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Internet Engineering Task Force                              B. Foster
Internet Draft                                            F. Andreasen
Document: <draft-foster-mgcp-redirect-04.txt>            Cisco Systems
Category: Informational                                      June 2003

    Media Gateway Control Protocol (MGCP) Redirect and Reset Package

Status of this Document

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

  Internet-Drafts are working documents of the Internet Engineering
  Task Force (IETF), its areas, and its working groups.  Note that
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  The base Media Gateway Control Protocol (MGCP) specification (RFC
  3435) allows endpoints to be re-directed one endpoint at a time.
  This document provides extensions in the form of a new MGCP package
  that provides mechanisms for redirecting and resetting a group of
  endpoints.  It also includes the ability to more accurately re-direct
  endpoints by allowing a list of Call Agents to be specified in a
  preferred order.

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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                           Table of Contents

Table of Contents.....................................................2
1.  Introduction......................................................2
2.0.  Redirect and Reset Package......................................3
 2.1.  NotifiedEntityList Extension Parameter.........................3
 2.2.  Endpoint Specifier.............................................4
   2.2.1.  EndpointList and EndpointMap Extension Parameters..........4
   2.2.2.  Application to Out-of-Service Endpoints....................5
 2.3.  Redirect.......................................................6
 2.4.  Reset Extension Parameter......................................7
 2.5.  Return Codes...................................................7
3.0.  IANA Considerations.............................................8
4.0.  Security Considerations.........................................8
5.0.  Normative References............................................8
Authors' Addresses....................................................8
Intellectual Property Statement.......................................8
Full Copyright Statement..............................................9

1.  Introduction

  The base Media Gateway Control Protocol (MGCP) specification [2]
  allows a Call Agent to specify a new NotifiedEntity parameter in
  order to re-direct one or more endpoints to a new Call Agent.  This
  must be done in a NotificationRequest or a connection handling
  command.  However, because these commands affect endpoint or
  connection state, such a request cannot typically be sent to a group
  of endpoints with a single command.  This means that in a case where
  a new Call Agent takes over for a failed one, the new Call Agent must
  re-direct endpoints one at a time.  If there is a large number of
  endpoints (e.g., within a large trunking gateway) this could take a
  considerable amount of time.

  This document defines a new redirect and reset package for MGCP that
  allows the Call Agent to re-direct a group of endpoints without
  affecting endpoint or connection state.

  Also included is a new NotifiedEntityList parameter, which is similar
  to the NotifiedEntity parameter but allows for multiple domain names
  to be provided.  This allows the Call Agent to more accurately direct
  endpoints to a preferred ordered list of alternate Call Agents.

  A third capability contained within this package is the ability to
  efficiently reset and re-initialize one or more groups of endpoints.
  Such a capability is useful during Call Agent failover situations.

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2.0.  Redirect and Reset Package

  Package Name: RED
  Version: 0

  The purpose of this package is to:

     * Define a new NotifiedEntityList extension parameter.  This works
       the same as the NotifiedEntity parameter in [2] but allows more
       than one domain name to be specified.
     * Allow a Call Agent to pass a new NotifiedEntity or
       NotifiedEntityList to a collection of endpoints specified by an
       "all of" wildcard.  This is useful in the case where a new Call
       Agent takes over from a previous one and wants to re-direct
       endpoint(s) to send "Notifies" etc. to it from now on.
     * Allow a Call Agent to request one or more groups of endpoints to
       do a reset, which can be useful following certain types of

2.1.  NotifiedEntityList Extension Parameter

  The NotifiedEntityList parameter is encoded as "NL" and is followed
  by a colon and a comma-separated list of NotifiedEntity values as
  defined in the MGCP specification [2], e.g.:

    RED/NL: ca1@myca.whatever.net, ca2@mybackupca.whatever.net

  The NotifiedEntityList works in a similar way to the NotifiedEntity
  parameter, except that it allows multiple domain names to be listed.
  The NotifiedEntityList thus specifies a new "notified entity" for the

  The NotifiedEntityList parameter is optional in any command or
  response where the NotifiedEntity parameter is allowed.  Following a
  restart, the NotifiedEntityList is initially empty, unless
  provisioned otherwise.  In subsequent commands, it retains its
  current value until explicitly changed.  If both a NotifiedEntity
  parameter and a non-empty NotifiedEntityList parameter have been set
  (not necessarily at the same time), the NotifiedEntity parameter
  value will be viewed as implicitly added to the beginning of the
  NotifiedEntityList parameter.  The NotifiedEntity parameter thus
  always defines the first domain name to contact, unless it has
  explicitly been set to empty.  In that case, the NotifiedEntityList
  defines the "notified entity".  If the NotifiedEntityList is also
  empty, then the normal MGCP handling of having an empty "notified
  entity" applies.  We will refer to the list of domain names that
  result from the above rules as the "notified entity list".

