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IETF RFC 2997
Specification of the Null Service Type
Last modified on Monday, November 27th, 2000
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Network Working Group Y. Bernet
Request for Comments: 2997 Microsoft
Category: Standards Track A. Smith
Allegro Networks
B. Davie
Cisco Systems
November 2000
Specification of the Null Service Type
 Status of this Memo
This document specifies an Internet standards track protocol for the
Internet community, and requests discussion and suggestions for
improvements. Please refer to the current edition of the "Internet
Official Protocol Standards" (STD 1) for the standardization state
and status of this protocol. Distribution of this memo is unlimited.
Copyright Notice
Copyright © The Internet Society (2000). All Rights Reserved.
Abstract
In the typical Resource Reservation Protocol (RSVP)/Intserv model,
applications request a specific Intserv service type and quantify the
resources required for that service. For certain applications, the
determination of service parameters is best left to the discretion of
the network administrator. For example, ERP applications are often
mission critical and require some form of prioritized service, but
cannot readily specify their resource requirements. To serve such
applications, we introduce the notion of the 'Null Service'. The
Null Service allows applications to identify themselves to network
Quality of Service (QoS) policy agents, using RSVP signaling.
However, it does not require them to specify resource requirements.
QoS policy agents in the network respond by applying QoS policies
appropriate for the application (as determined by the network
administrator). This mode of RSVP usage is particularly applicable
to networks that combine differentiated service (diffserv) QoS
mechanisms with RSVP signaling [intdiff]. In this environment, QoS
policy agents may direct the signaled application's traffic to a
particular diffserv class of service.
Bernet, et al. Standards Track PAGE 1 
RFC 2997 Specification of Null Service Type November 2000
1. Motivation
Using standard RSVP/Intserv signaling, applications running on hosts
issue requests for network resources by communicating the following
information to network devices:
1. A requested service level (Guaranteed or Controlled Load).
2. The quantity of resources required at that service level.
3. Classification information by which the network can recognize
specific traffic (filterspec).
4. Policy/identity information indicating the user and/or the
application for which resources are required.
In response, standard RSVP aware network nodes choose to admit or
deny a resource request. The decision is based on the availability
of resources along the relevant path and on policies. Policies
define the resources that may be granted to specific users and/or
applications. When a resource request is admitted, network nodes
install classifiers that are used to recognize the admitted traffic
and policers that are used to assure that the traffic remains within
the limits of the resources requested.
The Guaranteed and Controlled Load Intserv services are not suitable
for certain applications that are unable to (or choose not to)specify
the resources they require from the network. Diffserv services are
better suited for this type of application. Nodes in a diffserv
network are typically provisioned to classify arriving packets to
some small number of behavior aggregates (BAs) [diffarch]. Traffic
is handled on a per-BA basis. This provisioning tends to be 'top-
down' with respect to end-user traffic flows in the sense that there
is no signaling between hosts and the network. Instead, the network
administrator uses a combination of heuristics, measurement and
experience to provision the network devices to handle aggregated
traffic, with no deterministic knowledge of the volume of traffic
that will arrive at any specific node.
In applying diffserv mechanisms to manage application traffic,
network administrators are faced with two challenges:
1. Provisioning - network administrators need to anticipate the
volume of traffic likely to arrive at each network node for each
diffserv BA. If the volume of traffic arriving is likely to
exceed the capacity available for the BA claimed, the network
administrator has the choice of increasing the capacity for the
BA, reducing the volume of traffic claiming the BA, or
compromising service to all traffic arriving for the BA.
Bernet, et al. Standards Track PAGE 2
RFC 2997 Specification of Null Service Type November 2000
2. Classification - diffserv nodes classify traffic to user and/or
application, based on the diff-serv codepoint (DSCP) in each
packet's IP header or based on other fields in the packet's IP
header (source/destination address/port and protocol). The latter
method of classification is referred to as MF classification.
This method of classification may be unreliable and imposes a
management burden.
By using RSVP signaling, the management of application traffic in
diffserv networks can be significantly facilitated. (Note that
RSVP/diffserv interoperability has been discussed previously in the
context of the Guaranteed and Controlled Load Intserv services.)
This document focuses on RSVP/diffserv interoperability in the
context of the Null Service.
2. Operational Overview
In the proposed mechanism, the RSVP sender offers the new service
type, 'Null Service Type' in the ADSPEC that is included with the
PATH message. A new Tspec corresponding to the new service type is
added to the SENDER_TSPEC. In addition, the RSVP sender will
typically include with the PATH message policy objects identifying
the user, application and sub application ID [identity, application].
