Re: The "Presentation" Layer

[Nathan Andelin <nandelin@xxxxxxxxx>]

> From: john e
> A green-screen terminal is also a peer in the network,
> but in practice it acts more as a server, and the program
> running on the host is the client. E.g. the program requests
> the terminal to display a format. So most of the time a
> terminal takes on the server role. However, at first, when
> logging into the system, a terminal initiates a session and
> has the client role.


John,

It seems to me that the problem with your definition of 5250 protocol is that it fails to take into account the role of the Workstation Controller, which is server based, and acts as an intermediary between the terminal (or terminal emulator), and the application program.

My understanding is that the terminal never functions as a server; only a client.  The Workstation Controller acts as an intermediary server to both the terminal and the application program.  The terminal is never requested to display a format.  That's the role of the Workstation Controller.  The Workstation Controller generates the 5250 data stream for the terminal, and the terminal displays it.

The terminal is never in control of the conversation.  The Workstation Controller is.  It can say, "Your session is expired", for example.

So I view 5250 as a client-server protocol, comparable to HTTP.  The main difference is that the "intelligence" of the browser is vastly superior.

Nathan.