Diameter Maintenance and Extensions J. Korhonen, Ed. (DIME) Nokia Siemens Networks Internet-Draft October 3, 2012 Intended status: Standards Track Expires: April 6, 2013 Diameter Overload Control Application draft-korhonen-dime-ovl-00.txt Abstract This specification documents a Diameter Overload Control Application (DOCA), which uses the normal Diameter application approach for the capability negotiation, propagation and management of Diameter overload control information between Diameter nodes. Requirements 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 [RFC2119]. Status of this Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." This Internet-Draft will expire on April 6, 2013. Copyright Notice Copyright (c) 2012 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of Korhonen Expires April 6, 2013 [Page 1] Internet-Draft DOCA October 2012 publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Korhonen Expires April 6, 2013 [Page 2] Internet-Draft DOCA October 2012 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 2. Solution Overview . . . . . . . . . . . . . . . . . . . . . . 4 2.1. Justification for the selected solution approach . . . . . 4 2.2. Initialization state with STATE_MAINTAINED . . . . . . . . 6 2.3. Initialization state with NO_STATE_MAINTAINED . . . . . . 7 2.4. Renegotiation and termination of the session . . . . . . . 8 2.5. Established state and the distribution of the overload control information . . . . . . . . . . . . . . . . . . . 8 2.5.1. Diameter client and server behavior . . . . . . . . . 8 2.5.2. Diameter agent behavior . . . . . . . . . . . . . . . 9 3. DOCA-Report-Request/Answer Commands . . . . . . . . . . . . . 9 4. Attribute Value Pairs . . . . . . . . . . . . . . . . . . . . 11 4.1. OC-Information AVP . . . . . . . . . . . . . . . . . . . . 11 4.2. OC-Scope AVP . . . . . . . . . . . . . . . . . . . . . . . 12 4.3. OC-Applications AVP . . . . . . . . . . . . . . . . . . . 13 4.4. OC-Action AVP . . . . . . . . . . . . . . . . . . . . . . 14 4.5. OC-Algorithm AVP . . . . . . . . . . . . . . . . . . . . . 14 4.6. OC-Level AVP . . . . . . . . . . . . . . . . . . . . . . . 15 4.7. OC-Utilization AVP . . . . . . . . . . . . . . . . . . . . 16 4.8. OC-Tocl AVP . . . . . . . . . . . . . . . . . . . . . . . 16 4.9. OC-Sending-Rate AVP . . . . . . . . . . . . . . . . . . . 17 4.10. OC-Best-Before AVP . . . . . . . . . . . . . . . . . . . . 17 4.11. OC-Origin AVP . . . . . . . . . . . . . . . . . . . . . . 17 4.12. OC-Priority AVP . . . . . . . . . . . . . . . . . . . . . 18 4.13. Attribute Value Pair flag rules . . . . . . . . . . . . . 19 5. Transport considerations . . . . . . . . . . . . . . . . . . . 19 6. Deployment considerations . . . . . . . . . . . . . . . . . . 20 6.1. Overload information propagation with STATE_MAINTAINED . . 20 6.2. Overload information propagation with NO_STATE_MAINTAINED . . . . . . . . . . . . . . . . . . . 20 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 20 7.1. Application Identifiers . . . . . . . . . . . . . . . . . 20 7.2. SCTP Payload Protocol Identifier . . . . . . . . . . . . . 21 7.3. Command codes . . . . . . . . . . . . . . . . . . . . . . 21 7.4. AVP codes . . . . . . . . . . . . . . . . . . . . . . . . 21 7.5. Result-Code values . . . . . . . . . . . . . . . . . . . . 21 7.6. New registries . . . . . . . . . . . . . . . . . . . . . . 21 8. Security Considerations . . . . . . . . . . . . . . . . . . . 22 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 22 10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 22 10.1. Normative References . . . . . . . . . . . . . . . . . . . 22 10.2. Informative References . . . . . . . . . . . . . . . . . . 22 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 22 Korhonen Expires April 6, 2013 [Page 3] Internet-Draft DOCA October 2012 1. Introduction The existing tool box offered by the Diameter Base Protocol [I-D.ietf-dime-rfc3588bis] to prevent and recover from signaling overload situations is rather limited. Apart from out-of-band altering of the transport connection congestion control behavior or other non-standard application level throttling, the protocol error DIAMETER_TOO_BUSY, the permanent error DIAMETER_UNABLE_TO_COMPLY (for some unspecified reason) and the Disconnect-Cause Attribute Value Pair (AVP) code BUSY or DO_NOT_WANT_TO_TALK_TO_YOU are more or less all there is. Unfortunately, the mentioned three indications are coarse, concerns one peer connection at time or lack proper information what is the cause of the signaled actions. They also treats all applications in a single Diameter node (identified by a single DiameterIdentity) as a lump. There is no way communicate any kind of grouping of applications or what is the scope/partitioning of the delivered