DTJ Number 3 September 1987 - Digital Technical Journals

The DECnet- VA X Product - An Integrated Approach to NetworkingTable 1Relationships between RMS and DECnet-VAXFile System RMS Programming DECnet-VAXQIO Function Service Language Operation Operation10$--ACC ESS $OPEN Open file Initiate or accept logical linkIO$_DEACCESS $CLOSE Close file Disconnect logical linkIO$_READVBLK $GET Read from file Read data across logical link10$-WRJTEVBLK $PUT Write to file Transmit data across logical link• The network ancillary control process ,NETACP, which handles those functions thatrequire a process context in which to executeNETDRIVER processes all QIO requests for thenetwork device. Network QIOs generally fallinto one of two categories: logical link traffic, ornetwork management requests. NETDRIVERforwards to NETACP any request for logical linkstart-up or shutdown (e.g., the IO LACCESS QIOused to create a logical link) , or for networkmanagement fu nctions. On the otherhand, NETDRIVER handles logical link transmitand receive requests (IQ $_WRITEVBLK andIOLREADVBLK) by itself.NETDRIVER also contains the bulk of the routinglayer of the DECnet-VAX software. Usinginformation provided by NETACP, NETDRIVERcan determine the optimal circuit on which tosend any received packet whose destination isanother node. By giving high priority to bothlogical link and routing-forwarding traffic,NETDRIVER eliminates the overhead of invokinga process to perform these high-throughputfunctions.NET ACP defines and provides access to thevolatile network database, which is the workingcopy of the permanent network database. Thevolatile database is allocated from NETACP's virtualaddress space. NETACP also controls thestate transitions of data links, the routing layer,and logical links. Both the start-up and shutdownof logical links are handled in NETACP, whichalso creates the process to receive an incominglogical link having no declared network task.In addition, NETACP provides support for Digital's X.25 packet switch network product, VAXPSI. Through "data link mapping," NETACPmakes it possible to map the functions normallyprovided by a data link driver onto an X.25 con-nection. This mapping causes the packet switchnetwork (PSN) to act as though it were a DECnetdata link, thus allowing DECnet nodes connectedto the same PSN (but not to each other) to communicateusing DECnet protocols. These protocolsin turn permit any applications layered onDECnet to function correctly between the DECnetnodes.DECnet-VAX provides two other components,called the network control process (NCP) andthe network management listener (NML) , whichwork together to provide local and remote networkmanagement capabilities. 1 NCP providesthe user interface to network management functions.Network management is the process ofcontrolling those parameters that allow thevarious components of a network to functionefficiently. These parameters reside in two separatedatabases: a permanent database that establishesthe default parameter values upon nodestart-up, and a volatile database that containsthe current parameter values in a functioningnetwork.Both the volatile and permanent databases canbe accessed through NCP by using a commonuser interface . NCP in turn passes the parsedrequests to NML for actual processing. NCP thenformats the results returned by NML for the user.NML is a server whose function is to performnetwork management operations on behalf ofsome client. NML receives its commands in aprotocol called NICE, either from a local NCPcopy or over a logical link from another node(usually, but not necessarily, from that node'sNCP). NML then returns the results via the sameNICE protocol.NML is also the agent that owns and maintainsthe permanent database. Upon receiving arequest for a permanent database operation, NML92Digital TecbnlcaljournalNo. 3 September 1986