Internet DRAFT - draft-donovan-dime-drmp
draft-donovan-dime-drmp
Diameter Maintenance and Extensions (DIME) S. Donovan
Internet-Draft Oracle
Intended status: Standards Track May 26, 2015
Expires: November 27, 2015
Diameter Routing Message Priority
draft-donovan-dime-drmp-01.txt
Abstract
When making routing and resource allocation decisions, Diameter nodes
currently have no generic mechanism to determine the relative
priority of Diameter messages. This document defines a mechanism to
allow Diameter endpoints to indicate the relative priority of
Diameter transactions. With this information Diameter nodes can
factor that priority into routing, resource allocation and overload
abatement decisions.
Status of This Memo
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This Internet-Draft will expire on November 27, 2015.
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the Trust Legal Provisions and are provided without warranty as
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology and Abbreviations . . . . . . . . . . . . . . . . 3
3. Conventions Used in This Document . . . . . . . . . . . . . . 4
4. Problem Statement . . . . . . . . . . . . . . . . . . . . . . 4
5. Use Cases . . . . . . . . . . . . . . . . . . . . . . . . . . 5
5.1. First Responder Related Signaling . . . . . . . . . . . . 5
5.2. Emergency Call Related Signaling . . . . . . . . . . . . 5
5.3. Differentiated Services . . . . . . . . . . . . . . . . . 5
5.4. Application Specific Priorities . . . . . . . . . . . . . 6
6. Theory of Operation . . . . . . . . . . . . . . . . . . . . . 7
7. Normative Behavior . . . . . . . . . . . . . . . . . . . . . 8
8. Attribute Value Pairs . . . . . . . . . . . . . . . . . . . . 9
8.1. DRMP AVP . . . . . . . . . . . . . . . . . . . . . . . . 9
8.2. Attribute Value Pair flag rules . . . . . . . . . . . . . 9
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
9.1. AVP codes . . . . . . . . . . . . . . . . . . . . . . . . 10
9.2. New registries . . . . . . . . . . . . . . . . . . . . . 10
10. Security Considerations . . . . . . . . . . . . . . . . . . . 10
11. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 10
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 11
12.1. Normative References . . . . . . . . . . . . . . . . . . 11
12.2. Informative References . . . . . . . . . . . . . . . . . 11
Appendix A. Design Considerations and Questions . . . . . . . . 11
A.1. Relationship with SIP Resource Priority . . . . . . . . . 11
A.2. Priority Encoding Method . . . . . . . . . . . . . . . . 12
A.3. Base Protocol versus Application Extension . . . . . . . 12
A.4. Scope of Priority Setting . . . . . . . . . . . . . . . . 12
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 13
1. Introduction
The DOIC solution [I-D.ietf-dime-ovli] for Diameter overload control
introduces scenarios where Diameter routing decisions made by
Diameter nodes can be influenced by the overload state of other
Diameter nodes. This includes the scenarios where Diameter endpoints
and Diameter agents can throttle requests as a result of the target
for the request being overloaded.
With currently available mechanisms these Diameter nodes do not have
a clean mechanism to differentiate request message priorities when
making these throttling decisions. As such, all requests are treated
the same meaning that all requests have the same probability of being
throttled.
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There are scenarios where treating all requests the same can cause
issues. For instance it might be considered important to reduce the
probability of transactions involving first responders during a
period of heavy signaling resulting from a natural disaster being
throttled during overload scenarios.
This document defines a mechanism that allows Diameter nodes to
indicate the relative priority of Diameter transactions. With this
information other Diameter nodes can factor the relative priority of
requests into routing and throttling decisions.
2. Terminology and Abbreviations
Diversion
As defined in [I-D.ietf-dime-ovli]. An overload abatement
treatment where the reacting node selects alternate destinations
or paths for requests.
DOIC
Diameter Overload Indication Conveyance.
DRMP
Diameter Routing Message Priority.
Overload Abatement
As defined in [I-D.ietf-dime-ovli]. Reaction to receipt of an
overload report resulting in a reduction in traffic sent to the
reporting node. Abatement actions include diversion and
throttling.
Priority
The relative importance of a Diameter message. A higher priority
value implies a higher relative importance of the message.
Throttling
As defined in [I-D.ietf-dime-ovli]. An abatement treatment that
limits the number of requests sent by the DIOC reacting node.
Throttling can include a Diameter Client choosing to not send
requests, or a Diameter Agent or Server rejecting requests with
appropriate error responses. In both cases the result of the
throttling is a permanent rejection of the transaction.