information. Furthermore, there is no way to signal when the overload situation is over. The request initiator and forwarders just have to keep trying to find it out. The situation is further complicated by the hop-by-hop nature of Diameter deployments. This makes the propagation of possible overload situation information non-trivial, even for exiting protocol errors (since every intermediate is allowed for to react to the error). Either the information is never propagated to the request originator or it takes unacceptable long time to reach the originator. The Diameter overload control challenges are further discussed and a set of solution requirements for an overall Diameter overload control mechanism are documented in [I-D.mcmurry-dime-overload-reqs]. This specification documents a Diameter Overload Control Application (DOCA), which fulfills the requirements of [I-D.mcmurry-dime-overload-reqs] and uses the normal Diameter application approach for the capability negotiation, propagation and management of Diameter overload control information between Diameter nodes. [Editor's note: There probably still are gaps between the requirements and the feature set of this specification.] 2. Solution Overview 2.1. Justification for the selected solution approach Section 1 discussed the motivation and the background for the Diameter enhancements for explicit Diameter overload control Korhonen Expires April 6, 2013 [Page 4] Internet-Draft DOCA October 2012 solution. This specification solves the overload control at the application level instead of 1) extending the Diameter base protocol or 2) piggybacking overload control information on top of existing applications and their commands. The reasoning is the following: 1. The support for Diameter overload control capability between Diameter peers is explicit (i.e. a new application-id is advertised) and thus not build on an exchange of optional Attribute Value Pairs (AVPs). 2. The support for Diameter overload control capability between Diameter client and server is explicit. 3. The peer selection follows the existing standards including DNS- based discovery [RFC6408] and does not assume additional peer selection criteria learnt from an exchange of optional AVPs. 4. The application based solution is able to traverse and also propagate overload control information through realms that deploy 'vanilla' relay agents without Diameter overload control support. 5. The propagation does not depend on a modified behavior of past, existing or future (base protocol) commands or their Command Code Format (CCF). 6. Pretending not to establish a state when there actually is an overload capability and information state still maintained. The state might not be at the application level but is there. 7. Trying to avoid information flooding, especially across administrative domains. 8. Applications allow established mechanisms for filtering and Diameter traffic engineering, since it does not differentiate, from a Diameter point of view, from any normal application. [Editor's note] Whether the application is proxiable or just between two peers is for further study. It is obvious that the Diameter Overload Control Application (DOCA) will contribute to the overall signaling traffic load. Therefore, the DOCA is designed to be as reticent as possible. Since Diameter does not, as such, support unidirectional message delivery at the application level, the DOCA behavior is simple request-reply each time. The application level solution usually requires maintaining an application state. However, the DOCA defines two modes of operation: 1. STATE_MAINTAINED where the DOCA client and server first negotiate the appropriate behavior for the subsequent reports of the overload information exchanges. The negotiation (initializing) state consist of one message pair and the reporting (established) state continues using the same message pair. AVPs and their values that remain the same after the session has been Korhonen Expires April 6, 2013 [Page 5] Internet-Draft DOCA October 2012 established do not need to be repeated in subsequent messaging, thus reducing the overall message size. [Editor's note: To be decided whether maintaining state is worth at all.] 2. NO_STATE_MAINTAINED where the DOCA client and server never leave the negotiation (initializing) phase and piggyback the overload information as part of the "negotiation" over and over again. The DOCA clients and servers MAY apply additional intelligence to learn the capabilities of the other DOCA peer. However, such behavior is not required or even expected. In the absence of a Diameter end-to-end security framework, this specification does not define one either. This implies that no mutual authentication between the Diameter client and server takes