Revive old terminals: remote servers help you capitalize on installed base

Communications News, March, 1990 by John Jesitus

REVIVE OLD TERMINALS

How can I talk to other hosts and networks out there," you ask, "without getting rid of my existing terminal and desktop equipment?"

Lots of ways.

For local-area connections, the answer often lies in remote terminal servers. Costing a few thousand dollars each, servers are used typically on Ethernet LANs to cluster terminals and talk with hosts.

Servers commonly provide DEC LAT (local area transport) connectivity and TCP/IP support for UNIX environments. "The sophisticated ones have a software switch to handle both," sayd Gary Krall of Advanced Computer Communications, Santa Barbara, Calif. When comparing products, consider such factors as price per port and number of ports served.

Also, make sure you're getting LAT and TCP/IP support in the same unit. Some vendors offer both capabilities, but in separate products.

Ron Watkins is network engineer at BBN, a diversified high-tech company in Cambridge, Mass. He's one user who finds servers a very economical way to link terminals to Ethernet hosts and to bridge circuit-switched and netword technologies.

With nearly $1 million invested in PBX and other circuit-switched equipment, he says, "Rather than throw the PBX away as LAN and terminal server technology is utilized, we need a way to blend the two together."

A rack of terminal servers on the company's Ethernet connects hosts not already on the Ethernet to PBX lines.

This way, any user with a circuit-switched connection to his desktop can simply type in "terminal server" at the command line to get to the Annex equipment via a Micom Series 40 PBX, according to Ron Watkins.

When BBN was looking for a way to connect its terminals, it found that circuit-switched access methods cost about $100 a port, while terminal lines run $200 to $250 a port--another reason to get as much mileage as possible out of embedded lines.

Easy Moves, Changes

The setup also simplifies moves and changes. "We can move anybody we want to," Watkins says, "and their office looks the same."

Despite these advantages, Watkins says the terminal-server solution is too slow: "It works, but you can't throw multimedia on an RS-232 line."

Combining E-mail with pictures and voice, or supporting videoconferencing from every desktop via Sun workstations, demands for too much bandwidth. "It's not clear to me that terminal servers will be around a while. You now see workstations and X terminals directly on Ethernet," he says.

These newer terminals support multiple windowing applications at speeds of 10 Mb and above. But terminals servers will last at least as long as industry's huge installed base of modems remains in use, Watkins believes.

At North Carolina State University, a school of about 24,000 students in Raleigh, they're checking out Infotron's Commix 32 as a way of linking some 200 users in six departments to a campus-wide Ethernet supporting TCP/IP and LAT.

The school's academic network supports legions of terminals, PCs, and other devices. "You name it," says Network Analyst Mohammad Fatmi, "the school uses it."

Users served by the Commix 32s occupy three buildings, each with its own LAN. Two buildings are linked directly to the campus-wide Ethernet. The third building houses an INX 4400 data switch that provides various asynchronous services.

Users connected to these boxes can access the INX 4400 services indirectly via two WAN cards in two remote Commix 32s, one connected to the network and the other connected to the 4400.

This facilitates inbound and outbound modem dialing through the switch. Campus users may access outside resources. Off-campus users may tap into the school's Ethernet.

Frozen Boxes

North Carolina State's Computing Center and Infotron have solved a lot of hardware and implementation hitches since beta testing began last summer.

"The boxes used to freeze all of a sudden," Fatmi says. "They'd look like they were working, but no one was communicating." This was due to pesky bugs in the servers' EPROM, the brains of the self-contained units. "As soon as we'd fix one bug, a second would show up."

John Deere, Moline, Ill., a manufacturer of heavy agriculatural equipment, uses Xylogics Annex terminal servers to keep machine tools running smoothly. Three servers in the Dubuque factory each save Deere an hour or two of uptime each day.

"We can pass numerical-control parts programs from the workstation down to the machine tools," says Senior Engineering Analyst Tom Gloden. "The alternative is to read a tape into a machine. This makes it much quicker and easier for the operators to load their next job, and even make changes at machine-tool level and send them back up to the workstation."

Previously, a programmer would create a hard program on a workstation, read it off to a tape punch, punch a tape, take it over to the machine tool, and read it in. Factory dirt often hampered tape reader performance.

The three sites now exchange data at 19.2 kb/s. The servers, which cost about $5000 each, also centralize file storage. "We can use the Ethernet and pass the data, and store the files centrally in a more secure spot," Gloden says. Previously, file storage was performed at a stand-alone disk-drive-equipped workstation.