network protocols handbook.pdf

290Protocols GuideIBM ProtocolsProtocol NameAPPC: Advanced Programto Program Communications(SNA LU6.2)Protocol DescriptionAdvanced Program-to-Program Communications (APPC), aprotocol roughly in the OSI resentation and session layer, is aprogramming interface standard that allows interconnected systemsto communicate and share the processing of programs.Originally developed by IBM as a remote transaction processingtool between Logic Units (LUs), APPC is now used to providedistributed services within a heterogeneous computing environment.APPC software enables high-speed communication to takeplace between programs residing on different computers, andbetween workstations and midrange and mainframe computerservers. APPC allows user written programs to perform transactionsin a Client-Server network. APPC is a standardized applicationprogramming interface which allows an application touse a pre-defined set of VERBS/API for sending and receivingdata to/from another program located in a remote node. Thisset of verbs/API, can only be used with an LU 6.2, which is whythe terms APPC, LU 6.2 and PU type 2.1 are very often usedinterchangeably.LU 6.2 is the set of SNA parameters used to support APPC whenit runs in the SNA network. Basically, LU6.2 acts as an interface,or protocol boundary, between SNA and an end user’s application.However, not all APPC communications are based onSNA. APPC also runs between two MVS or CMS program usingmainframe system services. Under Anynet, APPC can also runover the TCP/IP protocol used by the Internet.Protocol StructureAPPC functions and commands:Sessions, Conversations and Job Management - A client generatesa request. It is passed to the subsystem on the client nodeand is sent through the network to the subsystem on the servernode. A subsystem component called the Attach Manager theneither queues the request to a running program or starts a newserver program.Attach Manager and Transaction Programs:• Allocate - acquires temporary ownership of one of thesessions to the server node.• Deallocate - frees the session and ends the conversation.Sending Data (or Objects)• Send_Data - moves a record of data from the applicationmemory to buffers controlled by the subsystem.• Receive_and_Wait• Send_Error - Send_Error breaks the logical chain of incomingrecords. APPC is responsible for flushing anypending data (from the server node, the network, or theclient node). As soon as possible, the client is notified ofthe problem with a characteristic return code on the nextAPPC operation.• Confirm - Any pending data is sent, and after the otherprogram receives the data it gets an indication that Confirmis pending. If everything is acceptable, then the correctresponse is to call the Confirmed verb.Higher Level Programming:• Send file (disk to network)• Send SQL table (DBMS to network)• Send stack (REXX)• Send hyperspace (MVS)• Send clipboard (Windows)Related protocolsSNA, APPNSponsor SourceAPPC (LU6.2) is an IBM protocol.Referencehttp://publib-b.boulder.ibm.com/Redbooks.nsf/RedbookAbstracts/gg242537.html?OpenA CM/2 APPC/APPN Tutorialhttp://publib-b.boulder.ibm.com/Redbooks.nsf/RedbookAbstracts/sg243669.html?OpenInside APPN and HPR - The Essential Guide to the Next-GenerationSNA