Category: dual-mode

“When I use a word,” Humpty Dumpty said, in rather a scornful tone, “it means just what I choose it to mean — neither more nor less.”

The term “Fixed Mobile Convergence” is an umbrella for so many different things that it has become almost meaningless when used without elaboration. Here’s how it started out, in the 2004 press release announcing the formation of the FMCA:

Fixed-Mobile Convergence is a transition point in the telecommunications industry that will finally remove the distinctions between fixed and mobile networks, providing a superior experience to customers by creating seamless services using a combination of fixed broadband and local access wireless technologies to meet their needs in homes, offices, other buildings and on the go.

In this definition “Fixed broadband” means a connection to the Internet, like DSL, cable or T1. “Local access wireless” means Wi-Fi or something like it. BT’s initial FMC service actually used Bluetooth rather than Wi-Fi for the local access wireless. The advent of picocells and femtocells means that the local access wireless can be cellular radio technology.

The term “seamless services” in the quotation above is ambiguous. When talking about FMC, the word “seamless” usually refers to “seamless handover,” which means that a call in progress can move from the mobile (cellular) network to the fixed network on the same phone without interruption, as described in one of the FMCA specification documents:

Seamless is defined as there being no perceptible break in voice or data transmission due to handover (from the calling party or the called party”s perspective).

The term “Seamless services” sometimes means service equivalence across any termination point, fixed or mobile, so for example, dialing plans are identical and no change in dialed digits is required on a desk phone versus a mobile. A less ambiguous term for this might be “Network Agnostic Services.” To do it properly is very difficult, for example I have not been able to track down an Enterprise FMC system that offers SMS on the desktop phone.

The FMCA is a carrier organization, mainly oriented to consumer services. Enterprise phone systems are different. When Avaya announced its “Fixed Mobile Convergence” initiative in 2005, it was using a different definition. What Avaya and other PBX manufacturers were calling FMC was the ability for a PBX to treat a cell phone as an extension, and the ability for a cell phone to behave like a PBX extension phone:

Extension to Cellular technology: software seamlessly bridges office phone services to mobile devices, permitting the use of just one phone number and one voice mailbox.
Client software extends the capabilities of the PBX to a mobile smartphone – creating a virtual desk extension. This software runs on Nokia Series 60 phones and works in conjunction with Extension to Cellular.

In other words, this new definition of FMC didn’t include local access wireless and it didn’t include fixed broadband technology. The only defining characteristic it shared with the previous definition was seamless services, albeit without seamless handover.

“The question is,” said Alice, “whether you can make words mean so many different things.”
“The question is,” said Humpty Dumpty, “which is to be master – that’s all.”

We can regain mastery here by breaking out the features of the various definitions of Enterprise FMC, giving them names, and using those terms to describe the various solutions on offer. Here’s a first cut:

Session Redirection
This simply means moving a call in progress from the cell phone to desk phone or vice-versa, in much the same way as you might transfer a call from one extension to another. For example, you are in your car on the way to work, listening in on a conference call on your cell phone. You walk in to the office, sit down, and redirect the call (session) to your desk phone. Depending on the implementation, you might control the process from your cell phone, your desk phone or your PC, using touch-tones or something more user-friendly.

PBX Mobility
This is what the Avaya press release called “Extension to cellular,” and some other vendors call “PBX Extension.” You program the cell phone number into the PBX (or third party PBX Mobility device – see the paragraph below headed “PBX Agnostic”), and then when somebody calls your office number, the PBX dials your cell phone over the PSTN and bridges the call. The PBX treats the cell phone as though it is an analog extension, so you can invoke PBX features like hold and transfer by touch-tone commands. This means that you can use any cell phone and any carrier (see the paragraphs below headed “Handset Agnostic” and “Carrier Agnostic”.)

Treating the mobile phone as an analog extension to the PBX opens up several more possibilities. Various flavors of this service might include features like Single Number, Simultaneous Ringing and Single Voicemail.

“Single Number” means that the mobile phone and the desk phone share an extension number. So you only need to give out one phone number to receive calls on either your mobile or desk phone. But bear in mind that your cell phone probably still has its own number – it’s just that you don’t give it out to anybody. In order to make business calls from your cell phone, you dial an access number at your office, get a new dial tone, and then dial the destination number. This allows you to take advantage of corporate least-cost-routing, and it shows your office number on the Caller ID display of the person you are calling.

Single Voicemail is the option to use the corporate voice mail rather than the cell phone’s voice mail. This only works on calls made to your office number.

“Simultaneous Ringing” means that when somebody calls your office number, your desk phone and your mobile phone ring simultaneously.

When your cell phone receives a call made to your office number, the Caller ID display would normally show your office as the caller, since the call is routed though the PBX. When the client software on the cell phone can pre-empt the built-in phone software (depends on the handset and the client software vendor) this Caller ID is suppressed and the mobility controller passes the correct calling number and name to the client software on the handset using the cellular data channel. Alternatively, depending on your PBX and carrier, the system may be able to insert the Caller ID of the person calling you into the regular Caller ID notification (Caller ID spoofing). This will show the ‘correct’ Caller ID even on the built-in handset interface.

Client Software
PBX Mobility on a regular cell phone is not particularly user friendly, what with the touch-tone interface and the access number prefixing. With a smart phone things get a lot better. The definition of a Smart Phone is that it can run third-party software. If you happen to have a smart phone, and it is a model supported by your Enterprise FMC system, you will be able to run a “Client application” that puts a friendly user interface on the PBX Mobility features, allowing easy use of PBX features like 4 digit dialing to other extensions.

