Diameter ECN Attrs: Diameter Congestion and Filter Attributes
Four new Diameter attributes for matching ECN-marked traffic, reacting to congestion and counting flows and packets.
Bertz, L., Manning, S., and B. Hirschman, "Diameter Congestion and Filter Attributes", RFC 7660, DOI 10.17487/RFC7660, October 2015, <https://www.rfc-editor.org/info/rfc7660>.
@misc{rfc7660,
series = {Request for Comments},
number = 7660,
howpublished = {RFC 7660},
publisher = {RFC Editor},
doi = {10.17487/RFC7660},
url = {https://www.rfc-editor.org/info/rfc7660},
author = {L. Bertz and S. Manning and B. Hirschman},
title = {{Diameter Congestion and Filter Attributes}},
pagetotal = 9,
year = 2015,
month = oct,
} RFC text
Contents
Internet Engineering Task Force (IETF) L. Bertz
Request for Comments: 7660 S. Manning
Category: Standards Track Sprint
ISSN: 2070-1721 B. Hirschman
October 2015
Diameter Congestion and Filter Attributes
Abstract
This document defines optional Diameter attributes that can be used
to help manage networks that use Explicit Congestion Notification
(ECN) or Diameter traffic filters. These new attributes allow for
improved data traffic identification, support of ECN, and minimal
Diameter filter administration.
RFC 5777 defines a Filter-Rule Attribute Value Pair (AVP) that
accommodates extensions for classification, conditions, and actions.
It, however, does not support traffic identification for packets
using Explicit Congestion Notification as defined in RFC 3168 and
does not provide specific actions when the flow(s) described by the
Filter-Rule are congested.
Further, a Filter-Rule can describe multiple flows but not the exact
number of flows. Flow count and other associated data (e.g.,
packets) are not captured by accounting applications, leaving
administrators without useful information regarding the effectiveness
or appropriateness of the filter definition.
The optional attributes defined in this document are forward and
backwards compatible with RFC 5777.
Status of This Memo
This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 5741.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc7660.
Copyright Notice
Copyright (c) 2015 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
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
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the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. ECN-IP-Codepoint, Congestion-Treatment and Filter Attributes . 4
3.1. ECN-IP-Codepoint AVP . . . . . . . . . . . . . . . . . . . 4
3.2. Congestion-Treatment AVP . . . . . . . . . . . . . . . . . 4
3.3. Flow-Count AVP . . . . . . . . . . . . . . . . . . . . . . 5
3.4. Packet-Count AVP . . . . . . . . . . . . . . . . . . . . . 5
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
4.1. AVP Codes . . . . . . . . . . . . . . . . . . . . . . . . 5
5. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
5.1. Classifier Example . . . . . . . . . . . . . . . . . . . . 6
5.2. Diameter Credit Control (CC) with Congestion Information . 6
6. Security Considerations . . . . . . . . . . . . . . . . . . . 8
7. Normative References . . . . . . . . . . . . . . . . . . . . . 8
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 9
1. Introduction
Two optional AVPs related to Explicit Congestion Notification (ECN)
[RFC3168] are specified in this document. The first AVP provides
direct support for filtering ECN-marked traffic [RFC3168] and the
second AVP provides the ability to define alternate traffic treatment
when congestion is experienced.
This document also defines two optional AVPs, Flow-Count and Packet-
Count, used for conveying flow information within the Diameter
protocol [RFC6733]. These AVPs were found to be useful for a wide
range of applications. The AVPs provide a way to convey information
of the group of flows described by the Filter-Rule, IPFilterRule, or
other Diameter traffic filters.
The semantics and encoding of all AVPs can be found in Section 3.
Such AVPs are, for example, needed by some congestion-management
functions to determine the number of flows congested or used by
administrators to determine the impact of filter definitions.
Additional parameters may be defined in future documents as the need
arises. All parameters are defined as Diameter-encoded Attribute
Value Pairs (AVPs), which are described using a modified version of
the Augmented Backus-Naur Form (ABNF), see [RFC6733]. The data types
are also taken from [RFC6733].
2. Terminology
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 RFC2119 [RFC2119].
3. ECN-IP-Codepoint, Congestion-Treatment, and Filter Attributes
3.1. ECN-IP-Codepoint AVP
The ECN-IP-Codepoint AVP (AVP Code 628) is of type Enumerated and
specifies the ECN codepoint values to match in the IP header.
Value | Binary | Keyword | References
-----------------------------------------------------------------
0 | 00 | Not-ECT (Not ECN-Capable Transport)| [RFC3168]
1 | 01 | ECT(1) (ECN-Capable Transport) | [RFC3168]
2 | 10 | ECT(0) (ECN-Capable Transport) | [RFC3168]
3 | 11 | CE (Congestion Experienced) | [RFC3168]
When this AVP is used for classification in the Filter-Rule, it MUST
be part of the Classifier Grouped AVP as defined in RFC 5777.
