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   and provides evidence to third parties (i.e., non-repudiation).
   Accountability mechanisms can also be used to provide feedback to
   users as to consumption of resources. Internally an AD often decides
   to do away with such feedback under the premise that communication is
   a global good and should not be inhibited. There is not necessarily a
   "global good" across AD boundaries. Therefore, it becomes more
   appropriate to have resource usage visible to users, whether or not
   actual charging for usage takes place.  Another motivation that
   drives the need for accountability across AD boundaries is the
   greater variability in implementations. Different implementations of
   a single network protocol can vary greatly as to their efficiency
   [8].  We can not assume control over implementation across AD
   boundaries.  Feedback mechanisms such as metering (and charging in
   some cases) would introduce a concrete incentive for ADs to employ
   efficient and correct implementations.  PR should allow an AD to
   advertise and apply such accounting measures to inter-AD traffic.

   In summary, the lack of global authority, the need to support network
   resource sharing as well as network interconnection, the complex and
   dynamic mapping of users to ADs and rights, and the need for
   accountability across ADs, are characteristics of inter-AD
   communications which must be taken into account in the design of both
   policies and supporting technical mechanisms.

5  TOPOLOGY MODEL OF INTERNET

   Before discussing policies per se, we outline our model of inter-AD
   topology and how it influences the type of policy support required.
   Most members of the Internet community agree that the future Internet
   will connect on the order of 150,000,000 termination points and
   100,000 ADs. However, there are conflicting opinions as to the AD
   topology for which we must design PR mechanisms.  The informal
   argument is described here.

   SIMPLE AD TOPOLOGY AND POLICY MODEL Some members of the Internet
   community believe that the current complex topology of interconnected
   ADs is a transient artifact resulting from the evolutionary nature of
   the Research Internet's history.  (FOOTNOTE 9: David Cheriton of
   Stanford University articulated this side of the argument at an



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RFC 1125                  Policy Requirements              November 1989


   Internet workshop in Santa Clara, January, 1989). The critical points
   of this argument relate to topology and policy. They contend that in
   the long term the following three conditions will prevail:

   * The public carriers will provide pervasive, competitively
     priced, high speed data services.

   * The resulting topology of ADs will  be
     stub (not transit) ADs connected to regional
     backbones, which in turn interconnect via multiple,
     overlapping long haul backbones, i.e., a  hierarchy with
     no lateral connections between stub-ADs or regionals,
     and no vertical bypass links.

   * The policy requirements of the backbone and stub-ADs
     will be based only on charging for resource usage at the
     stub-AD to backbone-AD boundary, and to settling accounts
     between neighboring backbone providers (regional to long haul,
     and long haul to long haul).

   Under these assumptions, the primary requirement for general AD
   interconnect is a metering and charging protocol. The routing
   decision can be modeled as a simple least cost path with the metric
   in dollars and cents. In other words, restrictions on access to
   transit services will be minimal and the functionality provided by
   the routing protocol need not be changed significantly from current
   day approaches.

   COMPLEX AD TOPOLOGY AND POLICY MODEL The counter argument is that a
   more complex AD topology will persist. (FOOTNOTE 10:  Much of the
   remainder of this paper attempts to justify and provide evidence for
   this statement.) The different assumptions about AD topology lead to
   the significantly different assumptions about AD policies.

   This model assumes that the topology of ADs will in many respects
   agree with the previous model of increased commercial carrier
   participation and resulting hierarchical structure. However, we
   anticipate unavoidable and persistent exceptions to the hierarchy.
   We assume that there will be a relatively small number of long haul
   transit ADs (on the order of 100), but that there may be tens of
   thousands of regional ADs and hundreds of thousands of stub ADs
   (e.g., campuses, laboratories, and private companies).  The competing
   long haul offerings will differ, both in the services provided and in
   their packaging and pricing.  Regional networks will overlap less and
   will connect campus and private company networks. However, many
   stub-ADs will retain some private lateral links for political,
   technical, and reliability reasons.  For example, political
   incentives cause organizations to invest in bypass links that are not



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   always justifiable on a strict cost comparison basis; specialized
   technical requirements cause organizations to invest in links that
   have characteristics (e.g., data rate, delay, error, security) not
   available from public carriers at a competitive rate; and critical
   requirements cause organizations to invest in redundant back up links
   for reliability reasons.  These exceptions to the otherwise regular
   topology are not dispensible. They will persist and must be
   accommodated, perhaps at the expense of optimality; see Section 5 for
   more detail.  In addition, many private companies will retain their
   own private long haul network facilities. (FOOTNOTE 11:  While
   private voice networks also exist, private data networks are more
   common.  Voice requirements are more standardized because voice
   applications are more uniform than are data applications, and
   therefore the commercial services more often have what the voice
   customer wants at a price that is competitive with the private
   network option. Data communication requirements are still more
   specialized and dynamic.  Thus, there is less opportunity for economy
   of scale in service offerings and it is harder to keep up to date
   with customer demand. For this reason we expect private data networks
   to persist for the near future. As the telephone companies begin to
   introduce the next generation of high speed packet switched services,
   the scenario should change. However, we maintain that the result will
   be a predominance, but not complete dominance, of public carrier use
   for long haul communication.  Therefore, private data networks will
   persist and the routing architecture must accommodate controlled
   interconnection.)  Critical differences between the two models follow
   from the difference in assumptions regarding AD topology. In the
   complex case, lateral connections must be supported, along with the
   means to control the use of such connections in the routing
   protocols.

