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Network Working Group                                          B. FosterRequest for Comments: 3991                                  F. AndreasenCategory: Informational                                    Cisco Systems                                                           February 2005Media Gateway Control Protocol (MGCP) Redirect and Reset PackageStatus 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 ofRFC 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   The base Media Gateway Control Protocol (MGCP) specification (RFC3435) allows endpoints to be redirected 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 redirect   endpoints by allowing a list of Call Agents to be specified in a   preferred order.Foster & Andreasen           Informational                      [Page 1]

RFC 3991            MGCP Redirect and Reset Package        February 2005Table of Contents1.  Introduction..................................................21.1.  Conventions Used in This Document.......................32.  Redirect and Reset Package....................................32.1.  NotifiedEntityList Extension Parameter..................32.2.  Endpoint Specifier......................................4             2.2.1.  EndpointList and EndpointMap Extension                     Parameters......................................42.2.2.  Application to Out-of-Service Endpoints.........62.3.  Redirect................................................62.4.  Reset Extension Parameter...............................72.5.  Return Codes............................................83.  IANA Considerations...........................................94.  Security Considerations.......................................95.  Normative References..........................................9   Authors' Addresses................................................10   Full Copyright Statement..........................................111.  Introduction   The base Media Gateway Control Protocol (MGCP) specification [2]   allows a Call Agent to specify a new NotifiedEntity parameter in   order to redirect 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 if a new Call   Agent takes over for a failed one, the new Call Agent must redirect   endpoints one at a time.  If there is a large number of endpoints   (e.g., within a large trunking gateway), this could take considerable   time.   This document defines a new redirect and reset package for MGCP that   allows the Call Agent to redirect 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 in this package is the ability to reset   and re-initialize one or more groups of endpoints efficiently.  This   capability is useful in Call Agent failover situations.Foster & Andreasen           Informational                      [Page 2]

RFC 3991            MGCP Redirect and Reset Package        February 20051.1.  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 inBCP 14,RFC 2119 [1].2.  Redirect and Reset Package   Package Name: RED   Version: 0   This package does the following:      *  Defines 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.      *  Allows a Call Agent to pass a new NotifiedEntity or         NotifiedEntityList to a collection of endpoints specified by an         "all of" wildcard.  This is useful if a new Call Agent takes         over from a previous one and wants to redirect endpoint(s) to         send messages to it from now on.      *  Allows a Call Agent to request one or more groups of endpoints         to do a reset, which can be useful following certain types of         failures.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], as follows:      RED/NL: ca1@myca.whatever.net, ca2@mybackupca.whatever.net   The NotifiedEntityList works in a way similar to the NotifiedEntity   parameter, except that it allows multiple domain names to be listed.   The NotifiedEntityList thus specifies a new "notified entity" for the   endpoint.   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 being implicitly added to the beginning ofFoster & Andreasen           Informational                      [Page 3]

RFC 3991            MGCP Redirect and Reset Package        February 2005   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 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   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; therefore, retransmission to any of the IP addresses   for any of the domain names MUST NOT occur more than T-Max seconds   after the command is initially sent, 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; therefore, retransmission   to all IP addresses other than the last IP address of the last domain   name in the list 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 must be audited separately.  Support for the   NotifiedEntityList in AuditConnection is permissible, but it is   neither required nor recommended.2.2.  Endpoint Specifier2.2.1.  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.  To re-synchronize, the Call   Agent can use the reset extension parameter described insection 2.4   of this document, to ensure that idle endpoints are in fact idle.Foster & Andreasen           Informational                      [Page 4]

RFC 3991            MGCP Redirect and Reset Package        February 2005   However, these endpoints may be randomly distributed across the   available endpoints in a large trunk gateway.   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 a virtual endpoint corresponding to the gateway is   specified as the LocalEndpointName, such as:      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 endpoint names that can   include one or more lines in the following format:      "RED/EL:" 0*WSP RangedLocalName 0*("," 0*WSP RangedLocalName)   RangedLocalName is a LocalEndpointName that may include the range   wildcard notation described inAppendix E (section E.5) of [2] as   well as an "all" wildcard, but the two forms MUST NOT be mixed in a   single command:      RangeWildcard  = "*" / "[" NumericalRange *("," NumericalRange)"]"      NumericalRange = 1*(DIGIT) [ "-" 1*(DIGIT) ]   Example:      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"   "T" indicates that the command should be applied to the corresponding   endpoint, and "F" indicates that it should not.  This parameter can   be used in conjunction with the reset extension parameter described   insection 2.4 of this document to force arbitrarily distributed   endpoints into 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 the EndpointMap is referring to (the EndPointList MUST   NOT contain the "all" wildcard).  Several EndpointList andFoster & Andreasen           Informational                      [Page 5]