(Note that at this time, the new Tspec is defined only to carry the
maximum packet size parameter (M), for the purpose of avoiding
fragmentation. No other parameters are defined.)
Network nodes receiving these PATH messages interpret the service
type to indicate that the application is requesting no specific
service type or quantifiable resources. Instead, network nodes
manage the traffic flow based on the requesting user, the requesting
application and the type of application sub-flow.
This mechanism offers significant advantages over a pure diffserv
network. At the very least, it informs each network node which would
be affected by the traffic flow (and which is interested in
intercepting the signaling) of:
1. The demand for resources in terms of number of flows of a
particular type traversing the node.
2. The binding between classification information and user,
application and sub-application.
Bernet, et al. Standards Track PAGE 3
RFC 2997 Specification of Null Service Type November 2000
This information is particularly useful to policy enforcement points
and policy decision points (PEPs and PDPs). The network
administrator can configure these elements of the policy management
system to apply appropriate policy based on the identity of the user,
the application and the specific sub application ID.
PEPs and PDPs may be configured to return an RSVP RESV message to the
sender. The returned RESV message may include a DCLASS object
[dclass]. The DCLASS object instructs the sender to mark packets on
the corresponding flow with a specific DSCP (or set of DSCPs). This
mechanism allows PEP/PDPs to affect the volume of traffic arriving at
a node for any given BA. It enables the PEP/PDP to do so based on
sophisticated policies.
3.1 Operational Notes
3.1.1 Scalability Issues
In any network in which per-flow signaling is used, it is wise to
consider scalability concerns. The Null Service encourages signaling
for a broader set of applications than that which would otherwise be
signaled for. However, RSVP signaling does not, in general, generate
a significant amount of traffic relative to the actual data traffic
associated with the session. In addition, the Null Service does not
encourage every application to signal. It should be used by
applications that are considered mission critical or needing QoS
management by network administrators.
Perhaps of more concern is the impact on processing resources at
network nodes that process the signaling messages. When considering
this issue, it's important to point out that it is not necessary to
process the signaling messages at each network node. In fact, the
combination of RSVP signaling with diff-serv networks may afford
significant benefits even when the RSVP messages are processed only
at certain key nodes (such as boundaries between network domains,
first-hop routers, PEPs or any subset of these). Individual nodes
should be enabled or disabled for RSVP processing at the discretion
of the network administrator. See [intdiff] for a discussion of the
impact of RSVP signaling on diff-serv networks.
In any case, per-flow state is not necessarily required, even in
nodes that apply per-flow processing.
Bernet, et al. Standards Track PAGE 4
RFC 2997 Specification of Null Service Type November 2000
2.1.2 Policy Enforcement in Legacy Networks
Network nodes that adhere to the RSVP spec should transparently pass
signaling messages for the Null Service. As such, it is possible to
introduce a small number of PEPs that are enabled for Null Service
into a legacy network and to realize the benefits described in this
document.
2.1.3 Combining Existing Intserv Services with the Null Service
This document does not preclude applications from offering both a
quantitative Intserv service (Guaranteed or Controlled Load)and the
Null Service, at the same time. An example of such an application
would be a telephony application that benefits from the Guaranteed
Service but is able to adapt to a less strict service. By
advertising its support for both, the application enables network
policy to decide which service type to provide.
3. Signaling Details
3.1 ADSPEC Generation
The RSVP sender constructs an initial RSVP ADSPEC object specifying
the Null Service Type. Since there are no service specific
parameters associated with this service type, the associated ADSPEC
fragment is empty and contains only the header word. Network nodes
may or may not supply valid values for bandwidth and latency general
parameters. As such, they may use the unknown values defined in
[RFC 2216].
The ADSPEC is added to the RSVP PATH message created at the sender.
3.2 RSVP SENDER_TSPEC Object
An additional Tspec is defined to correspond to the Null Service. If
only the Null Service is offered in the ADSPEC, then this is the only
Tspec included in the SENDER_TSPEC object. If guaranteed or
controlled load services are also offered in the ADSPEC, then the new
Tspec is appended following the standard Intserv token-bucket Tspec
[RFC 2210].
3.3 RSVP FLOWSPEC Object
Receivers may respond to PATH messages by generating an RSVP RESV
message including a FLOWSPEC object. The FLOWSPEC object should
specify that it is requesting the Null Service. It is possible that,
in the future, a specific Rspec may be defined to correspond to the
new service type.
Bernet, et al. Standards Track PAGE 5
RFC 2997 Specification of Null Service Type November 2000
4. Detailed Message Formats
4.1 Standard ADSPEC Format
A standard RSVP ADSPEC object is described in [RFC 2210]. It includes
a message header and a default general parameters fragment.