   The different topologies imply different policy requirements.  The
   first model assumes that all policies can be expressed and enforced
   in terms of dollars and cents and distributed charging schemes. The
   second model assumes that ADs want more varied control over their
   resources, control that can not be captured in a dollars and cents
   metric alone. We describe the types of policies to be supported and
   provide examples in the following section, Section 6. In brief, given
   private lateral links, ADs must be able to express access and
   charging related restrictions and privileges that discriminate on an
   AD basis.  These policies will be diverse, dynamic, and new
   requirements will emerge over time, consequently support must be
   extensible.  For example, the packaging and charging schemes of any
   single long haul service will vary over time and may be relatively
   elaborate (e.g., many tiers of service, special package deals, to
   achieve price discrimination).

   Note that these assumptions about complexity do not preclude some



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RFC 1125                  Policy Requirements              November 1989


   collection of ADs from "negotiating away" their policy differences,
   i.e., forming a federation, and coordinating a simplified inter-AD
   configuration in order to reduce the requirements for inter-AD
   mechanisms.  However, we maintain that there will persist collections
   of ADs that will not and can not behave as a single federation; both
   in the research community and, even more predominantly, in the
   broader commercial arena.  Moreover, when it comes to interconnecting
   across these federations, non-negotiable differences will arise
   eventually.  It is our goal to develop mechanisms that are applicable
   in the broader arena.

   The Internet community developed its original protocol suite with
   only minimal provision for resource control [9].  This was
   appropriate at the time of development based on the assumed community
   (i.e., researchers) and the ground breaking nature of the technology.
   The next generation of network technology is now being designed to
   take advantage of high speed media and to support high demand traffic
   generated by more powerful computers and their applications [10].  As
   with TCP/IP we hope that the technology being developed will find
   itself applied outside of the research community. This time it would
   be inexcusable to ignore resource control requirements and not to pay
   careful attention to their specification.

   Finally, we look forward to the Internet structure taking advantage
   of economies of scale offered by enhanced commercial services.
   However, in many respects the problem that stub-ADs may thus avoid,
   will be faced by the multiple regional and long haul carriers
   providing the services. The carriers' charging and resource control
   policies will be complex enough to require routing mechanisms similar
   to ones being proposed for the complex AD topology case described
   here.  Whether the network structure is based on private or
   commercial services, the goal is to construct policy sensitive
   mechanisms that will be transparent to end users (i.e., the
   mechanisms are part of the routing infrastructure at the network
   level, and not an end to end concern).

6  POLICY TYPES

   This section outlines a taxonomy of internet policies for inter-AD
   topologies that allow lateral and bypass links.  The taxonomy is
   intended to cover a wide range of ADs and internets. Any particular
   PR architecture we design should support a significant subset of
   these policy types but may not support all of them due to technical
   complexity and performance considerations.  The general taxonomy is
   important input to a functional specification for PR. Moreover, it
   can be used to evaluate and compare the suitability and completeness
   of existing routing architectures and protocols for PR; see Section
   8.



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RFC 1125                  Policy Requirements              November 1989


   We provide examples from the Research Internet of the different
   policy types in the form of resource usage policy statements. These
   statements were collected through interviews with agency
   representatives, but they do not represent official policy. These
   sample policy statements should not} be interpreted as agency policy,
   they are provided here only as examples.

   Internet policies fall into two classes, access and charging.  Access
   policies specify who can use resources and under what conditions.
   Charging policies specify the metering, accounting, and billing
   implemented by a particular AD.

6.1  TAXONOMY OF ACCESS POLICIES

   We have identified the following types of access policies that ADs
   may wish to enforce. Charging policies are described in the
   subsequent section. Section 6.3 provides more specific examples of
   both access and charging policies using FRICC policy statements.

   Access policies typically are expressed in the form: principals of
   type x can have access to resources of type y under the following
   conditions, z. The policies are categorized below according to the
   definition of y and z.  In any particular instance, each of the
   policy types would be further qualified by definition of legitimate
   principals, , x, i.e., what characteristics x must have in order to
   access the resource in question.

   We refer to access policies described by stub and transit ADs.  The
   two roles imply different motivations for resource control, however
   the types of policies expressed are similar; we expect the supporting
   mechanisms to be common as well.

   Stub and transit access policies may specify any of the following
   parameters:

   * SOURCE/DESTINATION
   Source/Destination policies prevent or restrict communication
   originated by or destined for particular ADs (or hosts or user
   classes within an AD).

   * PATH
   Path sensitive policies specify which ADs may or may not be passed
   through en route to a destination. The most general path sensitive
   policies allow stub and transit ADs to express policies that depend
   on any component in the AD path. In other words, a stub AD could
   reject a route based on any AD (or combination of ADs) in the route.
   Similarly, a transit AD could express a packet forwarding policy that
   behaves differently depending upon which ADs a packet has passed



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RFC 1125                  Policy Requirements              November 1989


   through, and is going to pass through, en route to the destination.
   Less ambitious (and perhaps more reasonable) path sensitive policies
   might only discriminate according to the immediate neighbor ADs
   through which the packet is traveling (i.e., a stub network could
   reject a route based on the first transit AD in the route, and a
   transit AD could express a packet forwarding policy that depends upon
   the previous, and the subsequent, transit ADs in the route.)

   * QUALITY/TYPE OF SERVICE(QOS OR TOS)
   This type of policy restricts access to special resources or
   services.  For example, a special high throughput, low delay link may
   be made available on a selective basis.

   * RESOURCE GUARANTEE
   These policies provide a guaranteed percentage of a resource on a
   selective, as needed basis.  In other words, the resource can be used
   by others if the preferred-AD's offered load is below the guaranteed
   level of service.  The guarantee may be to always carry intra-AD
   traffic or to always carry inter-AD traffic for a specific AD.

   *  TEMPORAL
   Temporal policies restrict usage based on the time of day or other
   time related parameters.