Voice and Video


VoWi-Fi with Nokia, Apple, Android phones and a PBX

Many enterprise voice enthusiasts, including your correspondent, have an interest in connecting up their cellphones as PBX extensions. The usual scenario would be a corporate PBX (SIP-enabled for all the options below), with a WLAN and a smartphone with cellular and Wi-Fi capability.

Until last year there were limited options. In fact, only the Nokia phones would work off-the-shelf in this scenario. Nokia, as a hardware-and-software vendor, managed to build an integrated SIP-over-Wi-Fi stack into their OS, and it works well. Configure the Wi-Fi to connect and authenticate to the WLAN, then set up the SIP to register with the PBX as your extension, and Bob's your uncle - when in WLAN coverage, incoming calls to the PBX extension ring the phone, and outgoing calls can be made through the PBX. Nokia also did a stellar job of setting up their Wi-Fi client for good QoS and excellent inter-AP roaming: it's still the gold standard. So you can walk around the building on a SIP call and the phone will make good, prompt choices of new APs to associate with.

(To clarify, it's a two-number solution: if you want proper single-number service, you would need to involve an FMC specialist like Agito: what is discussed here is like having two phones in one skin, but it's easy and inexpensive to set up.)

We have a number of people around the company using Nokia phones in this way, with good success. Getting service over a RAP as well as in the office allows inexpensive VoIP calling at home and on the road.

Nokia's still the king of this application space, but there has been depressingly little progress over the last 18 months, and our users have found the overall stability of the software in the latest E75 difficult to overlook. So in recent weeks we have been looking into alternatives.

First we went to the iPhone, as it's very popular and has a good number of apps. The best SIP client we have come across is iSIP, from V-net, available at the Apple app store. It installs easily enough and works well with our Avaya SIP server, but there's one crucial issue, relating more to the OS than the app. Because apps can't run in the background, when an incoming call hits the phone and iSIP isn't running in the foreground, the phone never rings. There's a solution for Internet telephony providers (SIP) in the new Apple push notification service (APNS), but this is quite a complicated model, and it is difficult to see where a SIP PBX would be able to use it, so it remains a problem for us.

Outgoing calls are fine, and dial from the contact list. There's a general problem with dialing from contacts, in that Avaya rejects calls with + prepended, and needs a 9 for an outgoing trunk... I believe the latest Avaya code can handle the necessary translations from the normal contact list format, but we haven't invested in it yet. For now we are using an old (unreleased) Aruba digit manipulation feature, because it's too much to ask users to modify dial strings when they are dialing via Avaya rather than cellular. This applies to all the phones I am mentioning today.

So iSIP on iPhone is an OK solution, although there are still concerns at the Wi-Fi layer in QoS, inter-AP handover and a few other areas. Also, I have yet to get the message waiting indicator to work with Avaya voicemail... we generally use Avaya's email notification as a workaround to this.

Finally, the Android OS has been out for a while and we got hold of a Nexus One last week, although other Android phones with Wi-Fi can also work with a PBX. The app we found here is called SIPDroid. It seems a bit rougher than iSIP, for instance there is no mid-call DTMF so it's not possible to log into voicemail, but there's no problem with incoming calls: in fact, SIPDroid is very well-integrated with the Android dialer. I have it set so when it's connected over Wi-Fi, all calls are dialed via Avaya by default, with good results. But I can't get the message waiting indicator to light on this one, either.

That's the brief explanation of the choices: there's a lot more to look at with these apps, but they are certainly good enough for most people who are on their feet during the day and would like to be able to use PBX extension calling on an existing phone. With luck we will be seeing more SIP clients this year.
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