Oracle disconnect problem

Could anyone help me resolve the following problem:

There are several Pro*C programs which connect to a remote database via orasrv.

Intermittently, the programs will report that they are disconnected from the remote oracle database with the following error:  -3113 "end-of-file on communication channel"

Some things we have been looking into:
1. We have investigated the possibly that the disconnection is caused by the

    TCIP configuration parameter 'KEEPALIVE', but this was not the cause since     the programs where active (accessing the database) just prior to     disconnecting from the database.

2. We have compared the differences between some programs which have never

    had this problem to programs which suffer this malady. The only major     difference was that the programs which do NOT disconnect from Oracle     issue a sighold() just before entering Oracle statements in the Pro*C code     and releasing the sighold with sigset() when exiting the block of code     issuing the Oracle commands.

    Although the programs which hold signals do not disconnect from the     database, one individual I spoke to said this was purely coincidental     and we should NOT practice blocking signals inside Pro*C programs just     before performing Pro*C statements. This person believed the problem was     network related.

   Specific information:     

   Oracle version 6.0.37.6.1
   Pro*C version ORACLE Precompiler: Version 1.3.18.1.3    HW types

      database resides on  an HP 9000/887
	  with HPUX version A.09.04 E
      remote application which disconnects resides on an HP 9000/380 
	  with HPUX version B.08.00 B
      
      remote application which does NOT disconnect resides on an HP 9000/385
	  with HPUX version B.08.00 B

Do you know the cause of the problem and any possible solutions?

--
Michael Rosenthal