Introduction

The synchronous method is where a Tmax client or server requests a service and receives a response. In the opposite case, when the remote node requests a service, X25GW forwards the request to a Tmax service and returns the result to the remote node.

In the former case, X25GW operation depends on whether the Tmax service that sent the request to the remote node is blocking or non-blocking. If non-blocking, the result from the remote node is immediately returned to the requested channel.

When a Tmax client or server sends a request to the remote node in the synchronous mode, X25GW and the remote node must share the UID (unique ID).

In a blocking service, a Tmax server or client requests a service to X25GW and waits for a response. If the service that received the client request makes a tpcall to the X25GW service, then the Tmax service (SVC1 in the diagram) blocks until it receives the result from the remote node.

When X25GW executes, the service called by the client calls X25GW and blocks until it receives a reply. Even when tpacall is called, tpgetrply blocks until it receives a reply. In order to accommodate a large number of requests, many servers are required to make up for the blocking time period.

A blocking service is suitable for external communication since many servers are needed to prepare for external system failures (machines, network).

The following diagram shows the operating structure of X25GW when calling a service in a blocking synchronous mode.

A non-blocking service cannot be used when a Tmax client directly requests services to X25GW. It requires an intermediary server between the client and X25GW to send/receive the request/reply to/from X25GW and return the reply to the client. The sending and receiving services are placed in front of X25GW. The Tmax client calls the sending service, and the sending service terminates after forwarding the request to X25GW.

X25GW requests a service to the remote node, receives a reply, and sends it to the receiving service. The receiving service returns the reply to the client. In other words, the client requests a service and receives a reply (synchronous), but the server forwards the request and then terminates (asynchronous).

A non-blocking service can process more requests with fewer servers than a blocking service. Since a blocking service calls X25GW and then blocks, it requires more server processes to handle multiple requests simultaneously. However, since a non-blocking service is terminated after performing its tasks, it can process more requests with a small number of server processes.

A non-blocking service is more efficient for communication with external institutions.

The following diagram shows the operation of X25GW in a non-blocking service.

A remote node initiates a service request to X25GW. X25GW calls the requested service and receives a reply and sends it to the channel that requested the service. The remote node cannot make more than MAXSACALL number of concurrent calls to X25GW as defined in the Tmax environment file.

The remote synchronous call method is the most universal way of calling a Tmax service from a remote node. X25GW stores the remote node’s channel information and uses it to find the channel to send the reply. Other requests can be made as needed before the reply is returned to the channel. Since X25GW does not block the channel from the remote node and continues to receive other requests, requests are processed according to the X25GW operation method.

The following diagram shows the operation of X25GW when a service is called in the remote synchronous method.

The asynchronous method is where a Tmax client, server, or remote node requests a service and does not receive a reply, or the request is processed in another program. A Tmax service requests the service to X25GW and another service receives a reply.

A client request is processed asynchronously via tpacall without receiving a reply. Reversely, a service can be initiated from the remote node and may not receive a reply or receive the reply through another channel. This is called the asynchronous method.

A Tmax service makes a request via tpacall with TPNOREPLY to X25GW and then the service terminates. X25GW sends a request to the remote node and when it receives a reply it makes a tpacall to another service.

The following diagram shows the X25GW operation in an asynchronous service request.

When a remote node requests a service to X25GW, X25GW calls the Tmax service via tpacall. After processing, the Tmax service sends a reply to X25GW, and X25GW uses any available channel to return the reply to the remote node.

The following diagram shows the operation of X25GW when a service is requested from the remote node asynchronously.

The gateway header is used when calling X25GW from the Tmax client or server. Other X25GW libraries must be used to use the gateway header. The libx25gw.a, and libx25gw.so libraries are normally used, but the libx25gw.gwh.a, or libx25gw.gwh.so library must be used when using the gateway header. The gateway header must be placed in the very first offset position in all data buffers. When using the user header, it must be placed after the gateway header in the buffer.

The gateway header is used for various purposes, but only the svc item can be used in X25GW. This item is used to specify the service name to process the reply data when using the non-blocking mode or the asynchronous method. The gateway header is usually used when a service request is processed in message units without using a user header.

A non-blocking or asynchronous X25GW requires a Tmax service that will process a request or reply sent from the remote node. Since X25GW does not have service name information, the user must specify the service name. X25GW uses the following 3 methods to discover the service name.

The service name mentioned here must be registered in the Tmax configuration file.

When X25GW is configured completely in asynchronous mode, the user can specify the channel to the remote node in the [-a] option of the CLOPT section. In a completely asynchronous mode, no replies are exchanged between the two sides. The reply data must also be sent as a service request.

For example, if tpacall with TPNOREPLY is sent from a Tmax client or service to X25GW, X25GW sends data to the remote node and terminates the service without storing the UID or any other data related to the service request. When X25GW receives a reply from the remote node, it processes the reply as another service request. The same applies to the reverse case when the remote node imitates a request.

In the previous case, the remote node channel can be specified in the [-u] option in the CLOPT section. The channel can be set in the following two ways.

X25GW can exchange a reset operation with the remote node. Excessive number of reset exchanges may occur due to system failure, program bugs, or invalid remote configuration. If too many resets occur, the gateway can fall into a loop and not be able to process the application properly. To prevent such a problem, X25 gateway automatically closes the session of the channel and reconnects when reset count exceeds the specified limit (100).