The sky is falling on the number of global IP addresses, and IPv6 is the solution, executives from major technology companies have announced once more.

The exhaustion of available IP addresses using IPv4 (IP version 4) brought out the alarmist side of many industry executives.

"It's a crisis - not a market-oriented event," said Akinori Maemora, chairman of APNIC (Asia Pacific Network Information Centre), speaking at the Global IPv6 Summit in Beijing. "We have just three years until IPv4 addresses are depleted. These changes will come suddenly," he said.

The telecommunications industry is going through "a period of grief" over the end of IPv4 (IP version 4) said Tony Hain, IPv6 technical leader for Cisco Systems. "Most people in the world are still in a state of denial" about upgrading to IPv6. "No one will ask for IPv6 until they run out of IPv4 addresses," he said.

IP addresses allow individual devices, including computers, laptops and mobile handsets to connect to the Internet. Using the current IPv4 system, which offers a total of about 4.7 billion possible IP addresses, some countries, including China, will begin to run out of addresses they can allocate around 2010, according to estimates by the Internet Assigned Numbers Authority and the Internet Corporation for Assigned Names and Numbers.

By switching to IPv6, the number of possible addresses increases by billions more. This would also allow a far greater number of devices to connect, allowing features like the Internet-based remote control of security cameras, and even turning on home appliances from one's desktop at work.

With IPv6 therefore not an "if" but a "when," technology managers should "roll out applications for IPv6 today," said Sandeep K. Singhal, Microsoft's director of Windows networking. Microsoft used a phased approach to its own implementation of native and dual-stack IPv6 use, and Singhal urged other companies to do the same. "Don't simply wait until IPv6 is out there; start early and start learning."

One barrier to early IPv6 adoption is that intermediate measures, such as NAT (Network Address Translator), have been very effective. "NAT has worked too well to give over business to IPv6," said APNIC's Maemora. IPv6 deployments are being deferred due to short-term business pressures, he said. However, NAT is not a panacea, as servers cannot be connected using it.

China has one of the world's largest IPv6 networks, but currently only a fraction of that capacity is used, and only for academic and research institutes. Although China, now the world's largest Internet user market, will feel the address crunch earlier than other major markets, there is no timetable for a move to IPv6.

"The industry in China is not perfect," said Mao Wei, director of the China Internet Network Information Centre, a quasi-governmental Internet overseer. "Right now there is no mechanism to switch over to IPv6, nor do we know who will issue that order, which department?"