In practice it is often the case that a client communicates mainly with one particular UTM server. To simplify the configuration of UPIC clients and the programming of CPI-C client programs in such cases, you can define a DEFAULT server for your client application in the upicfile (see "Side information for standalone UTM applications"). In order to be connected to the DEFAULT server, the client program can omit specification of a symbolic destination name when initializing the conversation with Initialize_Conversation. It transfers an empty name to UPIC and is then automatically connected to the DEFAULT server.
You can also define a service on the DEFAULT server as the DEFAULT service. To do this, you specify the transaction code of this service in the DEFAULT server entry in the upicfile. If the CPI-C program then does not specify a transaction code when initializing a conversation for the DEFAULT server (it does not call Set_TP_Name), the conversation is automatically established with the DEFAULT service. If another service is to be started on the DEFAULT server, the client program must transfer the transaction code of this service to UPIC with Set_TP_Name (e.g. TP_name=KDCDISP must be selected at service restart).
In the same way, you can define a DEFAULT name for the local CPI-C client application in the upicfile. If the client program specifies an empty local application name when the application signs on to UPIC (with Enable_UTM_UPIC), the client is signed onto UPIC with the DEFAULT name and UPIC uses the address information assigned to the DEFAULT name to establish the conversation.
If a DEFAULT name is used for the CPI-C application, it may occur that several program runs of a UPIC client want to sign on to a UTM application with the same name at the same time. This is the case if the client program is started several times in parallel or if a program wants to establish several conversations with a UTM application in parallel (multiple conversations). To enable the server application to accept these sign-ons, the conditions described in the following section must be met.