Internet Engineering Task Force (IETF)
Request for Comments: 7660
Category: Standards Track
ISSN: 2070-1721

L. Bertz
S. Manning
Sprint
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

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 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.

   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