Cisco has continued its buying spree with the purchase of privately-held mobile telephony software company Orative for $31 million in cash.

Orative develops conferencing and collaboration software for mobile business users, and integrates those tools with users' existing communications systems. Cisco expects the transaction to close in the middle of next year.

This is Cisco's fourth acquisition in recent months. In August, it paid $50 million for 80 percent of data centre software developer Nuova Systems, and $92 million to acquire on-demand video company Arroyo Video Systems. In July, it bought security software vendor Meetinghouse for $43.7 million.