If you live in any of the major cities, then you couldn’t have missed the colorful pipes lying by the roadside everywhere. These pipes will carry fiber optic cable that will form the backbone for providing broadband access to homes and offices. All equipment used with this fiber-optic backbone would vary depending upon the broadband technology used. Currently, three such technologies, called Ethernet, cable modems, and xDSL, are being used. The choice of technology depends upon factors like user demand and the cost of equipment. Here, we won’t discuss which technology to choose, but explain how their setups differ.

The three technologies use different types of cables for their communication. Ethernet uses Cat 5 cabling, cable modems use coaxial cables, and DSL uses single pair copper cables. Due to this, all equipment has to have the proper termination to be able to join the fiber backbone. For each technology, let’s look at these terminations and other equipment that’s used. For the sake of clarity, we’ll start from the equipment used by end users and work our way towards the broadband service provider.

Broadband over Ethernet

The setup for this is similar to a typical Ethernet setup, and the speed would also be in the order of 10/100 Mbps. The typical subscribers for this would be large companies needing VPN connectivity among their various office locations. The termination at the subscriber end would be an Ethernet switch with RJ45 ports capable of taking Cat 5 cabling. The switch would be connected to a router, which would in turn be hooked to the broadband service provider. In some cases, it might be more convenient to have end-to-end fiber-optic connectivity from the broadband service provider to the subscriber.

Cable modem setup

A cable TV network was originally meant for audio and video broadcast. To provide data over the same network, meaning Net access, extra equipment needs to be added both at the subscriber’s and at the cable operator’s end. At the subscriber’s end, cable modems are installed. These would connect to what’s called an Optical Node (O/N) over coaxial cables. If there are several O/Ns, then they would all terminate into an Optical Shelf (O/S) over optical fiber cable.

The O/S terminates into a device called the CMTS (Cable Modem Termination System), again over fiber cabling. This is the most important and the costliest device in the setup as it’s responsible for both upstream and downstream transfer of data from the Internet. As we see, this setup is a mix of coaxial and fiber cabling. This sort of a setup is known as HFC, or Hybrid fiber-coaxial setup. However, it can also be done purely on coaxial or fiber.

DSL setup

There are many flavors of DSL, which we’ll cover in a separate article. Here, we’ll focus on ADSL (Asymmetric Digital Subscriber Line), which is becoming popular among broadband service providers. In a typical ADSL setup, the subscriber would have either a DSL modem or a router. These devices have the same interface as used in Ethernet networks. This could be directly connected to a computer with a network card, if it’s a home; or to a hub or a router if it’s an office.

The other end of the DSL modem or router would connect to a DSLAM (Digital Subscriber Line Access Multiplexer) through a plain single pair copper cable, which is essentially an ordinary telephone line. The DSLAM would be the termination point for all the subscribers in a particular area. This would in turn terminate into what’s called a DSL Aggregator over a high-speed digital fiber link called OC-3. This Aggregator in turn would connect into the broadband service provider’s network over a fiber cable.

In all the cases mentioned above, the distribution of bandwidth among subscribers and the placing of various equipment depend upon the broadband service provider. An optical node in a cable modem setup, for instance, could lie in the subscribers’ neighborhood, while the CMTS could lie at the cable operator’s end or with the broadband service provider. A DSLAM could lie in a subscriber’s place, such as a commercial building, where several offices need a DSL connection. It could also lie at a telephone exchange, from where the copper cabling that’s spread out for voice will also start carrying data traffic.

The choice of whether to use DSL, cable modem, or Ethernet depends largely upon the cost. For the time being, cable modems are used mostly for homes, while DSL and Ethernet are used mostly for offices. However, as broadband technologies become widespread, their costs will come down and they will become affordable even for the home user. In California, for example, most new apartment buildings are geared with DSL or other broadband technology. That may not happen so soon here. But keep looking outside your window; maybe they’re laying the fiber right now.

Anil Chopra with inputs from Pawan Pratap Singh of spectranet