The MultiProtocol Internet

Network Working Group                                          B. Leiner
Request for Comments: 1560                                          USRA
Category: Informational                                       Y. Rekhter
                                                                     IBM
                                                           December 1993


                       The MultiProtocol Internet

Status of this Memo

   This memo provides information for the Internet community.  This memo
   does not specify an Internet standard of any kind.  Distribution of
   this memo is unlimited.

Abstract

   This document was prepared by the authors on behalf of the Internet
   Architecture Board (IAB).  It is offered by the IAB to stimulate
   discussion.

   There has recently been considerable discussion on two topics:
   MultiProtocol approaches in the Internet and the selection of a next
   generation Internet Protocol. This document suggests a strawman
   position for goals and approaches for the IETF/IESG/IAB in these
   areas. It takes the view that these two topics are related, and
   proposes directions for the IETF/IESG/IAB to pursue.

   In particular, it recommends that the IETF/IESG/IAB should continue
   to be a force for consensus on a single protocol suite and internet
   layer protocol. The IETF/IESG/IAB should:

      - maintain its focus on the TCP/IP protocol suite,

      - work to select a single next-generation internet protocol and
        develop mechanisms to aid in transition from the current IPv4,
        and

      - continue to explore mechanisms to interoperate and share
        resources with other protocol suites within the Internet.

1.  Introduction

   The major purpose of the Internet is to enable ubiquitous
   communication services between endpoints. In a very real way, the
   Internet IS inter-enterprise networking. Therefore, the issue of
   multiprotocol Internet is not just the issue of multiple network
   layers, but the issue of multiple comparable services implemented
   over different protocols.

   The issue of multiprotocol Internet is multidimensional and should be
   analyzed with respect to two simultaneous principles:

      - It is desirable to have a single protocol stack. The community
        should try to avoid unconstrained proliferation of various
        protocol stacks.

      - In reality there will always be more than one protocol stack.
        Presence of multiple network layers is just one of the
        corollaries of this observation, as even within a single
        protocol stack, forces of evolution of that stack will lead
        to periods of multiple protocols.  We need to develop
        mechanisms that maximize the services that can be provided
        across all the protocol stacks (multiprotocol Internet).

2.  Background and Context

2.1.  The MultiProtocol Evolutionary Process

   In an IAB architectural retreat held in 1991 [Cla91], a dynamic view
   of the process of multiprotocol integration and accommodation was
   described, based on the figure below.

            ---------------             --------------
            !             !             !            !
            !             !             ! Interop-   !
            ! Primary     ! >>>>>>>>>>> ! erability  !>>>>>
            ! Protocol    !             !            !    v
            ! Suite       !             --------------    v
            !             !                               v
            !             !                               v
            !             !             --------------    v
            !             !             !            !    v
            !             ! >>>>>>>>>>> !  Resource  !    v
            !             !             !  Sharing   !>>>>v
            !             !             !            !    v
            ---------------             --------------    v
                  ^                                       v
                  ^      --------------                   v
                  ^      !            !                   v
                  <<<<<<<! Harmonize  !<<<<<<<<<<<<<<<<<<<<
                         !            !
                         !            !
                         --------------

            Figure 1: MultiProtocol Evolution Process

   The figure describes the process from the perspective of a community
   working on a single primary protocol suite (such as the IETF/IESG/IAB
   working on the TCP/IP protocol suite.) (Note: It must be kept in mind
   throughout this paper that, while the discussion is oriented from the
   perspective of the IETF/IESG/IAB and the TCP/IP protocol suite, there
   is a complementary viewpoint from the perspective of each of the
   communities whose primary focus is on one of the other protocol
   suites.) There are other protocol suites (for example, IPX, OSI,
   SNA).  Although the primary emphasis of the community is developing a
   system based on a single set of protocols (protocol suite), the
   existence of other protocol suites demands that the community deal
   with two aspects of multiprotocolism. The first is interoperability
   between the primary protocol suite and other protocol suites. The
   second is resource sharing between the primary protocol suite and
   other protocol suites.  Both interoperability and sharing may happen
   at multiple levels in the protocol suites.

