Cisco

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, fresh off throwing a scare into investors by detailing a 30% decline in its order backlog, now says its customers are having a harder time predicting how their businesses will perform in coming months.

Speaking at a conference in San Francisco, Chief Executive John Chambers said his conversations with executives of companies Cisco does business with indicate they are once again finding the elusive quantity known as "visibility" slip away.

The admission sent Cisco's shares down 3% to $11.62 in the Instinet premarket session.

"Their visibility ... is getting tighter, but I think that actually tightness has increased a little bit over the last several months in terms of what they're seeing," Chambers said, according to

Reuters

. "If CEOs think things are going to pick up in the first quarter of next year, they'll spend in December. ... If they feel like business is going to tighten in the first quarter of next year, they are probably going to be more conservative. And I think that is too early to call."

Chambers declined to give any guidance for the network router maker's fiscal first quarter, which ends Oct. 26.

Chambers' comments come a less than a week after Cisco said in a

Securities and Exchange Commission

filing that its backlog of orders not yet shipped but booked as revenue dropped 30% over the year ended Sept. 9. The filing called into question Cisco's long-espoused theory that it has been gaining market share on financially weaker competitors during the current downturn.