Last week's update about the Proxim-Avaya-Motorola voice-centric wireless roaming partnership made me wonder where the wireless overlay vendors fit into the "fast-roaming" craze. I'm talking about vendors such as client\/server software company NetMotion Wireless and gateway appliance maker Bluesocket.Currently, a number of wireless vendors enable fast, secure cross-subnet 802.11 roaming using proprietary technologies. Also, the new 802.11 Fast Roaming Study Group plans to standardize how fast handoffs take place across 802.11 subnets. And a new 802.21 working group is working on handoffs among all flavors of 802-based networks.For its part, NetMotion Wireless has long enabled data roaming across disparate network types (such as wireless LANs and cellular networks) without disrupting user application sessions. NetMotion's LAN-to-WAN roaming for data is analogous to what Proxim, Avaya, and Motorola are working on for voice, in particular (though the latter effort will not require client software).Wireless gateway company Bluesocket also enables fast, secure inter-subnet roaming in any vendor's Wi-Fi environment. Unlike NetMotion Wireless, Bluesocket says its handoffs are fast enough for voice. However, it doesn't support the Wi-Fi-to-cellular roaming component.Using NetMotion Mobility or Bluesocket products, if you start a data download on your laptop then wander across campus on your 802.11 network, your download keeps chugging away without interruption. NetMotion extends this capability into the cellular environment, too. Bluesocket is limited to roaming within an 802.11 network. But it supports Wi-Fi voice roaming, where NetMotion does not.NetMotion hasn't pursued the voice market, because its handoffs take 2 to 3 seconds, says Andy Willett, the company's senior vice president of product management and marketing.Eventually, Willett says, the NetMotion Mobility product might serve as a "data complement" to the Proxim-Avaya-Motorola setup for data session persistence independent of WLAN vendor.But I wonder. How many overlay networks will enterprises eventually require for things like security, internetwork roaming and quality of service? Increasingly, these capabilities are being built directly into wireless access points and switches, using proprietary technology or the emerging IEEE standards mentioned.On the other hand, while Proxim, Avaya and Motorola say they will enable both voice and data roaming, we will have to see if the group comes out with a dual-mode Wi-Fi\/cellular adapter for more data-centric devices such as laptops and PDAs. At this juncture, Motorola is expected only to contribute a dual-mode handset optimized for wireless voice.