Wireless Least-Cost Routing

The HP iPAQ h6315 is the first Phone Edition device sold in the U.S. that includes Wi-Fi as well as cellular data capabilities. What makes this so exciting is that it is now possible to use a faster and cheaper wireless LAN connection when it's available, and only use the more expensive cellular (GPRS) data connection when you can't connect to a wireless LAN.

The HP iPAQ h6315 has built-in mobile phone, Wi-Fi, and Bluetooth capability.

In most cases, the user needs to select the type of connection to make. In the case of the new h6315, HP and exclusive U.S. distributor T-Mobile have worked together to develop a feature that automatically selects the faster Wi-Fi connection when it is available and defaults to the GPRS network at other times. In network traffic engineering terminology, this feature is known as "least cost routing."

Data speed, not dollars!

The "cost" in "least cost routing" is not measured in dollars, but rather in the speed of the connection. This is because T-Mobile has a number of new data plans that offer unlimited GPRS data for a flat rate per month. But GPRS is the slowest wireless digital data network available. So using a much faster Wi-Fi connection saves you time—and your time has a cost, too.

Most mobile carriers are investing in faster data technology, such as 1EvDO (for CDMA carriers Verizon and Sprint), and EDGE or UMTS (for GSM carriers such as AT&T/Cingular). But T-Mobile has a different plan. Since they own an extensive Wi-Fi hotspot network, T-Mobile is concentrating on improving their voice network, and relying on their hotspot network for fast data. Therefore, the new h6315's ability to "sniff out" and automatically switch to a Wi-Fi network is an ideal fit for T-Mobile's combination of slower GPRS (about 40 kbps) and Wi-Fi hotspots (up to 11 Mbps.) In fact, when T-Mobile introduced the h6315, they also announced special rate plans specifically for h6315 users, starting at about $80 for 1000 voice minutes together with unlimited GPRS and SMS, plus unlimited use of their Wi-Fi hotspots.

Of course, you are not limited to T-Mobile hotspots. You can connect the h6315 to a home network or, if available, a wireless network at the office or elsewhere.

Battery drain an issue

In my testing, the system worked very well. First, I connected the h6315 to a laptop via IrDA and browsed the Web from the h6315 using the laptop's Internet connection. Then, after disconnecting from the laptop, I requested a new Web page in Pocket Internet Explorer and the h6315 automatically re-connected to the Web using its phone/GPRS capabilities. Then, I connected to the Web using the unit's Wi-Fi capabilities. When I walked away from the Wi-Fi access point and the connection was lost, it was again automatically re-established using the h6315's GPRS capability.

Leaving the Wi-Fi radio on all the time greatly reduces the battery life on the Pocket PC. This is especially true when you are outside the range of a wireless LAN because the Pocket PC will use the highest power setting to search for a valid Wi-Fi network. For this reason, while my tests of the automatic network selection worked as expected, I found it more useful to leave the Wi-Fi radio turned off most of the time, and turn it on manually when I knew I was within range of a Wi-Fi access point. And because I have the unlimited GPRS data plan from T-Mobile, I continued to use the slower cellular network when simply checking e-mails, regardless of the availability of a Wi-Fi network.

Because of the ease of switching between GPRS and Wi-Fi, the h6315 is an excellent choice for companies that want to provide their sales or service personnel with wireless connectivity—even when you factor in the power consumption issue.

The future of wireless least cost routing