USPS moves to a TCP/IP net

"At the stroke of midnight, I had my wife in one hand and a keyboard in the other,
watching the network die," said Rick Yost, telecommunications program manager at the
USPS National Network Service Center in Raleigh, N.C.


On schedule, the IBM Systems Network Architecture network went offline and the new WAN
went into business, with PCs replacing dumb terminals to run applications on mainframes at
USPS data centers. The TCP/IP conversion was the first step in building one of the world's
largest networks running Microsoft Windows NT.


"An any-to-any computing environment is key here," Yost said. "SNA
served us well. It was a really good protocol. It just wasn't an open protocol, and that
was the reason we had to get out of it.."


As many as 34,000 sites had to join the WAN "by hook or by crook" through
router, switch or dial-up connections, Yost said. "There's no way we could handle
that network with our staff. So we had to outsource that job," he said.


Management of the network, which by mid-June linked 1,068 sites, was turned over to MCI
Communications Corp. under a $100 million contract. In the initial phases, MCI will link
up to 600 new sites to the network each month through March 1998.


The new architecture will be flatter than USPS' current three-tier structure, program
manager Dennis K. Groce said. The current 15 first-tier backbone locations will give way
to 15 postal virtual points of presence (PVPs), which connect to a core router.


About 100 second-tier and 900 third-tier sites will connect over 56-kilobit/sec
circuits to T1 ports at the PVPs. Five critical sites--data centers in Minneapolis and San
Mateo, Calif., management and backup sites in Raleigh, and USPS headquarters in
Washington--will have direct connections to the core router serving the PVPs, Groce said.


What is now known as the Postal Virtual Network grew piecemeal, starting from an SNA
environment of mainframes and dumb terminals. In the late 1980s, independent LANs began to
spring up throughout USPS. To make the mainframes view the PCs as dumb terminals, USPS
offices used Synchronous Data Link Control adapters.


"As time went on, we saw that these LANs had to talk to each other as well as to
the mainframes," Yost said. By 1994, the network had 700 routers and 23 IBM front-end
processors, and "we began to see the handwriting on the wall," he said.


It was costing $10,000 a day to maintain that SNA network, an expense "we could
easily eliminate," Yost said.


In early 1995, a prototype TCP/IP network went up at a district office in Detroit, and
by that August, planning began for wholesale conversion to TCP/IP in place of SNA.
Installation of TCP/IP stacks on all stations took place throughout 1996. Most of the 3270
SNA protocol devices were removed, and by year's end, 20 of 23 IBM 3720, 3725 and 3745
front-end processors were ready to be shut down.


USPS initially used IBM hardware and software in the move away from SNA but has since
migrated to other products. IBM 3172 Channel Converters were the original IP front ends
for the mainframes. Those devices are being replaced by Cisco 7500 routers with channel
interface processor cards from Cisco Systems Inc. of San Jose, Calif.


A TCP/IP version for IBM's MVS operating system initially provided communication
between the MVS mainframes and the rest of the network. USPS then adopted TCPaccess from
Interlink Computer Sciences Inc. of Fremont, Calif. It now runs both products.


Yost said USPS learned several lessons along the way in replacing the SNA network.


"One thing we noticed is that we have a lot more users on the MVS systems
now," he said.


Replacing the old 9.6-kilobit/sec lines between terminals and mainframes with
56-kilobit/sec or T1 lines improved response time so much that mainframe use has risen by
33 percent. Yost said PCs, instead of taking over part of the mainframes' workload, made
more work for them.


"Mail tracking takes a lot of power," he said. "The reason you still
need the big iron is that you need the CPU power to run the applications we're using
now."


About the Author

William Jackson is a Maryland-based freelance writer.

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