Key Technical and Architectural Features
- Call signaling for Internet calls carried on PSTN SS7
- Internet calls established automatically if end devices are capable – users just dial a call
- PSTN controls call, even Internet calls – can transfer between analog & multimedia devices
- Avoids weaknesses of VoIP, SIP, ENUM, and the Internet
- Exploits carrier strengths – reliability, security, integrity.
Conceptual View – Screen Phone Connectivity:
In simple terms, a telephone (a screen phone) will have a data interface to the CO/PSTN, connecting to the SS7 network. You can think of this interface to the phone as being an ISDN-style interface, but only using the I-frame call control data channel. But, since ISDN has never grabbed
Merge the best of the Internet with the best of the telephone network
hold in the U.S., in more modern terms you could think of a DSL or cable VoIP modem that has an Ethernet connection to the phone, rather than a two-wire analog connection. The Ethernet connection carries signaling data as well as digitized audio, and conveys MultiMedia data from intervening or end systems.
For the first scenario, let’s assume that the called device is not compatible with the Next Generation MultiMedia, and must be treated as an analog phone call.
In the above illustration, the destination CO receives the call setup request, determines that the called device is not capable of an Internet communication, and accepts the call as an analog call.
In the following illustration, the called device is a Next Generation device capable of an Internet MultiMedia connection.
The underlying operation can be fairly simple, although more sophisticated arrangements offering additional benefits are possible. In the above illustration, a screen phone goes off-hook and dials a number. The local CO (or appropriate SS7 node) forwards the call setup message to the remote CO serving the called number. The destination CO responds as to whether or not the called system is capable of an Internet connection. If so, the destination CO forwards the call setup message to the end device (which might be a phone, a voice mail system, etc.). The call setup message includes the IP address of the calling phone. Upon receipt of the call setup message, the called phone learns both the telephone number and the IP address of caller. The called phone can then respond to the caller with high-speed MultiMedia information across the Internet, as shown below.
One of the virtues of this system is that the PSTN maintains call control. Among other things, this means that calls can be transferred transparently from analog to MultiMedia and back without the users having to know anything about the types of phone service or types of phones – the intelligence is built into the network, and users only need to know what they want to do. MultiMedia phones will offer users screen buttons to activate these operations, analog phone users will flash the switchhook, as they have always done – it’s just automatic.
Optionally, as shown above, the audio portion of a telephone call can be transmitted over the PSTN, providing guaranteed high quality audio, and all the other features in a “carrier class” environment, while transmitting the visual and Multimedia aspects over the Internet. MultiMedia telephone service will also allow carriers to offer the same intrinsic value and appeal as a computer with a graphical browser for accessing the Internet. This technology is available for use between land-based and cellular telephones interchangeably.
Some Points of This Architecture:
- All signaling conducted on PSTN
- Signaling data is secure
- No dependency on DNS (recall that, recently, hackers crashed the entire worldwide DNS system)
- PSTN controls call
- User just dials a call -- calls automatically complete best way
- Voice portion can ride across PSTN, high quality audio, no jitter or dropouts
- Can use standard billing systems & call rating schemes
These are the underlying mechanics. What you will really want to know is, “What value does this all bring?”