Alan Whitney がVSI検討グループのメンバー宛に送ったメール(1999.4.7)


This note is to invite you to become a member of the 'VLBI Technology Coordination Group' as part of an effort to try to establish standardization in VLBI data interfaces.


There has recently been renewed interest in both the astronomical and geodetic VLBI communities in trying to define a 'standard VLBI interface'. This is not the first time that such activity has taken place, but as the VLBI communities have grown over the past few years, the aggravations and complications of incompatibilities of various VLBI data systems have increased, as you are no doubt aware. This has now led to a somewhat more formalized structure within both the geodetic and astronomy VLBI communites to try to address the problem. As a result, two organizations, one from geodetic VLBI and one from astronomical VLBI, are now working towards a common goal.

The geodetic VLBI community has recently formed the International VLBI Service (IVS) organization to organize, coordinate and standardize geodetic VLBI practices. IVS counts some 80 organizations from 14 countries among its charter members, quite a few of them also involved with astronomical VLBI. Among the members of the IVS board of directors are a Technical Coordinator (Alan Whitney, MIT Haystack Observatory) and Technical Representatives (Wayne Cannon, York University, Canada and Tetsuro Kondo, CRL, Japan). Among the directives to this group is to 'strive to ensure the highest degree of global compatibility of VLBI data-acquisition systems'.

Within the astronomy VLBI community, the Global VLBI Working Group (GVWG), originally formed to assist the organization and execution of the space-VLBI programs of VSOP and RadioAstron, is still in place, with Richard Schilizzi of JIVE as the chairman. Some time ago Richard appointed Alan Whitney and Wayne Cannon as co-chairman of the GVWG Technology Coordination Group and charged them with, among other things, to pursue the holy grail of VLBI compatibility. We have been a bit slow to answer the charge, but action is now picking up.

As part of the process to move towards the compatibility goal, we feel that it is necessary to involve a group of technical experts, namely yourselves, who have had wide experience with the existing set of VLBI data-acquisition and correlator systems, and who collectively can exercise their wisdom to define a 'standard VLBI interface' towards which the VLBI community can strive. This idealistic future will not happen overnite, but the goal is to start on a path that will show the way, and then to encourage the worldwide community to follow it as systems are updated or created.

The Process

The process for defining and implementing a standard is not yet fully specified, but we propose the following informal guidelines:

1. Place a draft standard on the table (one exists, which you may or may not have yet seen).

2. Interact via e-mail communications to exchange comments, suggestions and constructive criticisms. [An e-mail exploder will be set up for easy communications within the group.]

3. Pursue a gentleman's agreement on a standard. At some point it may be necessary for some or all of the members of the committee to meet face-to-face to hammer out agreements on sticking points.

4. Formalize the standard in a technical memorandum to be distributed to the community.

5. Update the standard as necessary.

6. Guide and encourage implementation of the standard whenever possible.

If you feel this process can be improved upon, we are happy to hear your suggestions.

The Proposed Members of the Committee

The proposed members of the committee, covering both astronomical and geodetic interests, are:

Alan Whitney, MIT Haystack Observatory, USA (IVS Tech Coord, GVWG Tech Coord Group co-chair)
Wayne Cannon, York University, Canada (IVS Tech Representative, GVWG Tech Coord Group co-chair)
Tetsuro Kondo, CRL, Japan (IVS Tech Representative)
Brent Carlson, DRAO, Canada
Dick Ferris, ATNF, Australia
Dave Graham, MPI, Germany
Nori Kawaguchi, NAO, Japan
Sergei Pogrebenko, JIVE, The Netherlands
Jon Romney, NRAO, USA
Ralph Spencer, Jodrell Bank, England

Goal of the Standard

The intent of the VSI specification is to define a standard electrical and timing interface, along with a control philosophy, for the transmission of VLBI data. The interface should be equally applicable to recording (disc, tape, optical), and real-time or near-real-time data transmission over networks or dedicated wires. We do not expect to devise a fully 'plug and play' interface, but rather an interface which is directly hardware-compatible and will likely require some software adaption.

If the development of a VSI specification is successful, it may be desirable to try to extend standardization even further, defining standard 'sampler modules' and/or 'BBC modules' which may be of value to the VLBI community.

A Draft Proposal

Two complementary draft proposals are now available for review:

1. A proposal drafted by Alan Whitney following discussions arising from a meeting in Jan 99 in Japan involving Canadian, Japanese and American representatives. This document outlines primarily the high-level description of the proposed interfaces and lacks detailed electrical and timing information, which the Tetsuro Kondo and his associates at CRL graciously offered to fill in. This document, along with comments already received, can be viewed at

2. An electrical and timing draft proposal arising from work within CRL and with discussions in the broader Japanese community. This document can be viewed at

If you are willing to participate in this effort, please respond to Alan Whitney at with a short note. Please also indicate if you are willing to be added to the VSI e-mail exploder at so that we may efficiently communicate. If you are unable to participate, perhaps you could suggest an alternate representative from your organization.

We look forward to hearing from you in the near future.


Alan Whitney
Wayne Cannon
Tetsuro Kondo