Following the default general parameters fragment are fragments for
each supported service type.
4.2 ADSPEC for Null Service Type
The Null Service ADSPEC includes the message header and the default
general parameters fragment, followed by a single fragment denoting
the Null Service. The new fragment introduced for the Null Service
is formatted as follows:
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 6 (a) |x| Reserved | 0 (b) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
a - indicates Null Service (6).
x - is the break-bit.
b - indicates zero words in addition to the header.
Bernet, et al. Standards Track PAGE 6
RFC 2997 Specification of Null Service Type November 2000
A complete ADSPEC supporting only the Null Service is illustrated
below:
31 24 23 16 15 8 7
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1 | 0 (a) | Reserved | Msg length -1 (b) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2 | 1 (c) |x| Reserved | 8 (d) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
3 | 4 (e) | (f) | 1 (g) |
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
4 | IS hop cnt (32-bit unsigned) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
5 | 6 (h) | (i) | 1 (j) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
6 | Path b/w estimate (32-bit IEEE floating point number) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
7 | 8 (k) | (l) | 1 (m) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
8 | Minimum path latency (32-bit integer) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
9 | 10 (n) | (o) | 1 (p) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
10 | Composed MTU (32-bit unsigned) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
11 | 6 (q) |x| Reserved | 0 (r) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Word 1: Message Header:
(a) - Message header and version number
(b) - Message length (10 words not including header)
Words 2-10: Default general characterization parameters
(c) - Per-Service header, service number 1 (Default General
Parameters)
(x) - Global Break bit (NON_IS_HOP general parameter 2)
(d) - Length of General Parameters data block (8 words)
(e) - Parameter ID, parameter 4 (NUMBER_OF_IS_HOPS general
parameter)
(f) - Parameter 4 flag byte
(g) - Parameter 4 length, 1 word not including header
(h) - Parameter ID, parameter 6 (AVAILABLE_PATH_BANDWIDTH general
parameter)
(i) - Parameter 6 flag byte
(j) - Parameter 6 length, 1 word not including header
(k) - Parameter ID, parameter 8 (MINIMUM_PATH_LATENCY general
parameter)
(l) - Parameter 8 flag byte
Bernet, et al. Standards Track PAGE 7
RFC 2997 Specification of Null Service Type November 2000
(m) - Parameter 8 length, 1 word not including header
(n) - Parameter ID, parameter 10 (PATH_MTU general parameter)
(o) - Parameter 10 flag byte
(p) - Parameter 10 length, 1 word not including header
Word 11: Null Service parameters
(q) - Per-Service header, service number 6 (Null)
(x) - Break bit for Null Service
(r) - Length (0) of per-service data not including header word.
Note that the standard rules for parsing ADSPEC service fragments
ensure that the ADSPEC will not be rejected by legacy network
elements. Specifically, these rules state that a network element
encountering a per-service data header which it does not understand
should set bit 23 (the break-bit) to indicate that the service is not
supported and should use the length field from the header to skip
over the rest of the fragment.
Also note that it is likely that it will not be possible for hosts or
network nodes to generate meaningful values for words 5 and/or 7
(bandwidth estimates and path latency), due to the nature of the
service. In this case, the unknown values from [RFC 2216] should be
used.
4.3 SENDER_TSPEC Object Format
The following Tspec is defined to correspond to the Null Service:
31 24 23 16 15 8 7
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1 | 6 (a) |0| Reserved | 2 (b) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2 | 128 (c) | 0 (d) | 1 (e) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
3 | Maximum Packet Size [M] (32-bit integer) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Word 1: Service header
(a) - Service number 6 (Null Service)
(b) - Length of per-service data, 2 words not including per-service
header
Word 2-3: Parameter
(c) - Parameter ID, parameter 128 (Null Service TSpec)
(d) - Parameter 128 flags (none set)
(e) - Parameter 128 length, 1 words not including parameter header
Bernet, et al. Standards Track PAGE 8
RFC 2997 Specification of Null Service Type November 2000
Note that the illustration above does not include the standard RSVP
SENDER_TSPEC object header, nor does it include the sub-object header
(which indicates the message format version number and length),
defined in RFC 2205 and RFC 2210, respectively.
In the case that only the Null Service is advertised in the ADSPEC,
the Tspec above would be appended immediately after the SENDER_TSPEC
object header and sub-object header. In the case that additional
service types are advertised, requiring the token bucket specific
Tspec defined in RFC 2210, the Tspec above would be appended following
the token bucket Tspec, which would in turn follow the object header
and sub-object header.
