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Versions: 00 01 rfc2996                                                 
                                                        Y.Bernet, Microsoft
Internet Draft
Document: draft-ietf-issll-dclass-00.txt                   August, 1999

       Usage and Format of the DCLASS Object With RSVP Signaling

Status of this Memo

   This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of RFC2026.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups. Note that
   other groups may also distribute working documents as Internet-

   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."

   The list of current Internet-Drafts can be accessed at
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   Distribution of this memo is unlimited.

   Copyright Notice

   Copyright (C) The Internet Society (1998). All Rights Reserved.

1. Abstract

   RSVP signaling may be used to enhance the manageability of
   application traffic's QoS in a differentiated service (diff-serv)
   network [intdiff]. In this model, certain network elements within or
   at the edges of the diff-serv network may use RSVP messages to
   effect admission control or to apply QoS policy. One mechanism by
   which network elements may apply QoS policy is by causing a DCLASS
   object to be returned to a sending host in an RSVP RESV message. The
   DCLASS object indicates one or more diff-serv codepoints (DSCPs)
   that the sender should include when submitting packets on the
   admitted flow, to the diff-serv network. This draft describes the
   usage and format of the DCLASS object.

3. Signaling Protocol

   This section describes the mechanics of using RSVP signaling and the
   DCLASS object for effecting admission control and applying QoS
   policy within a diff-serv network. It assumes a standard RSVP sender

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   and a diff-serv network somewhere in the path between sender and
   receiver. At least one RSVP aware network element resides in the
   diff-serv network. This network element may be a policy enforcement
   point (PEP) associated with a PDP, or may simply act as an admission
   control agent, admitting or denying resource requests based
   exclusively on the availability of resources. The network element is
   typically a router and will be considered to be so for the purpose
   of this draft.

   The sender composes a standard RSVP PATH message and sends it
   towards the receiver on the remote end of the diff-serv network. The
   PATH message traverses one or more network elements that are PEPs
   and/or admission control agents for the diff-serv network. These
   elements install appropriate state and forward the PATH message
   towards the receiver. If admission control is successful downstream
   of the diff-serv network, then a RESV message will arrive from the
   direction of the receiver. As this message arrives at the PEPs
   and/or admission control agents that are RSVP enabled, each of these
   network elements must make a decision regarding the admissibility of
   the signaled flow to the diff-serv network.

   If the network element determines that the request represented by
   the PATH and RESV messages is admissible to the diff-serv network,
   it must decide which diff-serv service level (or behaviour
   aggregate) is appropriate for the traffic represented in the RSVP
   request. It then adds a DCLASS object containing one or more DSCPs
   corresponding to the behaviour aggregate, to the RESV message. The
   RESV message is then sent upstream towards the RSVP sender.

   If the network element determines that the RSVP request is not
   admissible to the diff-serv network, it sends a RESV error message
   towards the receiver. No DCLASS is required.

   Note that a network element may terminate RSVP signaling, in which
   case it effectively provides admission control to all regions of the
   network downstream (including the receiver). In this case, no actual
   RESV message will arrive from the receiver. Instead, the network
   element may act as a proxy, composing the RESV message on behalf of
   the downstream nodes.

4. Format of the DCLASS Object

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   The DCLASS object has the following format:

               0              1               2               3


      |         Length (>= 8)         | C-Num (225)   |       1       |


      |         Unused                                | 1st DSCP  |   |


      |         Unused                                | 2nd DSCP  |   |


      |         Unused                                | . . . .   |   |


   The first word contains the standard RSVP object header (the Class
   Num for the DCLASS object is 225). The length field indicates the
   total object length in bytes. The object header is followed by one
   or more 32-bit words, each containing a DSCP in the six high-order
   bits of the least significant byte. The length field in the object
   header indicates the number of DSCPs included in the object.

   The network may return multiple DSCPs in the DCLASS object in order
   to enable the host to discriminate sub-flows within a behaviour
   aggregate. For example, in the case of the AF PHB group [AF], the
   network may return the DSCPs 001010, 001100, and 001110
   corresponding to increasing levels of drop precedence within Class 1
   of the AF PHB group. Note that this draft makes no statements
   regarding the significance of the order of the returned DSCPs.
   Further interpretation of DSCP sets is dependent on the specific
   service requested by the host and is beyond the scope of this draft.

