The core of z/OS, also referred as Multiple Virtual Storage (MVS) basically operates in two environments Time Sharing Option (TSO), which is used for interactive computing and Job Entry System (JES), which is used for Batch processing. In z/OS environment both MVS datasets and UNIX System Services (USS) files are transferred through FTP. To deal with the incompatibility between these two files MVS datasets are presented as logical volumes to UNIX System Services. z/OS communication server uses FTP and TELNET for transferring data in MVS and UNIX environments. Although FTP is a widely used network protocol for transferring files, because of few shortcomings it is not preferable to use FTP in big business. The shortcomings of FTP are as follows :
The User Ids, Passwords and data files in FTP transmissions can be easily accessed by unauthorized users.
Data compression is rarely done for the files to be transferred through FTP.
In FTP transmission data integrity cannot be verified in the application level, which leads to damage or alteration of transferred data.
For commands and data FTP transfers require two separate connections. That is why it is not so easy to use FTP in firewall-secured network.
Because of these shortcomings FTP is replaced by SSH File Transfer Protocol (SFTP) and SSH Copy (SCP) for UNIX environments. This OpenSSH defacto standard can only access the UNIX files on ZFS and HFS, but not the MVS datasets. But the UNIX commands cp, cat and mv are extended for MVS dataset access. TSO commands OGET, OPUT, OCOPY are the alternative options for the file exchange between USS and MVS. For a file transfer on z/OS platform SFTP first transfers the files into ZFS/HFS file and then the above mentioned commands are used to copy the UNIX files into MVS datasets. These new MVS datasets are then used for the batch processing.
But the FTP migration to SFTP impacts the batch jobs drastically. As it is required to modify the batch jobs in both server and client sides, it is advisable to have a software to perform the huge migration task. In comparison to SFTP, FTPS is the easier way for security improvement, although it increases the risk of incompatibility. On the other hand SFTP is more router and firewall friendly and it is widely deployed in UNIX/Linux environments. In addition to that SFTP has very few incompatibilities between the implementations versus FTPS.