4.4 FLOWSPEC Object Format
The format of an RSVP FLOWSPEC object originating at a receiver
requesting the Null Service is shown below. The value of 6 in the
per-service header (field (c), below) indicates that Null Service is
being requested.
31 24 23 16 15 8 7
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
1 | 0 (a) | reserved | 3 (b) |
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
2 | 6 (c) |0| Reserved | 2 (d) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
3 | 128 (e) | 0 (f) | 1 (g) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
4 | Maximum Packet Size [M] (32-bit integer) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
(a) - Message format version number (0)
(b) - Overall length (3 words not including header)
(c) - Service header, service number 6 (Null)
(d) - Length of data, 2 words not including per-service header
(e) - Parameter ID, parameter 128 (Null Service TSpec)
(f) - Parameter 128 flags (none set)
(g) - Parameter 128 length, 1 words not including parameter header
4.5 DCLASS Object Format
DCLASS objects may be included in RESV messages. For details
regarding the DCLASS object format, see [dclass].
5. Security Considerations
The message formatting and usage rules described in this note raise
no new security issues beyond standard RSVP.
Bernet, et al. Standards Track PAGE 9
RFC 2997 Specification of Null Service Type November 2000
6. References
[RFC 2205] Braden, R., Zhang, L., Berson, S., Herzog, S. and S.
Jamin, "Resource Reservation Protocol (RSVP) - Version
1 Functional Specification", RFC 2205, September 1997.
[RFC 2216] Shenker, S. and J. Wroclawski, "Network Element QoS
Control Service Specification Template", RFC 2216,
September 1997.
[RFC 2210] Wroclawski, J., "The Use of RSVP with IETF Integrated
Services", RFC 2210, September 1997.
[intdiff] Bernet, Y., Yavatkar, R., Ford, P., Baker, F., Zhang,
L., Nichols, K., Speer, M., Braden, B. and B. Davie, "A
Framework for Integrated Services Operation over
Diffserv Networks", RFC 2998, November 2000.
[diffarch] Blake, S., Black, D., Carlson, M., Davies, E., Wang, Z.
and W. Weiss, "An Architecture for Differentiated
Services", RFC 2475, December 1998.
[identity] Yadav, S., Yavatkar, R., Pabbati, R., Ford, P., Moore,
T., Herzog, S., "Identity Representation for RSVP", RFC
2752, January 2000.
[application] Bernet, Y., "Application and Sub Application Identity
Policy Objects for Use with RSVP", RFC 2872, June 2000.
[dclass] Bernet, Y., "Format of the RSVP DCLASS Object", RFC
2996, November 2000.
7. Acknowledgments
We thank Fred Baker, Dinesh Dutt, Nitsan Elfassy, John Schnizlein,
Ramesh Pabbati and Sanjay Kaniyar for their comments on this memo.
Bernet, et al. Standards Track PAGE 10
RFC 2997 Specification of Null Service Type November 2000
8. Authors' Addresses
Yoram Bernet
Microsoft
One Microsoft Way
Redmond, WA 98052
Phone: +1 (425) 936-9568
EMail: Yoramb@microsoft.com
Andrew Smith
Allegro Networks
6399 San Ignacio Ave.
San Jose, CA 95119, USA
FAX: +1 415 345 1827
Email: andrew@allegronetworks.com
Bruce Davie
Cisco Systems
250 Apollo Drive
Chelmsford, MA 01824
Phone: +1 (978)-244-8000
EMail: bsd@cisco.com
Bernet, et al. Standards Track PAGE 11
RFC 2997 Specification of Null Service Type November 2000
9. Full Copyright Statement
Copyright © The Internet Society (2000). All Rights Reserved.
This document and translations of it may be copied and furnished to
others, and derivative works that comment on or otherwise explain it
or assist in its implementation may be prepared, copied, published
and distributed, in whole or in part, without restriction of any
kind, provided that the above copyright notice and this paragraph are
included on all such copies and derivative works. However, this
document itself may not be modified in any way, such as by removing
the copyright notice or references to the Internet Society or other
Internet organizations, except as needed for the purpose of
developing Internet standards in which case the procedures for
copyrights defined in the Internet Standards process must be
followed, or as required to translate it into languages other than
English.
The limited permissions granted above are perpetual and will not be
revoked by the Internet Society or its successors or assigns.
This document and the information contained herein is provided on an
"AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Acknowledgement
Funding for the RFC Editor function is currently provided by the
Internet Society.
Bernet, et al. Standards Track PAGE 12
Specification of the Null Service Type
RFC TOTAL SIZE: 25071 bytes
PUBLICATION DATE: Monday, November 27th, 2000
LEGAL RIGHTS: The IETF Trust (see BCP 78)
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