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Host Sessions are 3270 or 5250 screen sessions that have been started by some agent process. In many environments, the "owner" of a screen session is a 3270 controller, such as a 3174 control unit, or a 5250 controller. These controllers represent one or more connected terminal devices such as 3278, 3279 or 5251-11 terminals. When a user turns-on his or her terminal, a host session is started in the control unit, and the logon screen (first screen of the session) appears.
When a user has a personal computer, the personal computer can execute software to provide terminal emulation. When terminal emulation is installed on a PC, the user is able to open one or more windows and view host 3270/5250 sessions in each of those windows. When this happens, the host session is managed by the terminal emulation software executing in the PC.
Screensurfer Host Sessions
The Screensurfer host session is started when the user selects the "CONNECT" on the home page or from a bookmark. This starts a host session in the Screensurfer server and is the same as if a user turned-on a physical terminal device connected to a controller.
The Screensurfer host session will continue being "live" until the user selects the "Exit" link. The session can also be stopped if Screensurfer times-out the user due to lack of activity, or the Screensurfer console operator stops the user's host session.
At any time, all of the active Screensurfer sessions may be viewed in the Adminstrator's console by clicking on the "Active" button.
SNA-based Host Sessions
Systems Network Architecture, or SNA, is a definition used in many IBM networks to deliver host screen sessions to the end user. In many organizations, SNA access to 3270 applications is the only option available, as the primary network connecting to the mainframe is not executing any internet protocols.
For Screensurfer to connect to SNA-based Host Sessions, a Microsoft SNA Server or IBM Communications Server is required to be installed on the same network as the server that Screensurfer is installed on. SNA Server or Communications Server then provide to Screensurfer the necessary response unit interface (RUI) for accessing the SNA sessions. A terminal emulation package on a PC has a similar requirement for such a gateway, but may use a proprietary gateway such as the Novell SAA Gateway (not currently supported by Screensurfer).
TN3270 Host Sessions
When available in an organization, the TN3270 host session is provided using internet protocols to any supporting client addressable in the network. TN3270 provides an Internet access mechanism to host sessions and is easier to configure and access from a personal computer or server than is an SNA-based session.
TN3270 sessions are usually provided from some kind of gateway, which may be Microsoft SNA Server or a UNIX-based system. Many router manufacturers have also started to offer TN3270 protocol conversion as a built-in function of the router. This greatly simplifies 3270 application access, as the router is a natural node to provide this functionality.
For those with very up-to-date versions of IBM mainframe software installed, TN3270 may be directly supported from the "top down," with no need for intermediate gateways or router options.
Screensurfer accesses TN3270 sessions directly using standard internet sockets and the TN3270 protocol.
TN3270E Host Sessions
An extension to TN3270, the TN3270E protocol offers additional functionality over standard TN3270, and Screensurfer supports both full TN3270E as well as "basic" TN3270E. A chief advantage of TN3270E is the ability to specify specific Logical units (terminal identifiers) when logging on, which provides additional compatibility in some environments.
TN5250 Host Sessions
For connecting to an AS400, Screensurfer supports the TN5250 protocol. This is favored by many purchasers of the latest AS400 models, which incorporate high performance IP-processing capabilities and naturally support TN5250.
For older AS400 models, or those not supporting TCP/IP, a Microsoft SNA Server license installed either on the same machine as Screensurfer or on another server, can provide direct connections to the AS400 and provide the TN5250 protocol to Screensurfer.