Draft Report on the
WORKSHOP ON CO/CL INTERWORKING
Corporation for National
Research Initiatives
July 24-26, 1990
Reported by Workshop Co-chairs
Phillip Gross (CNRI) and Les Clyne (JNT)
1. Introduction
On July 24-26, 1990, an invited panel met at the Corporation for
National Research Initiatives in Reston Virginia to consider the
issues involved with interworking between protocol stacks based
on Connection-mode Network Service (CONS, or CO) and
Connectionless-mode Network Service (CLNS, or CL). The main example
of a CO stack is OSI TP0 over X.25. Examples of CL protocol
stacks include OSI TP4 over CLNP and TCP over IP.
The workshop was convened at the direction of RARE and the U.S.
Federal Networking Council (FNC). The meeting was organized and
co-chaired by Les Clyne (UK Joint Network Team) and Phillip Gross
(Corporation for National Research Initiatives). An electronic
mailing list was established for use by both attendees and a wider
audience of experts.
This report gives an overview and synopsis of the deliberations at
the meeting, and it describes the outcome.
The major result of the workshop is given next in section 2, followed
by a brief synopsis of the workshop deliberations in section 3.
Finally, the milestones for concluding the papers and reporting
the results are given in section 4.
Attachment 1 provides the Terms of Reference for the meeting, agreed
to beforehand by RARE and the FNC. Attachment 2 gives the working
agenda, which provided the framework of the workshop. Attachment 3
lists the attendees. Attachment 4 gives an annotated list of documents
distributed to attendees prior to the workshop.
2. Workshop Conclusions
The workshop attendees decided to address the issues of CO/CL
interworking in a series of 4 documents, the first of which would
serve as an introduction and tutorial. The following description
of the approach and the 4 document set is taken from the first document
``An Approach to CO/CL Interworking -- Part I: Introduction'', M.T.
Rose (editor):
``Towards a Solution
In the best solution, there is a single mode of OSI network
service which is truly ubiquitous. In this case, a single
community exists and interworking is achieved through the use
of network-layer relays. In preparation for this long-term
scenario, technology must be identified and perhaps
incrementally advanced to promote a homogeneous network
service. In the meantime, a large TCP/IP-based community
exists and a TP0/CONS community is growing. Some interworking
requirements exist today and these requirements are expected
to increase. This suggests a short-term solution to address
immediate requirements, an intermediate-term solution
applicable as the TP0/CONS community grows large, and a long-
term solution applicable once two large OSI communities, one
CO-mode and the other CL-mode, exist and have interworking
requirements.
Thus, an approach towards the solution consists of three
parts, and three companion memos have been been written, each
corresponding to the short-term, intermediate-term, and long-
term:
In the short-term, one must rely on TS-bridges to provide
connectivity between non-internetworking communities. The
first companion memo, (see [a] below) describes the operation of
TS-bridges in such an environment.
The fundamental component of the long-term is the use of
network-layer relays, supporting either the CO- or CL-mode OSI
network service. Use of network-layer relays is well-
understood. The second companion memo, (see [b] below), describes
how steps can be taken to provide full CONS-interworking.
However, even in the long-term, situations will arise in which
both network services are required. In this case, TS-bridges
are still necessary. The third companion memo, (see [c] below),
describes the operation of TS-bridges in such an environment.''
[a] M.T. Rose (editor). An Approach to CO/CL Interworking --
Part II: The Short-Term -- Conventions for Transport-
Service Bridges in the absence of Internetworking, CO/CL
Interworking Workshop, (July, 1990).
[b] C. Huitema (editor). An Approach to CO/CL Interworking
-- Part III: The Intermediate-Term -- Provision of the
CONS over TCP and X.25 subnetworks, CO/CL Interworking
Workshop, (to be published).
[c] C. Huitema (editor). An Approach to CO/CL Interworking:
-- Part IV: The Long-Term -- Conventions for Network-
Layer Relays and Transport-Service Bridges in the
presence of Internetworking, CO/CL Interworking Workshop,
(to be published).
3. Synopsis of Workshop Deliberations
This synopsis follows the final agenda (given in Attachment 2).
3.1 TUESDAY, JULY 24, 1990
INTRODUCTIONS ---
Bill Bostwick (Executive Director of the FNC) opened the meeting
with greetings to the attendees,and a discussion of the spirit of
cooperation between U.S. and European networking interests.