3.2. Congestion-Treatment AVP
The Congestion-Treatment AVP (AVP Code 629) is of type Grouped. It
indicates how to treat traffic IP (5-tuple) flow(s) when congestion
is detected. The detection of congestion can be based on the
reception of IP packets with the Congestion Experience (CE) codepoint
set (see [RFC3168]) or by any other administratively defined
criteria.
A Filter-Rule may contain a Classifier that describes one or many
5-tuples per RFC 5777. This treatment applies to all packets
associated to all 5-tuples (flows) captured by the Filter-Rule.
If the Congestion-Treatment AVP is absent, the treatment of the
congested traffic is left to the discretion of the node performing
quality-of-service (QoS) treatment.
Congestion-Treatment ::= < AVP Header: 629 >
{ Treatment-Action }
[ QoS-Profile-Template ]
[ QoS-Parameters ]
* [ AVP ]
Treatment-Action, QoS-Profile-Template, and QoS-Parameters are
defined in RFC 5777. The Congestion-Treatment AVP is an action and
MUST be an attribute of the Filter-Rule Grouped AVP as defined in RFC
5777.
3.3. Flow-Count AVP
The Flow-Count AVP (AVP Code 630) is of type Unsigned64.
It indicates the number of protocol-specific flows. The protocol is
determined by the filter (e.g., IPFilterRule, Filter-Id, etc.).
3.4. Packet-Count AVP
The Packet-Count AVP (AVP Code 631) is of type Unsigned64.
It indicates the number of protocol-specific packets. The protocol
is determined by the filter (e.g., IPFilterRule, Filter-Id, etc.).
4. IANA Considerations
4.1. AVP Codes
IANA allocated AVP codes in the IANA-controlled namespace registry
specified in Section 11.1.1 of [RFC6733] for the following AVPs that
are defined in this document.
+------------------------------------------------------------------+
| AVP Section |
|AVP Code Defined Data Type |
+------------------------------------------------------------------+
|ECN-IP-Codepoint 628 3.1 Enumerated |
|Congestion-Treatment 629 3.2 Grouped |
|Flow-Count 630 3.3 Unsigned64 |
|Packet-Count 631 3.4 Unsigned64 |
+------------------------------------------------------------------+
5. Examples
The following examples illustrate the use of the AVPs defined in this
document.
5.1. Classifier Example
The Classifier AVP (AVP Code 511) specified in RFC 5777 is a grouped
AVP that consists of a set of attributes that specify how to match a
packet. The addition of the ECN-IP-Codepoint is shown here.
Classifier ::= < AVP Header: 511 >
{ Classifier-ID }
[ Protocol ]
[ Direction ]
[ ECN-IP-Codepoint ]
* [ From-Spec ]
* [ To-Spec ]
* [ Diffserv-Code-Point ]
[ Fragmentation-Flag ]
* [ IP-Option ]
* [ TCP-Option ]
[ TCP-Flags ]
* [ ICMP-Type ]
* [ ETH-Option ]
* [ AVP ]
Setting the ECN-IP-Codepoint value to 'CE' would permit the capture
of CE flags in the Flow.
Another Classifier with the ECN-IP-Codepoint value of 'ECT' could be
specified and, when coupled with the Flow-Count AVP, reports the
number of ECT-capable flows.
5.2. Diameter Credit Control (CC) with Congestion Information
Diameter nodes using Credit Control can use the Congestion-Treatment
AVP to trigger specific actions when congestion occurs. This is
similar to the Excess-Treatment Action. The ability to detect when
congestion occurs is specific to the AVPs in the Filter-Rule and
Diameter Client and is no different than how 'Excess' can be
determined for Excess-Treatment. If conditions associated with
Excess-Treatment [RFC5777] or Congestion-Treatment have occurred,
Diameter Clients may autonomously send Credit-Control Requests (CCRs)
during the Service Delivery session as interim events. This is shown
in Figure 1.
