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Versions: 01 02 03 04 05 rfc2998                                        
                                                    Y. Bernet, Microsoft
                                                      R. Yavatkar, Intel
                                                      P. Ford, Microsoft
                                                         F. Baker, Cisco
                                                          L. Zhang, UCLA
                                              M. Speer, Sun Microsystems
                                                          R. Braden, ISI
Internet Draft
Expires: September, 1999
Document: draft-ietf-issll-diffserv-rsvp-01.txt             March, 1999


          Interoperation of RSVP/Intserv and Diffserv Networks


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-Drafts.

   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
      http://www.ietf.org/ietf/1id-abstracts.txt

      The list of Internet-Draft Shadow Directories can be accessed at
      linebreak http://www.ietf.org/shadow.html.

1. Abstract

   RSVP/Integrated Services and Differentiated Services provide
   complementary approaches to the problem of providing end-to-end QoS
   in the Internet.  These approaches must be able to coexist and
   effectively inter-operate.  This document describes a framework by
   which the two approaches inter-operate to provide end-to-end QoS for
   quantitative applications (applications for which QoS requirements
   are readily quantifiable, and which rely on these QoS requirements
   to function properly).

2. Introduction

   Work on QoS-enabled IP networks has led to two distinct approaches:
   the Integrated Services architecture (intserv)[12] and its
   accompanying signaling protocol, RSVP [1], vs. the Differentiated
   Services architecture (diffserv)[10].

2.1 RSVP/Intserv


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   RSVP is a signaling protocol that applications may use to request
   resources from the network. The network responds by explicitly
   admitting or rejecting RSVP requests. Certain applications that have
   quantifiable resource requirements express these requirements using
   intserv parameters. It is important to emphasize that RSVP and
   intserv are separable; RSVP is a signaling protocol. Intserv is a
   set of models for expressing service types, quantifying resource
   requirements and for determining the availability of the requested
   resources at relevant network elements (admission control).

   The current prevailing model of RSVP usage is based on a combined
   RSVP/intserv architecture. In this model, RSVP signals per-flow
   resource requirements to network elements, using Intserv parameters.
   These network elements apply Intserv admission control to signaled
   requests. In addition, traffic control mechanisms on the network
   element are configured to ensure that each admitted flow receives
   the service requested in strict isolation from other traffic. To
   this end, RSVP signaling configures 'MF' [10] packet classifiers in
   intserv capable routers along the path of the traffic flow. These
   classifiers enable per-flow classification of packets based on IP
   addresses and port numbers.

   The following factors have impeded deployment of the RSVP/Intserv
   architecture in the Internet at large:

   1. The use of per-flow state and per-flow processing raises
      scalability concerns for large networks.

   2. Only a small number of hosts currently generate RSVP signaling.
      While this number is expected to grow dramatically, many
      applications may never generate RSVP signaling.

   3. The necessary policy control mechanisms -- access control,
      authentication, and accounting -- are not available.

2.2 Diffserv

   The market is pushing for immediate deployment of a QoS solution
   that addresses the needs of the Internet as well as enterprise
   networks. This push led to the development of diffserv. In contrast
   to the per-flow orientation of RSVP/intserv, diffserv networks
   classify packets into one of a small number of aggregated flows or
   'classes', based on the diffserv codepoint (DSCP) in the packet's IP
   header.  This is known as 'BA' classification [10]. At each diffserv
   router, packets are subjected to a 'per-hop behaviour' (PHB), which
   is invoked by the DSCP. The primary benefit of diffserv is its
   scalability. Diffserv eliminates the need for per-flow state and
   per-flow processing and therefore scales well to large networks.

2.3 Complementary Roles of RSVP/Intserv and Diffserv

   We view RSVP/intserv and diffserv as complementary technologies in
   the pursuit of end-to-end QoS. Together, these mechanisms can
   facilitate deployment of applications such as IP-telephony, video-

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   on-demand, and various non-multimedia mission-critical applications.
   RSVP/intserv enables hosts to request per-flow, quantifiable
   resources, along end-to-end data paths and to obtain feedback
   regarding admissibility of these requests. Diffserv enables
   scalability across large networks.

2.3 Components of RSVP/intserv and Diffserv

   Before proceeding, it is helpful to identify the following
   components of the QoS technologies described:

   RSVP signaling - This term refers to the standard RSVP per-flow
   signaling protocol. RSVP signaling is used by hosts to signal per-
   flow resource requirements to the network (and to each other).
   Network elements use RSVP signaling to return an admission control
   decision to hosts. RSVP signaling may or may not carry intserv
   parameters. Admission control at a network element may or may not be
   based on the intserv model.

   RSVP/Intserv - This term is used to refer to the prevailing model of
   RSVP usage which includes RSVP signaling with intserv parameters,
   intserv admission control and per-flow traffic control at network
   elements.

   MF traffic control - This term refers to traffic control which is
   applied independently to individual traffic flows and therefore
   requires recognizing individual traffic flows via MF classification.