Following the opening round of introductions, the attendees examined
and agreed on the Terms of Reference and agenda with only minor adjustments.
PRESENTATIONS ---
Note: Hardcopy of all slides and handouts were provided to attendees, and
can be provided by Phill Gross (CNRI) upon request.
--- Kevin Mills (NIST)
Kevin Mills described the two main OSI protocol stacks (i.e., CO and CL).
He also described the current UK and US OSI profiles (ie, GOSIPs) for
utilizing OSI in each respective government; His proposal involves dual
stack machines on wide-area networks; He suggests that his proposal may
look more attractive after we've gone through all the issues involved in
transport service bridging; He also showed the DoD approach to interworking
(pure stacks with application layer bridging).
--- Les Clyne (JNT)
Les Clyne described RARE, Eureka, and COSINE. Briefly, RARE is the association
of European research networking organizations and their users, with over 20
member countries in Europe; Eureka formed COSINE (Cooperation for OSI
networking in Europe); RARE developed the COSINE specifications). He showed
slides of COSINE implementation funding and timetable for pilot projects and
services. He also showed IXI service access topology and status. (IXI
provides 1984 X.25 services.)
--- Marshall Rose (PSI)
Marshall Rose described the transport layer and the CO/CL problem. He defined
the Transport-Service Bridge as a solution, which uses transport service
primitives to ``copy'' from TS-stack to TS-stack. He gave a good synopsis
of problems with TS-bridging (see his slides), and concluded by explaining
terminolgy of ISO DTR "Active transport layer relay" vs "Passive transport
layer relay").
--- Mitchell Tasman (University of Wisconsin)
Mitchell Tasman's presentation was based on the distibuted Wisconsin paper
(see Attachment 4) which described the Wisconsin implementation of a
transport-service bridge.
--- Christian Huitema (INRIA)
Christian Huitema was concerned with the problem of ``locating''the
TS-bridge. In current implementations, the originating host is required
to know which destination addresses need to be reached via a TS-bridge,
and the originating host also needs to know the address of the TS-bridge.
He proposed treating transport-service bridge as network level gateway,
and let IS/IS help solve the problem of locating the bridge. This removes
the knowledge and functionality from the end system allows reliance on the
networking and routing infrastructure to solve for you. This would not be
a ``near-term'' solution, but it was viewed favorably by many attendees as
a "longer-term" approach for alleviating the necessity of the originating
host to know the TS-bridge address. He described various methods to cope
with multiple parallel bridges/relays, including NSAP gateway subscription
and modification of TP4. He also described enhancements to RFC 1006 based
on the X.25 Subnetwork Convergence Protocol to make TCP look like a special
case of ISO CONS. The associated routing involved using ISO 10030
(CONS ES Routeing Exchange Protocol).
DEVELOP LIST OF ISSUES ---
Les Clyne led a discussion of issues that needed to be solved. This
included both implementation and deployment issues, and short- and long-
term issues.
The issues included:
- Determination of TS-stack associated with a network address
- Ordering of addresses
- TS-bridge addressing
- Accounting
- Access control
- Load balancing
- Concatenation of IFUs
- Availability of address extension facilities (X.25(84))
- Routeing to the gateway
- Directory service and location independence
- Address administration at the gateway
- Modifications to the transport protocol/use of TP user data
- Extensions to RFC 1006 to support OSI NS
- Coordination of 8473 PDU Data Unit identifiers and Transport
Reference number allocation
- Alignment with DTR 10172
- Impact on end system implementations
The requirement to be able to map between the RFC 1006 environment and
TP0/CONS, where addresses on the CONS side are carried in the X.25(84)
address extension fields, if available, was raised.
3.2 WEDNESDAY, JULY 25, 1990
Rose distributed a proposal for separating the TS-bridging problem
into a short and long term approach. This proposal was modified in
discussion to encompass a 3 step plan. In the short term approach, we
would specify a method for encoding TS-bridge addressing in the NSAP. In
the long-term, we would focus on Huitema's aproach of relying on the
network layer to locate TS-bridges. Huitema's other proposal for
enhancements to RFC 1006 would also be included as part of the transitional
framework to the long-term solution.
Other issues, such as security and end-to-end integrity were deemed beyond
the scope of the workshop.
