Guard changes X.25 provider

Guard changes X.25 provider

Major transition from AT&T to Sprint is one of first under FTS 2001 program

By William Jackson

GCN Staff

The Coast Guard has switched its X.25 network linking 138 remote navigational facilities to Sprint Corp.

The move came after AT&T Corp. announced in late 1998 that it no longer would offer X.25 service, giving users one year to move it or lose it.

'It represented one of the first major transitions from AT&T under the FTS 2000 contract to a new vendor under FTS 2001,' said Lt. Cmdr. Dave Newton, chief of the Communications Services Branch of the Coast Guard's Telecommunications and Information Services Command in Alexandria, Va.

The remote sites, which support two air and marine navigational systems, are scattered from the Aleutian Islands to the Virgin Islands, and from Maine to the Baja Peninsula. The transition did not go perfectly, but it was almost on time and did not interrupt service, Newton said.

By the time AT&T was set to pull the plug in September, all but five of 138 sites had moved to the Sprint network. The General Services Administration persuaded AT&T to extend its deadline two weeks to accommodate the transition.

The sites are part of the Coast Guard's Long-Range Aid to Navigation (LORAN-C) system and Differential Global Positioning System, which provide navigational aid for aircraft and vessels in the United States and its coastal waters.


The Coast Guard's Differential Global Positioning System stations broadcast radio signals to improve GPS accuracy and will provide nearly nationwide coverage by the end of this year.


Radio coverage

LORAN's 24 radio-navigation stations provide complete coverage of the continental United States and most of Alaska. Together with Canadian and Russian stations, they cover Canadian waters and the Bering Sea down to one-quarter nautical mile. The Coast Guard formerly ran the LORAN system globally, but the host countries now operate the stations within their borders.

DGPS transmits a correction signal to improve the accuracy of satellite GPS data. DGPS compares a known reference location against the computed GPS location, then transmits the differential information to users by radio, improving accuracy to within 10 meters compared with about 100 meters for uncorrected GPS. DGPS started up in 1996 and became fully operational last March.

LORAN and DGPS sites are located on large inland waterways and cover the coastal waters. They connect to network control centers at the Coast Guard's Navigation Center in Alexandria and in Petaluma, Calif., which monitor availability and integrity.

Most of the sites are unmanned, and many are distant from communications infrastructures. Some, such as the DGPS site at Potato Point in Alaska, can be reached only by helicopter. Because of the absence of optical fiber or new copper cabling to handle digital traffic, slow-but-steady X.25 is the protocol of choice for communicating with them.

'We can't get there from here with any of the more modern protocols because of the condition of the infrastructure,' Newton said.

X.25 provides switched data service at up to 56 Kbps over public networks. Designed for the noisy analog lines of the mid-1970s, it does robust error detection and retransmission'just what the Coast Guard needs to keep in touch with its remote sites. Most of the circuits are only 9.6 Kbps.

'It's old and pass', but it works,' Newton said. 'It meets our needs.'

Although X.25 was marginal for AT&T, it is required under the Federal Technology Service's FTS 2001 long-haul telecommunications contracts. The Coast Guard picked up the service under Sprint's bridge contract that covered the transition between FTS 2000 and FTS 2001.

Sprint had to install local loops to the sites, configure and deliver equipment, and coordinate AT&T's live traffic cutovers. To expedite installation, Sprint preconfigured equipment before shipping it to the remote sites.

Some of the sites had vague addresses such as 'five miles north on fork road,' and many of the telephone area code and exchange numbers were not in local carriers' databases.

Among the most remote were 24 Alaskan sites. One in the Aleutian chain was accessible only by a chartered flight that ran once every two weeks. At the opposite corner of the continent, equipment for a site on Egmont Key off the Florida coast had to be installed during hurricane conditions.

The Coast Guard is not wedded to X.25 if other protocols become feasible, Newton said, but economics makes an infrastructure upgrade unlikely for many of the remote sites.

He said the Coast Guard is confident the X.25 service will remain available because FTS 2001 requires it for the next eight years. Sprint also is a global provider of X.25. Although the protocol is marginal in the United States, it still is heavily used in other parts of the world.

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