   Aggregate traffic control - This term refers to traffic control
   which is applied collectively to sets of traffic flows. These sets
   of traffic flows are recognized based on BA (DSCP) classification.
   In this draft, we use the terms 'aggregate traffic control' and
   'diffserv' interchangeably.

   We will refer to RSVP/intserv regions of the network and diffserv
   regions of the network. RSVP/intserv regions are those regions in
   which both RSVP signaling and MF traffic control are supported.
   These regions include hosts and network elements that are
   RSVP/intserv capable. (RSVP/intserv regions are not precluded from
   supporting aggregate traffic control as well as MF traffic control).
   Diffserv regions are those regions in which aggregate traffic
   control is supported.

2.4 The Framework

   In the framework we present, end-to-end, quantitative QoS is
   provided by coupling RSVP/Intserv regions at the periphery of the
   network with diffserv regions in the core of the network. The
   diffserv regions may, but are not required to, participate in the
   end-to-end RSVP signaling for the purpose of optimizing resource
   allocation and supporting admission control.

   From the perspective of RSVP/intserv, diffserv regions of the
   network are treated as virtual links connecting RSVP/Intserv capable

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   routers or hosts (much as an 802.1p network region is treated as a
   virtual link in [5]). Within the diffserv regions of the network
   routers implement specific PHBs (aggregate traffic control). We use
   RSVP to apply admission control to each PHB in the diffserv region.
   As a result we expect that the diffserv regions of the network will
   be able to extend the intserv style services requested from the
   periphery. As such, we often refer to the RSVP/intserv network
   regions as 'customers' of the diffserv network regions.

   In our framework, we address the inter-operability between the
   RSVP/intserv regions of the network and the diffserv regions of the
   network. Our goal is to enable seamless inter-operation. As a
   result, the network administrator is free to choose which regions of
   the network act as RSVP/intserv regions and which act as diffserv
   regions. In one extreme the diffserv region is pushed all the way to
   the periphery, with hosts alone comprising the RSVP/intserv regions
   of the network. In the other extreme, RSVP/intserv is pushed all the
   way to the core, with no diffserv region.

2.5 Contents

   In section 3 we discuss the benefits that can be realized by using
   RSVP/intserv together with the aggregate traffic control provided by
   diffserv network regions. In section 4, we present the framework and
   the reference network. Section 5 details two realizations of the
   framework. Section 6 discusses the implications of the framework for
   diffserv. Appendix A contains a list of some important terms used in
   this document.

   Though the primary goal of this draft is to describe a framework
   for inter-operation of RSVP/intserv network regions and diffserv
   network regions, the draft currently does not address the issues
   specific to IP multicast flows.

3. Benefits of Using RSVP/intserv with Diffserv

   The primary benefit of diffserv aggregate traffic control is its
   scalability. In this section, we discuss the benefits that
   interoperation with RSVP/intserv can bring to a diffserv network
   region. Note that this discussion is in the context of servicing
   quantitative applications specifically.

3.1 Resource Based Admission Control

   In RSVP/Intserv networks, quantitative QoS applications use RSVP to
   request resources from the network. The network may accept or reject
   these requests in response. This is 'explicit admission control'.
   Explicit admission control helps to assure that network resources
   are optimally used. To further understand this issue, consider a
   diffserv network region providing only aggregate traffic control
   with no signaling. In the diffserv network region, admission control
   is applied implicitly by provisioning policing parameters at network
   elements. For example, a network element at the ingress to a


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   diffserv network region could be provisioned to accept only 50 Kbps
   of traffic for the EF DSCP.

   While such implicit admission control does protect the network to
   some degree, it can be quite ineffective. For example, consider that
   there may be 10 IP telephony sessions originating outside the
   diffserv network region, each requiring 10 Kbps of EF service from
   the diffserv network region. Since the network element protecting
   the diffserv network region is provisioned to accept only 50 Kbps of
   traffic for the EF DSCP, it will discard half the offered traffic.
   This traffic will be discarded from the aggregation of traffic
   marked EF, with no regard to the microflow from which it originated.
   As a result, it is likely that of the ten IP telephony sessions,
   none will obtain satisfactory service when in fact, there are
   sufficient resources available in the diffserv network region to
   satisfy five sessions.

   In the case of explicit admission control, the network will signal
   rejection in response to requests for resources that would exceed
   the 50 Kbps limit. As a result, upstream network elements (including
   originating hosts) and applications will have the information they
   require to take corrective action. The application might respond by
   refraining from transmitting, or by requesting admission for a
   lesser traffic profile. The host operating system might respond by
   marking the application's traffic for the DSCP that corresponds to
   best-effort service. Upstream network elements might respond by re-
   marking packets on the rejected flow to a lower service level. In
   any case, the integrity of those flows that were admitted would be
   preserved, at the expense of the flows that were not admitted. Thus,
   by appointing an RSVP conversant admission control agent for the
   diffserv region of the network it is possible to enhance the service
   that the network can provide to quantitative applications.