place. The intermediate Diameter agents are not either authenticated and the integrity of the delivered overload control information cannot be guaranteed. If these security properties are desired, a future revision of this document may add those. Finally, the DOCA concerns Diameter nodes as whole, not a single session. A single persistent DOCA session can cover multiple applications, transport connections and Diameter sessions. One DOCA client MAY also represent a pool of other Diameter nodes. The different Diameter nodes are and can be differentiated based on their DiameterIdentities. How one DOCA capable Diameter node is selected to represent a pool of other Diameter nodes is out of scope of this specification. Furthermore, how the DOCA information is disseminated within the pool is also out of scope this specification. 2.2. Initialization state with STATE_MAINTAINED The DOCA is bi-directional when it comes to the distribution of the overload control information and has no concept of statically assigned initiator or responder roles. However, before any overload control information can be sent to a specific destination (Destination-Realm and Destination-Host pair), a DOCA session has to be set up between two Diameter nodes. We call this step as the 'initialization state', which involves: o Establishing a session between two Diameter nodes who both can then be originators and consumers of the overload control information. o Agreeing on the scope of the overload control information i.e. whether it concerns the client and server only, any node in a specific realm that happens to be on the path, or any node in any realm on the path. Korhonen Expires April 6, 2013 [Page 6] Internet-Draft DOCA October 2012 o Agreeing on the set of applications to be monitored. o Agreeing on the 'algorithm' to apply when overload situation takes place. o Agreeing on the maximum rate for a periodic overload control information delivery. The initialization state is started by sending a DOCA-Report-Request, which promotes the request initiator as the 'client' for the forthcoming DOCA session. The Auth-Session-State AVP MUST be set to value STATE_MAINTAINED. If the DOCA-Report-Response contains the Auth-Session-State AVP set to value NO_STATE_MAINTAINED then the DOCA client MUST NOT proceed to the 'established state' (see Section 2.5) and the possible information exchanged during the DOCA-Report- Request/Answer concerns only this one message exchange. In a case two nodes enter the initialization phase simultaneously, the election algorithm as defined in [I-D.ietf-dime-rfc3588bis] is applied to select the 'client'. The winner of the election process becomes the 'client' of the DOCA session. Once the initialization state has completed, i.e. the 'server' has sent a DOCA-Report-Answer with a success Result-Code and the 'client' has received a DOCA- Report-Answer, then the DOCA session shifts to the 'established state' (see Section 2.5). The agreed parameter set MUST be a set of parameters that both the 'client' and the 'server' have in common. Of course, the Diameter nodes do not need to advertise all the parameter they have, rather a subset based on some local policy. 2.3. Initialization state with NO_STATE_MAINTAINED A DOCA client that wishes not to maintain a session state MUST set the Auth-Session-State AVP to the value NO_STATE_MAINTAINED and SHOULD include the OC-Information AVP with overload information into the DOCA-Report-Request it sends to a DOCA server. If the DOCA server cannot agree on a 'stateless' DOCA overload information exchange it MUST answer with a DOCA-Report-Response including the Result-Code AVP set to value DIAMETER_INVALID_AVP_VALUE and the Failed-AVP AVP containing the Auth-Session-State AVP. If the DOCA server agrees on a 'stateless' DOCA overload information exchange, then the answer DOCA-Report-Response message MUST contain the Auth- Session-State AVP set to value NO_STATE_MAINTAINED. The use of 'stateless' DOCA overload information exchange SHOULD be used with caution. In principle each DOCA-Report-Request/Answer message exchange is independent and the DOCA client and peer MAY have conflicting views on the supported parameters and information content. This may lead to an exchange of information that is a) Korhonen Expires April 6, 2013 [Page 7] Internet-Draft DOCA October 2012 always silently discarded by the other end and b) considered just as excess signaling. It RECOMMENDED that the 'stateless' DOCA usage is limited into a single realm only. If the 'stateless' use of DOCA is preferred, any the DOCA capable Diameter node MAY initiate a DOCA-Report-Request at any given time. The receiver of the DOCA-Report-Request acknowledges with a DOCA- Report-Answer and includes the Result-Code AVP indicating whether it could honor the action/report in the request. The DOCA-Report-Answer SHOULD also piggyback overload control information. When the session state is not maintained, the DOCA client is implicitly in an 'established state'. The consideration regarding various DOCA related timers serve only as a hint as they cannot be formally mandated due the lack of the session state. 