The group decided to use Rose's draft ``Implementation Agreements for
Transport Service Bridges'' (see Attachment 4), as the basis for
an introduction to the workshop conclusions. In effect, Rose's paper
was reworked into 2 documents. one document would contain a transport
service bridge tutorial (which would also be applicable for reference
in the long-term approach) and an explanation of the overall plan.
The specific addressing methodology for the short-term approach would
be placed into a second 2-4 page paper.
Including two other papers to describe 1) the long-term approach, and
2) the proposed transitional modifications to RFC 1006, the group proposed
a four document set:
Doc #1 - I) TS-Bridge Tutorial and relation to ISO
II) Explanation of Strategies for CO/CL Interworking
- short-term solution (TS-Bridge Addressing)
- Transitional modifications to RFC 1006
- long-term
Doc #2 - Short-term specification
Doc #3 - Transitional Modifications to RFC 1006
Doc #4 - Long-term Specification
a. Subnet Gateway
b. Internet Gateway
Rose reworked his draft into documents #1 and #2 for review the following
morning. Huitema volunteered to draft document #3 at the meeting for review
on the following morning. The group agreed on a framework for document #4,
and Rose produced an outline for the following morning.
3.3 THURSDAY, JULY 26, 1990
On the concluding morning, the group reviewed Documents #1 and #2 by
Rose, and document #3 by Huitema. Huitema agreed to produced document
#4 after returning to France. After review and editing by the attendees,
Rose produced preliminary drafts of document #1 and #2, and distributed
these documents to the Workshop mailing list for review. Finally, we
developed the plan for reporting the workshop results to CCIRN, RARE, FNC,
and IAB/IETF. These proposed milestones are given in the next section.
4. Workshop Milestones
Documents and workshop report
July 1990 Produce drafts of Documents 1 and 2; mail to COCL
electronic mailing list for wider review (DONE)
Aug 1990 Produce preliminary workshop report for RARE and FNC,
Distribute initially to workshop attendees (DONE)
Aug 1990 Produce drafts of Documents 3 and 4 and distibute
for review (DONE)
RARE/FNC Review
Sept 1990 Present workshop report to RARE CoA and FNC
Sept 1990 Present workshop results (report and other
appropriate documents) for review at RARE WG4
Oct 1990 Present workshop results (report and other
appropriate documents) for review at CCIRN
Dec 1990 Present workshop results for approval at RARE
CoA and FNC
IETF/IAB Review
Sept 1990 Present workshop results (report and other
appropriate documents) to IETF OSI Integration
working group for review
Sept 1990 Distribute Documents 1-4 as IETF Internet-Drafts
Dec 1990 Documents 1-4 reviewed in IETF, recommendation
forwarded to IAB
Jan 1991 IAB considers Documents 1-4 to be published as
Internet RFCs
Attachment 1 -- Workshop Terms of Reference
Terms of Reference
for
Workshop on CO/CL Interworking
July 24-26, 1990
The use of different OSI lower layer architectures will act as an
impediment to the development of global OSI connectivity if it is
not possible to interwork between them. This problem is
particularly significant for interworking between the US and
European research communities. Several solutions have been
proposed to provide interworking and there is a need to agree a
specification which meets the service requirements of the
international research community. The CO/CL Workshop has been set up
to recommend a specification that can be used to provide suitable
interworking units.
The workshop
a) is asked to develop a technical specification for a general
purpose TP0/CONS-TP4/CLNS interworking unit, taking into
account existing or proposed solutions. The requirement to
interconnect large national or international service networks
is particularly important.
b) should take into account the ISO work in this area and the
recommended specification should align with the emerging ISO
technical report wherever possible.
c) is also requested to advise on the technical specification of
a convertor which supports TP0/X.25-TP0/TCP interworking
as there is an immediate requirement in this area to support
OSI applications.
The participants in the workshop will be invited experts from the
US and Europe. It is expected that the workshop will hold one
meeting complemented by the use of electronic mail to support its
activities. The workshop is requested to report to RARE and FNC
in autumn 1990.
Attachment 2 -- Workshop Agenda
Agenda and Issues for
Workshop on CO/CL Interworking
July 24-26, 1990
o Introductions and Administration
- Introduction by Bill Bostwick (CCIRN Co-Chair,
FNC Executive Director)
- Agreement on chairing and secretarial duties
- Review Terms of Reference
- Agreement on agenda and objectives.
o Presentations:
- Kevin Mills (NIST) -- US OSI activity
- Les Clyne (JANET) -- RARE/COSINE OSI activity.