3.2 Policy Based Admission Control

   In an RSVP/intserv network region, resource requests can be
   intercepted by RSVP aware network elements and can be reviewed
   against policies stored in policy databases. These resource requests
   securely identify the user and the application for which the
   resources are requested. Consequently, the network element is able
   to consider per-user and/or per-application policy when deciding
   whether or not to admit a resource request. So, in addition to
   optimizing the use of resources in a diffserv network region (as
   discussed in 3.1) RSVP conversant admission control agents can be
   used to apply specific customer policies in determining the specific
   customer traffic flows entitled to use the diffserv network region's
   resources. Customer policies can be used to allocate resources to
   specific users and/or applications.

   By comparison, in diffserv network regions without per-flow RSVP
   signaling, policies are typically applied based on the diffserv
   customer network from which traffic originates, not on the
   originating user or application within the customer network.


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3.3 Assistance in Traffic Identification/Classification

   Within diffserv network regions, traffic is allotted service based
   on the DSCP marked in each packet's IP header. Thus, in order to
   obtain a particular level of service within the diffserv network
   region, it is necessary to effect the marking of the correct DSCP in
   packet headers. There are two mechanisms for doing so, host marking
   and router marking. In the case of host marking, the host operating
   system marks the DSCP in transmitted packets. In the case of router
   marking, routers in the network are configured to identify specific
   traffic (based on MF classification) and to mark the DSCP as packets
   transit the router. There are advantages and disadvantages to each
   scheme. Regardless of the scheme used, RSVP signaling offers
   significant benefits.

3.3.1 Host Marking

   In the case of host marking, the host operating system marks the
   DSCP in transmitted packets. This approach has the benefit of
   shifting per-flow classification and marking to the edge of the
   network, where it scales best. It also enables the host to make
   decisions regarding the mark (and hence the relative priority that
   is requested) that is appropriate for each transmitted packet. The
   host is generally better equipped to make this decision than the
   network.

   Host marking requires that the host be aware of the interpretation
   of DSCPs by the network. This information can be configured into
   each host. However, such configuration imposes a management burden.
   Alternatively, RSVP/intserv hosts can use RSVP signaling to query
   the network for a mapping from intserv service type to DSCP. This is
   achieved via the RSVP DCLASS object [17] and is explained later in
   this draft.

3.3.2 Router Marking

   In the case of router marking, MF classification criteria must be
   configured in the router. This may be done dynamically, by request
   from the host operating system, or statically via manual
   configuration or via automated scripts.

   There are significant difficulties in doing so statically.
   Typically, it is desirable to allot service to traffic based on the
   application and/or user originating the traffic. At times it is
   possible to identify packets associated with a specific application
   by the IP port numbers in the headers. It may also be possible to
   identify packets originating from a specific user by the source IP
   address. However, such classification criteria may change
   frequently. Users may be assigned different IP addresses by DHCP.
   Applications may use transient ports. To further complicate matters,
   multiple users may share an IP address. These factors make it very
   difficult to manage static configuration of the classification
   information required to mark traffic in routers.


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   An attractive alternative to static configuration is to allow host
   operating systems to signal classification criteria to the router on
   behalf of users and applications. As we will show later in this
   draft, RSVP signaling is ideally suited for this task. In addition
   to enabling dynamic and accurate updating of MF classification
   criteria, RSVP signaling enables classification of IPSec [16]
   packets (by use of the SPI) which would otherwise be unrecognizable.

3.4 Traffic Conditioning

   Those network elements that do provide RSVP/intserv support will
   condition traffic at a per-flow granularity, by some combination of
   shaping and/or policing. Pre-conditioning traffic in this manner
   before it is submitted to the diffserv region of the network is
   beneficial. In particular, it enhances the ability of the diffserv
   region of the network to provide quantitative services using
   aggregate traffic control.

4. The Framework

   In the general framework we envision an Internet in which hosts use
   RSVP/intserv to request reservations for specific services from the
   network. The network includes some combination of RSVP/intserv
   regions (in which MF classification and per-flow traffic control is
   applied) and diffserv regions (in which aggregate traffic control is
   applied). Individual routers may or may not participate in RSVP
   signaling regardless of the type of network region in which they
   reside.

   We will consider two specific realizations of the framework. In the
   first, resources within the diffserv regions of the network are
   statically provisioned and these regions include no RSVP aware
   devices. In the second, resources within the diffserv region of the
   network are dynamically provisioned and select devices within the
   diffserv network regions participate in RSVP signaling.

