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G&R

Whereas a simple handler might have no session protocol unit size restriction it

might have a transport size restriction, or a network packet size restriction (e.g.

TCP/IP packet size) that would cause fragmentation of the application record

for transmission purposes. Depending on the interface between the handler and

the lower level protocol this might cause the receiver to see a series of data

blocks with enclosure ‘none’.

In two-way-alternate sessions ‘end of group’ is used to signal that a reply is

now required (turn). The DSA record header indicates enclosure and turn, and

in the DSA/ISO Work station protocol (DIWS) this is mapped to the OSI data

token that allows the holder to transmit. There is really no turn concept in a

two-way-simultaneous dialog, and no data token in two-way-simultaneous OSI

sessions. However, the DSA records of the DSA/DIWS handler can still use

‘end of group’ enclosures and indicate turn to the Bull mainframe applications,

which although they might support two-way-simultaneous dialog, can still

require a DSA ‘end of group’ before they will handle an incoming message.

Note that most Host Links products and host applications are not in fact

two-way-simultaneous in the sense that they send and receive simultaneously at

the application level. Two-way-simultaneous means in practice that the

application or communications product can break the ‘send, receive, send,

receive’ pattern of interactive dialog. Thus an emulator or concentrator

connected to a DMIV TP application using DACQ configured for two-way

simultaneous dialog will be able to send a second transaction before it receives

an answer to the first. In general this allows applications to not answer certain

transaction types (data entry) for efficiency.

Host Links products by default always offer to establish either two-way

simultaneous or two-way alternate sessions, and it is the mainframe application

that chooses the mode.

Gline Line Handlers and Configuration

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Eicon Networks CX1 Installationshandbuch Seite 16