Head: Illuminet: Making the connection since 1981
Copy: As the owner of the largest independent SS7 network in the nation, Illuminet has been providing the connection points and routing instructions for millions of voice and data calls for more than 20 years. Today, Illuminet is the leader in developing cutting edge services and products that expand the capabilities of the nation’s wireline and wireless data networks. The result: communication solutions that are widely available, easy to use and affordable.
Illuminet was created through the merger of two companies with impressive track records of innovation and leadership in the telecommunications industry. Independent Telecommunications Network (ITN) and US Intelco Networks (USIN) worked together to take advantage of the capabilities of the SS7 protocol, which uses a separate digital channel to carry a phone call’s signaling instructions (how the call is set up, routed and terminated) and the actual conversation or data that’s being exchanged during the call.
SIDEBAR
Head: Anatomy of a phone call
Copy: Making a phone call seems pretty simple to the average user. Pick up the receiver, punch in a few numbers, wait for the phone to ring on the other end and either speak to the person you’re calling or leave a message on voicemail.
But behind the scenes, a lot of steps happen before you even punch in the first digit.
Before the advent of the SS7 network in the early 80s, calls were routed through a series of electrical and mechanical switches. Once you dialed the number, the telephone company, or carrier, compared the digits you dialed with a routing table that provided the switch with the information needed to allow it to connect with another switch in the network and so forth until your phone was connected to the recipient’s phone. The call and the signaling required to connect it tied up a single phone line for the duration of the call.
For decades, this was a workable plan. But as more homes became connected and business flourished, the number of available lines dwindled as demand soared.
Fortunately, researchers had developed ways to break telephone calls up into small bits of information and route them using two separate channels of a single line. The carrier could then send hundreds or even thousands of signals at a time without having to cover the countryside with more phone lines. The solution to the one-call/one-line problem is known as Common Channel Signaling (CCS), upon which SS7 is based.
Thanks to SS7, millions of bits of information, known as packets, are routed by the network to their destinations, allowing the same phone line to exchange multiple phone voice and data calls simultaneously. SS7 is the protocol that allows us to have 800 and 900 numbers, Caller ID, calling cards, test messaging to cell phones, and a host of other programmable services unheard of just a generation or so ago.
BREAKOUT ARTICLE
Head: A Brief Introduction to the SS7 Network
Copy: At the heart of Illuminet’s SS7 network are a series of digital switchers that quickly route packets via the shortest and most direct route possible. These Signaling Transfer Points (STPs) find out where the call data is headed, consults a routing table to find out where that destination is located and sends it on its way.
If you look at Illuminet’s SS7 map, you’ll notice that STPs are always paired. In telecommunications, redundancy is the key so each STP in our network is always paired with another one to keep things moving along smoothly. Depending on the destination, calls can be routed within STP pairs, linked to other pairs within the network or connected to pairs on other SS7 networks crisscrossing the U.S. Each call is broken into bits of information, or packets, so that lines can be shared simultaneously by many callers.
So how do these packets know when they’ve reached their destination? Signaling End Points (SEPs) are the answer. Each of these SEPs uses a Signaling Point Code (SPC) to tell the packet where to go and let it know when it has arrived. The SEP breaks the code down into Network, Cluster and Member portions, much like a phone number is broken geographically into an area code, prefix and line number. These portions describe how the STPs are tied together and how the endpoints are connected to the STPs.
Of course, there’s a lot more to the complex task of identifying, routing and managing phone calls. But this provides a good overview of how the Illuminet SS7 network works once a call is initiated.