4.1 Reference Network

   The two realizations of the framework will be discussed in the
   context of the following reference network:

            /        \       /              \       /        \
           /          \     /                \     /          \
    |---| |        |---|   |---|          |---|   |---|        | |---|
    |Tx |-|        |ER1|---|BR1|          |BR2|---|ER2|        |-|Rx |
    |---| |        |-- |   |---|          |---|   |---|        | |---|
           \          /     \                /     \          /
            \______  /       \___ _________ /       \__ _____/

    RSVP/Intserv region      Diffserv region      RSVP/Intserv region

                 Figure 1: Sample Network Configuration



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   The reference network includes a diffserv region interconnecting two
   RSVP/intserv regions. The diffserv region contains a mesh of
   routers, at least some of which provide aggregate traffic control.
   The RSVP/intserv regions contain meshes of routers and attached
   hosts, at least some of which are RSVP/intserv capable.

   In the interest of simplicity we consider a single QoS sender, Tx in
   one of the RSVP/intserv network regions and a single QoS receiver,
   Rx in the other. The edge routers (ER1, ER2) within the RSVP/intserv
   regions interface to the border routers (BR1, BR1) within the
   diffserv regions.

   From an economic viewpoint, we may consider that the diffserv region
   sells service to the RSVP/intserv regions, which provide service to
   hosts.  Thus, we may think of the RSVP/intserv regions as customers
   of the diffserv region.  In the following, we use the term
   'customer' for the RSVP/intserv regions.

4.1.1 Components of the Reference Network

   We now define the major components of the reference network.

4.1.1.1 Hosts

   Both sending and receiving hosts use RSVP/intserv to communicate the
   quantitative QoS requirements of QoS-aware applications running on
   the host. Typically, a QoS process within the host operating system
   generates RSVP signaling on behalf of applications. This process may
   also invoke local traffic control.

   In this example, traffic control in the host marks the DSCP in
   transmitted packets, and it shapes transmitted traffic to the
   requirements of the intserv service in use. In alternate
   realizations of the framework, the first-hop router within the
   RSVP/intserv network regions may provide these traffic control
   functions.

4.1.1.2 End-to-End RSVP Signaling

   We assume that RSVP signaling messages travel end-to-end between
   hosts Tx and Rx to support RSVP/intserv reservations in the
   RSVP/intserv network regions.  We require that these end-to-end RSVP
   messages are carried across the diffserv region. Depending on the
   specific realization of the framework, these messages may be
   processed by none, some or all of the routers in the diffserv
   region.

4.1.1.3 Edge Routers

   ER1 and ER2 are edge routers, residing in the RSVP/intserv network
   regions. The functionality of the edge routers varies depending on
   the specific realization of the framework. In the case in which the
   diffserv network region is RSVP unaware, edge routers act as
   admission control agents to the diffserv network. They process

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   signaling messages from both Tx and Rx, and apply admission control
   based on resource availability within the diffserv network region
   and on customer defined policy. In the case in which the diffserv
   network region is RSVP aware, the edge routers apply admission
   control based on local resource availability and on customer defined
   policy. In this case, the border routers act as the admission
   control agent to the diffserv network region.

   We will later describe the functionality of the edge routers in
   greater depth for each of the two realizations of the framework.

4.1.1.4 Border Routers

   BR1 and BR2 are border routers, residing in the diffserv network
   region. The functionality of the border routers varies depending on
   the specific realization of the framework. In the case in which the
   diffserv network region is RSVP/intserv unaware, these routers act
   as pure diffserv routers. As such, their sole responsibility is to
   police submitted traffic based on the service level specified in the
   DSCP and the agreement negotiated with the customer (aggregate
   traffic control). In the case in which the diffserv network region
   is RSVP/intserv aware, the border routers participate in RSVP
   signaling and act as admission control agents for the diffserv
   network region.

   We will later describe the functionality of the border routers in
   greater depth for each of the two realizations of the framework.

4.1.1.5 RSVP/Intserv Network Regions

   Each RSVP/intserv network region consists of RSVP/intserv capable
   hosts and some number of routers.  These routers may reasonably be
   assumed to be RSVP/intserv capable, although this might not be
   required in the case of a small, over-provisioned network region. If
   they are not RSVP/intserv capable, we assume that they will pass
   RSVP messages unhindered. Routers in the RSVP/intserv network region
   are not precluded from providing aggregate traffic control to non-
   quantitative traffic passing through them.

4.1.1.6 Diffserv Network Region

   The diffserv network region supports aggregate traffic control and
   is not capable of MF classification. Depending on the specific
   realization of the framework, some number of routers within the
   diffserv region may be RSVP aware and therefore capable of per-flow
   signaling and admission control. If devices in the diffserv region
   are not RSVP aware, they will pass RSVP messages transparently with
   negligible performance impact (see [8]).

   The diffserv network region provides two or more levels of service
   based on the DSCP in packet headers. It may include sub-regions
   managed as different administrative domains.

4.1.1.7 Service Mapping

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   RSVP/intserv signaling requests specify an intserv service type and
   a set of quantitative parameters known as a 'flowspec'. At each hop
   in an intserv network, the RSVP/intserv service requests are
   interpreted in a form meaningful to the specific link layer medium.
   For example at an 802.1 hop, the intserv parameters are mapped to an
   appropriate 802.1p priority level [5].