If the phone supports it, well written client applications can completely hide the native phone user interface. Otherwise users will have two different screens from which to dial calls – the built-in one and the client application.

RIM has built PBX signaling features into its handsets running firmware version 4.2.1 or higher. This means that Blackberries can access PBX features through menus rather than touch-tones, even without add-on client software.

Dual-mode Phone Support
A dual-mode phone is a cell phone that also has Wi-Fi. The Wi-Fi can be for data only (like the iPhone), for voice only (like the Nokia 6086), or for both.

There are two main categories of wireless extensions to PBXs: those that work over Wi-Fi (VoWLAN, or VoWi-Fi), and those that use other radio technologies like DECT. Client software can make a dual-mode smart phone act as a Wi-Fi extension to the PBX. This gives the handset a split personality: a regular cell phone and a VoIP PBX extension, each having its own phone number. These two personalities can be well integrated, completely separate or something in between. Session Redirection as described above moves the call between devices; with a dual-mode phone, you can do Session Redirection between the two networks, keeping the call on the same handset.

Well integrated dual-mode user interfaces are sometimes described as “Network Agnostic” (see below).

Session Continuity
Dual mode handset clients can completely hide their split personality, taking the onus of Session Redirection off the user, and dealing with it automatically. When the system senses that you have walked into Wi-Fi coverage it moves the call over onto the VoWi-Fi side. When you move out of Wi-Fi coverage it moves the call back to the cellular side. This is also sometimes called “seamless handover” or “automatic handover.” To do it imperceptibly to the user is technically challenging. This automatic, seamless flavor of Session Redirection is often termed VCC, or Voice Call Continuity. The term VCC has the disadvantage that it specifically mentions voice, while FMC systems are evolving towards multimedia sessions where voice is only one of the elements. So a better term might be Session Continuity.

Session Continuity requires client software support in the handset, either with built-in VCC client software, or (more commonly in Enterprise FMC) as a part of the client software from the Enterprise FMC system vendor.

Mobility Controller
VCC is a term lifted from the IMS (IP Multimedia Subsystem) specifications published by the international bodies concerned with standardizing cellular technologies. In IMS terminology, VCC is done by software called the “Call Continuity Control Function,” or CCCF.

Session Redirection and Session Continuity require a device in the network that routes and reroutes the call over either the fixed or mobile network as needed (that is to say, something that embodies the CCCF.) There are many terms for this device, and each of these terms can also mean something else. Also the various devices that incorporate Session Redirection or Session Continuity usually also do other things. These devices have names like “Mobility Server,” “Mobility Controller,” “Mobility Router,” “Mobility Appliance” or “Mobility Gateway.”

Carrier FMC and Enterprise FMC
The path of a call transits both the service provider network and the enterprise network, and the Mobility Controller can be located just about anywhere on that path. If it is in the service provider network we call the system Carrier-based FMC, if in the enterprise network, Enterprise FMC. This is the defining characteristic of Enterprise FMC.

Most Carrier-based FMC is aimed at the consumer market, but there are some implementations that support enterprise features like PBX Mobility. Carrier-based FMC can support PBX Mobility either by installing a PBX Mobility control device near the PBX in the enterprise network (the approach taken by Tango Networks), or perhaps by offering the PBX functionality as a network service (Centrex), the approach taken by Sotto Wireless.

Carrier FMC normally uses one of two technologies to implement Session Continuity, VCC or UMA (Unlicensed Mobile Access, also known as GAN, for Generic Access Network). UMA is an older technology, which transports GSM packets through the IP network; the handset uses the same GSM signaling stack for Wi-Fi calls as for cellular. With the predicted conversion of the carrier networks to all-IP, UMA has been superseded by VCC, which uses SIP signaling.

Handset Agnostic
We mentioned above that basic PBX Mobility can work with any cellular handset. At the other extreme, Carrier FMC usually only works with particular handsets. For example the T-Mobile@Home service works with only three handsets, one each from Nokia, Motorola and RIM. Client software for Enterprise FMC almost always works on phones that run the Windows Mobile or S60 operating systems, particularly the HTC phones and the Nokia Eseries respectively. Other smartphone operating systems that may be supported include Linux and RIM, and in the future OSX and Android. Handset agnosticism is a major selling point. A handset agnostic system is more attractive to Enterprise FMC customers than one that limits the choice of handsets.

Carrier Agnostic
A system with the Mobility Controller in the enterprise network can work with any carrier, provided the carrier will allow the phones to connect to their network. The benefit of this is that the customer gets a wide selection of phones, and the FMC system will work on employees’ personal phones, even when those phones are on an assortment of carriers.

A system with the Mobility Controller in the carrier network is not carrier agnostic from the point of view of the customer. They have to buy service from that carrier.

PBX Agnostic
Each of the PBX vendors offers a mobility capability. Some developed it internally. Some, like Cisco or Avaya, bought a third party developer, and some license their offering from a company like Telepo , Comdasys or Counterpath (formerly FirstHand). There is another set of vendors that offers Enterprise FMC that works with any PBX, for example DiVitas, Agito, Tango and RIM. This is beneficial to both large and small customers. Large customers may have PBXes from multiple vendors, yet still wish to roll out a unified FMC solution. Small customers appreciate having a choice of supplier, rather than being tied to their PBX vendor.

Network Agnostic Interface
Some vendors use this term to mean that all features are available through a uniform user interface in both cellular and Wi-Fi networks. This means that the user should not be able to perceive which network is carrying their session on a dual-mode phone.

Conclusion
Agonizing over minute definitions is tedious, but when evaluating competing solutions it is essential to be able to recognize when two vendors use the same term in different ways, when they use different terms for the same feature, or when they describe a feature without giving it a name.