   Achieving interoperability and resource sharing is difficult, and
   often unanticipated interactions occur. Interoperability can be
   difficult for reasons such as lack of common semantics. Resource
   sharing can run into problems due to lack of common operational
   paradigms. For example, sharing bandwidth on a link may not work
   effectively if one protocol suite backs off in its demands and the
   other does not. Interoperability and resource sharing both require
   cooperation between the developers/users of the different protocol
   suites. The challenge in this area, then, is to develop mechanisms
   for interoperability and resource sharing that have minimal negative
   affect on the primary protocol suite.

   The very attempts to achieve interoperability and resource sharing
   therefore lead to an attempt to bring the multiple protocol suites
   into some level of harmonization, even if it is just to simplify the
   problems of interoperability and sharing. Furthermore, the
   communications between the communities also leads to a level of
   harmonization. These processes, together with the normal process of
   evolution, lead to changes in the primary protocol suite, as well as
   the other suites.

   Thus, the need for new technologies and the need to accommodate
   multiple protocols leads to a natural process of diversion. The
   process of harmonization leads to conversion.

   While this discussion was oriented around the relation between
   multiple protocol suites, it can also be applied somewhat to the
   process of evolution within the primary protocol suite. So, for
   example, as new technologies develop, multiple approaches for
   exploiting those technologies will also develop. The process then
   hopefully leads to a process of harmonization of those different
   approaches.

2.2.  The Basis of the Internet

   The rapid growth of the Internet has resulted from several forces.
   Some of them are "practical", such as the bundling of TCP/IP with
   Berkeley Unix and the early decision to base NSFNet on TCP/IP.
   However, we believe that there is a more fundamental reason for this
   growth. The Internet (and the TCP/IP protocol suite) were targeted at
   Inter-Enterprise Networking. Although the availability of TCP/IP on
   workstations and the desire to have a single environment serve both
   intra- and inter-enterprise networking led to the use of TCP/IP
   within organizations, the major contribution of the Internet and
   TCP/IP was to provide to user communities the ability to communicate
   with other organizations/communities in a straightforward manner
   using a set of common and basic services.

   Fundamental to this ability was the fact that the Internet was based
   on a single, common, virtual network service (IP) with a supporting
   administrative infrastructure. This allowed a ubiquitous underlying
   communication infrastructure to develop serving the global community,
   upon which a set of services could be provided to the user
   communities. This also allowed for a large market to develop for
   application services that were built upon the underlying
   communications.

   An important corollary to having a single common virtual network
   service available to the end user (open network service) is that the
   selection of applications becomes the province of the end-user
   community rather than the intermediate network provider. By having
   this common underlying infrastructure, user communities are able to
   select their desired/required application services based on their
   unique needs, with assurance that the intermediate networking service
   will support their communication requirements.  We believe that this
   has been of considerable importance in the success of the Internet.

   In addition to providing network layer services for TCP/IP transport
   layer and applications, IP may be used to provide network layer
   services for non-TCP/IP transport layer and applications. Such use is
   clearly beneficial, since it allows preservation of all the benefits
   of a single, common, virtual network service (IP), while at the same
   time widening the set of applications available to the end users.

3.  Directions for Multiprotocolism

   Over the past few years, with the increasing scope of the Internet,
   has come an increasing need to develop mechanisms for accommodating
   other protocol suites. Most techniques have fallen into the regime of
   either interoperability (techniques that allow for communications
   between users of different protocol suites) or resource sharing
   (allowing common resources such as links or switches to jointly
   service communities using different protocol suites.) It must be
   noted that such techniques have been quite limited, with
   interoperability happening primarily at application layers and
   resource sharing happening to limited extent.

   This need to deal with multiple protocol suites has led to discussion
   within the community concerning the role of the IETF/IESG/IAB
   regarding the TCP/IP protocol suite versus other protocol suites.
   Questions are asked as to whether the TCP/IP protocol suite is the
   sole domain of interest of the IETF/IESG/IAB or if the community
   needs also to deal with other protocol suites, and if so, in what
   manner, given these other protocol suites have their own communities
   of interest pursuing their development and evolution.