  When the "notified entity list" is non-empty, transmission is first
  attempted with the first domain name in the list as in the normal
  MGCP retransmission procedures described in [2].  Each of the IP-
  addresses for this domain name MUST first be tried as specified in
  [2], and if this is unsuccessful, each of the IP-addresses for the
  second domain name MUST then be attempted, etc. following the normal

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  MGCP retransmission procedures, with "N" (the number of
  retransmissions) set to zero for each domain name (see Section 4.3 in
  [2]).  Whenever retransmission to a new domain name is initiated, the
  default retransmission timer value (RTO) etc. SHOULD be used - the
  estimator (T-DELAY) and measurements (AAD and ADEV) used for the
  transmission to the previous domain name are considered obsolete.
  Note however, that the maximum transaction lifetime considerations
  apply as usual, and hence retransmission to any of the IP-addresses
  for any of the domain names MUST NOT occur more than T-Max seconds
  after the initial sending of the command, irrespective of where it
  was sent.  The Max1 DNS query MAY be performed for each of the domain
  names, or it MAY simply be performed for the first domain name.  The
  Max2 DNS query however MUST NOT be performed for any but the last
  domain name.  Also note, that only the last IP-address for the last
  domain name can reach Max2 retransmissions, and hence retransmission
  to all other IP-addresses MUST end after Max1 retransmissions.

  The current value of the NotifiedEntityList parameter can be audited
  via AuditEndpoint; the value of the NotifiedEntity parameter will not
  be included here and hence must be audited separately.  Support for
  the NotifiedEntityList in AuditConnection is permissible, but it is
  neither required nor recommended.

2.2.  Endpoint Specifier

2.2.1.  EndpointList and EndpointMap Extension Parameters

  A simple "all-of" wildcard as defined in [2] may not be sufficient to
  accurately specify endpoints of interest.  An example of this is a
  case where a Call Agent fails over, resulting in a state mismatch for
  endpoints involved with transient calls.  In order to re-synchronize,
  one Call Agent procedure involves using the reset extension parameter
  described in section 2.4 of this document to ensure that idle
  endpoints are in fact idle.  However, these endpoints may be randomly
  distributed across the available endpoints in a large trunk gateway.

  In order to satisfy this requirement, the RED package introduces some
  new parameters that MAY be used to specify the endpoints of interest
  for the EndpointConfiguration Command.  These are the EndpointList
  and the EndpointMap extension parameters.  These parameters MUST only
  be used when specifying a virtual endpoint corresponding to the
  gateway as the LocalEndpointName i.e.:

     EPCF 1200 MG@gw1.whatever.net MGCP 1.0

  where "MG" is the virtual endpoint name associated with the gateway.

  The EndPointList parameters is a list of the endpoint names which can
  include one or more lines in the following format:

     "RED/EL:" 0*WSP RangedLocalName 0*("," 0*WSP RangedLocalName)

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  where RangedLocalName is a LocalEndpointName that may include the
  ranged wildcard notation described in Appendix E (section E.5) of
  [2], i.e.:

    RangeWildcard  = "*" / "[" NumericalRange *("," NumericalRange)"]"
    NumericalRange = 1*(DIGIT) [ "-" 1*(DIGIT) ]


     RED/EL: ds/ds1-1/[1-24], ds/ds1-2/[1-24], ds/ds1-3/[1-24]

  Including an EndpointMap parameter with the following format can
  further specify the endpoints:

     "RED/MP:" 0*WSP TrueOrFalse 0*(TrueOrFalse)

     TrueOrFalse = "T" / "F"

  where "T" indicates that the command should be applied to this
  endpoint and "F" indicates that it should not.  This parameter can be
  used in conjunction with the reset extension parameter described in
  section 2.4 of this document to force arbitrarily distributed
  endpoints to an idle state.

  If the EndpointMap parameter is used it MUST be immediately preceded
  (i.e. on the previous line) by an EndPointList parameter to specify
  the endpoints that the EndpointMap is referring to.  Several
  EndpointList and EndpointMap parameter lines MAY be provided.  It is
  considered to be an error if the EndpointMap parameters extend beyond
  the endpoints specified in the preceding EndPointList parameter.  In
  that case, return code 800 MUST be used (see section 2.5).

  The EndpointList and EndpointMap parameters MUST only be used with
  the EndpointConfiguration command.  The EndpointList parameter MAY be
  provided without an EndpointMap parameter.  However, as indicated
  earlier, an EndpointMap parameter MUST be immediately preceded by an
  EndpointList parameter.  Neither of these parameters is auditable.

  For an example of EndpointMap parameter usage, refer to section 2.4.

2.2.2.  Application to Out-of-Service Endpoints

  Note that the EndpointConfiguration command is normally only valid
  for in-service endpoints.  If an EndpointConfiguration request is
  sent to a wild-carded LocalEndpointName [2] and any of the endpoints
  specified are out-of-service, the command will fail with return code
  501 (endpoint not ready).