2.4. Renegotiation and termination of the session The following applies only when the session state is maintained. If there is a need to renegotiate parameters, the DOCA client just sends a DOCA-Report-Request with a new parameter set and enters the initialization state. Similarly, the DOCA server can request a renegotiation of the parameters by sending a Re-Auth-Request to the DOCA client, which then eventually enters the initialization state. The DOCA server MAY hint about the new parameter set by including specific DOCA AVPs into the Re-Auth-Request. A DOCA session is terminated using the standard Session-Termination-Request/Answer and/or Abort-Session-Request/Answer exchange. 2.5. Established state and the distribution of the overload control information 2.5.1. Diameter client and server behavior Either the DOCA client or server MAY initiate a DOCA-Report-Request at any given time. The receiver of the DOCA-Report-Request acknowledges with a DOCA-Report-Answer and includes the Result-Code AVP indicating whether it could honor the action/report in the request. The DOCA-Report-Answer SHOULD also piggyback overload control information instead of the responder initiating a DOCA- Report-Request immediately after responding with the DOCA-Report- Answer, assuming an overload control information reporting has been scheduled to the near future. A care should be taken not to send DOCA-Report-Requests too frequently. The sending rate, in a case of normal status reporting, SHOULD follow the Tolc timer negotiated during the initialization state. In case of emerging overload situation and once the overload Korhonen Expires April 6, 2013 [Page 8] Internet-Draft DOCA October 2012 situation normalizes, the node is allowed to send a DOCA-Report- Request regardless of the Tolc timer value (which also leads to resetting the Tolc timer). When a Diameter node receives overload control information and is also requested to act on it, the DOCA functionality is applied to all specified applications within a given scope. How the Diameter node accomplishes the node wide DOCA action enforcement is implementation specific. When a Diameter node receives (interim) overload information but the overload condition has not started, then the receiver is not required to act based on the received information. However, it is RECOMMENDED that the receiver makes proactive actions to avoid entering the overload condition based on the newly received overload information. 2.5.2. Diameter agent behavior There can be zero or more intermediate Diameter agents on the path between the DOCA client and the server. Understanding the DOCA functionality is not expected from both Relay and Redirect agents. A Diameter proxy, which obviously understands the DOCA application, MAY inspect the DOCA related AVPs in the DOCA-Report-Request/Answer message pair and depending on the value of the OC-Scope AVP (see Section 4.2) inject its own information. A proxy is always RECOMMENDED to react according to the overload information when it comes to, for example, peer selection and traffic throttling. [Note: in practice there is no way to prohibit proxies to mangle AVPs due the lack of proper end-to-end security] When a Diameter agent receives overload control information and is also requested to act on it, the DOCA functionality is applied to all specified applications within a given scope. How the Diameter agent accomplishes the node wide DOCA action enforcement is implementation specific. 3. DOCA-Report-Request/Answer Commands The DOCA-Report-Request (DRR) is used to report overload condition information. The message can be originated as a result of emerging overload condition or as a periodic unsolicited report. Korhonen Expires April 6, 2013 [Page 9] Internet-Draft DOCA October 2012 ::= < Diameter Header: TBD2, REQ, PXY > < Session-Id > { Auth-Application-Id } { Origin-Host } { Origin-Realm } { Destination-Realm } { Auth-Request-Type } { Destination-Host } [ Auth-Session-State ] * [ Class ] [ Origin-State-Id ] * [ Proxy-Info ] * [ Route-Record ] { OC-Scope } [ OC-Algorithm ] [ OC-Action ] [ OC-Tocl ] [ OC-Applications ] * [ OC-Information ] * [ AVP ] The DOCA-Report-Answer (DRA) is used as a response to the DOCA- Report-Request. The message MAY piggyback overload condition information in order to avoid unnecessary DOCA-Report-Request messages to the opposite direction. Korhonen Expires April 6, 2013 [Page 10] Internet-Draft DOCA October 2012 ::= < Diameter Header: TBD2, PXY > < Session-Id > { Result-Code } { Origin-Host } { Origin-Realm } [ Auth-Session-State ] * [ Class ] [ Error-Message ] [ Error-Reporting-Host ] [ Failed-AVP ] [ Origin-State-Id ] * [ Redirect-Host ] [ Redirect-Host-Usage ] [ Redirect-Max-Cache-Time ] * [ Proxy-Info ] { OC-Scope } [ OC-Algorithm ] [ OC-Action ] [ OC-Tocl ] [ OC-Applications ] * [ OC-Information ] * [ AVP ] The OC-Algorithm, OC-Tocl and OC-Applications AVPs can be left out when the DOCA peers do not maintain state. These AVPs at main level of the command are meant for the state maintaining mode negotiation of the overload information set of interest. 