Service Element
End User (CC Client) CC Server
| | |
|(1) Service Request | |
|-------------------->| |
| |(2) CCR (Initial, |
| | QoS-Resources(QoS-Desired)) |
| |--------------------------------->|
| |(3) CCA (Granted-Units, |
| | QoS-Resources(QoS-Authorized))|
| |<---------------------------------|
|(4) Service Delivery | |
|<------------------->| |
| (5) Congestion Detected |
| (6) Congestion Treatment Occurs |
| |(7) CCR (Termination, Used-Units, |
| | Flow-Count, Packet-Count, |
| | QoS-Resources(QoS-Delivered)) |
| |--------------------------------->|
| |(8) CCA |
| |<-------------------------------->|
| | |
| | |
|(9) End of Service | |
|-------------------->| |
| |(10)CCR (Termination, Used-Units, |
| | Flow-Count, Packet-Count, |
| | QoS-Resources(QoS-Delivered)) |
| |--------------------------------->|
| |(11) CCA |
| |<---------------------------------|
Figure 1: Example of a Diameter Credit Control with
Congestion Information
The 'Used-Service-Units' described in RFC 5777 examples is
customarily a Service-Units, Time-Units, or Byte-Count AVP. This is
insufficient to represent network state and does not differentiate
between throughput and good-put (good or quality throughput) even
though the filters may imply good or poor throughput.
Flow-Count and Packet-Count AVPs defined in this document could be
sent with a CCR when the triggering event is related to Congestion-
Treatment. This provides the CC Server with a better view of the
type of congested traffic for improved decision making and charging.
Sending such AVPs under any condition permits rudimentary traffic
profiling regardless of network conditions. For instance, low byte
counts per packet is indicative of web traffic and high byte counts
per packet with a small number of flows may be indicative of video
traffic. Enriched reporting described here provides relief from Deep
Packet Inspection load and loss of information as traffic becomes
increasingly encrypted.
Some services, e.g., streaming services, limit the number of flows,
Flow-Count, as opposed to other units, i.e. Byte-Count. In such a
case, the Flow-Count AVP may be used in place of Service-Units.
6. Security Considerations
This document describes an extension of RFC 5777 that introduces a
new filter parameter applied to ECN as defined by [RFC3168]. It also
defines a new Grouped AVP that expresses what action to take should
congestion be detected. The Grouped AVP reuses attributes defined in
RFC 5777. As these are extensions to RFC 5777, they do not raise new
security concerns.
The Flow-Count and Packet-Count AVPs can be provided in conjunction
with customary AVPs, e.g., Bytes, Time, Service units, during
accounting activities as described in the base protocol [RFC6733] or
other Diameter applications. These new AVPs provide more information
that can be privacy sensitive. The privacy sensitivity is directly
related to traffic captured by filters and associated reports.
Narrow filtering, which creates the highest level of privacy
sensitivity, is too resource intensive to be widely applied on large
networks. Paradoxically, improving reporting information lessens the
depth of inspection required to characterize traffic for many
congestion management activities as noted in Section 5.2.
If an administrator can provide congestion actions without the need
to report them to a Diameter application, they should use the
Congestion-Treatment AVP, which also reduces Diameter traffic during
congestion events.
The Security Considerations of the Diameter protocol itself have been
discussed in RFC 6733 [RFC6733]. Use of the AVPs defined in this
document MUST take into consideration the security issues and
requirements of the Diameter base protocol.
7. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
[RFC3168] Ramakrishnan, K., Floyd, S., and D. Black, "The Addition
of Explicit Congestion Notification (ECN) to IP",
RFC 3168, DOI 10.17487/RFC3168, September 2001,
<http://www.rfc-editor.org/info/rfc3168>.
[RFC6733] Fajardo, V., Ed., Arkko, J., Loughney, J., and G. Zorn,
Ed., "Diameter Base Protocol", RFC 6733,
DOI 10.17487/RFC6733, October 2012,
<http://www.rfc-editor.org/info/rfc6733>.
[RFC5777] Korhonen, J., Tschofenig, H., Arumaithurai, M., Jones, M.,
Ed., and A. Lior, "Traffic Classification and Quality of
Service (QoS) Attributes for Diameter", RFC 5777,
DOI 10.17487/RFC5777, February 2010,
<http://www.rfc-editor.org/info/rfc5777>.
Acknowledgements
We would like to thank Avi Lior for his guidance and feedback during
the development of this specification.
Authors' Addresses
Lyle Bertz
Sprint
6220 Sprint Parkway
Overland Park, KS 66251
United States
Email: lyleb551144@gmail.com
Serge Manning
Sprint
6220 Sprint Parkway
Overland Park, KS 66251
United States
Email: sergem913@gmail.com
Brent Hirschman
Email: Brent.Hirschman@gmail.com
AI ELI5
On this page
§1The Gap in Diameter Filters
Diameter is the base protocol in RFC 6733, and RFC 5777 defines the Filter-Rule AVP, which can carry classification, conditions and actions. RFC 7660 points out three gaps. Filter-Rule cannot identify packets that use Explicit Congestion Notification (RFC 3168), gives no specific action when the described flows are congested, and can describe many flows without saying how many there are. Flow counts and related data such as packets are not captured by accounting applications, so administrators lack information about how effective a filter is.
