New questions raised about SS7 phone system

WASHINGTON — WASHINGTON -- DSC Communications Corp., whose software has been linked to recent phone outages, knew a year ago that there were potential problems with the new signaling systems used by the "Baby Bell" phone companies to handle calls, a DSC official told a House subcommittee yesterday.

The admission raised new questions about whether Bellcore, the research arm of the seven regional Bells, had adequately investigated the "Signaling System 7" technology it helped develop. Technical standards developed by Bellcore are used by all seven Bells.


Under a SS7 configuration, a few, powerful computers tell an extensive network of electronic switches which routes to use when handling telephone calls.

Frank Perpiglia, DSC's vice president for technology and product development, said that some DSC customers noticed as long as a year ago that SS7 computers could be prone to overload from "maintenance messages" -- signals a computer sends itself to confirm that its components are working properly.


That kind of overload problem has been linked to the recent spate of phone outages, including the one in Maryland on June 26 that left up to 5 million customers without local phone service for most of the day. The recent spate of outages has been traced, in part, to some faulty DSC software.

But software bugs notwithstanding, Mr. Perpiglia said that SS7 has an inherent problem. That problem, he said, is this: When engineered to the precise specifications of Bellcore and other standard-setting organizations, SS7 has no way to disregard maintenance messages.

Mr. Perpiglia said that some DSC customers became alarmed by that omission after conducting their own, independent laboratory tests.

He said that DSC subsequently engineered a software "patch" to fix the problem and handed it out to customers who asked for it. The first patch, which is basically a rewrite of a piece of software, was released about a year ago, Mr. Perpiglia said.

A similar patch was given recently to Bell Atlantic Corp. and Pacific Bell, which have experienced half a dozen outages and near-outages in the past two weeks.

DSC has so far kept a low profile on basic design issues related to SS7. But there are indications of concern within the company about the system.

In an undated memo sent to its regional Bell customers after the June 26 outage, DSC urged the Bells to adopt a new set of specifications not approved by Bellcore, according to Electronic News, a trade publication.

In an article published July 8, Electronic News said that the DSC memo "warned, without further elaboration, that the new specifications are 'in opposition to Bellcore's specifications' for SS7." The new specifications have been adopted by Bell Atlantic, Pacific Bell and two other Baby Bells, Electronic News reported.


At yesterday's hearing before the House subcommittee on government information, justice and agriculture, Mr. Perpiglia said that the patches given to Bell Atlantic and Pacific Bell don't conform with Bellcore-approved standards for SS7. He characterized the patches as a "violation of a piece of SS7" that raises a "theoretical design issue."