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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 (C) The Internet Society (2000).  All Rights Reserved.


 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

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
 The ADSPEC is added to the RSVP PATH message created at the sender.


 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


 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 [RFC2210].  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
    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
  (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
  (f) - Parameter 4 flag byte
  (g) - Parameter 4 length, 1 word not including header
  (h) - Parameter ID, parameter 6 (AVAILABLE_PATH_BANDWIDTH general
  (i) - Parameter 6 flag byte
  (j) - Parameter 6 length, 1 word not including header
  (k) - Parameter ID, parameter 8 (MINIMUM_PATH_LATENCY general
  (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 [RFC2216] should be

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
  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 RFC2210, 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

 [RFC2205]     Braden, R., Zhang, L., Berson, S., Herzog, S. and S.
               Jamin, "Resource Reservation Protocol (RSVP) - Version
               1 Functional Specification", RFC 2205, September 1997.
 [RFC2216]     Shenker, S. and J. Wroclawski, "Network Element QoS
               Control Service Specification Template", RFC 2216,
               September 1997.
 [RFC2210]     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
 One Microsoft Way
 Redmond, WA 98052
 Phone: +1 (425) 936-9568
 Andrew Smith
 Allegro Networks
 6399 San Ignacio Ave.
 San Jose, CA 95119, USA
 FAX: +1 415 345 1827
 Bruce Davie
 Cisco Systems
 250 Apollo Drive
 Chelmsford, MA 01824
 Phone: +1 (978)-244-8000

Bernet, et al. Standards Track [Page 11] RFC 2997 Specification of Null Service Type November 2000

9. Full Copyright Statement

 Copyright (C) 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
 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


 Funding for the RFC Editor function is currently provided by the
 Internet Society.

Bernet, et al. Standards Track [Page 12]

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