The TCP connection information server (SYSTCPCN) presents information about the establishment and closing of TCP connections as they occur. Type 119 SMF TCP connection initiation and termination records (subtypes 1 and 2) are stored in the data buffer to reflect this activity. Each record in the data buffer is a complete type 119 SMF record, of subtype 1 or 2.

Additionally, if requested, the server fills one or more buffers with the list of currently active connections. This list is provided as type 119 TCP connection initiation records (subtype 1), so that entries in the list are indistinguishable from newly established connections (except that the connection establishment timestamp is in the past). This set of records is sent only once per new connection, after the initialization.

For the TCP connection information server, the ctefmtid for the CTE is always equal to the subtype of the SMF record (either 1 or 2) following the CTE in the data buffer.

Applications can use this interface to dynamically maintain a list of active TCP connections. As a result of timing issues, it is possible that an application will receive two initiation records for a given connection (if the connection is established around the time the client connects, its initiation record will be sent, as will a record identifying it as a preexisting established connection). It is also possible that an application will receive a termination record for a connection for which it has not received an initiation record. Client applications should be prepared to handle both of these possibilities.

SMF recording for TCP connection initiation and termination records does not need to be active for this service to function. Moreover, activating this service does not cause TCP connection initiation and termination SMF records to be recorded into the SMF data sets if they are not already enabled.

C structures for mapping the SMF type 119 records can be found in ezasmf.h. Assembler mappings for the structures can be found in EZASMF77 in SYS1.MACLIB.