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3. Conventions Used in This Document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
RFC 2119 [RFC2119] interpretation does not apply for the above listed
words when they are not used in all-caps format.
4. Problem Statement
With the introduction of overload control mechanisms, Diameter nodes
will be required to make decisions regarding which Diameter request
messages should be throttled as a result of overloaded Diameter
nodes.
There is currently no generic mechanism to indicate which request
messages should be given preferential treatment when these throttling
decisions are made.
As a result, all messages are treated equally and, as such, have an
equal probability of being throttled.
There are a number of scenarios where it is appropriate for an
application to mark a request as being of a higher priority than
other application requests. These are discussed in the next section.
This document defines a mechanism for applications to indicate
priority for individual transactions, reducing the probability of
those transactions being throttled if there are other lower priority
transactions that are eligible for throttling treatment.
While the primary usage of DRMP defined priorities is for input to
Diameter overload control related throttling decisions, it is also
expected that the priority information could also be used for other
routing related functionality. This might include giving higher
priority transactions preferential treatment when selecting routes.
It is also envisioned that DRMP priority information could be used by
Diameter endpoints to make resource allocation decisions. For
instance, a Diameter Server might choose to use the priority
information to treat higher priority requests ahead of lower priority
requests.
Note: There are a number of application specific definitions
indicating various views of application level priority for
different requests. Using these application specific priority
AVPs as input to throttling and other Diameter routing decisions
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would require Diameter agents to understand all applications and
do application specific parsing of all messages in order to
determine the priority of individual messages. This is considered
an unacceptable level of complexity to put on elements whose
primary responsibility is to route Diameter messages.
5. Use Cases
This section discussed various scenarios where Diameter transactions
can benefit from the use of priority information.
5.1. First Responder Related Signaling
Natural disasters can result in a considerable increase in usage of
network resources. This can be made worse if the disaster results in
a loss of network capacity.
The combination of added load and reduced capacity can lead to
Diameter nodes becoming overloaded and, as a result, the use of DOIC
mechanisms to request a reduction in traffic. This in turn results
in requests being throttled in an attempt to control the overload
scenario and prevent the overloaded node from failing.
There is the need for first responders and other individuals
responsible for handling the after effects of the disaster to be
assured that they can gain access to the network resources in order
to communicate both between themselves and with other network
resources.
Signaling associated with first responders needs to be given a higher
priority to help ensure they can most effectively do their job.
The United States Wireless Priority Services (WPS) and Government
Emergency Telecommunications Service (GETS) are examples of systems
designed to address these first responder needs.
5.2. Emergency Call Related Signaling
Similar to the first responder scenario, there is also signaling
associated with emergency calls. Given the critical nature of these
emergency calls, this signaling should also be given preferential
treatment when possible.
5.3. Differentiated Services
Operators may desire to differentiate network-based services by
providing a service level agreement that includes preferential
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Diameter routing behavior. This might, for example, be modeled as
Platinum, Gold and Silver levels of service.
In this scenario an operator might offer a Platinum SLA the includes
ensuring that all signaling for a customer who purchases the Platinum
service being marked as having a higher priority than signaling
associated with Gold and Silver customers.
5.4. Application Specific Priorities
There are scenarios within Diameter applications where it might be
appropriate to give a subset of the transactions for the application
a higher priority than other transactions for that application.
For instance, when there is a series of transactions required for a
user to gain access to network services, it might be appropriate to
mark transactions that occur later in the series at a higher priority
than those that occur early in the series. This would recognize that
there was potentially significant work done by the network already
that would be lost if those later transactions were throttled.
There are also scenarios where an agent cannot easily differentiate a
request that starts a session from requests that update or end
sessions. In these scenarios it might be appropriate to mark the
requests that establish new sessions with a lower priority than
updates and session ending requests. This also recognizes that more
work has already taken place for established sessions and, as a
result, it might be more harmful if the session update and session
ending requests were to be throttled.
There are also scenarios where the priority of requests for
individual command codes within an application depends on the context
that exists when the request is sent. There isn't always information
in the message from which this context can be determined by Diameter
nodes other than the node that originates the request.
This is similar to the scenario where a series of requests are needed
to access a network service. It is different in that the series of
requests involve different application command-codes. In this
scenario it is requests with the same command-code that have
different implied priorities.
One example of this is in the 3GPP application [S6a] where a ULR
request resulting from an MME restoration procedure might be given
a higher priority than a ULR resulting from an initial attach.
