T-Mobile's HotSpot @Home: Hot Or Not, From My Geodesic Dome?

Continued from ‘T-Mobile’s HotSpot @Home: Wi-Fi VoIP Plus GSM Roam‘….

A few comments on the WRT54G-TM, before I continue with my hands-on discourse. Google search results such as this one (which also includes some nice internal teardown shots) suggest that the router’s hardware platform is identical to that of the Linux-based WRT54GL. However, I doubt that T-Mobile would be thrilled about its UMA ’secret sauce’ being released to the open source community, so I suspect that the WRT54G-TM’s firmware is based on closed-source VxWorks, as is the case with the WRT54G. Also, the comments below are all I’ve succeeded (so far) in getting from Linksys regarding HotSpot @Home optimizations:

In a nutshell, the Linksys router optimizes Wi-Fi performance of a T-Mobile dual-mode Wi-Fi/GSM handset. Here are examples of how we have optimized the VoIP over WiFi performance:

• Battery Life: To improve battery life, we’ve implemented UAPSD (Unscheduled Automatic Power Save Delivery), which is part of the WiFi Multimedia specification. This specification allows Wi-Fi devices to go into "power save" mode.
• Security: We have implemented an algorithm by which handsets and the wireless access point can create a secure association via an easy to use push-button on the access point.

Notably, Linksys hasn’t (yet) answered my question about whether or not the WRT54G-TM supports QoS optimizations for VoIP traffic. If the answer’s ‘no’, then my WRT54GC (which is paired to a Ubicom-based Linksys OGV200 Network Optimizer) might actually deliver a superior VoIP quality experience in heavily loaded WAN traffic situations….although since the OGV200 locates in-between the router and DSL modem, not within the router, it can’t QoS-manage intra-LAN traffic.

To test HotSpot @Home, I called my home office’s Broadvoice VoIP line and left voicemail messages. Keep this potentially quality-degrading fact in mind as you listen to the resultant audio archives, which I’ve converted from their original nonstandard 32 kbps codec to 128 kbps MP3 for convenience’s sake. I’ve loaded them up on my Omnidrive and Xdrive accounts as a consolidated ZIP; access the links at the beginning of this sentence for the file, and see this past post for download instructions.

The phone came configured with SSID profiles for ‘HotSpot’ (which reflects T-Mobile’s HotSpot network) and ‘@Home’ (which I presume mates up with a similar pre-configured profile in the WRT54G-TM router). I was able to manually add my router’s SSID and encryption details, but the phone only ’saw’ the wireless network after I subsequently enabled SSID broadcast. This added security-preventing limitation is a long-standing pet peeve of mine, which I also discussed in detail in the midst of my Sandisk Sansa review (and still hasn’t been fixed by Sandisk, Yahoo! and/or ZING).

I was also amused to see that the handset, in the presence of a strong GSM signal, seemed to prioritize that connection over a pre-configured Wi-Fi network that was simultaneously and strongly broadcasting. I had to go into the phone’s settings and manually initiate a Wi-Fi connection in order to activate UMA mode. Apparently (and obviously, in retrospect), although T-Mobile now provides an option for unlimited calling, they’d still prefer that you use up your plan’s cellular minutes.

My first test file (Test1.mp3), showcasing the Gettysburg Address ;-), was exclusively conducted over UMA. It actually wasn’t my first connection attempt; the first call I tried to make resulted in a spontaneous handset reboot immediately after I entered the outgoing phone number and punched the ‘dial’ button. To my ears, the recording sounds like a typical VoIP or cellular call….frequency range-constrained, a bit glitchy, but definitely discernable. Next, to test 802.11-to-GSM handoff, I disabled the WRT54GC’s SSID broadcast mid-call (this settings change also restarts the router). As you’ll hear (Test2.mp3), the call continued past that point for quite some time, but my outgoing voice can no longer be heard. Since I wasn’t speaking to another person ‘live’, I have no way of knowing if voice traffic heading the opposite direction (i.e towards my handset) was similarly disrupted.

Based on yesterday’s experiments, I was set to deliver a warm-but-not-hot ‘not yet fully baked’ review rating to HotSpot @Home….until I re-read Engadget’s hands-on review this morning and saw that 802.11-to-GSM handoff also consistently failed for them when they abruptly terminated the Wi-Fi connection. Theorizing that perhaps my atypical testing situation yesterday had not given the HotSpot @Home infrastructure sufficient warning and time to work its hand-off magic, I re-tested this morning under a more normal usage scenario….walking away from the home (and therefore beyond its Wi-Fi network’s reach). The result, as you’ll hear in Test3.mp3, was a nearly seamless 802.11-to-GSM transfer….leaving me quite impressed with T-Mobile’s system. Now if the company would just add my Wi-Fi-inclusive Windows Mobile Smartphone to the supported handset mix….