PeSIT

A PROTOCOL FOR THE BANKING PROFESSION

PeSIT first started operations in 1986, and to date at least seven different companies have developed the protocol.

PeSIT is available for a wide range of hardware including :

• IBM 390, IBM PC and compatibles (Windows 95 or NT environments),
• operate flexibly as regards communication media (specialised links, public networks, local area networks etc.)

The ISO file transfer protocol, FTAM, could have met these requirements had its production process been sufficiently rapid to guarantee that the banking community would have access to FTAM products at a date compatible with the SIT project schedule.

Since this was not the case, the banking profession therefore decided in 1985 to define a file transfer protocol for connecting to the SIT network.The result is PeSIT.

This protocol is based on the same philosophy as FTAM (integration in the ISO model, virtual file model etc.), and the PeSIT service (interface with the protocol user) is identical to the FTAM service. However, PeSIT offers only a subset of the planned functions of FTAM.

PeSIT, A WIDELY USED PROTOCOL

At present, PeSIT has spread far beyond the banking profession. PeSIT is the only tried-and-tested protocol to allow dialoguing between the most commonly used transfer monitors employed in the French market.

PeSIT today exists in four operating profiles :

• "PeSIT SIT" for connecting to the SIT Payment and Stock market networks,
• "PeSIT Hors SIT" for monitor-to-monitor dialogue (common protocol for major monitors currently used in the French market),
• "PeSIT ETEBAC 5" supporting the ETEBAC 5 standard (defined by the CFONB), for telematic transfers between banks and businesses,
• "PeSIT" - now available for use with a TCP/IP layer.

WHAT DOES PeSIT DO ?

PeSIT is a file transfer protocol which allows the writing and reading of files between one computer and another; using a connection established over a telecommunications link (specialised connection, public network, local area network).

In order to avoid differences between the file management systems internal to each computer, PeSIT uses the "virtual file" concept, which provides a common file organisation model suitable for all computers.

Each PeSIT user manages translations between real computer files and the virtual files transferred by the protocol.. To comply with the terminology adopted by international standards, distinction is made between :

• The PeSIT service which is the interface between the file transfer software and the user,
• and the PeSIT protocol which defines the necessary dialogue rules and formats for messages exchanged between two PeSIT parties.

The PeSIT Technical specifications describe both the PeSIT service and the PeSIT protocol.

PeSIT FUNCTIONS :

Remote file-writing

This function allows a PESIT user to transfer the contents of a file towards another PESIT user. To this end, the sender must first set up a logical connection with the remote party. The user setting up the call is known as the "Caller"; the remote user is called the "Server". In this case, the file (data) transfer occurs between the Caller/sender and the Server/receiver.

Remote file-reading

This function allows a PESIT user to request another PESIT user to transfer the contents of a file. To this end, the user wanting to receive the file (the "Caller") must first set up a logical connection with the remote user the "Server"). In this case, the file (data) transfer takes place between the Server/sender and the Caller/receiver.

Setting checkpoints

This function allows the file sender to insert indicators, known as checkpoints, numbered sequentially, in the course of the transfer. The party receiving the data can acknowledge these points, which signifies that he has correctly received and stored the data issued up to this point. This mechanism ensures that in the event of an error, a transfer can be restarted from a point other than the top of the file.

Restarting a transfer

This function allows the caller to restart a prematurely interrupted transfer. Restarting is possible whether the transfer is performing a read or a write, but it is always decided by the caller. Which checkpoint is used for restarting the transfer is decided by the party receiving the file.

Resynch during transfer

This function allows a user to request the remote party to restart the transfer from an earlier checkpoint if a fault occurred during the data transfer. Unlike restarting - which occurs after interruption of the transfer (accompanied by closing and deactivation of the file) - resynch takes place during the transfer and the file remains open and active.

Suspended transfer

This function allows a user to interrupt a transfer (that is, close and deselect the file in question) in order to use the current connection for running a higher-priority transfer. The suspended transfer will afterwards be processed under the restart procedure.

Transfer protection

This function allows PESIT users to implement mechanisms offering various functions such as :

• reverse authentication of parties,
• confidentiality of transmitted data,
• integrity of transmitted data.

Data compression

This function allows PESIT users to employ data compression on transmitted files, in order to reduce the transfer volume.

Error checking

This function employs an error-detection polynomial associated with each message in the PeSIT protocol, to ensure that messages are not altered by transmission onto unreliable mediums.