   In our framework, diffserv regions of the network are analogous to
   the 802.1p capable switched segments described in [5]. Admission
   control agents for diffserv network regions must map intserv service
   types to a corresponding diffserv service level (DSCP or PHB) that
   can reasonably extend the intserv service type requested by the
   application. The admission control agent can then approve or reject
   resource requests based on the capacity available in the diffserv
   network region at the mapped service level.

   One of two schemes may be used to map intserv service types to
   diffserv service levels.

4.1.1.7.1 Default Mapping

   In this scheme, there is some standard, well-known mapping from
   intserv service type to a DSCP that will invoke the appropriate
   behavior in the diffserv network.

4.1.1.7.2 Network Driven Mapping

   In this scheme, RSVP aware routers in the diffserv network region
   may override the well-known mapping described in 4.1.1.7.1. RSVP
   RESV messages originating from receivers will carry the usual
   intserv service type. RSVP aware routers within the diffserv network
   region may append a DCLASS [17] object to RESV messages as they are
   forwarded upstream. When a RESV message carrying a DCLASS object
   arrives at a sending host (or in the case of router marking, at an
   intermediate router), the sender starts marking transmitted packets
   with the DSCP indicated.

   A decision to override the well-known service mapping may be based
   on configuration and/or a policy decision.

5. Detailed Examples of the Interoperation of RSVP/Intserv and Diffserv

   In this section we provide detailed examples of our framework in
   action. We discuss two examples, one in which the diffserv network
   region is RSVP unaware, the other in which the diffserv network
   region is RSVP aware.

5.1 RSVP Unaware Diffserv Network Region

   In this example, no devices in the diffserv network region are RSVP
   aware. The diffserv network region is statically provisioned. The
   owner(s) of the RSVP/intserv network regions and the owner of the
   diffserv network region have negotiated a static contract (service

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   level agreement, or SLA) for the transmit capacity to be provided to
   the customer at each of a number of standard diffserv service
   levels.

   It is helpful to consider the edge routers in the customer network,
   to consist of two halves, a standard RSVP/intserv half, which
   interfaces to the customer's RSVP/intserv network regions and a
   diffserv half which interfaces to the diffserv network region. The
   RSVP/intserv half has full RSVP capability. It is able to
   participate in RSVP signaling and it is able to identify and process
   traffic on per-flow granularity.

   The diffserv half of the router can be considered to consist of a
   number of virtual transmit interfaces, one for each diffserv service
   level negotiated in the SLA. The router contains a table that
   indicates the transmit capacity provisioned, per the SLA at each
   diffserv service level. This table, in conjunction with the default
   mapping described in 4.1.1.7.1, is used to apply admission control
   decisions to the diffserv network region.

5.1.1 Sequence of Events in Obtaining End-to-end QoS

   The following sequence illustrates the process by which an
   application obtains end-to-end QoS.

   1. The QoS process on the sending host Tx generates an RSVP PATH
   message that describes the traffic offered by the sending
   application.

   2. The PATH message is carried toward the receiving host, Rx. In the
   RSVP/intserv network region to which the sender is attached,
   standard RSVP/intserv processing is applied at capable network
   elements.

   3. At the edge router ER1, the PATH message is subjected to standard
   RSVP processing and PATH state is installed in the router. The PATH
   message is sent onward to the diffserv network region.

   4. The PATH message is carried transparently through the diffserv
   network region and then processed at ER2 according to standard RSVP
   processing rules.

   5. When the PATH message reaches the receiving host Rx, the
   operating system generates an RSVP RESV message, indicating interest
   in offered traffic of a certain intserv service type.

   6. The RESV message is carried back towards the diffserv network
   region and the sending host. Consistent with standard RSVP/intserv
   processing, it may be rejected at any RSVP node in the RSVP/intserv
   network region if resources are deemed insufficient to carry the
   traffic requested.

   7. At ER2, the RESV message is subjected to standard RSVP/intserv
   processing.  It may be rejected if resources on the downstream

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   interface of ER2 are deemed insufficient to carry the resources
   requested.  If it is not rejected, it will be carried transparently
   through the diffserv network region, arriving at ER1.

   8. In ER1, the RESV message triggers admission control processing.
   ER1 compares the resources requested in the RSVP/intserv request to
   the resources available in the diffserv network region at the
   corresponding diffserv service level. The corresponding service
   level is determined by the intserv to diffserv mapping discussed
   previously. The availability of resources is determined by the
   capacity provisioned in the SLA. ER1 may also apply a policy
   decision such that the resource request may be rejected based on the
   customer's specific policy criteria, even though the aggregate
   resources are determined to be available per the SLA.

   9. If ER1 approves the request, the RESV message is admitted and is
   allowed to continue upstream towards the sender. If it rejects the
   request, the RESV is not forwarded and the appropriate RSVP error
   messages are sent. If the request is approved, ER1 updates its
   internal tables to indicate the reduced capacity available at the
   admitted service level on its transmit interface.

