Introduction to TRANSFER Delivery System

Deciding to Use TRANSFER Applications Developing TRANSFER Applications
5-2 109426—Introduction to TRANSFER Delivery System
Deciding to Use TRANSFER Applications
With all its versatility and efficiency, there are times when you might decide not to use
TRANSFER. Depending on traffic, priorities, processor load, and network availability,
TRANSFER cannot always guarantee that a package will arrive at a precise time. The
narrower the timeframes specified for packages, the greater the chance that external
factors can prevent on-time delivery.
Application designers must consider the relationship between two application
requirements: the need for packages to be delivered within a narrow timeframe and the
need for a certain percent of packages to be delivered. An application that requires both
a narrow timeframe and a high rate of successful deliveries probably should not use
TRANSFER. For example, interactive dialogue between operators requires both
immediate and guaranteed delivery; therefore, TRANSFER might not be well suited to
such an application.
Just as TRANSFER cannot guarantee the exact delivery time of a package, it cannot
guarantee the amount of time a package will spend in transit. An application can send a
package to multiple recipients, but it cannot count on all recipients receiving it
simultaneously. Even two recipients at the same node might receive the package at
different times. For instance, a local recipient on a remote distribution list is likely to
receive it later than another local recipient who is not on the remote distribution list.
Developing Clients
A client is a requester program that provides the interface between correspondents and
TRANSFER, such as the PS MAIL clients offered by Tandem. Most clients are user-
written. Clients are usually SCREEN COBOL program units executing within
PATHWAY TCPs. The advantages of using SCREEN COBOL clients are significant:
■ Interprocess communication is easier to code in SCREEN COBOL than in other
languages.
■ A SCREEN COBOL program can take advantage of PATHWAY server classes and
online load-balancing features.
■ TRANSFER requires requesters to have TMF, and TMF is easy to code in SCREEN
COBOL.
■ A TCP can run as a fault-tolerant program; the application programmer need not do
any coding to provide for fault tolerance.
■ TRANSFER requires PATHWAY: the TRANSFER asynchronous requesters , the
PS MAIL clients, and the ADMIN and TMANAGER programs management
applications are written in SCREEN COBOL to issue requests to TRANSFER
server classes. When you write a client in SCREEN COBOL, all resource
management for your application is handled by PATHWAY. By having all
components under PATHWAY control, not only can you manage your resources
better, but the application is easier to administer and tune.