Internet DRAFT - draft-foster-mgcp-lockstep
draft-foster-mgcp-lockstep
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
Mechanism
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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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 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",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
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:
"LCK/LST:" 0*WSP LSTIME
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
reporting.
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
[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 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
EMail: bfoster@cisco.com
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MGCP Lockstep State Reporting Mechanism July 2003
Flemming Andreasen
Cisco Systems
499 Thornall Street, 8th Floor
Edison, NJ 08837
EMail: fandreas@cisco.com
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