   The answer to this question lies in understanding the role of the
   IETF/IESG/IAB with respect to the process described above (Figure 1).
   The continued success of the Internet relies on a continued strong
   force for convergence, making sure that the primary protocol suite
   (TCP/IP) is successful through an evolutionary process in
   accommodating both the changing user requirements and emerging
   technologies.

   Since this process requires a continued effort to accommodate other
   protocol suites within the overall Internet, efforts at
   interoperability and sharing must continue. Thus, we can summarize
   the directions for the IETF/IESG/IAB as two-fold:

      - Have as a primary focus the evolution of the primary protocol
        suite (TCP/IP), acting as a force for convergence at all times
        towards a single set of protocols, and

      - Make provision for other protocol suites within the global
        Internet through mechanisms for interoperability and resource
        sharing.

4.  Next Generation Internet Protocol

   The principles described above for multiprotocolism can also be
   applied to the discussions regarding the next generation internet
   protocol. Currently, there are several candidates for IPng, which
   raises the question of how to deal with multiple protocols at that
   level. We note that even if just one is selected, there is an issue
   involved in transitioning from IPv4 to IPng.

   Selection of a single Internet protocol is not the only way of
   dealing with this issue. Even if a layer of ubiquity is required
   (such as that provided currently by IP), we might consider providing
   ubiquity at a different layer. For example, we could imagine having a
   common transport protocol running over multiple internet protocols.
   We also could imagine achieving interoperability by use of common
   application services (such as directory services) running over
   diverse communication services (both transport and network layers).

   These alternatives do not provide the considerable benefits of a
   single internet protocol, and therefore would be undesirable.  Having
   a single internet protocol provides a common communication
   infrastructure across the various networks, thereby achieving the
   following:

      - Communities of end users can select their desired applications,
        independent of the technologies used to support the intermediate
        networks.

      - The common underlying infrastructure provides a common
        marketplace upon which application developers can create new and
        exciting applications. Installation of these applications does
        not require end users to select a corresponding network protocol
        (although some advanced applications may require enhancements,
        such as high-bandwidth approaches).

   Thus, the community (IETF/IESG/IAB) should continue to act as a force
   for convergence by selecting a single next generation Internet
   protocol and developing methods to ease the transition from IPv4 to
   IPng. Specifically, at the applications layer, it is desirable to
   promote different approaches and "let the marketplace decide."
   However, it is unacceptable to treat the internet protocol layer in
   the same way.

5.  Conclusion

   Historically, the IETF/IESG/IAB has acted as a strong force for the
   development of the Internet by acting as a force for convergence on
   and evolution of a single primary protocol suite.  This has served
   the community well, and this approach should be continued for the
   future.  In particular, the IETF/IESG/IAB should:

      - maintain its focus on the TCP/IP protocol suite,

      - work to select a single next-generation internet protocol and
        develop mechanisms to aid in transition from the current IPv4,
        and
      - continue to explore mechanisms to interoperate and share
        resources with other protocol suites within the Internet.

6.  References

      [Cla91]  Clark, D., Chapin, L., Cerf, V., Braden, R., and
               R. Hobby, "Towards the Future Internet Architecture",
               RFC 1287, MIT, BBN, CNRI, ISI, UC Davis, December 1991.

Security Considerations

   Security issues are not discussed in this memo.

Authors' Addresses

   Dr. Barry M. Leiner
   Senior Scientist
   Universities Space Research Association
   625 Ellis Street, Suite 205
   Mountain View, CA  94043

   Phone: (415) 390-0317
   Fax: (415) 390-0318
   EMail: leiner@nsipo.nasa.gov


   Yakov Rekhter
   T.J. Watson Research Center, IBM Corp.
   P.O. Box 218,
   Yorktown Heights, NY 10598

   Phone: (914) 945-3896
   EMail: yakov@watson.ibm.com