   Note that the Class-Num for the DCLASS object is chosen from the
   space of unknown class objects that should be ignored and forwarded
   by nodes that do not recognize it. This is to assure maximal
   backward compatibility.

5. Admission Control Functionality

   From a black-box perspective, admission control and policy
   functionality amounts to the decision whether to accept or reject a
   request and the determination of the DSCPs that should be used for
   the corresponding traffic. The specific details of admission control
   are beyond the scope of this document. In general the admission
   control decision is based both on resource availability and on
   policies regarding the use of resources in the diff-serv network.
   The admission control decision made by RSVP aware network elements
   represents both considerations.

   In order to decide whether the RSVP request is admissible in terms
   of resource availability, one or more network elements within or at
   the boundary of the diff-serv network must understand the impact
   that admission would have on specific diff-serv resources, as well

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   as the availability of these resources along the relevant data path
   in the diff-serv network.

   In order to decide whether the RSVP request is admissible in terms
   of policy, the network element may use identity objects describing
   users and/or applications that may be included in the request. The
   router may act as a PEP/PDP and use data from a policy database or
   directory to aid in this decision.

   See Appendix A for a simple mechanism for configurable resource
   based admission control.

8. Security Considerations

   There are no security considerations beyond those of standard RSVP.

9. References

   [INTDIFF], Bernet, Y., Yavatkar, R., Ford, P., Baker, F., Zhang, L.,
   Speer, M., Braden, R., Davie, B., "Integrated Services Operation
   over Diffserv Networks", Internet Draft, June 1999

   [AF], Heinanen, J., Baker, F., Weiss, W., Wroclawski, J., "Assured
   Forwarding PHB Group", RFC 2597, June 1999

10.  Acknowledgments

   Thanks to Fred Baker and Carol Iturralde for reviewing this draft.
   Thanks to Ramesh Pabbati, Tim Moore, Bruce Davie and Kam Lee for

11. Author's Addresses

   Bernet, Yoram
   One Microsoft Way,
   Redmond, WA 98052
   Phone: (425) 936-9568
   Email: yoramb@microsoft.com

Appendix A - Simple Configurable Resource Based Admission Control

   Routers may use quite sophisticated mechanisms in making the
   admission control decision, including policy considerations, various
   intra-domain signaling protocols, results of traffic monitoring and
   so on. It is recommended that the following basic functionality be
   provided to enable simple resource based admission control in the
   absence of more sophisticated mechanisms. This functionality can be
   used with configurable, standalone routers. It applies to standard
   RSVP/Intserv requests. This minimal functionality assumes only a
   single DSCP is included in the DCLASS object, but may readily be
   extended to support multiple DSCPs.

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   It must be possible to configure two tables in the router. These are
   described below.

A.1 Service Type to DSCP Mapping

   One table provides a mapping from the intserv service-type specified
   in the RSVP request to a DSCP that can be used to obtain a
   corresponding service in the diff-serv network. This table contains
   a row for each intserv service type for which a mapping is
   available. Each row has the following format:

   Intserv service type : DSCP

   The table would typically contain at least three rows; one for
   Guaranteed service, one for Controlled Load service and one for
   Best-Effort service. (The best-effort service will typically map to
   DSCP 000000, but may be overridden). It should be possible to add
   rows for as-yet-undefined service types.

   This table allows the network administrator to statically configure
   a DSCP that the router will return in the DCLASS object for an
   admitted RSVP request. In general, more sophisticated and likely
   more dynamic mechanisms may be used to determine the DSCP to be
   returned in the DCLASS object. In this case, these mechanisms may
   override the static table based mapping.

A.2 Quantitative Resource Availability

   Standard intserv requests are quantitative in nature. They include
   token bucket parameters describing the resources required by the
   traffic for which admission is requested. The second table enables
   the network administrator to statically configure quantitative
   parameters to be used by the router when making an admission control
   decision for quantitative service requests. Each row in this table
   has the following form:

   DSCP : Token bucket profile

   The first column specifies those DSCPs for which quantitative
   admission control is applied. The second column specifies the token
   bucket parameters which represent the total resources available in
   the diff-serv network to accommodate traffic in the service class
   specified by the DSCP.

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