HP OpenVMS Systems

Feature Summary

» using USP
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» technical summary

Using USP

• USP is a message broker providing fundamental services for distributed applications. USP can be a building block for your distributed application implementation.

• USP is integrated with HP Secure Web Server (based on Apache).

• USP supports traditional client/server RPC technology and message broadcasting and thus provides tremendous flexibility in the design of your distributed application according to your business needs.

• USP is an excellent tool for integrating existing applications running on OpenVMS systems. USP can be used to web-enable or modernize your applications for use in an intranet or Internet environment.

• USP will help you to develop and deploy a high performance distributed system in a timely and cost-effective manner. An application implemented with USP is reliable and easy to manage.

Features

Service Types

USP handles simultaneous requests for different service types:

• Application Services
• Session Services
• Request Services
• Broadcast Services

An application service is a synchronous, stateful service, that is active as long as a client is connected to it. As soon as the client disconnects, the service is free and the server process exits. A virtual channel is established between the client and the server instance for the lifetime of the server instance. An application service executes the server code in the context of an authenticated user.

A session service is a synchronous stateful, service, that is active for a long time regardless of the client’s connection. The USP allocates a free server instance upon the client’s demand. A virtual channel is established between the client and the server instance for the duration of the session. As soon as the client disconnects, the service is freed but the server instance does not exit. It awaits a connection from another client. A typical example for a session service is a transactional database server.

A request service is a synchronous, stateless service, similar to session service that is active just for the execution of a single request only. A free server instance is allocated by the USP upon the client’s demand. A virtual channel is established between the client and the server instance until the request is pending. As soon as the client receives the response,  the service is freed and the server can accept a request from another client. A typical example for a request service is a transactional database server executing a single query.

A broadcast service asynchronously delivers messages from one or multiple servers to many clients. It is based on the subscribe and publish principle. USP handles the client subscriptions and distributes all broadcast messages to the clients automatically. The delivery of a message is reliable and the ordering of messages within one service is guaranteed. Multiple broadcast services can be defined and active at the same time. Subscription filters can be defined dynamically by the client to specify a fine granularity of the client’s interest. Properly designed filters help to minimize the network traffic and optimize performance.

Subsystems

USP includes the following subsystems:

• USP/RPC Dynamic Remote Procedure Call subsystem
  This subsystem acts as a dispatcher for incoming requests from clients and passes them on to the appropriate server instances. Responses are passed back to the clients synchronously. As opposed to other RPC systems, USP allows you to dynamically set the size of exchanged data.
  
• USP/BCT Publish-Subscribe Broadcast subsystem
  This subsystem manages client subscriptions and asynchronously distributes messages from the servers to all subscribed clients.
  
• USP/SSL-Proxy Secure Communication subsystem
  This subsystem is responsible for secure communication across Internet. It exploits standard security mechanism based on OpenSSL and ensures authentication and encryption of all messages. This subsystem is optional and can be omitted in trusted environments.
  
• USP/Proxy subsystem
  This optional subsystem provides bundling and concentration of messages and thus a significant reduction of network traffic as well as secure communication for local clients. It increases scalability of high performance internet applications.

The business functionality of the client and of the server is application-specific and fully under the control of the developer. USP allows you to divide applications into client and server parts according to your business needs.

The roles of servers and clients are interchangeable. Servers may act as clients and use services provided by other servers. In this way services can be cascaded and distributed across the systems.

Configuration

The configuration of the USP provides the information required to manage and control the services (i.e. the location of services, relationships between services and servers or the number of particular server instances). Service types can be configured as:

• local - the service is defined on node B.
• remote - the service is defined on node A, but the server runs remotely on node B. The access to USP on node A is required to resolve the location of the server.
• re-directed - the service is defined on node A and all messages are passed through the local USP to the USP on node B.

All service types are fully transparent to the client. Any client can connect to any type of service from any node within the network.

Local services are the most frequently used service types. Remote services are used to access shared resources from several locations without the need for data replication. The re-directed service is one of the most powerful features of the USP. It bundles the network traffic between the message brokers for the USP/RPC subsystem and provides fan-out of messages for USP/BCT subsystem. This means, that for all clients subscribing to a re-directed USP/BCT service, only a single message is passed between node A and B. See the schema above.

Location Transparency

The location of a service is defined in the configuration file, not in the client application. This allows services to be moved across nodes and platforms by simply revising the configuration. With a small application effort, load balancing can be implemented for multi-node, high availability systems.

Dynamic Server Control

Each service can be served by multiple server instances. The initial and maximal number of server instances per service can be configured. The USP monitor dynamically controls the start-up and shutdown of server instances. A time-out definition optimizes the overall system load and reduces concurrent network connections.

Error Isolation

Each server instance executes code in the context of a separate process. The failure of one server instance has no impact on other instances. USP will automatically start a new server instance to fill the gap.

Communication

The USP handles TCP/IP or DECnet network protocols transparently. These protocols can be mixed on the same node. The communication between the client and the USP and between the server and the USP may use different protocols. Data passed over the network is in XML format. The communication protocol (XML/RPC) allows the transport of dynamic objects. See "Security" for the encryption feature. With TCP/IP, multiple unicast is used for BCT services. UDP is not supported.

Security

The network traffic between the client and the server can be secured with industry standard technology. SSL 3.0 / TLS 1.0 is used for authentication and encryption. Certificate handling is shared with the Secure Web Server (based on Apache). Authentication data is available to the server and can be used for further authorization.

The application service allows execution of a server in a user context and requires authentication with a user name and password, that is valid in the server environment.

Connections from clients to the USP are always initiated from the client, even for the Broadcast Services. Network traffic can be screened by a firewall. The definition of redirected services, together with the usage of USP/Proxy located between two firewalls, allows development of high security systems, suitable for critical applications like electronic trading systems.

Operation and Management

A built-in monitor allows you to create, modify and maintain an entire configuration. You can create and start new services at run-time without disruption of other running services. Each service has an individual state and is controlled individually.

The monitor utility allows observation of all services, network connections and the USP message broker itself. It is a reliable building block for mission critical applications requiring a non-stop execution environment.

Integration

The USP is an optimal tool for integrating existing applications running on OpenVMS systems. Use it to Web-enable your application with a Web service or build transactional jacket-services around your application. Because of its open nature USP can seamless integrate any type of application with a reasonable effort.

Development Support

USP provides powerful features to speed up software creation and testing as well as tools to ensure high quality of the product. The following features are included:

• Definition of USP configuration and service interface in XML format (export/import)
• Interactive debugging support for any type of server on OpenVMS platform.
• Prelude procedures for environment specific set-up for each service.
• User definable parameters passed as attributes to a server.
• Trace and log facility for troubleshooting

Technical Summary

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