Sunday, November 01, 2009

Smartphones, 4G, IP, and IMS – Part II: Why is this G like no previous G

Making a phone call is an activity that seems almost as natural as walking, or drinking, but it has a history. About 120 years ago the layout of the phone terminal, with transducers for speaking and listening, was a settled matter of design. In another 20 years the matter of dialing phone numbers was settled as automatic electromechanical telephone exchanges were introduced. A phone call is a blend of humans making accommodations to machines and machines being designed for humans, and much of the early outcome of that blending persists today.

If you look at the software in any mobile phone, the key thing that makes it a phone is the call-state management. This is what keeps track of the state of phone calls (and, in 2.5G and 3G, data connections, too). It enables the user interface of the phone to display the correct state visually and play the right call progress tones (the ones that originate in the handset) at the right time. It also hooks into power management to light the LCD backlight at the right times, the switch that detects if a flip phone is closed, the keyboard lock, and performs other operations that create the user experience of a telephone.

The design of all mobile call state management is based on having one bearer channel to a circuit switch, plus SMS and data. The first implementations of mobile call state management had minimalist requirements: Display the on-hook dialed phone number on a numeric display, play call progress tones the user would find familiar from the landline user experience, and enable control over a small set of switch-based functions like call-waiting, where the call on the single radio channel to the phone is switched to a second call. It is familiar enough to be accepted by customers and accommodating enough to the way the network works to be efficiently deployed.

There are some differences between CDMA, GSM, iDEN, etc. but they are close enough to share a lot of the implementation. 2G, 2.5G, and 3G differ in the richness of the circuit switched signaling (but not so much that users are aware of it), and in whether and how much data you have. GSM and UMTS/WCDMA data and HSPA differ from CDMA data in detail, but, again, there's not much user awareness of the differences. Color LCD displays on phones make text messaging nicer, but the impact on the mobile phone call user experience has been limited to presenting a contact list and call log.

4G is the first fundamental break from the roughly 25 year old model of cellular mobile telephony. In 4G, the radio is part of a network interface on an IP network, like a WiFi radio. There are no bearer channels dedicated to voice calls. You either do IP telephony using SIP, in the IMS case, or you simulate circuit switched telephony on top of IP in the VoLGA case. There is no practical limit to the number of voice calls and other kinds of communication sessions a 4G device can juggle. Packets traversing the carrier's network carrying voice to other endpoints are no different from packets flowing between the endpoint and a third party or private gateway/switch with a telephone network interface. Identity, communications services, media (how voice or video is encoded), etc., all become decoupled from the network.

So we are entering a product development phase where the winners will be, in part, determined by how well they can make compelling new communications features and capabilities based on this change without confusing the end-user. What it means to be a phone is now infinitely malleable.

Surely, at the bottom of this a phone call has the same limitations as a face to face conversation plus the further limitations of not being actually face to face. No, even this can be called into question. The ability to redefine the phone call experience is comprehensive and the potential is limitless. And the potential ranges from the obvious – what the user sees on a screen – down to the subtlest microsecond-level manipulation of the human voice.

But will this potential be realized? That is more in doubt than that the potential exists. So far, the modern general purpose pocket-sized telecomputer surfs the Web and plays games. It will take the realization that new communications products can be created, and sold, to motivate reconsideration of how phones enable communication.

No comments:

Post a Comment

Post a Comment