The document adds four optional AVPs to fill these gaps. Two relate to ECN: one matches ECN-marked traffic and the other defines alternate treatment under congestion. Two, Flow-Count and Packet-Count, convey information about the group of flows a filter describes. All are Diameter AVPs written in the modified ABNF of RFC 6733.
The old rules could not tell warning-flagged cars apart, did not say what to do in a jam, and could not count cars. These new labels fix all three.
§3ECN-IP-Codepoint and Congestion-Treatment
The ECN-IP-Codepoint AVP (code 628, type Enumerated) names the ECN codepoint to match in the IP header. When used for classification in a Filter-Rule it MUST be part of the Classifier grouped AVP from RFC 5777.
The Congestion-Treatment AVP (code 629, type Grouped) says how to treat IP 5-tuple flows when congestion is detected. Detection can be based on packets with the Congestion Experienced (CE) codepoint set, or on any other administratively defined criteria. It applies to all packets of all 5-tuples captured by the Filter-Rule. If the AVP is absent, the treatment of congested traffic is left to the discretion of the node doing quality-of-service treatment.
It contains a required Treatment-Action, an optional QoS-Profile-Template and optional QoS-Parameters, all defined in RFC 5777. Because it is an action, it MUST be an attribute of the Filter-Rule grouped AVP.
One label says which warning flag a car has. The other says what to do with those cars when the road gets jammed. If nobody says, the traffic cop decides.
- 0 (00)Not-ECT — Not ECN-Capable Transport.
- 1 (01)ECT(1) — ECN-Capable Transport.
- 2 (10)ECT(0) — ECN-Capable Transport.
- 3 (11)CE — Congestion Experienced.
§4Flow-Count and Packet-Count
Flow-Count (code 630) and Packet-Count (code 631) are both of type Unsigned64. They give the number of protocol-specific flows or packets, where the protocol is determined by the filter, for example an IPFilterRule or a Filter-Id.
They describe the group of flows a Filter-Rule, IPFilterRule or other Diameter traffic filter covers. Congestion-management functions can use them to learn how many flows are congested, and administrators can use them to judge the impact of a filter definition.
One counter says how many separate trips happened and the other says how many cars drove by, for whatever group of traffic a rule covers.
§5Examples and Credit Control Use
In the Classifier example, ECN-IP-Codepoint is added as an optional member of the RFC 5777 Classifier AVP (code 511). Setting it to CE captures the CE flags in the flow. A second Classifier with the value ECT, combined with Flow-Count, reports the number of ECT-capable flows.
In Diameter Credit Control, a node can use Congestion-Treatment to trigger actions when congestion occurs, similar to the Excess-Treatment action. If either has occurred, Diameter clients may autonomously send Credit-Control Requests during the service session as interim events. Flow-Count and Packet-Count can ride in the CCR, giving the credit control server a better view of the congested traffic for decisions and charging.
The RFC adds that sending these AVPs under any condition permits rudimentary traffic profiling: low byte counts per packet indicate web traffic, and high byte counts per packet with few flows may indicate video. It states this reporting relieves Deep Packet Inspection load as traffic becomes more encrypted. Where a service limits the number of flows rather than bytes, Flow-Count may be used in place of Service-Units.
A shop that sells by the trip rather than by the pound can count trips. And just by seeing a few big trucks or lots of little cars, you can guess what kind of traffic it is without opening any boxes.
- Service Request
- CCR (Initial)Carries QoS-Resources(QoS-Desired).
- CCAGranted-Units and QoS-Authorized.
- CCR (Termination)After congestion is detected and treated: Used-Units, Flow-Count, Packet-Count.
- CCA
§6AVP Codes
IANA allocated the four codes in the AVP namespace registry defined in Section 11.1.1 of RFC 6733. They are ECN-IP-Codepoint 628 (Enumerated), Congestion-Treatment 629 (Grouped), Flow-Count 630 (Unsigned64) and Packet-Count 631 (Unsigned64).
Each new label gets its own official number so everyone uses the same one.
§7Security and Privacy
The RFC says the new filter parameter and the Congestion-Treatment AVP are extensions of RFC 5777 that reuse its attributes, so they do not raise new security concerns. Use of the AVPs MUST take into account the security issues and requirements of the Diameter base protocol.
Flow-Count and Packet-Count provide more information that can be privacy sensitive, in proportion to the traffic captured by filters and reports. Narrow filtering gives the highest sensitivity but is too resource intensive for large networks. If an administrator can apply congestion actions without reporting them to a Diameter application, they should use Congestion-Treatment, which also reduces Diameter traffic during congestion.
Counting more things tells people a little more about what is going on, so be careful who sees the counts.