4. Attribute Value Pairs 4.1. OC-Information AVP The OC-Information AVP (AVP Code TBD3) is of type Grouped and contains a set AVPs that identify the source of the overload control information (the OC-Origin AVP), the overload information itself and which applications the information concerns. Korhonen Expires April 6, 2013 [Page 11] Internet-Draft DOCA October 2012 OC-Information ::= < AVP Header: TBD3 > { OC-Origin } { OC-Best-Before } [ OC-Level ] [ OC-Algorithm ] [ OC-Sending-Rate ] [ Vendor-Id ] [ OC-Applications ] [ Product-Name ] [ OC-Utilization ] [ OC-Priority ] * [ AVP ] Depending on the negotiated scope (see Section 4.2) any Diameter node on path MAY add one or more OC-Information AVPs into the DOCA-Report- Request/answer messages. 4.2. OC-Scope AVP The OC-Scope (AVP Code TBD4) is of type Unsigned32 and contains the scope where and concerning what the overload control information can be injected. The OC-Scope is formatted as a vector of scope flag bits. The following scopes are supported: Host scope (0x00000001) The OC-Information AVP concerns only a single host within a realm (which internally MAY represent of pool). Realm scope (0x00000002) The OC-Information AVP concerns a realm. No specific hosts are identified. Only origin realm (0x00000004) The OC-Information AVP can only be included by a Diameter node on the path that has the same Origin-Realm as the DOCA client. Application information (0x00010000) The OC-Information AVP MAY contain application related information (the OC-Applications AVP). Korhonen Expires April 6, 2013 [Page 12] Internet-Draft DOCA October 2012 Node utilization information (0x00020000) The OC-Information AVP MAY contain node wide load related information (the OC-Utilization AVP). Application priorities (0x00040000) The OC-Information AVP SHOULD priority information (the OC- Priority AVP) so when the overload condition is on, Diameter nodes are able to prioritize between different applications, for example, when dropping or throttling messages. Any other value is reserved. A scope is active when a corresponding flag is set in the OC-Scope AVP. During the initialization state a DOCA client includes those scopes it supports and is interested in. A DOCA server then returns the scope that it has in common with the DOCA client (and intends to use). The common scopes are then used during the established state. Note that some scope combinations make little sense while still being valid. The general guide when multiple scopes collide is that the least restrictive wins. A sender of the overload information MUST adhere to the scope it announces regarding the information it itself sends. If a DOCA server does not have a common scope with a DOCA client or the DOCA server cannot agree on one based on a local policy, then the DOCA server MUST send the DOCA-Report-Answer indicating an error and set the Result-Code to the DIAMETER_NO_COMMON_SCOPE value. 4.3. OC-Applications AVP The OC-Applications (AVP Code TBD5) is of type Grouped and contains a list of Application-IDs of interest when found in the DOCA-Report- Request/Answer command main level and meant to be used during the initialization state to agree on the common set of supported applications of monitoring interest. When used within the OC- Information AVP, the OC-Applications AVP identify those applications the overload information concerns. The OC-Applications AVPs on the command main level and inside the OC-Information AVP MUST NOT have conflicting views of the applications of interest. However, the OC- Applications AVP can be see as a superset of applications i.e., not all applications of interest need to be included every time into the OC-Information AVP. Korhonen Expires April 6, 2013 [Page 13] Internet-Draft DOCA October 2012 OC-Applications ::= < AVP Header: TBD3 > * [ Auth-Application-Id ] * [ Acct-Application-Id ] * [ Vendor-Specific-Application-Id ] * [ AVP ] The absence of the OC-Applications AVP indicates the Diameter node has no specific preference or interest in specific applications. The overload information is then signalled as concerning the whole Diameter node. This default behavior is useful when the DOCA does not maintain session state. If there are no common applications, then the DOCA-Report-Answer MUST contain the Result-Code with the DIAMETER_NO_COMMON_APPLICATION value. When the DOCA maintains state, there is no need to include the OC- Applications AVP into the DOCA-Report-Request/Answer command main level after the initial message exchange. The agreed common set of application is expected to be known by both DOCA client and server throughout the session lifetime. 