Wi-Fi heretic launches single channel voice WLAN
Don't want hand-off and drop-outs? Use a single frequency!
Israeli WLAN start-up Extricom reckons it has solved the voice on Wi-Fi problem - with a heretical wireless switch that puts all access points on the same channel, using the same frequency.
The approach has some similarities with that from Meru (read a Meru white paper).
"Everyone is looking at voice on WLANs," said Alon Segal, vice president of sales, at Extricom at London's WLAN Event last week. "We have zero latency mobility and no site survey required." Next week, he's off to Networld Interop in Las Vegas. So just when we thought the wireless LAN industry was in merger-and-acquisition mode, along comes another approach.
We first heard from Extricom back in November, when it got some funding and started to make announcements. However, faced with extravagant and vague claims ("Is 1Gbps Wi-Fi on the Horizon?"), that we followed commentators like Wi-Fi Networking News and dismissed the company as a snake oil merchang.
As it turns out, the claims of high speeds, refer to an aggregate across several clients in several cells. The interesting thing is that all the cells are on the same frequency. The Extricom site now has more white papers explaining what it does.
How does it work?
All the access points attached to a given switch use the same radio channel, on the same frequency. This sounds like a recipe for disastrous interference, but Segal says otherwise, Techworld saw a demonstration in London, that seemed to back him up - and the product has also been tested in Japan.
"The switch decides on a packet level, which AP a client should be connected to," said Segal. The APs are "ultra-thin" - little more than antennas and signal processors, that data packets from radio to the wire, with the entire media access control (MAC) layer at the switch. So, once a client is in contact with the WLAN, it never hands off to a different channel: when it moves within range of a different access point, the switch diverts the data connection to that AP, and the client device is none the wiser.
In the demonstration - which needs to be checked under lab conditions - Segal set up a voice conversation to us, using a Pulver WISIP phone (read review). As we moved to the other end of the stand, a screen display showed we were now connected to a different AP, without any break in signal.
As with any WLAN, multiple clients can use one AP. Because the switch reduces the power level it transmits to the level those clients require, explained Segal, the same channel can be "re-used" in other parts of the building. The access points also have two radios, for more capacity.
Switch intelligence avoids interference
Via algorithms, the switch can "see" the entire radio environment in real time - all the access points and wireless clients, and every packet moving between them, CEO Gideon Rottem told Network World: "If Access Point 1 and Access Point 2 transmit at the same time, you'll have interference," he said. "So the switch doesn't let them. By knowing at all times the complete radio map of the network, we can assess when and where to transmit, and through which access point."
Compared with conventional WLANs, Extricom lets more users be closer to a larger number of access points, and therefore lets them connect at the maximum possible throughput rates of 5 to 7 Mbit/s for 802.11b and 20 to 25 Mbit/s for 802.11g and 802.11a, Rottem says.
The real-time calculations required to direct flows to the right base stations are complex, but Segal expects the level of "re-use" (multiple conversations) to go up in future releases.
Tested in Japan
Sangikyo, a network engineering firm in Yokohama, Japan, has been beta testing the Extricom switch, initially for wireless VoIP covering the four floors of its headquarters. Sangikyo set up the switch and eight access points, testing up to 10 WLAN phones over 802.11b and 802.11a connections. "We've been able to support up to 10 simultaneous calls on one" access point, Matthew Drechsler, a test engineer with Sangikyo's business development division told Network World.
In one test, Drechsler put two access points near each other, placed 10 calls on one of them, and then unplugged that access point's Ethernet cable. "All the clients 'roamed' smoothly to the remaining access point with no delay or perceivable change in voice quality," he says. "It was quite impressive."
"You have guaranteed throughput for all clients, no co-channel interference, and voice that is smooth and latency free," he says.
To support high guaranteed data rates, Extricom users will have to add more access points in a given area, compared with other WLAN systems, Drechsler says. Currently the product supports only small networks - it has eight ports. "We would like to see Extricom come out with a large-scale switch," he says.
Extricom's ultra-thin approach will be an interesting contrast to other "thin AP" vendors, who dispute where to split the MAC between the AP and the switch, but always have some MAC functions there.
Plans for more features
The switch has WEP and WPA2 (802.11i) security but, says Segal: "it has fewer features than the competition, though we have a good roadmap. Location, and other bells and whistles will come."
The Extricom switch, with eight access points, will ship in May, priced between US$8,000 and $14,000 depending on quantity and options, such as Power over Ethernet. The switch is intended to cover one floor of a building, or a branch office. The company is expected to ship a 32-port switch in the fall.
"We will have a similar price to other vendors," said Segal. "Below Cisco and with better performance."
Intriguingly, although the processing in the switch is "patent-pending", Segal thinks that other vendors will take the single-channel approach: "You can't patent single channel WLANs," he said. Our patents will be on the mechanism for reuse and for controlling APs."
We'll suspend judgement till we've used the system for real.