4G Voice is coming like a freight train, code name “VoLTE” (Voice over LTE). Unless you understand the IMS, everything you know is wrong. The new voice services platforms are 100% software, and represent just a portion of the real-time arsenal of services that complement voice, like video, Instant Message, and Presence. Call routing is completely separate from feature service and there is not a traditional telephone switch to be found anywhere. The driving force is the ever increasing gravitational pull towards everything IP. This means that access, which was circuit based in 3G, is now all packet in 4G.
This changes things big time for operators. As a general rule, operators love to backhaul data to the home network. Let’s say you live in New York and take a quick trip to Sweden. While you are walking around Stockholm, you whip out your phone to check where you will buy that next jar of pickled herring which you think is the next best thing to Czechoslovakian beer. You want a bar that has both, so you break out your phone to look for that jar of herring and beer, but the web seems a little slow. This is because every byte you are seeing crosses the Atlantic so that your service provider back in New York can see where you are surfing, and more importantly, how many bits you are using. They want to bill you by mega character. Your data backhauls because you are walking around Stockholm with your phone that has been assigned an IP address from New York. Welcome to 3G thinking. It doesn’t get any worse.
Now enter the IMS APN. Suddenly your phone is assigned an IP address from Stockholm. Everything speeds up. You finds lots of pickled herring bars. The local carrier does not backhaul any traffic back to the remote carrier, except the invoice for the IMS service. The idea is to import the data policy from New York to Stockholm, and enforce policy locally in Stockholm. Now the bits do not cross the Atlantic, just the service policy. But how is this done? Well that’s where SIP comes in. Each time the phone accesses a real-time service, SIP traffic does cross the Atlantic to make sure the service policy has not changed. This is a very small amount of traffic compared to the traffic that is about to flow locally in Stockholm. Once approval is granted, following the SDP Offer/Answer, your IP based service operates in real-time. Things are a lot better. You think 4G is great and regarding 3G, you never look back.