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6. Theory of Operation
This section outlines the envisioned usage of DRMP.
The expected behavior depends on the role (request sender, agent or
request handler) of the Diameter node handling the request.
The following behavior is expected during the flow of a Diameter
transaction.
1. Request sender - The sender of a request, be it a Diameter Client
or a Diameter Server, determines the relative priority of the
request and includes that priority information in the request.
The method for determining the relative priority is application
specific and is outside the scope of this specification. The
request sender also saves the priority information with the
transaction state. This will be used when handling the answer
messages.
2. Agents handing the request - Agents use the priority information
when making routing decisions. This can include determining
which requests to route first, which requests to throttle and
where the request is routed. For instance, requests with higher
priority might have a lower probability of being throttled. The
mechanism for how the agent determines which requests are
throttled is implementation dependent and is outside the scope of
this document. The agent also records the transaction priority
in the transaction state. This will be used when handling the
associated answer message for the transaction.
3. Request handler - The handler of the request, be it a Diameter
Server or a Diameter Client, can use the priority information to
determine how to handle the request. This could include
determining the order in which requests are handled and resources
that are applied to handling of the request.
4. Answer sender - The handler of the request is also the sender of
the answer. The answer sender uses the priority information
received in the request message when sending the answer. This
implies that answers for higher priority transactions are given
preferential treatment to lower priority transactions.
5. Agent handling the answer - Agents handling answer messages use
the priority information stored with the transaction state to
determine the priority of relaying the answer message. This
implies that answers for higher priority transactions are given
preferential treatment to lower priority transactions.
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6. Answer handler - The handler of the answer message uses the
priority of the transaction when allocating resources for
processing that occurs after the receipt of the answer message.
7. Normative Behavior
This section contains the normative behavior associated with Diameter
Resource Message Priority (DRMP).
When routing priority information is availble, Diameter nodes SHOULD
include Diameter routing message priority in all Diameter request
messages.
Note: The method of determining the priority value included in the
request is application specific and is not in the scope of this
specification.
The priority marking scheme SHOULD NOT require the Diameter Agents to
understand application specific AVPs.
When routing priority information is availble, Diameter nodes SHOULD
use DRMP information when making Diameter overload related throttling
decisions.
Diameter agents MAY use DRMP information when relaying messages.
This includes the selection of routes and the ordering of messages
relayed.
The priority information included applies to both the request
message and answer message associated with the transaction. As
such it is used in the processing of both types of messages.
Diameter endpoints MAY use DRMP information when making resource
allocation decisions for the transaction associated with the request
message that contains the DRMP information.
Diameter endpoints MAY use DRMP information when making resource
allocation decisions for the transaction associated with the answer
messages using the DRMP information associated with the transaction.
When there is a mix of transactions specifying priority in request
messages and transactions that do not have the priority specified,
transactions that do not have a specified priority SHOULD be treated
as having the PRIORITY_0 priority.
When setting and using priorities, PRIORITY_0 MUST be treated as the
lowest priority.
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When setting and using priorities, PRIORITY_1 MUST be treated as a
higher priority than PRIORITY_0 and a lower priority than PRIORITY_2.
When setting and using priorities, PRIORITY_2 MUST be treated as a
higher priority than PRIORITY_1 and a lower priority than PRIORITY_3.
When setting and using priorities, PRIORITY_3 MUST be treated as a
higher priority than PRIORITY_2 and a lower priority than PRIORITY_4.
When setting and using priorities, PRIORITY_4 MUST be the highest
priority.
Editor's note: It is likely that there are other considerations
for setting and using priorities. For instance, it might be good
to use priority 1 to indicate elevated priority for strictly
protocol reasons (e.g.; the S6a use case). Priorities 3, 4 and 5
would then be used for non protocol reasons.
8. Attribute Value Pairs
This section describes the encoding and semantics of the Diameter
Overload Indication Attribute Value Pairs (AVPs) defined in this
document.
8.1. DRMP AVP
The DRMP (AVP code TBD1) is of type Enumerated. The value of the AVP
indicates the routing message priority for the transaction. The
following values are initially defined:
PRIORITY_0 0 Priority 0 is the lowest priority.
PRIORITY_1 1 Priority 1 is the second lowest priority.
PRIORITY_2 2 Priority 2 is the middle priority.
PRIORITY_3 3 Priority 3 is the second higest priority.