   10. The RESV message proceeds through the RSVP/intserv network
   region to which the sender is attached. Any RSVP node in this region
   may reject the reservation request due to inadequate resources or
   policy. If the request is not rejected, the RESV message will arrive
   at the sending host, Tx.

   11. At Tx, the QoS process receives the RESV message. It interprets
   receipt of the message as indication that the specified traffic flow
   has been admitted for the specified intserv service type (in the
   RSVP/intserv network regions) and for the corresponding diffserv
   service level (in the diffserv network regions).

   12. Tx begins to mark the DSCP in the headers of packets that are
   transmitted on the admitted traffic flow. The DSCP is the value
   which maps to the intserv service type specified in the admitted
   RESV message.

   In this manner, we obtain end-to-end QoS through a combination of
   networks that support RSVP/Intserv and networks that support
   diffserv.

5.2 RSVP Aware Diffserv Network Region

   In this example, the customer's edge routers are standard RSVP
   routers. The border router, BR1 is RSVP aware. In addition, there
   may be other routers within the diffserv network region which are
   RSVP aware. Note that although these routers are able to participate
   in RSVP signaling, they process traffic in aggregate, based on DSCP,
   not on the per-flow classification criteria used by standard
   RSVP/Intserv routers. It can be said that their control-plane is
   RSVP while their data-plane is diffserv. This approach exploits the


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                      Use of RSVP with Diffserv           March, 1999

   benefits of RSVP signaling while maintaining much of the scalability
   associated with diffserv.

   In the former example, there is no RSVP signaling between the
   RSVP/intserv network regions and the diffserv network region. The
   negotiation of an SLA is the only explicit exchange of resource
   availability information between the two network regions. ER1 is
   configured with the information represented by the SLA and as such,
   is able to act as an admission control agent for the diffserv
   network region. Such configuration does not readily support
   dynamically changing SLAs, since ER1 requires reconfiguration each
   time the SLA changes. It is also difficult to make efficient use of
   the resources in the diffserv network region. This is because
   admission control does not consider the availability of resources in
   the diffserv network region along the specific path that would be
   impacted.

   By contrast, when the diffserv network region is RSVP aware, the
   admission control agent is part of the diffserv network. As a
   result, changes in the capacity available in the diffserv network
   region can be indicated to the RSVP/intserv network regions via
   traditional RSVP. By including routers interior to the diffserv
   network region in RSVP signaling, it is possible to improve the
   efficiency of resource usage. This is because admission control can
   be linked to the availability of resources along the specific path
   that would be impacted. We refer to this benefit of RSVP signaling
   as 'topology aware admission control'. A further benefit of
   supporting RSVP signaling within the diffserv network region is that
   it is possible to effect changes in the provisioning of the diffserv
   network region response to resource requests from the RSVP/intserv
   network regions.

   Various mechanisms may be used within the diffserv network region to
   support dynamic provisioning and topology aware admission control.
   These include aggregated RSVP, per-flow RSVP and bandwidth brokers,
   as described in the following paragraphs.

5.2.1 Aggregated or Tunneled RSVP

   A number of drafts [8,10,18, 19] propose mechanisms for extending
   RSVP to reserve resources for an aggregation of flows between edges
   of a network. Border routers may interact with core routers and
   other border routers using aggregated RSVP to reserve resources
   between edges of the diffserv network region. Initial reservation
   levels for each service level may be established between major
   border routers, based on anticipated traffic patterns. Border
   routers could trigger changes in reservation levels as a result of
   the cumulative per-flow RSVP requests from peripheral RSVP/intserv
   network regions reaching high or low-water marks.

   In this approach, admission of per-flow RSVP requests from
   RSVP/intserv networks would be counted against the appropriate
   aggregate reservations for the corresponding service level.


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                      Use of RSVP with Diffserv           March, 1999

   The advantage of this approach is that it offers dynamic, topology
   aware admission control to the diffserv network region without
   requiring the level of RSVP signaling processing that would be
   required to support per-flow RSVP.

5.2.3 Per-flow RSVP

   In this approach, routers in the diffserv network region respond to
   the standard per-flow RSVP signaling originating from the
   RSVP/intserv network regions. This approach provides the benefits of
   the previous approach (dynamic, topology aware admission control)
   without requiring aggregated RSVP support. Resources are also used
   more efficiently as a result of the per-flow admission control.
   However, the demands on RSVP signaling resources within the diffserv
   network region may be significantly higher.

5.2.4 Oracle

   Border routers might not use any form of RSVP signaling within the
   diffserv network region but might instead use custom protocols to
   interact with an 'oracle'. The oracle is a hypothetical agent that
   has sufficient topology awareness to make admission control
   decisions. The set of RSVP aware routers in the previous two
   examples can be considered collectively as a distributed oracle. In
   various definitions of the 'bandwidth broker' [4], it is able to act
   as a centralized oracle.

