Getting In Formation for the 'Handoff'

Handing off telephone calls from a cellular-telephone network to a cable system is a challenge that has yet to be surmounted by any communications-service provider.

But dual-mode wireless phones, wireless fidelity (Wi-Fi) gateways and a combination of hardware and software that use communications standards known as the Internet Multimedia Subsystem (IMS) are expected to be the key ingredients that will allow the new Sprint Nextel Corp. joint venture with Comcast Corp., Time Warner Cable, Cox Communications Inc. and Advance/Newhouse Communications to manage the feat.

The ability to switch phone calls from the wireless network to the cable network inside a consumer's home is one of the key goals of the Sprint/cable joint venture. John Garcia, the Sprint executive who'll run that business, estimates that 30% of all cell phone minutes occur inside the home, so such handoffs would reduce the amount of voice traffic on cell phone networks.

Reducing call volume on crowded wireless phone networks will save Sprint money — savings that can ultimately be passed on to consumers, Garcia said. Cable's infrastructure allows for a way to “transmit phone calls that are less expensive than using the wireless network,” Garcia said.

In order to switch a cellular phone call from the wireless network to a cable system, a consumer would need a new handset and the cable operator would have to install new equipment in the home and in their network.

To start, a consumer would have to buy a new “dual-mode” cell phone, which would be capable of communicating with the wireless network and cable's Internet protocol infrastructure.


“A dual-mode handset has two radios,” said Jeff Walker, senior director of marketing at Motorola Inc., which began marketing its A910 dual-mode handset late last year.

One radio relays voice calls to and from the cellular network. The other radio is equipped to communicate with a wireless-networking device, known as a Wi-Fi gateway, that the cable operator would install in the home. The new dual-mode phone would also contain IMS software, which would translate the contents of a call from the wireless network to the cable network.

“The IMS client communicates to a wireless access point in the home using SIP [Session Initiation Protocol] software,” Walker said.

“The wireless access point would be a new device in the home that would include a Wi-Fi antenna and gateway, a cable modem and a multimedia terminal adapter,” Walker said.

That gateway device would communicate through a subscriber's cable modem with an IMS switch, located beside the cable-modem termination system in a cable system headend, Walker said. That switch would handle communication with the cellular phone network to transfer phone calls.

“As the dual-mode handset moves into the home, it automatically checks to see for an authorized access point as signal power declines on the call,” Walker said. The cell phone is preprogrammed to “look” for the Wi-Fi gateway, he said. The gateway, in turn, has been programmed to receive signals from that particular cell phone.

If, for instance, the strength of a signal starts to weaken while a caller is still using the dual-mode handset inside the home, the handset will automatically switch the call to the Wi-Fi gateway and onto the cable network, before it is lost.

Walker said the new dual-mode phones allow consumers to configure some options. They may, for instance, want to automatically switch phone calls to the cable network as soon as they are inside the home, without waiting for a signal to degrade.

“You can configure it so it automatically hits the Wi-Fi access point, saving you cell phone minutes, or you can stay on the cellular network to the point it starts to degrade,” Walker said.


Once the call is handed off to the in-home wireless gateway, the voice packets are sent through the cable plant to the Internet Multimedia Subsystem switch in the headend.

“The Internet Multimedia Subsystem switch will then communicate to the cellular switches in network,” Walker said. “It will say: 'I want to talk to the home location register. This call is on this switch and I want to take over this call.'”

Calls that travel through the IMS switch then proceed through a media gateway, which converts the call from the packets that adhere to the Internet communications protocol used by cable to the code-division multiple access (CDMA) format used by Sprint.

Cable operators who've deployed voice-over-Internet protocol service have already installed media gateways, Walker said.

Walker said Motorola is building wireless gateways for use in cable networks that would cost $100 apiece.

“Those gateways have advanced capabilities,” he said, including a Wi-Fi router with a firewall and software to insure different applications running through the gateway receive the bandwidth they need.

“Voice may be one session, and you may have multiple PCs running, including someone downloading video off the same gateway. You want to give priority to voice traffic,” Walker said.

“Another aspect is security,” he added. “You want to make sure the call is encrypted and authorized. You want only authorized users sending information back up to network.”


Walker said that when a consumer brings home a dual-mode handset and gets the Wi-Fi gateway installed, prompts on the cell phone will give the subscriber a series of commands to “pair” the cell phone with the gateway. “It has automatic pairing capability,” much like how a newly installed cable modem “looks” for the cable-modem termination system in the cable headend to launch high-speed Internet access.

The quality of signal coverage inside the home will degrade the further a cell phone user is from a wireless access point, just like a personal computer in a wireless network in a home.

But “we do have the ability to set power levels and boost signal strength [of the gateways],” Walker said. “Typically, the cell phone connection in the home is not great in many parts of the home. Wi-Fi tends to have a much better signal strength. It will be much better than cellular experience.”

The new cell phones also will conserve battery strength. “The wireless access point is always throwing out beacons looking for traffic,” Walker said. “We have a power save function so the gateway isn't pinging the cell phone constantly [and draining the battery],” he said, such as when the overnight hours when the cell phone is in the house, but the user is asleep.

Walker said Motorola's gateway supports both 802.11b and 802.11g formats. The two wireless-communications specifications are capable of delivering data at speeds of 11 Megabits per second and 50 Mbps, respectively.

Walker said Motorola intends to start marketing dual mode handsets “shortly,” even though cell phone-to-cable hand-off services have not been deployed. “It is pre-positioned for these value-added services,” Walker said. “We'll help the service provider get them out.”

As for the consumer's need to purchase yet another new cell phone, they're use to that, Walker said.

“People buy cell phones almost every year,” he said, adding that in many cases, handsets come free, depending on the level of services or features a consumer buys.

And the promise of saving minutes might just be enough to entice consumers to get yet another cell phone, Walker said — a marketing ploy cable operators are banking on.