DTJ Number 3 September 1987 - Digital Technical Journals

New ProductsNON-LAT HOSTSVAX/VMSHOSTETHERNETTERMINALSERVERDECserver 100TERMINALSTERMINALS DIAL-IN PERSONALMODEMS COMPUTERSFigure 6Ethernet Configured as a Service NodeVersion 2_0 of the Ethernet Terminal Server,released in August 1985, added the reverse-IATimplementation, permitting a server to offeradditional services to which terminal userscan connect_ This implementation permitssessions to be created within the box as we llas across the network, thus fo rming a switchstyle of operation in a single server. The types ofservices that may be offered by the terminalserver can be grouped into the following threecategories.The first category is connections to non-IAThosts. In this mode , the server acts as the Ethernetconnection for systems (typically not madeby Digital) that cannot themselves offer IAT serviceson the Ethernet. Asynchronous ASCII portson these systems are connected to a terminalserver. Terminal users on the same or differentterminal servers can connect to the serviceoffered. They can then communicate with thenon-IAT host as though it were connected to theEthernet.The second category is service for dial-outmodems. Terminal users can connect to a port ina pool of dial-out modems. The users can thenuse the appropriate ASCII protocol to create adialed connection and then access the remotesystem via its own dial-in port.'The third category is service for personal computers(PC) . They can be cbnnected to terminalIservers and run in either of the terminal emulationmodes. Each PC thus acts as though it werea dumb terminal. A PC can ' also run in file transfermode when connected to another PC via .thesame , or another, terminal server. Figure 6 illustratesthe terminal server as a service node .Subsequent versions of the Ethernet TerminalServer, the DECserver 100, and the VMSLTDRIVER software all permit asynchronousprinters to connect to terlninat servers. Theseversions also allow print qu¢ues to be directed tothe printers from hosts. The IAT protocol hasbeen enhanced so that th connection mechanismremains under the ctintrol of the terminalj.server (for the reasons of efficiency mentionedpreviously) . That enhancement allows a host to"solicit" a connection from a port on a terminalserver. Once the connection has been made, datatransfer can occur as in the normal interactiveterminal case, except that the printer output isunder the direction of a VMS print symbiont. It ispossible, with these implementations, to directthe queues from multiple systems to a singleprinter or bank of printers being offered as acommon service. When a connection request ismade while the printer is eing used by anotherIIDigital TechntcaljournalNo. 3 September 198685