This is the error what I see.
C OCISessionBegin(OCI_DEFAULT) failed with SQL error 3135:
C ORA-03135: connection lost contact
C Server handle (con=0,svchp=6934448,srvhp=6936a10) detached
C *** ERROR => CONNECT failed with SQL error '3135'
[dbsloci.c 15581]
B ***LOG BY2=> sql error 3135 performing CON [dbsh 1246]
B ***LOG BY0=> ORA-03135: connection lost contact [dbsh 1246]
B ***LOG BY2=> sql error 3135 performing CON [dblink 544]
B ***LOG BY0=> ORA-03135: connection lost contact [dblink 544]
M ***LOG R19=> ThInit, db_connect ( DB-Connect 000256) [thxxhead.c 1521]
Start with this SAP note
1902517 - ORA-03135 general trouble shooting steps
Regards
RB