"We calculate that just a 6% slice of the addressable enterprise business from Nortel --  $754 million in annual revenue -- would represent 16% of our 2009 revenue growth forecast for Juniper," Kidron states in his report.

Virtually all of Nortel's enterprise businesses -- switching, routing, security and VoIP -- are "up for grabs," according to Oppenheimer. Nortel has seen its market share deteriorate over the past two to three years in these areas, although its still retains a "solid, credible position" in VoIP, the firm asserts.

For Cisco, the overall impact of Nortel's precarious position will be muted, Oppenheimer notes. A 6% share gain of Nortel's enterprise revenue could add $152 million to Cisco's fiscal 2009 sales of $38 billion, slightly improving Cisco's year-over-year growth to -3% vs. -4%, the firm states.

F5 may not benefit meaningfully from the fallout of Nortel's situation because Nortel hasn't been a serious competitor in the Layer 4 to Layer 7 market for years, according to Oppenheimer. F5 has already penetrated Nortel's customer base, limiting the positive impact, the firm notes.