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G&R

Enclosures and ‘turn’

The interface between a Host Links product and the line handler is global

throughout the G&R product range, and for all user applications using one of

the GlAPI programmatic interfaces for communication.

The functions for receiving and sending data include an indication of the

‘enclosure’ level for the data received, or to be sent. Enclosures are very impor-

tant in the more advanced line handlers, particularly the Bull DSA handler.

Enclosures are supported for all line handlers to make the API global and to

make applications using the API independent of the type of communications

line. If the enclosure level signaling is unreliable the product using the line

handler will need special parameters to help it 'guess' when mainframe output is

finished and it is able to process the data received.

The following enclosures are defined:

none

the enclosure is used for convenience of delivery to or from a lower layer of

protocol and has no significance for the product using the interface.

end of segment

This is a complete session protocol unit, but is treated as ‘none’ above.

end of message

Defines a complete logical block of data transmitted or received, but

indicates that more logical blocks will follow. This is the Bull DSA 'End of

Quarantine Unit'.

end of group

Used by interactive products to indicate that the sender will now wait for

input before continuing. This is known as the ‘turn’ concept.

Using Bull DSA terminology; when transmitting or receiving data, an

application record, called a ‘message’, can be split (partitioned) into several

DSA session protocol units called ‘letters’. The letter can be segmented due to

size constraints at the session level (the maximum letter size). The session

protocol units might have to be split again into several transport protocol units

called ‘fragments’ for transmission due to size constraints at the transport level.

Finally the transport units might be split again into ‘packets’ because of con-

straints at the network level.

Gline Line Handlers and Configuration

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Eicon Networks CX1 Installationshandbuch Seite 15