About transfer requests

Registering the request

Transfer CFT executes the transfer commands that are saved in the catalog. It sends and receives the files through the commands:

  • SEND TYPE = FILE for sending
  • RECV TYPE = FILE for receiving

It sends messages through the commands:

  • SEND TYPE = MESSAGE for a simple message
  • SEND TYPE = REPLY for a reply to a previous transfer type message

In the catalog, a transfer request made with the parameter STATE=HOLD is marked with an H (Hold) state. This transfer cannot be activated by Transfer CFT without operator action (START command) or without a request from the remote partner. For more information refer to Activating a transfer below.

A transfer requested by the command STATE = DISP is marked with a D, at Disposal, state. This transfer is activated as soon as Transfer CFT resources and the partner’s access rights permit. The transfer may be refused in certain cases.

Activating a transfer

Transfer CFT scans the catalog at regular intervals to activate pending transfers, entries in the D state. For each of these entries, Transfer CFT determines whether it can be activated as a function of the parameter setting, and selects the exchange protocol.

The transfer may be held if, for example:

  • Partner access is inhibited by time slots, parameters of the *MINTIME/*MAXTIME type
  • The maximum number of simultaneous transfers is exceeded

In these cases, the entries remain in the D state.

The transfer may be aborted if:

  • The file to be sent is not present, or the receiving file does not exist as required by the parameter setting (FDISP, FACTION parameters)
  • The partner is not defined

Particular case: the EXITs and directory allow a partner description to be dynamically complemented or created.

  • The IDF or file is not authorized for the user

The security system is activated and does not provide the required authorizations.

In these cases, the entries change to the H (Hold) or K (Keep) state.

Connecting to the network

When Transfer CFT has the resources for an At Disposal (D) transfer, it attempts to make the connection to the communication system attached to the partner of this transfer.

The transfer remains in the D state throughout this connection attempt period.

The transfer may fail as a result of a network incident, line disconnected, call number unknown, etc., after all the attempts and use of the various call numbers and protocols. The catalog entry changes to the H or K state.

In general, Transfer CFT uses a SAP sent at the time the network connection is made, to inform the partner of the dialog protocol. For more information see the SAP parameter.

Exchanging protocol information

When the network connection is established, the transfer changes to the in process C state. From then on, the partners participate in an exchange of messages in accordance with the chosen protocol, forming the protocol reciprocal recognition and parameter negotiation phase, during which the transfer may fail, in particular if:

  • The partner detects a problem during the recognition phase, name and password verification
  • The partner refuses the transfer as it is not within the authorized time slot
  • The associated operating parameters or protocols are incompatible (no protocol unit reciprocal recognition or negotiation impossible)
  • A directory type EXIT generates a refusal

In these cases, the catalog entry changes to the H or K state, according to the severity of the error. The data exchanged during this phase differs according to the protocol.

Creating the file

Once the partner is recognized and the protocol is defined, the type of transfer is determined:

  • File send or receive, and the file is designated
  • Message send

The transfer may fail locally if:

  • The file to be sent is not known or protected
  • There is an inconsistency between the parameter setting of the SEND command and the file to be sent (FORG incorrect, for example)
  • There is an inconsistency between the parameter setting of the RECV command and the file to be received. FDISP = NEW and the file already exists, for example
  • The file is not authorized for the user, operating security system parameter setting

The transfer may fail remotely if:

  • The transfer of such a file is not authorized by the partner

In these cases, the corresponding catalog entry changes to the H or K state.

Transferring data

The data in the file is transferred item by item, broken down into or concatenated with the data units conveyed over the network, as necessary. The exchange protocol may, depending on the type, include re-synchronization and compression functions.

The file type EXIT allows the user to:

  • Handle the data at any time during the transfer
  • Initiate transfer refusals

Disconnecting

On completion of data transfer, the files are closed, the network connection is cut after the expiration of the associated hold time-out. According to the protocol, the monitor parameter setting allows a network session to be held open to permit several transfers to be made in sequence. Network disconnection is at the initiative of the requesting Transfer CFT or the server Transfer CFT. .

Server transfer

This section describes the steps involved in a server transfer.

Receiving an incoming call

An incoming connection on the communication system is always accepted by the Transfer CFT . There is no need to negotiate a network connection for a server transfer, as no transfer is yet associated with the open session.

The Transfer CFT then decides if it can continue the transfer. This depends on the limitations set in terms of connections to the requested network resource, or number of simultaneous transfers. If Transfer CFT cannot continue due to parameter limitations, the network connection is closed.

Exchanging protocol information

The messages exchanged during this phase are part of the reciprocal partner recognition (authorization checks: passwords, time slots, etc.). The messages also help in negotiating protocol parameters. The data exchanged during this phase differs according to the protocol.

Transfer CFT may refuse the transfer if:

  • The partner is unknown, does not give the right password, or is not authorized at that time, time slot, and so on
  • The requested protocol is not supported for this partner
  • The number of connections with this partner is exceeded
  • A directory type EXIT generates a refusal
  • Negotiation is impossible

A catalog entry has not yet been created.

Creating or releasing the file

Once the recognition phase is complete, Transfer CFT receives a request to create a file (receive), open a file (send), or receive a message. This is followed by one of the two following events:

  • Transfer release

There is already a catalog entry, in the H state, corresponding to the request received. This transfer may be in the H state as a result of:

  • A SEND ... STATE=HOLD command - this is a request by the requester to release a transfer previously put on hold at the server end
  • A HALT command - this is then a request to resume an intentionally halted transfer
  • An accidental transfer interruption; the request is then a resumption request

Transfer CFT is able to link the transfer request with the existing entry.

  • Transfer creation

There is no catalog entry corresponding to this transfer and one is then created.

The Transfer CFT may refuse the transfer, in the following case in particular:

  • It is impossible to create or open the file (file not known or inaccessible, characteristics incompatible with the Transfer CFT description, for example)

No entry is created in the catalog.

Transferring data

The data in the file is transferred item by item, broken down, or concatenated with, the data units conveyed over the network. The exchange protocol may include re-synchronization and compression functions.

Disconnecting

When the data transfer is complete, the files are closed, and the network connection is cut after the expiration of the associated hold time-out. Depending on the protocol, the Transfer CFT parameter setting allows a network session to be held open to permit several transfers to be made in sequence.

Network disconnection is at the initiative of the requesting Transfer CFT or the server Transfer CFT.

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