One could argue that the telephone paved the way for modern society as we know it, connecting friends, relatives, co-workers, employers, and employees in ways never before seen in human history. We've all essentially grown up on the telephone, talking to our distant relatives when we were kids, or as teens sneaking to stay up late talking to the opposite sex. In the last 10 years, we've witnessed the explosion that has been the cellular telephone industry, and coupled with that, the improvement in the technology of the handsets themselves, marrying telecommunications and computing capabilities. The times, they are a-changin'.
Much of the hoopla (technical term) over the past few years in the telecom industry has been over the concept of Unified Communications, which is essentially just the idea of running voice services over a data (or Internet Protocol) network. While the carriers have been doing it for years, this more recent push for Voice over IP (VoIP) has been typically seen as something done within an organization, utilizing a company’s already in-place routing and switching infrastructure, and even extending voice and IM services to those über intelligent mobile handsets. Voice services to the outside world have always been provided by the archaic, limited in function, soon to be obsolete Public Switched Telephone Network (PSTN).
Modern phone companies can trace their roots all the way back to the invention of the telephone in 1875 by Alexander Graham Bell. The technology has evolved, but the basics remain the same. You pick up the receiver, and you end up talking to someone on the other end. The modern PSTN utilizes a numbering plan that allows for regional phone companies to facilitate easy, operator-less calls between parties. This includes the intra-country dial-plan, as well as allowing for interoperating with outside countries via country codes. For example, in the US our international dialing prefix is 011, which we follow with the country code, followed by that country’s dial-plan. For instance, for me to call the office of the City of Melbourne, Australia, I would dial 011 61 3 9658 9658. There will be some pricey international charges for that call, as the phone companies bill customers back for long distance and international calls. This has led a lot of businesses to restrict who has access to dialing internationally from their PBX.
What if I wanted to send an email to a friend that lives in Australia? Well when I click "send", my mail server fires up a request to the local Domain Name System (DNS) server to see what Mail eXchange (MX) record exists for the domain name used in my friend’s email address. Once my mail server knows the address, it sends the email to the Simple Mail Transfer Protocol (SMTP) service running on port 25 on the destination server, and voila! the email is delivered. Have you ever stopped to ask yourself why we don’t pay for international email charges? Quite simply, the internet was designed as a foundation for whatever services and protocols that clever, inventive computer scientists could dream up. Email just happens to be one of them.
As it turns out, there’s another protocol out there capable of doing the exact same thing that email does, but for voice communication. Session Initiation Protocol (SIP) was designed to mimic that same decentralized session establishment that SMTP utilizes, but for any type of interactive session. This has led to the use of SIP for myriad of different services, such as video, Instant Messaging, and especially voice communication, since voice is one of those legacy technologies that was due for some market disruption. SIP was created back in 1996, and ratified in its current iteration in 2002. SIP came out of the Internet Engineering Task Force (IETF), as opposed to the normal batch of telecommunications protocols, which are controlled by the International Telecommunications Union (ITU). This highlights a very key point in our story, which is that SIP came out of the standards body responsible for the protocols that run the Internet, not the one made up of all the world’s phone companies. Thus, the focus, intent, and application of SIP has typically come from companies like Cisco, who at their very core are Internet Protocol dependent.
One of the biggest challenges with SIP early on was that the original standards documents (called RFCs, or Requests for Comments) left a lot of room for interpretation in implementing certain features. I called SIP the Subject to Interpretation Protocol for years, having seen first hand all the challenges with interoperability of various products and services. With SIP coming into its prime in the last 5 years and telecom manufacturers developing very effective methods for accounting for operability, telcos have started offering SIP-based trunking services to businesses all over the world. This is a great thing for the enterprise, the small and medium business, and especially the phone companies. They get to remain the voice clearinghouse, charging for access fees, international calling, and of course, benefiting from those pesky billing mistakes that always manage to sneak past accounts payable departments everywhere.
Part 2 coming soon!