- Marshall Rose (PSI) -- Transport service bridging.
- Mitch Tasman (U. of Wiscosin) -- ISO TP4 - TP0 gateway.
- Christian Huitema (INRIA) -- NSAPs and transparent OSI
transport bridges.
- Others Issues or Approaches?
o Determine what protocol stacks need to interwork and what priority the
workshop should place on developing solutions for each scenario.
- Issues -- Is it mainly connection between large CO and CL WAN
communities with one or a small number of interworking units in
the same geographic location, or do we deal with WAN-WAN
connections in different countries, LAN-WAN-WAN-LAN connections
with multiple serial interworking units and alternative routes etc.
The complexity has an impact on problems of routeing and address
management. On what timescales are the various interworking
units needed ?
o Develop detailed description of candidate solutions (e.g., Transport
bridging, ISO Active Transport Level Relay, etc) for each
combination of protocol stacks that need to interwork.
Issues to consider include:
- Impact on end systems of proposed solutions.
- Address management.
- Routeing considerations.
- Agreement on further work, assignment of responsibilities,
timescales, etc.
o Reporting to RARE/FNC.
Attachment 3 -- Workshop Attendees
Workshop on CO/CL Interworking
at
Corporation for National
Research Initiatives
July 24-26, 1990
Name Organization Email
William Bostwick Federal Net. Council bostwick@darpa.mil
Les Clyne Joint Network Team L.Clyne@RUTHERFORD.AC.UK
Walid Dabbous INRIA walid.dabbous@MIRSA.INRIA.FR
Steve Goldstein Nat. Science Foundation goldstein@note.nsf.gov
Phill Gross Corp. Nat'l Res. Init. pgross@nri.reston.va.us
Christian Huitema INRIA Christian.Huitema@MIRSA.INRIA.FR
Steve Kille Univ. College London S.Kille@CS.UCL.AC.UK
Kevin Mills NIST mills@osi.ncsl.nist.gov
Julian Onions Nottingham University J.Onions@cs.nott.ac.uk
Marshall Rose Perf. Sys. International mrose@psi.com
Rachid Sijelmassi NIST sijel@osi.ncsl.nist.gov
Mitchell Tasman Univ. of WI - Madison tasman@cs.wisc.edu
Full postal mailing addresses and phone numbers of each attendee are
available on request from CNRI:
Corporation For National Research Initiative
1895 Preston White Drive, Suite 100
Reston Virginia 22132
Attn: Phill Gross
Phone: 703-620-8990
FAX: 703-620-5490
Attachment 4 -- Distributed Documents
There were several documents and position papers distributed to attendees
that provided a beginning point of view for the workshop. Many of these
documents were authored by workshop attendees. An annotation of each
distributed paper is provided below (based on the description given in
``An Approach to CO/CL Interworking -- Part I: Introduction''. These
documents can be provided on request by either of the workshop co-chairs.
- In "Implementation Agreements for Transport Service Bridges",
Rose outlined the basic model of transport-layer relaying and
proposed the basis for an approach in the short-term. This
formed the basis for the first document of the workshop ``An
Approach to CO/CL Interworking -- Part 1: Introduction''.
- In "A Survey of Solutions to the Connectionless/Connection-
mode and the OSI/DoD Interworking Problems", West and
Sijelmassi outlined the various approaches and assigned
comparative metrics.
- The ISO/IEC Draft Technical Report 10172 (SC 6 N 5906)
outlined a framework for transport-layer relaying.
- In "An ISO TP4-TP0 Gateway", Landweber and Tasman described an
implementation of a TS-bridge.
- In "An NSAP approach to build transport OSI transport bridges,
Huitema and Dabbous described how ES-transparency can be
achieved, and in "Extension of OSI TP4 to support transport
bridging", they described modifications to the TP4 protocol to
aid in achieving the ES-transparency effect.
- In "CO-CL and TCP/IP Interworking and Coexistence", Mills
suggested that the problem can be solved by using a single
mode of network service (CLNS), and further that
interoperability with TCP/IP-based environments would occur
through the use of application gateways.
Copies of these documents are available upon request from CNRI:
Corporation For National Research Initiative
1895 Preston White Drive, Suite 100
Reston Virginia 22132
Attn: Phill Gross
Phone: 703-620-8990
FAX: 703-620-5490