Revved-up DREN will route data on ATM switched virtual circuits

Defense Department officials have tested a new AT&T Corp. asynchronous transfer
mode service at five of its 10 DREN sites. DOD plans to make the ATM service available to
all DREN users in July after AT&T completes testing at all sites.

The change will make DREN the first federal network to exploit switched virtual circuit
(SVC) connections over a long-haul public ATM service, DOD officials said.

The transformation grew out of the DREN Intersite Services Contract, or DISC, which the
Army Information Systems Selection and Acquisition Agency awarded to AT&T a year ago.
The Defense Information Systems Agency has since taken over the contract, potentially
worth $430 million over five years.

"The concept of DISC is radically different from a private-line network, because
we're buying a service, not a network," said Eduardo Schonborn Jr., DISC program
manager in the Advanced Information Technology Services Joint Program Office of DISA and
the Advanced Research Projects Agency.

With the SVC service, DOD can replace or upgrade existing 1.5- and 45-megabit/sec
leased lines to 155-megabit/sec ATM connections. These ultimately can be revved up to 2.4

SVCs imitate the public telephone network, where a connection between two points is set
up dynamically for the duration of a call and then torn down. In contrast, the permanent
virtual circuits (PVCs) that are more common on ATM networks resemble leased lines. They
must be established manually between locations that want to exchange information.

"We asked for SVCs because PVCs are unmanageable and unscalable in an environment
like this," said Michael Fidler, a lead communications engineer for Mitre Corp. of
Bedford, Mass., which provides support to the joint program office.

"You don't want to be constantly managing the setup and teardown of PVCs in a
community as diverse and dynamic as that served by DISC," Fidler said.

AT&T laid claim to becoming the first long-distance company to offer SVCs last

Federal agencies in the Washington area have yet another SVC source in Bell Atlantic
Federal Systems, which recently announced it is the only local phone company to offer SVCs
as a tariffed service.

But the SVC services of the two carriers are not yet interconnected.

Bell Atlantic's service, operating from 1.5 megabits/sec to 622 megabits/sec, uses a
pair of ATM switches from Fore Systems Inc. of Pittsburgh.

George Mather, a Bell Atlantic senior engineer, said only two agencies currently use
the tariffed PVC service, although there has been "a lot of interest from a lot of
agencies" in SVCs.

The new DREN architecture also will use Fore Systems switches as edge devices at
customer facilities. AT&T built its ATM backbone with switches from Northern Telecom

DREN's service delivery points will rely on the Fore Systems switches plus other
AT&T-owned equipment such as Fore Systems' CellPath circuit emulation device and
from Cisco Systems Inc. of San Jose, Calif.

The routers support the Internet Engineering Task Force's Request for Comments 1577
specification for classical IP over ATM and Next Hop Resolution Protocol (NHRP) services.

NHRP lets routers on ATM networks learn the media access control layer addresses of
other routers so they can communicate without intermediate hops.

The service delivery points essentially will act as a wall jack for four different
services: IP dial tone, ATM, circuit emulation for running existing 1.5-megabit/sec T1
lines across an ATM network and gateway services for things such as maintenance of routing

What should DREN individual sites order? "If you have an IP-based LAN, you order
an IP service delivery point. If you have an ATM LAN, you order an ATM SDP,"
Schonborn said.

Because pricing will depend on function rather than usage, a location that orders an
ATM service delivery point pays the same monthly fee whether it communicates with just one
site or dozens.

DOD officials expect DREN to evolve further. For example, at this time a location
cannot hook up its router to an ATM service delivery point unless the router supports the
NHRP routing scheme used by AT&T for IP traffic over its ATM network.

Although the revamped DREN supports IP multicasting, ATM multicast capability does not
yet exist for many-to-many communications over SVCs.

But the contract requires AT&T to continue upgrading the infrastructure to the
latest protocols, Schonborn said.

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