* Cuban Internet transmission speed increases
* Experts say long dormant underwater cable operational
* Government mum on island's first fiber-optic cable
By By Marc Frank
HAVANA, Jan 22 (Reuters) - An undersea fiber-optic cable that promises to bring Cuban Internet and phone communications into the 21st Century stirred to life this week, two years after it was laid between Venezuela and the Caribbean island.
Financed by the Venezuelan government, the ALBA-1 cable under the Caribbean was laid with much fanfare in 2010 and connected to Cuba in February 2011. Since then it has been dormant and the government silent as to why.
"I had my eye on it. People have been asking why has this cable not been in use," said Doug Madory, who works for global Internet monitor Renesys and first reported cable activity on Sunday on the U.S.-based company's web page.
When fully operational, the cable will provide download speeds 3,000 times faster than Cuba's current Internet and be capable of handling millions of phone calls simultaneously, the government said when it was being laid.
Up to now, Cuba has linked to the Internet through satellite hook-ups that are excruciatingly slow due to restrictions under the U.S. trade embargo.
The cable was scheduled to be up and running by July 2011.
Cuba monopolizes communications in the state-controlled economy. There is no broadband Internet in Cuba and the relatively few Internet users suffer through agonizingly long waits to open an email, let alone view a photo or video, which also hampers government and business operations.
The National Statistics Office reported the number of "Internet" users reached 2.6 million in 2011, out of a population of 11.2 million, although almost all were likely on the government-filtered "intranet" offered through state-run computer clubs, schools and offices.
Cuba reports intranet use as Internet use even though access to the Internet is banned without government permission.
Neither the government nor Cuba's state-run telecommunications firm, ETECSA, would comment about Tuesday's increased transmission speed.
"When there is some unusual data we will spot it. We can see how long packets take down a path. We can see if there is a new path and if traffic is going faster," said Madory, who noted that a new non-satellite provider, Spain's Telefonica, was now showing up as handling a major share of Cuba's Internet traffic.
"In this case it was too fast to be a pure satellite transfer, though it is still pretty slow and would be unacceptable in most developed countries," Madory added.
On Tuesday the speed of Reuters' Internet transmissions at its Havana office significantly increased as ETECSA apparently began linking customers to the cable.
"At 9 this morning our ping latency significantly improved ... and there is no explanation other than the cable," a Reuters' communications technician in Cuba said.
Ping latency registers the time it takes to send data to a location and receive confirmation it arrived from the original server.
If the latency declines, transmission speed is up.
Due to the law of physics satellite transfers can't be more than a certain latency because of the speed of light out to the satellite and back. (Additional reporting and editing by David Adams; editing by Andrew Hay)