Cisco Systems moved to acquire a company focused on high-quality audio over Internet software and also announced its intention to buy back an additional $5 billion in stock.

In an all-stock deal valued at $13.5 million, Cisco will buy privately held SignalWorks, Inc. of Mountain View, CA.

The move is part of Cisco’s ever-growing move into Voice over Internet Protocol telephony, a market that is expected to reach $900 million this year and $4.3 billion by 2006.

SignalWorks is developing software for the delivery of high-performance audio over VoIP. Cisco said the deal is expected to close later this year. SignalWorks was founded in 1994.

“The acquisition of SignalWorks reinforces Cisco’s continued commitment to leadership in IP telephony,” said Marthin De Beer, vice president and general manager of Cisco’s enterprise voice and video business unit.

Cisco (Nasdaq: CSCO) was up 3 cents at $14.23 in late afternoon trading.

The stock repurchase plan is the second one approved recently by Cisco’s board. The company still is acquiring $8 billion in stock as authorized under a previous plan.

Cisco had more than $21 billion in cash and investments at the end of its most recent quarter.