5.2.5 Granularity of Deployment of RSVP Aware Routers

   In 5.2.2 and 5.2.3 some subset of the routers within the diffserv
   network is RSVP signaling aware (though traffic control is
   aggregated as opposed to per-flow). The relative number of routers
   in the core that participate in RSVP signaling is a provisioning
   decision that must be made by the network administrator.

   In one extreme case, only the border routers participate in RSVP
   signaling. In this case, either the diffserv network region must be
   extremely over-provisioned and therefore, inefficiently used, or
   else it must be carefully and statically provisioned for limited
   traffic patterns. The border routers must enforce these patterns.

   In the other extreme case, each router in the diffserv network
   region might participate in RSVP signaling. In this case, resources
   can be used with optimal efficiency, but signaling processing
   requirements and associated overhead increase.

   It is likely that network administrators will compromise by enabling
   RSVP signaling on some subset of routers in the diffserv network
   region. These routers will likely represent major traffic switching
   points with over-provisioned or statically provisioned regions of
   RSVP unaware routers between them.

6. Implications of the Framework for DiffServ Network Regions


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                      Use of RSVP with Diffserv           March, 1999

   We have described a framework in which RSVP/intserv style QoS can be
   provided across end-to-end paths that include diffserv network
   regions. This section discusses some of the implications of this
   framework for the diffserv network region.

6.1 Requirements from Diffserv Network Regions

   A diffserv network region must meet the following requirements in
   order for it to support the framework described in this draft.

   1. A diffserv network region must be able to provide standard QoS
   services between its border routers. It must be possible to invoke
   these services by use of a standard DSCP.

   2. There must be appropriate service mappings from intserv service
   types to these diffserv services.

   3. Diffserv network regions must provide admission control
   information to intserv network regions.  This information can be
   provided by a dynamic protocol or, at the very least, through static
   service level agreements.

   4. Diffserv network regions must be able to pass RSVP messages, in
   such a manner that they can be recovered at the egress of the
   diffserv network region. The diffserv network region may, but is not
   required to, process these messages. Mechanisms for transparently
   carrying RSVP messages across a transit network are described in
   [8,10,18, 19].

   To meet these requirements, additional work is required in the areas
   of:

   1. Mapping intserv style service specifications to services that can
   be provided by diffserv network regions.
   2. Definition of the functionality required in network elements to
   support RSVP signaling with aggregate traffic control (for network
   elements residing in the diffserv network region).
   3. Definition of mechanisms to efficiently and dynamically provision
   resources in a diffserv network region (e.g. aggregated RSVP,
   tunneling, MPLS, etc.).

6.2 Protection of Intserv Traffic from Other Traffic

   Network administrators must be able to share resources in the
   diffserv network region between three types of traffic:

   a. RSVP/intserv signaled  - this is traffic associated with
   quantitative applications. It requires a specific quantity of
   resources with a high degree of assurance.

   b. Qualitative - this is traffic associated with applications that
   are not quantitative. Its resource requirements are not readily
   quantifiable. It requires a 'better than best-effort' level of
   service.

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                      Use of RSVP with Diffserv           March, 1999


   c. All other (best-effort) traffic

   These classes of traffic must be isolated from each other by the
   appropriate configuration of policers and classifiers at ingress
   points to the diffserv network region, and by appropriate
   provisioning within the diffserv network region.  To provide
   protection for RSVP/intserv signaled traffic in diffserv regions of
   the network, we suggest that the DSCPs assigned to such traffic not
   overlap with the DSCPs assigned to other traffic.

7. Multicast

   To be written.

8. Security Considerations

8.1 General RSVP Security

   We are proposing that RSVP signaling be used to obtain resources in
   both diffserv and RSVP/intserv regions of a network. Therefore, all
   RSVP security considerations apply [11].  In addition, network
   administrators are expected to protect network resources by
   configuring secure policers at interfaces with untrusted customers.

8.2 Host Marking

   Though it does not mandate host marking, our proposal does recommend
   it. Allowing hosts to set the DSCP directly may alarm network
   administrators.  The obvious concern is that hosts may attempt to
   'steal' resources.  In fact, hosts may attempt to exceed negotiated
   capacity in diffserv network regions at a particular service level
   regardless of whether they invoke this service level directly (by
   setting the DSCP) or indirectly (by submitting traffic that
   classifies in an intermediate marking router to a particular diff-
   serv DSCP).

   In either case, it will be necessary for each diffserv network
   region to protect its resources by policing to assure that customers
   do not use more resources than they are entitled to, at each service
   level (DSCP). If the sending host does not do the marking, the
   boundary router (or trusted intermediate routers) must provide MF
   classification, mark and police. If the sending host does do the
   marking, the boundary router needs only to provide BA classification
   and to police to ensure that the customer is not exceeding the
   aggregate capacity negotiated for the service level.

