IBM Advanced Peer-to-Peer Networking
In the ' classical ' IBM Network Architecture (SNA ) is the communication of two peripheral systems (LUs, logical units ) only through a central instance (mainframe using SNA software, such as VTAM ) is possible, therefore dependent ( Dependant ) LUs '.
APPN now sees these peripheral systems as equal partners (peers) that can build up even without a central control mechanism SNA connections with each other as ' independent Logical Units '.
Was aided design of APPN by the continuous increase since the introduction of SNA in 1974 computing power on the handset side. Did the classic SNA design still ' dumb ' screen and printer terminals before, as more and more multi-functional systems were temporarily deployed on which the terminal emulation, thus providing the user interface for a mainframe application, only one of many tasks had. Thus, these systems were additional tasks, such as self- mediation of LU - LU sessions and negotiating the optimum connection ( Routing) to be transferred.
APPN was when it was introduced initially received little attention, as it touched down solely on the LU type 6.2 (APPC ) protocol. So it was for a replacement of the mainframe -based interactive applications based on the IBM 3270 terminal type, grown historically ' dependent logical units ' unsuitable.
Only with the introduction of dependent LU server ( on the mainframe ) and dependent LU requester ( DLUS / DLUR ) were the terminals previously used with the SNA protocols LU Type 2 ( 3270 display terminal ), LU Type 1 (printer terminal) and LU Type 0 ( freely defined ) in the APPN network, which are operated entirely ' new SNA '.
Since its conception, APPN has been further developed: Component High Performance Routing (HPR ) support the optimal use of fast line connections between APPN nodes.
However, the new flexibility also means getting used to the Administration: Were the classical SNA definitions all carried out centrally on the mainframe, it must be distributed in the APPN model.
- Network protocol