreasen, B. Foster "Media Gateway Control Protocol (MGCP)
      Version 1.0", RFC 3435, January 2003.

Authors' Addresses

  Bill Foster
  Phone: +1 250 758 9418

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  Flemming Andreasen
  Cisco Systems
  499 Thornall Street, 8th Floor
  Edison, NJ 08837

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