Adding A Cellular Trunk To A Home Office VOIP System: Part 2

Originally published June 6, 2008 at www.smallnetbuilder.com

Welcome back! In Part 1, I took you through the thought process that led me to want to add cellular-based access to my home’s VoIP system. I ended up with the following project goals:

• Ensure the ability to make outgoing calls should our DSL fail
• Provide access to 911 service
• Provide access to 411 service
• Provide a low/no cost way to stay in touch when I’m traveling
• Provide a means of making oversea calls from my cell phone without paying cellular carriers oversea long distance rates

In this second and final part, I’ll focus on the little box that makes it all possible.

Portech MV-370

Normally in a product review I would not dwell upon the purchase process in any detail. However, in this case I feel it’s worth sharing the experience of buying a system directly from a manufacturer who is located in the Far East. While this might cause some concern, the experience was good and I feel I was dealt with promptly and fairly.

Having made the decision to buy a GSM gateway and researched the various products available, I decided to order the Portech MV-370. I was a little surprised to find that Portech, a Taiwanese company, doesn’t really have solid distribution system in the US.

While Portech lists a distributor on its website, that dealer’s web presence left me feeling that I should buy the unit elsewhere. Out of curiosity, I checked E-Bay and found that the device was available for purchase directly from the manufacturer. So that’s the way I went.

There are, in fact, several variants of this device, so check details and specifications before ordering! I initially purchased a tri-band variant with a 220 V power supply because the voltage on the power supply was not clearly stated in the catalog (but was detailed in the email confirmation of the order). Since that power supply was inappropriate, I contacted the manufacturer and modified the order to include a 110 V power supply. During that contact Portech also recommended the quad-band model that would cover all possible US GSM carriers and was only slightly more expensive.

Getting Service

Before the MV-370 arrived, I paid a visit to my local T-Mobile store to get a SIM card for the gateway. During that visit, I changed my calling plan from a zillion minutes/month on one line to a “family plan” with two lines sharing the pool of minutes.

T-Mobile was only too happy to do this, as I was very near the end of a two-year commitment. Since I was providing my own hardware for the second line, they required a further commitment of only one year to make the change.

The change didn’t cost me a penny, although T-Mobile may have had the impression that I was going to use my old Motorola RAZR for the second line. That may have come from the fact that I brought that phone with me to the store so they could “install” the new SIM card, although we never actually spoke about it.

Setup

When the product arrived, I opened the box to find a small plastic device about the size of a novel. It arrived with a power supply, antenna, Ethernet cable and a printed manual.

The gateway has a removable panel on the bottom that reveals the SIM card slot. It has an SMA type connector for the antenna and the antenna itself includes a 2m attached cable.

The device boots up with a default IP address of 192.168.0.100. But since my LAN is on a different subnet, I used a crossover cable to access the device’s internal web server and enable DHCP. Then I put it on my network and it acquired a more appropriate IP address from my router.

I later discovered that you can also define the gateway’s basic network settings via an interactive voice menu accessed by calling the gateway from a cell phone. This menu is only available in the initial 20 seconds after the device boots, while the front panel light marked “Mobile” is flashing.

Configuration #1: Use With A Hosted IP-PBX

When the gateway was initially delivered, I was a bit short on time to experiment with its configuration. The fastest way to get a little experimentation in before I left on a business trip was to link the device to a hosted IP-PBX service that I use for my day job. This initial configuration took only about half an hour.

In the admin portal for the hosted PBX, I set up a new user. This resulted in a set of login credentials that I loaded into realm 1 on the MV-370’s Service Domain settings menu. This menu supports settings for three separate SIP registrars, each referred to as a “realm.”

As a convenience, you can enable or disable each without losing the settings. The gateway places all outgoing IP calls through the first available realm. But it will answer incoming IP calls from any enabled realm.

With the new credentials loaded, and after the usual reboot, the status for the server was shown as “registered” (Figure 2), which I also confirmed with the provider’s management portal (Figure 3).