More commonly known to enterprises for its digital certificate services, VeriSign recently announced trials of the company's Wireless IP Connect Service. VeriSign noted the involvement of three major universities at which users will have a single mobile device that roams between Wi-Fi and cellular networks. The company is also a member of mobileIGNITE, a network convergence industry body led by BridgePort Networks.

In an interview with Tom Kershaw, VeriSign Communication Services' vice president of Next Generation Services, he says VeriSign is "all about connecting different VoIP islands." Currently, there is no VoIP peering point that interconnects Vonage with SIPphone, Packet8, FreeWorldDialup, etc. Emblematic of FMC (fixed-mobile convergence), VeriSign plans to bridge VoIP, cellular and traditional voice. Touting its existing roaming and settlement agreements with carriers as well as its current SS7 (Signaling System 7) connections to all major carriers, VeriSign will operate a gateway that connects external VoIP media and signaling flows to the appropriate mobile or fixed voice carrier.

Kershaw casts some necessary doubt on the PBX-centric model demonstrated in the Motorola/Avaya/Proxim solution. This trio, which initiated the SCCAN forum, splits the functionality among handset, PBX and WLAN gateway, respectively. What's unique is that the PBX needs to have an SS7 link to the wireless carrier so that location registration and call control can be handled. Not many PBXes have such interfaces, and carriers are uncomfortable in opening up their SS7 networks to enterprises and university campuses alike.

Mobile carriers are partial to UMA (Unlicensed Mobile Access, now transferred to 3GPP) because it essentially allows a cheaper (and perhaps organization- supported) pico-cell, by way of a wireless network, to connect to their existing GSM networks. A secure tunnel is built over the wireless IP link, which registers the handset onto the carrier's network. UMA is not based on SIP, and to that extent excludes the solution from interfacing directly with existing enterprise VoIP networks. On the flip side, there is some significant momentum with this technology. Nokia recently committed to using UMA in its infrastructure equipment, and there are already several handsets in the works, with Motorola participating, too.

The VeriSign model takes a more carrier-agnostic approach. Enterprise VoIP traffic terminates on VeriSign's hosted gateway, distinctively named "Wi-Fi Mobile Gateway" (WMG), and performs the necessary SIP to GSM/CDMA inter- working. Besides the necessary signaling and enhanced service delivery, it also updates the native mobile carrier's database with the network location of the handset. Owing to its existing relationships with major carriers, VeriSign can almost immediately provide transparent and equal access to all mobile carriers without either a forklift PBX upgrade or requiring an organization to limit its cellular relationship to just one provider.

Because mobile carriers are essentially extending their cellular networks to third-party Wi-Fi networks, they are naturally concerned about quality, reliability and service levels. VeriSign's Kershaw confirms what Motorola executives remarked in an earlier briefing: Mobile carriers want assurances that the organization's Wi-Fi network has the necessary QoS, seamless and ubiquitous coverage, reliability and optimized operation between handheld device and access point. Carriers' other concerns include feature parity between Wi-Fi and cellular networks and handset functionality. SIP, as defined and expanded in multiple IETF (Internet Engineering Task Force) RFCs, lacks some of the extra features needed for specific implementations of FMC. Appreciably, SIP is extensible and, hopefully, that functionality will be rolled into future standards- body work.

The three universities participating in VeriSign's trial--University of Michigan, Northwestern University and Texas A&M University--are using faculty and students as guinea pigs, with the number of users across all the trials numbering just over a hundred. Similar to what was rumored with the TalkTelecom deployment in Ireland, this pilot does not use traditional candy-bar or flip-phone handsets; rather, it is based on PDA-style HP iPaqs that include GSM and 802.11b support. According to Kershaw, mobile voice usage in the university setting, encompassing college dorms, classrooms and faculty offices, is about 60 to 70 percent of the subscriber's total airtime. This is much higher than the oft-quoted average of 30 to 40 percent in the enterprise space, and it was a contributing factor in selecting higher education as a place to initiate these trials. Because some schools have comprehensively deployed their wireless LANs across their campuses, it might well be possible for students to spend almost their entire day within proximity of a Wi-Fi access point.

Progress is definitely being made on the wireless convergence front. Although the market is very young and the supporting technology awkward and immature, different approaches to convergence are being worked out. The Motorola/Avaya/Proxim partnership has the advantage of a well-tested and feature-rich solution with a custom handset that's more acceptable than the bulky PDA used in the VeriSign trials. Proxim and Motorola have also tweaked their respective parts so that roaming between Wi-Fi actually works within acceptable tolerances. But replacing your existing PBX with one by Avaya (or, in the future, with Cisco's CallManager) is not a lighthearted task. VeriSign does well by demonstrating an alternative dual-mode solution. Time will tell how these competing, and sometimes complementing, concepts fair in the marketplace.