Channels in OHP

From: Hugh Davis (
Date: Fri 06 Jun 1997 - 03:35:50 CDT

This mail is specifically for the attention of Pete Nuernburg and Ken Anderson (because they have already expressed opions on this subject) but mailed to the list, as all replies are welcome.

_(fwd link)_In OHP we originally inserted the idea of a "Channel". This was an opaque identifier inserted by the linkservice which was unique for that linkservice, and which enabled the linkservice and the client to communicate assynchonously. i.e. one could send a message, and the other could reply at a later time, rather than hold the socket open until it is ready to reply. In otherwords, this channel held the required information to route the message!

I have had some trouble with this as people keep telling me that routing information should not be in the protocol. However I find that this information *does* need to be present,since the linkservice and the session manager actually have to look at this information at times.

Following a chat with Pete some time ago, Sigi and I have a proposal that contains a Session Id appended to all messages and this would be made up of the following information:

    _(fwd link)_
  1. HostId (typically IP address)
  2. SessionManagerId (typically the Port the session manager is listening on. The session manager is what used to be called the client side shim or Runtime or tool integrator, and there is one per machine per user)
  3. ApplicationId (typically the name of application)
  4. SubProcessId (because some applications may manage more than one doc)

The linkservice must be able to understand 1 & 2, so they cannot be opaque. 3 and 4 need only be understood by the session manager which allocated them in the first place, so their form is unimportant.

We also find it necessary to carry a UserId on every message for authentication and to be ready to deal with later extensions for collaboration.

Comments would be welcome.

Hugh and Sigi.

Hugh Davis                        ( )
The Multimedia Research Group,    ( )
Electronics and Computer Science, ( Room 1051, Building 16)
University of Southampton,        ( Tel: +44 (0)1703 593669 )
Southampton,  SO17 1BJ, U.K.      ( Fax: +44 (0)1703 592865 )

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