To understand how Microsoft’s Voice and Unified Communications vision will change the telecommunications industry, it’s first important to understand how the telecommunications industry has evolved. I love how some movies or books start with a “In the beginning....” In keeping with tradition, I will also say, “In the beginning, there was Plain Old Telephone Service (POTS).” POTS was the first communications layer to enable one person to talk to another without having to ride a horse, fly a plane, or drive a car to see someone in person. Some say that this was the beginning of the end in human communication in that we are now seeing more and more individuals hiding behind the phone and spending less time in person, which I completely agree with, but hope to live in a time where we can evolve communications to enforce visual presence. However, POTS enabled the first wave of communications. End users of a POTS line would use a first edition phone device, designed and manufactured by Alexander Graham Bell himself, to communicate to the same type of device held by another end user with a POTS phone (see Figure 1.3).
Figure 1.3 POTS (analog) line
Lines were terminated by switches, which soon led to a release of a new technology launched in the vibrant 1970s, the Public Switch Telephone Network (PSTN), which enabled a company, remember Ma Bell, to terminate calls to enable long-distance calling internationally. Back then, we all paid, well, you paid, because I was too young to have a phone in my own name, exorbitant fees at each termination resulting in an expensive phone bill if long distance was used. Basically the PSTN connected POTS phones across cities, states, countries, and ultimately oceans to enable voice packets to be sent and received across PSTN networks in each region of the world (see Figure 1.4).
Figure 1.4 POTS/PSTN integration
Within the same decade, Private Branch eXchange (PBX) systems, illustrated in Figure 1.5, were released to enable corporations to host their own telephone network without having to pay for individual POTS lines for each office worker. PBX telephone users would call each other using a four- or seven- digit extension, and if they had to dial one of the enabled outside POTS lines, they would normally dial a 9 and then the number. Remember dialing 9 at school to call home? Yep, that’s where this comes from. Anyway, POTS lines are shared within the PBX network so that 16 to 20 employees may use eight POTS lines in a given company, and that’s how most PBX systems are still sold today in an 8x16 model. PBX systems connect to PSTN systems as well as connect PBX phones to long-distance callers.
Figure 1.5 Private Branch eXchange
Around the 1990s, PBX and PSTN systems and networks started to accept digital voice packets. By accepting digital packets, PBX systems were able to advance using Internet Protocol (IP) communications connecting voice over the Internet and creating a new way to communicate using what we now know as VoIP. VoIP is a protocol or a vessel by which communications including voice, video, and data pass over an IP line. VoIP uses another protocol called Session Initiation Protocol (SIP; see Figure 1.6) to pass this data. (This will be important for you to remember later.)
Figure 1.6 Session Initiation Protocol
What is needed for this to work? Simple, an Internet connection. With new Wi-Fi and WiMax technology, obtaining an Internet connection is easier and more broad reaching than ever before, and in the future, Internet connections will blanket the earth. PSTN networks are also crucial in this development as voice calls are carried from a VoIP service provider, known as an Internet Telephony Service Provider (ITSP) to the PSTN using digital packets to terminate a connection to a POTS line as well as cellular/mobile lines.
As depicted in Figure 1.7, PBX systems can take advantage of this because they can now utilize SIP as the primary communications layer for external communication instead of having to rely on POTS or analog lines. Internally, PBX systems also upgraded their service protocols by moving away from Primary Rate Interface (PRI) and Binary Rate Interface (BRI) lines to IP-based Ethernet-enabled cabling, creating the IP-PBX as we know today.
Figure 1.7 PBX/SIP integrated architecture