PRIORITY_4 4 Priority 4 is the higest priority.
8.2. Attribute Value Pair flag rules
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+---------+
|AVP flag |
|rules |
+----+----+
AVP Section | |MUST|
Attribute Name Code Defined Value Type |MUST| NOT|
+--------------------------------------------------+----+----+
|DRMP TBD1 8.1 Grouped | | V |
+--------------------------------------------------+----+----+
9. IANA Considerations
9.1. AVP codes
New AVPs defined by this specification are listed in Section 8. All
AVP codes are allocated from the 'Authentication, Authorization, and
Accounting (AAA) Parameters' AVP Codes registry.
9.2. New registries
There are no new IANA registries introduced by this document.
Editor's Note: The current assumption is that there is no need to
extend the number of priorities beyond the five defined in this
specification. This assumption needs to be verified. If there is
the need for extensability then a new IANA registry would be
required. This new registry would be established as part of the
standardization effort associated with the definition of new
priority values.
10. Security Considerations
The DRMP could be used to get better access to services. This could
result in one segment of a Diameter network limiting service to
another segment of a Diameter network.
11. Contributors
The following people contributed substantial ideas, feedback, and
discussion to this document:
o Janet P. Gunn
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12. References
12.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226,
May 2008.
[RFC6733] Fajardo, V., Arkko, J., Loughney, J., and G. Zorn,
"Diameter Base Protocol", RFC 6733, October 2012.
12.2. Informative References
[I-D.ietf-dime-ovli]
Korhonen, J., Donovan, S., Campbell, B., and L. Morand,
"Diameter Overload Indication Conveyance", draft-ietf-
dime-ovli-08 (work in progress), February 2015.
[RFC4412] Schulzrinne, H. and J. Polk, "Communications Resource
Priority for the Session Initiation Protocol (SIP)", RFC
4412, February 2006.
[S6a] 3GPP, "Evolved Packet System (EPS); Mobility Management
Entity (MME) and Serving GPRS Support Node (SGSN) related
interfaces based on Diameter protocol", 3GPP TS 29.272
10.8.0, June 2013.
Appendix A. Design Considerations and Questions
This section contains a list of questions that will influence the
design of the DRMP mechanism. It is expected that this section will
be removed once the DRMP mechanism is defined.
A.1. Relationship with SIP Resource Priority
Question 1: Is there value with aligning the Diameter Routing Message
Priority design with the SIP Resource Priority [RFC4412]work?
Current thoughts: SIP Resource Priority is considered to be
addressing a superset of the requirements that DRMP addresses. The
concensus seems to be that there is no need for multiple name spaces
with DRMP.
Question 2: If so, is there value in reusing the existing SIP
Resource Priority name spaces and request handling strategies?
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Current thoughts: Given that the direction for DRMP is to have a
single set of priority values, DRMP will not reuse name spaces.
A.2. Priority Encoding Method
Question 3: Is there a preference for handling DRMP by introducing
AVPs or by using existing bits in the Diameter Command Flags field?
Current thoughts: The advantage of using bits in the Command Flags
field is that it would reduce parsing overhead for elements that need
access to the routing priority information. The question is whether
this optimization in parsing overhead is worth the expense of using
the reserved bits.
There are four bits remaining in the Command Flags header. If this
approach is taken then the expectation would be that three of the
bits would be used, allowing for eight priority levels.
This approach has questionable utility if multiple namespaces are to
be used as the namespace identity would still require an AVP. Once
the requirement for parsing the namespace AVP is introduced the
incremental savings from utilizing the Command Flags would be
minimal.
The current direction is to use AVPs to communicate priority. This
gives the ability to extend the DRMP mechanism if additional
functionality, such as name spaces, is determined to be required.
A.3. Base Protocol versus Application Extension
Question 4: Should DRMP be base protocol behavior or should Diameter
applications be required to explicitly incorporate DRMP behavior?
The direction is to make the behavior generic across all
applications.
A.4. Scope of Priority Setting
Question 5: Which of the following does the DRMP priority apply to:
Messages - meaning that a separate priority can be set for request
messages and answer messages?
Transactions - meaning that the priority set in the request
message also applies to the answer messages?
Request messages - meaning that answer message priority always has
an implied higher priority than all request messages?
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Current thoughts: The consensus is to have the DRMP priority apply to
transactions.
Author's Address
Steve Donovan
Oracle
7460 Warren Parkway
Frisco, Texas 75034
United States
Email: srdonovan@usdonovans.com
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