4.4. OC-Action AVP The OC-Action (AVP Code TBD6) is of type OctetString and size of one octet. The octet has the following three possible values: Start (1) Signals the start of the overload condition. This implies the receiver is requested to act according to the information found in the OC-Information. Stop (2) Signals the end of the overload condition. Interim (3) Updates the overload information. The interim can be sent during the overload condition or during the normal condition. This is the default value. Any other value is reserved. 4.5. OC-Algorithm AVP The OC-Algorithm (AVP Code TBD7) is of type Unsigned32. The contains supported 'algorithms' to mitigate the overload condition. The OC- Algorithm AVP is formatted as a vector of algorithm flag bits. The Korhonen Expires April 6, 2013 [Page 14] Internet-Draft DOCA October 2012 following 'algorithms' are supported: Drop (0x00000001) Messages are plain dropped. It is RECOMMENDED to drop messages selectively based, for example, on application priorities. This is the default algorithm. Throttle (0x00000002) The message sending rate is according to the OC-Sending-Rate AVP. Prioritize (0x00000004) Apply priorities among applications and the other used means for holding traffic. Any other value is reserved. The 'algorithms' are only applied at a Diameter node when the overload condition has been signaled. During the initialization state a DOCA client includes those algorithms it supports and is interested in. A DOCA server then returns the algorithm that it has in common with the DOCA client (and intends to use). One or more common algorithms are then used during the established state. If a DOCA server does not have a common algorithm with a DOCA client or the DOCA server cannot agree on one based on a local policy, then the DOCA server MUST send the DOCA-Report-Answer indicating an error and set the Result-Code to the DIAMETER_NO_COMMON_ALGORITHM value. 4.6. OC-Level AVP The OC-Level (AVP Code TBD8) is of type OctetString and size of one octet. The octet has the following five possible values: Normal (1) Everything is in control. Meaningful only when the OC-Action is set to 'Interim' since when the overload condition level is considered normal, the overload condition SHOULD be stopped. This is the default value. Korhonen Expires April 6, 2013 [Page 15] Internet-Draft DOCA October 2012 Raising (2) There is a sign of increasing load. Alarming (3) The overload condition is reaching the level where quick measures SHOULD be done to mitigate the overload condition. Panic (4) The overload condition is severe. Apply any measure to mitigate the overload condition but still allowed to send messages. Hold (5) Do not send any messages, please. When this level is signaled, the OC-Best-Before time SHOULD NOT be respected but an explicit overload condition stop has to be received (with an exception the Diameter node realizes its other end has rebooted or otherwise lost its state). Switch servers (6) Do not talk to me again. When this level is signaled, the DOCA peer MUST switch to an alternative server. Any other value is reserved. If the receiver cannot agree on or does not understand the OC-Level AVP value, the an error MUST be returned with the Result-Code AVP set to the value DIAMETER_INVALID_AVP_VALUE and the Failed-AVP AVP containing the OC-Level AVP. 4.7. OC-Utilization AVP The OC-Utilization (AVP Code TBD9) is of type Float32 and tells the overall utilization level percentage of the Diameter node. Values between 0.0 to 100.0 are valid. 4.8. OC-Tocl AVP The OC-Tocl (AVP Code TBD10) is of type Unsigned32 and tells the Tolc timer value in milliseconds. This timer defines the interval for sending periodic DOCA-Report-Request messages with the OC-Action AVP set to 'Interim'. The value of zero (0) means no periodic DOCA- Report-Request messages are sent or desired. The default value is Korhonen Expires April 6, 2013 [Page 16] Internet-Draft DOCA October 2012 120000. During the initialization state both a DOCA client and server express their preferred Tolc value for receiving periodic updates. As a result both ends will have their own Tolc values. If a DOCA server find the Tocl value proposed by a DOCA client either too small (i.e. too frequent periodic messages) or too big (i.e. too seldom periodic messages), then the DOCA server MUST send the DOCA- Report-Answer indicating an error and set the Result-Code either to the DIAMETER_TOCL_TOO_SMALL or DIAMETER_TOCL_TOO_BIG value. In the case of 'stateless' DOCA usage, the OC-Tocl AVP can be considered as a hint for a desired sending rate of subsequent messages. 