One document matched: draft-ietf-issll-dclass-00.txt
Y.Bernet, Microsoft
Internet Draft
Document: draft-ietf-issll-dclass-00.txt June, 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.
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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
input.
11. Author's Addresses
Bernet, Yoram
Microsoft
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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