   In summary, the security concerns of marking the DSCP at the edge of
   the network can be dismissed since each diffserv provider will have
   to police at their boundary anyway.  Furthermore, this approach
   reduces the granularity at which border routers must police, thereby
   pushing finer grain shaping and policing responsibility to the edges
   of the network, where it scales better.  The larger diffserv network
   regions are thus focused on the task of protecting their networks,

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                      Use of RSVP with Diffserv           March, 1999

   while the RSVP/intserv network regions are focused on the task of
   shaping and policing their own traffic to be in compliance with
   their negotiated intserv parameters.

   7. Acknowledgments

   Authors thank the following individuals for their comments that led
   to improvements to the previous version(s) of this draft: David
   Oran, Andy Veitch, Curtis Villamizer, Walter Weiss, and Russel
   White.

   Many of the ideas in this document have been previously discussed in
   the original intserv architecture document [12].

   8. References

   [1] Braden, R., Zhang, L., Berson, S., Herzog, S. and Jamin, S.,
       "Resource Reservation Protocol (RSVP) Version 1 Functional
       Specification", RFC 2205, Proposed Standard, September 1997

   [2] Yavatkar, R., Hoffman, D., Bernet, Y., Baker, F. and Speer, M.,
       "SBM (Subnet Bandwidth Manager): A Protocol For RSVP-based
       Admission Control Over IEEE 802 Style Networks", Internet Draft,
       March 1998

   [3] Berson, S. and Vincent, R., "Aggregation of Internet Integrated
       Services State", Internet Draft, December 1997.

   [4] Nichols, K., Jacobson, V. and Zhang, L., "A Two-bit
       Differentiated Services Architecture for the Internet", Internet
       Draft, December 1997.

   [5] Seaman, M., Smith, A. and Crawley, E., "Integrated Services Over
       IEEE 802.1D/802.1p Networks", Internet Draft, June 1997

   [6] Elleson, E. and Blake, S., "A Proposal for the Format and
       Semantics of the TOS Byte and Traffic Class Byte in Ipv4 and
       Ipv6 Headers", Internet Draft, November 1997

   [7] Ferguson, P., "Simple Differential Services: IP TOS and
       Precedence, Delay Indication, and Drop Preference", Internet
       Draft, November 1997

   [8] Guerin, R., Blake, S. and Herzog, S.,"Aggregating RSVP based QoS
       Requests", Internet Draft, November 1997.

   [9] Nichols, Kathleen, et al., "Definition of the Differentiated
       Services Field (DS Field) in the IPv4 and IPv6 Headers", RFC
       2474, December 1998.

   [10] Blake, S., et al., "An Architecture for Differentiated
        Services." RFC 2475, December 1998.

   [11] Baker, F., "RSVP Cryptographic Authentication", Internet Draft,


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                      Use of RSVP with Diffserv           March, 1999

        August 1997

   [12] Braden, R., Clark, D. and Shenker, S., "Integrated Services in
        the Internet Architecture: an Overview", Internet RFC 1633,
        June 1994

   [13] Garrett, M. W., and Borden, M., "Interoperation of Controlled-
        Load Service and Guaranteed Service with ATM", RFC2381, August
        1998.

   [14] Weiss, Walter, Private communication, November 1998.

   [15] Berson, S. and Vincent, S., "Aggregation of Internet Integrated
        Services State", Internet Draft, August 1998.

   [16] Kent, S., Atkinson, R., "Security Architecture for the Internet
        Protocol", RFC 2401, November 1998.

   [17] Bernet, Y., "Usage and Format of the DCLASS Object with RSVP
        Signaling", Internet Draft, February 1999.

   [18] Baker, F., Iturralde, C., "RSVP Reservation Aggregation",
        Internet Draft, February 1999.

   [19] Terzis, A., Krawczyk, J., Wroclawski, J., Zhang, L., "RSVP
        Operation Over IP Tunnels", Internet Draft, February 1999.

Author's Addresses:

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

   Raj Yavatkar
   Intel Corporation
   JF3-206 2111 NE 25th. Avenue, Hillsboro, OR 97124
   Phone: (503) 264-9077
   Email: raj.yavatkar@intel.com

   Peter Ford
   Microsoft
   One Microsoft Way, Redmond, WA 98052
   Phone: (425) 703-2032
   Email: peterf@microsoft.com

   Fred Baker
   Cisco Systems
   519 Lado Drive, Santa Barbara, CA 93111
   Phone: (408) 526-4257
   Email: fred@cisco.com

   Lixia Zhang

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                      Use of RSVP with Diffserv           March, 1999

   UCLA
   4531G Boelter Hall Los Angeles, CA 90095
   Phone: +1 310-825-2695
   Email: lixia@cs.ucla.edu

   Michael Speer
   Sun Microsystems
   901 San Antonio Road UMPK15-215 Palo Alto, CA 94303
   Phone: +1 650-786-6368
   Email: speer@Eng.Sun.COM

   Bob Braden
   USC Information Sciences Institute
   4676 Admiralty Way Marina del Rey, CA 90292-6695
   Phone: 310-822-1511
   Email: braden@isi.edu

   This draft expires September, 1999





































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