4.9. OC-Sending-Rate AVP The OC-Sending-Rate (AVP Code TBD11) is of type Float32 and tells the the maximum Diameter message sending rate per second the sender of this information wishes to receive Diameter messages. Only positive values are valid. A value of zero (0.0) of the absence of this AVP means the information sender has no specific rate preference. If a DOCA server finds the sending rate value proposed by a DOCA client too big (i.e. too frequent periodic messages), then the DOCA server MUST send the DOCA-Report-Answer indicating an error and set the Result-Code to the DIAMETER_RATE_TOO_BIG value. 4.10. OC-Best-Before AVP The OC-Best-Before (AVP Code TBD12) is of type Time and tells the expiration time/date for the information received in the OC- Information. For example, when the overload condition is on, the expiration of the 'best before' timer causes the same as receiving a DOCA-Report-Request/Answer with the OC-Action set to 'Stop'. [Editor's node: to be decided whether a duration timer is a better measure. Using Time has the assumptions nodes have actually clocks that a running approximately same time.] 4.11. OC-Origin AVP The OC-Origin (AVP Code TBD13) is of type DiameterIdentity and tells the identity of the Diameter node that originated included the overload control information. Both host and realm information MUST be included in the OC-Origin AVP. Note, if the OC-Scope AVP indicates only a realm wide scope for the overload information, then Korhonen Expires April 6, 2013 [Page 17] Internet-Draft DOCA October 2012 the realm part of the OC-Origin AVP is meaningful and the host information only serves as an additional information of the representative for the realm wide information. 4.12. OC-Priority AVP The OC-Priority (AVP Code TBD14) is of type Unsigned32 and defines the priority level. The value of 0x00000000 is the highest priority and the value of 0xffffffff is the lowest priority. The absence of the OC-Priority AVP means there is not specific priority level defined and the priority SHOULD be considered as the lowest possible. When used within the OC-Information grouped AVP, the OC-Priority AVP defines the priority for the listed applications within the OC- Applications AVP. Korhonen Expires April 6, 2013 [Page 18] Internet-Draft DOCA October 2012 4.13. Attribute Value Pair flag rules +---------+ |AVP flag | |rules | +----+----+ AVP Section | |MUST| Attribute Name Code Defined Value Type |MUST| NOT| +---------------------------------------------------+----+----+ |OC-Information TBD3 x.x Grouped | M | V | +---------------------------------------------------+----+----+ |OC-Scope TBD4 x.x Unsigned32 | M | V | +---------------------------------------------------+----+----+ |OC-Application TBD5 x.x Grouped | M | V | +---------------------------------------------------+----+----+ |OC-Action TBD6 x.x OctetString | M | V | +---------------------------------------------------+----+----+ |OC-Algorithm TBD7 x.x Unsigned32 | M | V | +---------------------------------------------------+----+----+ |OC-Level TBD8 x.x OctetString | M | V | +---------------------------------------------------+----+----+ |OC-Utilization TBD9 x.x Float32 | M | V | +---------------------------------------------------+----+----+ |OC-Tocl TBD10 x.x Unsigned32 | M | V | +---------------------------------------------------+----+----+ |OC-Sending-Rate TBD11 x.x Float32 | M | V | +---------------------------------------------------+----+----+ |OC-Best-Before TBD12 x.x Time | M | V | +---------------------------------------------------+----+----+ |OC-Origin TBD13 x.x DiameterIdentity | M | V | +---------------------------------------------------+----+----+ |OC-Priority TBD14 x.x Unsigned32 | M | V | +---------------------------------------------------+----+----+ 5. Transport considerations In case of Stream Control Transmission Protocol (SCTP) transport, the DOCA application is RECOMMENDED to mark its Diameter packets using the DOCA defined SCTP Payload Protocol Identifier (PPID) TBD1. The PPID MAY be used by intermediating network nodes or agents to peek into SCTP message and find out that this is about overload control. Such information can be used for prioritizing SCTP packet handling as an example. Korhonen Expires April 6, 2013 [Page 19] Internet-Draft DOCA October 2012 6. Deployment considerations 6.1. Overload information