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TIBCO Rendezvous® 8.8.0

# Service Selection

Rendezvous daemon (`rvd`) processes communicate using UDP services. The `service` parameter instructs the Rendezvous daemon to use this service whenever it does network communications on behalf of this transport.

As a direct result, services divide the network into logical partitions. Each transport communicates over a single service; a transport can communicate only with other transports on the same service. To communicate with more than one service, a program must create more than one transport.

## Interaction between Service and Network Parameters

Within each Rendezvous daemon, all the transports that use a specific service must also use the same network parameter. That is, if the `service` parameters resolve to the same UDP port, then the `network` parameter must also be identical. (This restriction extends also to routing daemons.)

For example, suppose that the program `foo`, on the computer named `orange`, has a transport that communicates on the service `svc1` over the network `lan1`. It is illegal for any program to subsequently create a transport to that `rvd` on `orange` to communicate on `svc1` over any other network—such as `lan2`. Once `rvd` binds `svc1` to `lan1`, that service cannot send outbound broadcast messages to any other network. Attempting to illegally rebind a service to a new network fails; the transport creation call produces the status code `TIBRV_INIT_FAILURE`.

To work around this limitation, use a separate service for each network.

The limitation is not as severe as it might seem at first, because it only affects outbound broadcast messages.

| • | Point-to-point messages on the transport’s service travel on the appropriate network (as determined by the operating system) irrespective of the transport’s `network` parameter.

| • | Inbound broadcast messages on the transport’s service can arrive from any network, irrespective of the transport’s `network` parameter.

## Specifying the UDP Service

Programs can specify the service in one of several ways, listed in order of preference in Specify UDP Service.

Specify UDP Service

Port number | When a program specifies a UDP port number, it must be a string representing a decimal integer. For example:
       "7890"
Service name | When a program specifies a service name, the transport creation function searches the network database using `getservbyname()`, which searches a network database such as NIS, DNS or a flat file such as `/etc/services` (in some versions of UNIX).
Default (Non-Secure Daemons) | If a program does not specify a service, or it specifies null, the transport creation function searches for the service name `rendezvous`. If `getservbyname()` does not find `rendezvous`, the Rendezvous daemon instructs the transport creation function to use a hard default of port `7500`. We strongly recommend that administrators define `rendezvous` as a service, especially if port `7500` is already in use. For example, network administrators might add the following service entry to the network database:
       rendezvous 7500/udp
Once this entry is in the network database, programmers can conveniently specify `NULL` or the empty string as the `service` argument to create a transport that uses the default Rendezvous service.
Default (Secure Daemons) | Secure daemons use internal defaults, which must be set explicitly by the administrator; see Default Network and Service.
Direct Communication | To enable direct communication, specify two parts separated by a colon:
| • | UDP service for regular communication
| • | UDP service for direct communication
You may specify both parts either as a service name or a port number. Direct communication is not available when connecting to a remote daemon. For a general overview, see Direct Communication on page 91 in TIBCO Rendezvous Concepts.

The `rvd` daemon interprets this service as a UDP service.

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