RFC 3991            MGCP Redirect and Reset Package        February 2005   EndpointMap parameter lines can be provided.  It is considered an   error if an EndpointMap parameter extends beyond the endpoints   specified in the preceding EndPointList parameter.  In that case,   return code 800 MUST be used (seesection 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, seeSection 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 wildcarded 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, it can apply the endpoint configuration command to   endpoints specified by the EndpointList and/or EndpointMap parameters   (regardless of whether those endpoints are in-service).  Of course,   the endpoint configuration information will not be maintained over   gateway restarts (as the Call Agent would have to reapply the   endpoint configuration after it receives an RSIP with the restart   method "restart").  For example, if a new "notified entity" was   provided, it would have no effect since the provisioned value would   be used upon restart.   EndpointList and/or EndpointMap parameters MUST only be used with a   virtual endpoint name corresponding to the gateway (as indicated   above).  If it is 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.netFoster & Andreasen           Informational                      [Page 6]

RFC 3991            MGCP Redirect and Reset Package        February 2005   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   unchanged.   If 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 first.   The NotifiedEntityList parameter can also be specified in an endpoint   configuration command, such as follows:      EPCF 1200 *@gw1.whatever.net MGCP 1.0      RED/NL: ca1@myca.whatever.net, ca2@mybackupca.whatever.net   Note that this command will only succeed if all the endpoints on the   gateway are in-service.   As indicated insection 2.2, it can also apply this to the gateway   virtual endpoint:      EPCF 1200 MG@gw1.whatever.net MGCP 1.0      RED/EL: *      RED/NL: ca1@myca.whatever.net, ca2@mybackupca.whatever.net   Note that the outcome of this command is not affected by the service   state of the endpoints on the gateway.   As indicated insection 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 therefore the "RED/N" parameter cannot be audited).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:Foster & Andreasen           Informational                      [Page 7]

RFC 3991            MGCP Redirect and Reset Package        February 2005      "RED/R:" 0*WSP "reset"   This has the effect of resetting 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).   Example:      EPCF 1200 mg@gw1.whatever.net MGCP 1.0      RED/EL: ds/e1-3/[1-30]      RED/MP: TFTTTTTFFFTTTTTFFFFTFFTTFTTTFF      RED/EL: ds/e1-5/[1-30]      RED/MP: TFFFFFTFFFTTFTTFFFFTFFFTFTTTTT      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 command.  There is no default value for   the parameter, and therefore it is unaffected when omitted.  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"   package:      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,              Of Parameters            such as EndpointList parameter,                                       used where the endpoint name was                                       not the virtual endpoint name                                       corresponding to the gateway.Foster & Andreasen           Informational                      [Page 8]

RFC 3991            MGCP Redirect and Reset Package        February 20053.  IANA Considerations   The MGCP package title "Redirect and Reset" with the name "RED" and   version number 0 has been registered with IANA, as indicated inAppendix C.1 in [2].4.  Security ConsiderationsSection 5 of the base MGCP specification [2] discusses security   requirements for the base protocol that apply equally to the package   defined in this document.  Use of a security protocol that provides   per message authentication and integrity services, such as IPsec (RFC2401 [3],RFC 2406 [4]), is required in order to ensure that requests   and responses are obtained from authenticated sources and that   messages have not been modified.  Without these services, gateways   and Call Agents are open to attacks.   For example, an attacker could masquerade as a Call Agent and   initiate a denial of service attack by resetting endpoints that were   involved in valid calls.  Another attack using the package described   in this document could involve redirecting endpoints to the attacker   so that it acts as the Call Agent for those endpoints.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.   [3]  Kent, S. and R. Atkinson, "Security Architecture for the        Internet Protocol",RFC 2401, November 1998.   [4]  Kent, S. and R. Atkinson, "IP Encapsulating Security Payload        (ESP)",RFC 2406, November 1998.Foster & Andreasen           Informational                      [Page 9]

RFC 3991            MGCP Redirect and Reset Package        February 2005Authors' Addresses   Flemming Andreasen   Cisco Systems   499 Thornall Street, 8th Floor   Edison, NJ 08837   EMail: fandreas@cisco.com   Bill Foster   Cisco Systems   EMail: bfoster@cisco.comFoster & Andreasen           Informational                     [Page 10]

RFC 3991            MGCP Redirect and Reset Package        February 2005Full Copyright Statement   Copyright (C) The Internet Society (2005).   This document is subject to the rights, licenses and restrictions   contained inBCP 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   ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,   INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE   INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED   WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.Intellectual Property   The IETF takes no position regarding the validity or scope of any   Intellectual Property Rights or other rights that might be claimed to   pertain to the implementation or use of the technology described in   this document or the extent to which any license under such rights   might or might not be available; nor does it represent that it has   made any independent effort to identify any such rights.  Information   on the ISOC's procedures with respect to rights in ISOC Documents can   be found inBCP 78 andBCP 79.   Copies of IPR disclosures made to the IETF Secretariat and any   assurances of licenses to be made available, or the result of an   attempt made to obtain a general license or permission for the use of   such proprietary rights by implementers or users of this   specification can be obtained from the IETF on-line IPR repository athttp://www.ietf.org/ipr.   The IETF invites any interested party to bring to its attention any   copyrights, patents or patent applications, or other proprietary   rights that may cover technology that may be required to implement   this standard.  Please address the information to the IETF at ietf-   ipr@ietf.org.Acknowledgement   Funding for the RFC Editor function is currently provided by the   Internet Society.Foster & Andreasen           Informational                     [Page 11]