DTJ Number 3 September 1987 - Digital Technical Journals

Terminal Servers on Ethernet Local Area Networkssystem, the connection request can be queued.This queuing provides a basic mechanism forsharing printers among multiple systems.Some of Digital's personal computers nowimplement the master end of the IAT protocoland can operate as simple single-session terminalservers. These servers are implemented as part ofthe DECnet-DOS and ProjDECnet releases andallow the PC to emulate a terminal connected toa terminal server. Combining this feature withthe servers that offer services, a PC user can connectto any PC that is connected to a terminalserver for file transfer applications, to a dial-outmodem, or to a non-LAT host system. Dataintegrity is provided "end-to-end" in PC-basedimplementations due to the lack of twisted pair,or simihir, wiring. Figure 7 shows the connectionsto asynchronous printers and IAT from personalcomputers.Within the IAT environment, the service nameoffered by a host system does not always have torepresent the command interpreter on a givensystem, though this is by far the most commonuse today. Instead, a service name could representan application program, which might be runautomatically when a connection request ismade. Alternatively, using the solicited-connectionmechanism currently employed for printers,applications programs could initiate connectionsto terminals (or other asynchronous devices)located within the LAN .DECserver 200The DECserver 1 00 interconnects terminals inan office environment at a very low price. Soonafter it was announced, it became clear thatmodem-controlled lines and connections to nonrAThost systems should also be priced justas low.Thus the DECserver 200 project was initiatedto produce a new server based on the DECserver1 00 design, but with modem control capabilities.Moreover, this product had to meet theoriginal cost goals of the DECserver 1 00. Thisproject involved a redesign of the printed circuitboard, yet retained the same system architecture.A faster version (1 0 MHz) of the same MC68000microprocessor was used, and memory wasincreased from 128KB to 384KB of RAM andfrom 512 bytes to 2KB of NVRAM. This increaseallowed room for the implementation of modemcontrol software and support for non-IAT hosts(i.e., reverse-rAT capabilities) . The increase alsoallowed a larger service directory database to bestored and an enhanced on-line help capabilityto be added.NON-LA T HOSTSVAX/VMSHOSTETHERNETTERMINALSERVERDECnet-DOSDECserver 100PRO/DECnetETHERNETTERMINALSERVER .TERMINALS ASYNCHRONOUS TERMINALS DIAL-IN ASYNCHRONOUSPRINTERS MODEMS PRINTERSFigure 7Asynchronous Printers and LA Ton PCs86 Digital TecbnicaljournalNo. 3 September 1986I