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Walkthrough Wednesdays

The Future of Federation


In many ways, Voice over IP is an old technology. Its actually been around quite a long time. Initial work on sending voice on packet networks began in the late 1970's. This work was academic in nature, and VoIP entered the marketplace in a real way in the mid to late 1990's. That's over a decade - and almost two - of commerical VoIP. By modern standards, a decade of technological evolution is nearly an eternity.

By other measures, VoIP is a new technology. The technology it replaces - circuit switched telephony - had achieved near ubiquity, and the replacement is far from complete. That replacement has been happening in bits and pieces, and operating at different paces. VoIP is used broadly for traffic backhaul within carrier networks. WIthin enterprises, it has made tremendous inroads and represents more than 50% of new product sales into that space. In other areas, VoIP is still in its infancy. Usage of VoIP in the home for landline telephony is just getting started, and usage of VoIP for cellular telephony has yet to even begin. Another area where VoIP is in its infancy is business-to-business federation. Today, even though many enterprises run VoIP internally, calls between enterprises still go over the Public Switched Telephone Network (PSTN).

When looking towards the future of federation, two paths seem possible. One, called open federation, is important for realizing the vision of rich unified communications. The other, overlay federation, is more incremental but will likely stifle much of what UC can offer.

Open federation allows for true any-to-any interconnection, without any prior arrangement. If someone in company one calls someone in company two, that call can go directly between companies one and two, without anything in between except IP. In an overlay federation model, company A and company B connect to their respective SIP service providers, and those providers in turn connect to each other, possibly other service providers, passing calls amongst each other. This model is an overlay since, not only does it ultimately require IP between companies A and B, but it also requires a SIP network to be built on top of IP, in order for company A to reach company B.

In many ways, overlay federation represents the natural evolution from today’s circuit based interconnection to SIP-based interconnection. The circuits that exist today between two organizations (such as an enterprise and their voice provider) are replaced with IP and SIP, but the ‘Public Switched Telephone Network’ still exists, just in SIP form. Indeed, the PSTN becomes two intertwined networks – an IP network and the SIP network that runs ontop of it. In essence, the SIP network becomes a worldwide overlay ontop of the IP network.

In open federation, by contrast, the circuits that exist today are replaced by connectivity to the Internet. The Internet acts as the universal glue, allowing all forms of traffic to flow between any two organizations connected to it. That traffic includes voice and video, but includes everything else that domains need to exchange with each other, including mail, messaging, streaming video, web traffic, and future services we have yet to see. The power of IP – and the power of the Internet – lies in its ability to carry any kind of data anywhere in the network, without any dependencies in between. That crucial characteristic – the ability to add new functionality without changing the entire network - is the engine that has driven the amazing innovation that the Internet has wrought, and that same characteristic is the essence of the open federation model.

To make this concrete, let’s use an example. Consider two companies, and They both deployed a new communications feature called "click-to-meet". With this feature, when two users are in a call together, either one can press a button on their phone, causing both of them to be dropped into a Webex session automatically. No need to email or IM a meeting URL; one click does it all. This feature works by leveraging SIP’s ability to carry new content  - a URL for the meeting in this case.

In an open federation model, for ‘click-to-meet’ to work between and, only and need to implement it. However, in an overlay federation model, not only do and need to implement it, but a.coms provider,’s provider and any other service providers in between, all need to support it. In essence, the network itself – the infrastructure that interconnects everyone together – needs to support this new feature, rather than just the two endpoints participating in the session. Can you imagine what the web would look like if each and every new web innovation – Javascript, Flash, streaming video, and so on – all needed to be supported by the browser, the website, and by the ISPs in between? The web would still be the static HTML we had ten years ago.

Will the future of federation follow the Internet model, allowing the same kind of innovation we’ve seen on the web, or will it gradually evolve into the next-generation telephone network? It will come as a surprise to no one that I strongly favor the open model; it has been a cornerstone of SIP’s design.

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