propagation with STATE_MAINTAINED The following example shows how a DOCA session is created and the vital capabilities are negotiated. The OC-Scope AVP has no "Only origin realm" set, which allows for any node of the path add their overload information into the DOCA messages. The proxy on the edge of the example.org makes use of this. Note that if an intermediate node from other realm than the originating realm (example.net) adds additional information that is for informational purposes only. The reason is that only the message originator can set the OC-Action AVP value. TBD. DOCA Proxy Proxy DOCA Client (pool) example.net example.org Server | | | | : : : : | | | | | | | | 6.2. Overload information propagation with NO_STATE_MAINTAINED The following example shows how a 'stateless' DOCA usage could be done. Note that both client and server are within the same realm. TBD. DOCA Proxy Proxy DOCA Client (pool) example.net example.net Server | | | | : : : : | | | | | | | | 7. IANA Considerations 7.1. Application Identifiers This specification reserves a new Diameter Application-ID TBD14 for the Diameter Overload Control Application (DOCA) from the 'Authentication, Authorization, and Accounting (AAA) Parameters' Application IDs registry. Korhonen Expires April 6, 2013 [Page 20] Internet-Draft DOCA October 2012 7.2. SCTP Payload Protocol Identifier Section 5 reserves a new SCTP Payload Protocol Identifier for the DOCA application usage. The value is reserved from the existing SCTP Payload Protocol Identifiers registry. 7.3. Command codes One Diameter command is defined in Section Section 3. The DOCA- Report-Request/Answer Command Code is TBD2. Both are allocated from the 'Authentication, Authorization, and Accounting (AAA) Parameters' Command Codes registry. 7.4. AVP codes New AVPs defined by this specification are listed in Section 4. All AVP codes allocated from the 'Authentication, Authorization, and Accounting (AAA) Parameters' AVP Codes registry. 7.5. Result-Code values This specification adds several Diameter Overload Control Application specific Permanent Failure codes from the 'Authentication, Authorization, and Accounting (AAA) Parameters' Result-Code AVP Values (code 268) - Permanent Failure registry: AVP Values | Attribute Name | Reference -----------+-------------------------------+---------- 5xxx | DIAMETER_NO_COMMON_SCOPE | RFCxxxx 5xxx | DIAMETER_NO_COMMON_ALGORITHM | RFCxxxx 5xxx | DIAMETER_TOCL_TOO_SMALL | RFCxxxx 5xxx | DIAMETER_TOCL_TOO_BIG | RFCxxxx 5xxx | DIAMETER_RATE_TOO_BIG | RFCxxxx 7.6. New registries Four new registries are needed under the 'Authentication, Authorization, and Accounting (AAA) Parameters' registry: o OC-Scope AVP Values: the policy for this registry is Specification Required. o OC-Action AVP Values: the policy for this registry is Standards Action. o OC-Level AVP Values: the policy for this registry is Standards Action. o OC-Algorithm AVP Values: the policy for this registry is Specification Required. Korhonen Expires April 6, 2013 [Page 21] Internet-Draft DOCA October 2012 8. Security Considerations The security properties of the Diameter Overload Control Application (DOCA) follow the general [I-D.ietf-dime-rfc3588bis] security model. This implies there is no proper means to verify the message and AVP content correctness if multiple intermediate Diameter agents are present on the path between the DOCA client and server. As a result a malicious intermediate could feed incorrect overload control information to DOCA clients and peers, and thus affect negatively to the overload condition recovery. Possible ways to overcome the obvious security vulnerability are mandating only end to end transport connections between DOCA clients and servers, or some future specification defining an end to end security for the DOCA. 9. Acknowledgements The author thanks Annett Seefeldt for her constructive comments on the technical aspects on this document. 10. References 10.1. Normative References [I-D.ietf-dime-rfc3588bis] Fajardo, V., Arkko, J., Loughney, J., and G. Zorn, "Diameter Base Protocol", draft-ietf-dime-rfc3588bis-34 (work in progress), June 2012. [I-D.mcmurry-dime-overload-reqs] McMurry, E. and B. Campbell, "Diameter Overload Control Requirements", draft-mcmurry-dime-overload-reqs-01 (work in progress), June 2012. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. 10.2. Informative References [RFC6408] Jones, M., Korhonen, J., and L. Morand, "Diameter Straightforward-Naming Authority Pointer (S-NAPTR) Usage", RFC 6408, November 2011. Korhonen Expires April 6, 2013 [Page 22] Internet-Draft DOCA October 2012 Author's Address Jouni Korhonen (editor) Nokia Siemens Networks Linnoitustie 6 Espoo FIN-02600 Finland Email: jouni.nospam@gmail.com Korhonen Expires April 6, 2013 [Page 23]