This is an idea that’s been percolating for a while, but Dameon’s recent rant about how VoIP hardware is boring has triggered two responses.
One is that I have started explaining what I do with VoIP to the rest of the world as, “I have become my own telco.” If I want a service, I can define and implement it myself, without needing to wait for a big market to develop and catch the eye of the telco. (I did this recently to make Asterisk handle incoming telephone calls in a time-aware fashion for my international travels.)
But, more on point, I’m also excited by the proliferation of wireless LAN phones. The dual-mode phone is a way of communicating traditionally (with the cell side of the device) as well as with services that I can define myself (with the 802.11 side). Unfortunately, most of the phones on the market are hardly interesting. Here’s my “hit list” of features that you have to implement to make me pay attention:
- WPA(2). This shouldn’t even be hard at this point. We’ve worked out all of the kinks from these protocols, and there are multiple open-source implementations. There is no excuse for bringing any wireless LAN device to market that doesn’t support good security in 2007.
- WMM. Last year at Interop, I was able to demonstrate that WMM can give you voice quality, even with significant background traffic. There are plenty of reference designs from hardware vendors that do WMM. Selecting only WMM phones drops you to just eight Wi-Fi Certified devices.
- PMK caching. This is an under-appreciated feature that was part of the 802.11i amendment. It’s a way of saving master keys to cut down on roaming times. Combined with the “opportunistic” version that establishes master keys on APs before it’s needed, you can get some impressive handoff times between APs, and you’re hard pressed to hear a difference.
- U-APSD. This is an acronym for Unscheduled Automatic Power Save Delivery. Anybody who’s used an early 802.11 phone has undoubtedly noticed that the battery life is, to put it nicely, awful. U-APSD works keep the 802.11 radio powered down when it’s not used, so that almost all of the 802.11 radio (and power) usage is devoted to transmitting voice. Anecdotally, it can extend battery life by 50-100%, but there are so few implementations I can’t speak from a wealth of data.
Naturally, even after you get to the end of this list, there’s a lot more that can be done, but it’s relatively small potatoes compared to the big four. There are some further quality of service parameters that can be used to help an 802.11 phone in a big network select the right AP to go to, and there are some features that help further smooth out handoffs. To be honest, there are so few phones that can get to #2 on the list that I’m not worried about writing up #5 through #10.