Figure 391 Ibm Sna Maps to All Seven Levels of the OSI Model

SNA 051

Transaction services


Presentation services



Data flow control


Transmission control


Path control

Data Imk

Data link control



A key construct defined within the overall SNA network model is the path control network, which is responsible for moving information between SNA nodes and facilitating internetwork communication tsetween nodes on different networks. Tho pathi orntsol netwvork environment uses lunctio no isrovided by the path control and data link control (DLC). The path control network is a subset of the IBM transport network.

IBM SNA Physical Entities

Traditional SNA physical entities assume one of the following four forms: hosts, communications controllers, establishment controllers, and termi nals. Hosts in SNA control a1 l or part of a ntnwork and oy^nally a^svide nomautation, prognam oxecution, database accesst ditectory semces, and netwvork management. (An example ofa hont device withm a trad^onal SNA envisonmenn in an S/370 mainframe.) Cnmwunicatbns controllers manage the physical network Cod control communication Hnks. In particulasr communications controllers—also called fronrand processors (FEPs)— are relied upon to route data through a trnditiocal SNA network. (An axample of1 a communications controller is a 3745.)

RstabMshment contro l ters ate cnmmoniy call ed ulustet contro1 iets. These d pv^es control input and output ofoerations of1 attached devices, such as tetminals. (An eyample of an establisnment nontroller |s a 31.774.) Terminals, alsn referred to as wotkstations, provide toe user inwerface tio the netwo ck. (A ty eicai example wvonld be a 33270). Figure 39t2 i llnsorates eacf of tisese physical sntities in the context of d (ten^ralized SNA netwvork diagram.t

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