Diameter Overload Control Application
draft-korhonen-dime-ovl-00
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| Author | Jouni Korhonen | ||
| Last updated | 2012-10-03 | ||
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draft-korhonen-dime-ovl-00
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
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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.
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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
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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
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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
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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.
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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)
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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
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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.
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<DOCA-Report-Request> ::= < 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.
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<DOCA-Report-Answer> ::= < 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.
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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).
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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.
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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
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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.
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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
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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
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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.
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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.
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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.
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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.
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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.
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Author's Address
Jouni Korhonen (editor)
Nokia Siemens Networks
Linnoitustie 6
Espoo FIN-02600
Finland
Email: jouni.nospam@gmail.com
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