Is it possible to execute commands without allocate pty?

[S.Svec]

Hi,

I am currently implementing SSH ver1 client for my school work and testing  
it with OpenSSH servers. Unfortunately I cannot execute commands after  
succesful login without allocate pty. My client send SSH_CMSG_EXEC_SHELL  
packet on server, but dont receive any answer. According RFC defined SSH1,  
server should send SSH_SMSG_SUCCESS or SSH_SMSG_FAILURE message. So I  
tried send SSH_CMSG_EXEC_CMD with command, but after executing command  
server send EXIT_STATUS message. I dont understand why, because RFC  
document define EXEC_CMD message this way: "Starts executing the given  
command, and enters interactive session mode." Would you please explain me  
why OpenSSH server doesnt response to SSH_CMSG_EXEC_SHELL message or  
closing connection after EXEC_CMD message? Thank you.

S.Svec (CZ)