In The Hunt
SpectraLink is the Vo-Fi pioneer. Its product came to market in 1999 with the proprietary protocols necessary to realistically support early wireless VoIP, developing and adding a wider range of PBX integration as the offering matured. SpectraLink has established itself as the market leader and just introduced a new line of handsets that reflects the next wave of Vo-Fi technology.
Cisco's Vo-Fi handset is similarly proprietary, offering no vendor-supported integration with non-Cisco PBX platforms. It's clearly meant to provide a mobile aspect to Cisco's PBX product line. Vocera Communications took a different approach. With an emphasis on hands-free voice, it uses advanced speech recognition to provide internal voice communications, with some ties into existing telephony systems. Its badge-form-factor devices are very popular in hospitals. In fact, most of its customers are in the health-care industry.
Hitachi's Hitachi Cable division represents a new era of wireless VoIP handsets built entirely around industry standards like 802.11 and SIP. These devices are an obvious choice for organizations that have a PBX with a SIP interface. Get complete results of our tests of handsets from Hitachi, SpectraLink and Vocera at nwcreports.com.
Miles To Go
Before we can recommend VoWLAN for most enterprises, vendors must overcome performance and security limitations. Although standards to address some challenges have been settled, gaps remain, notably in fast-secure roaming, call-admission control and load balancing. Fixes are being worked on, but are likely a year or three away.
Unlike data applications, which are virtually insensitive to roaming events that take several hundred milliseconds (ms) or more, VoIP demands a consistent packet flow with minimal loss, latency and jitter. Even a few missing packets can be detected by the listener. To better appreciate the challenges, we diagrammed a typical roam (see "A Typical VoWLAN Roam").
The commonly accepted target roaming/cut-over/gap-time metric for voice transitions is 50 ms, generally considered the maximum acceptable break in audio. Our tests demonstrated that, with an appropriately configured WLAN infrastructure and handsets, this target time can be easily achieved ... if you don't want security. Add in WPA-PSK (Wi-Fi Protected Access with Pre-Shared Key), or even more problematic, 802.1X-based authentication, and roam times jump to hundreds of milliseconds, even in controlled circumstances.
Another concern is that the QoS resources of the target AP are not known until the roam completes. Ideally, the handset will know before the roaming event occurs if the necessary QoS is available.
AP vendors have not stood still. Cisco introduced CCKM (Cisco Centralized Key Management) many years ago to address secure roaming concerns, but CCKM requires a Cisco WLAN infrastructure. This proprietary fast-roaming functionality was introduced with Cisco's LEAP (Lightweight Extensible Authentication Protocol), with EAP-FAST (EAP-Flexible Authentication via Secure Tunneling) following. Cisco added more 802.1X types (PEAP, EAP-MSCHAP, and EAP-TLS) in CCX (Cisco Compatible Extensions) Release 4, but most are supported only in the very latest Cisco WLAN infrastructure devices and cards, with the appropriate software.
Meru Networks and Extricom have taken a different approach: Don't let the client roam at all. In their architectures, each AP shares the same BSSID (MAC address). From the client perspective, it sees one large AP. The WLAN infrastructure manages which AP communicates with a given client. Although elements of this design remain problematic--for example, when roaming across APs on different controllers, delay will be around 50 ms--the benefits for Vo-Fi deployments are obvious.
So where are the standards? The IEEE has a task group working on IEEE 802.11r, which aims to minimize roaming time between APs. Although there's been speculation that fast-secure roaming would match the 20 ms to 30 ms of WEP (Wired Equivalent Privacy), the task group hasn't been able to agree on specifics regarding times.
The IEEE 802.11 schedule points to ratification of 802.11r in fall 2007, with products supporting that standard following many months later. For most enterprises this can't happen soon enough. In the meantime, organizations that don't use Cisco gear can remain open; use WEP, which is only a casual deterrent because there are attacks that can break the keys in seconds; or use WPA-PSK or 802.1X and expect occasional detectable roaming events, say, if a user is walking while talking on the phone.
