We have multithreaded application, one of the application thread used sftp for file transfer...so it launches a "sh" 
process, which inturn launches a "sftp" process and "sftp" inturn launches a "ssh" process for communication. 

The application thread calls popen() with the following command string. 
sftp -oPasswordAuthentication=no -oStrictHostKeyChecking=no -oNumberOfPasswordPrompts=0 -oPort=22 -oIdentityFile=FILE. 
ssh.prv userID@IP 

After it successfully launches the above commad, we see 3 processes in a normal working scenario. 

388177965 proc/boot/sh 
388177967 usr/local/bin/sftp 
388182064 usr/local/bin/ssh 

In the scenario, where we see the ssh process becomes zombie we see the following 

388177965 proc/boot/sh SIGSUSPEND 
388177967 usr/local/bin/sftp REPLY (PIPE process) 
388182064 (Zombie) 

and the application thread is
335899 App appThread reply 1 

We want to know why would the ssh process becomes zombie and this is not handled by the SFTP process that has launched 
it?? Does any network error can cause the ssh process die abruptly and make sftp unaware of it??

any help????