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Network Working Group                                            Y. BernetRequest for Comments: 2997                                       MicrosoftCategory: Standards Track                                         A. Smith                                                          Allegro Networks                                                                  B. Davie                                                             Cisco Systems                                                             November 2000Specification of the Null Service TypeStatus 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.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 20001. 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 Notes3.1.1 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 20002.1.2 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 Details3.1 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   [RFC2216].   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   [RFC2210].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 20004. Detailed Message Formats4.1 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   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 byteBernet, 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   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 headerBernet, 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 inRFC 2205 andRFC 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 inRFC2210, 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 header4.5 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 20006. 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",RFC2752, 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",RFC2996, 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 20008. 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.comBernet, et al.              Standards Track                    [Page 11]

RFC 2997           Specification of Null Service Type      November 20009.  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   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]