  However, as long as the gateway is in-service and able to respond to
  MGCP commands, the gateway can apply the endpoint configuration
  command to endpoints specified by the EndpointList and/or EndpointMap
  parameters (regardless of whether those endpoints are in-service or
  not).  The endpoint configuration information of course will not be
  maintained over gateway restarts (i.e. the Call Agent would have to

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  re-apply the endpoint configuration after it receives an RSIP with
  restart method "restart").

  EndpointList and/or EndpointMap parameters MUST only be used with a
  virtual endpoint name corresponding to the gateway (as indicated
  above).  If used with any other endpoint name (whether wild-carded or
  not), then error code 801 (section 2.5) MUST be returned.

2.3.  Redirect

  A new extension parameter for use with the EndpointConfiguration
  command is defined.  A new NotifiedEntity value can be included with
  a "RED/N" parameter as follows:

     EPCF 1200 *@gw1.whatever.net MGCP 1.0
     RED/N: ca1@ca1234.whatever.net

  This changes the "notified entity" for the endpoint(s) to the value
  specified.  If the "all of" wildcard convention is used, the
  NotifiedEntity value replaces all of the existing "notified entities"
  for those endpoints.  If NotifiedEntity is omitted in a subsequent
  EndpointConfiguration command, the "notified entity" remains

  In the case where the "notified entity" is a domain name that
  resolves to multiple IP addresses, one of the resolved addresses MUST
  be selected.  If one of those IP addresses is the IP address of the
  Call Agent sending the request, that IP address SHOULD be selected

  The NotifiedEntityList parameter can also be specified in an endpoint
  configuration command, e.g.:

     EPCF 1200 *@gw1.whatever.net MGCP 1.0
     RED/NL: ca1@myca.whatever.net, ca2@mybackupca.whatever.net

  As indicated in section 2.2, it can also apply this to the gateway
  virtual endpoint e.g.:

     EPCF 1200 MG@gw1.whatever.net MGCP 1.0
     RED/EL: *
     RED/NL: ca1@myca.whatever.net, ca2@mybackupca.whatever.net

  As indicated in section 2.1, the NotifiedEntityList ("RED/NL")
  parameter MAY be used with any command for which a NotifiedEntity
  parameter is allowed.  However, the "RED/N" parameter SHOULD only be
  used with the endpoint configuration command.

  The "RED/N" parameter does not have a default value, and the auditing
  behavior for auditing the "NotifiedEntity" is unchanged from that
  specified in [2], regardless of how the "NotifiedEntity" was set
  (i.e. there is no specific audit associated with the "RED/N"
  parameter and hence the "RED/N" parameter cannot be audited).

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2.4.  Reset Extension Parameter

  Another EndpointConfiguration parameter ("RED/R"), allows the Call
  Agent to reset one or more endpoints.  The ABNF syntax for the
  parameter line is as follows:

     "RED/R:" 0*WSP "reset"

  This has the effect of re-setting and re-initializing the specified
  endpoints (i.e. any connections on the endpoint will be deleted, and
  the endpoint will be returned to its clean default state without any
  active signals, etc.).


     EPCF 1200 mg@gw1.whatever.net MGCP 1.0
     RED/EL: ds/e1-3/[1-30]
     RED/EL: ds/e1-5/[1-30]
     RED/R: reset

  In this case, the particular endpoints specified by "T" by the
  EndpointMap parameter in the E1 spans ds/e1-3 and ds/e1-5 are reset.

  The "RED/R" parameter MUST NOT be used with any command other than
  the endpoint configuration parameter.  There is no default value for
  the parameter and hence when omitted, it does not affect operation.
  There is no specific audit behavior associated with this parameter,
  i.e. it cannot be audited.

2.5.  Return Codes

  The following package specific return codes are defined for the "RED"

     Code   Text                     Explanation

     800    EndpointMap              Either the EndpointMap parameters
            Out of Range             are outside the range specified by
                                     the EndpointList parameter or the
                                     EndpointList Parameter was not
                                     included when an EndpointMap
                                     parameter was included.

     801    Incorrect Usage          Incorrect usage of parameters such
            Of Parameters            as EndpointList parameter used
                                     where the endpoint name was not
                                     the virtual endpoint name
                                     corresponding to the gateway.

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3.0.  IANA Considerations

  The MGCP package title "Redirect and Reset" with the name "RED" and
  version number 0 should be registered with IANA as indicated in
  Appendix C.1 in [2].

4.0.  Security Considerations

  The MGCP extensions defined in this document do not require any
  further security considerations beyond those indicated in the base
  MGCP specification [2], however it should be noted, that the ability
  to redirect and reset endpoints in bulk can have severe security
  consequences.  As stated in [2], the use of IPsec with MGCP to
  counter this is recommended.

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

  Flemming Andreasen
  Cisco Systems
  499 Thornall Street, 8th Floor
  Edison, NJ 08837
  EMail: fandreas@cisco.com

  Bill Foster
  Cisco Systems
  EMail: bfoster@cisco.com

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B.  Foster, F.  Andreasen    Informational                     [Page 8]

                    MGCP Redirect and Reset Package           June 2003

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