In order to better understand the concept of FTTH and MSAN applications we must first understand the transport mechanism for both. Note that in the course of this article we refer to FTTH as FTTx to widen the discussion to include Fiber to the Premise, Fiber to the Curb and Fiber to Building applications.
For both FTTx and MSAN applications the backhaul transport mechanism is optical fiber. Fiber optic communication is a method of transmitting information or data from one place to another by sending light through an optical fiber. First developed in the 1970's, fiber optics communication systems have revolutionized the telecommunications industry and played a major role in the advent of the information age. Because of advantages over electrical transmission, the use of optical fiber has largely replaced copper wire communication in the core networks in the developed world. With that, new issues and opportunities have risen for most of the parties in this field. Many of us have seen the fiber optic installations take place in our city streets. While during the installation we were blessed with hours of traffic and detours, we are now, finally, in a position to take advantage of the infrastructure that was put in place. However, for the fiber industry there was not always bright light. The market has been slow to develop and for many of the companies involved, the deployment model has been anything but bright. But the times are changing and demand is catching up with the technology.
Optical fiber is used by many telecommunications companies to transmit telephone and internet as well as video signals. Cable companies also use fiber optics for their communications backhaul mechanism. There are many reasons why fiber has been selected as the mechanism of choice, but some of the top advantages are lower attenuation and interference, better flexibility and longer life span.
Optical fiber can be used as a medium for telecommunication and networking because it is flexible and can be bundled as cables. It is especially advantageous for long distance communications because light propagates through the fiber with little attenuation compared with electrical cables. This allows long distances to be spanned with few repeaters.
Fiber to the premises (FTTP) is a form of fiber optic communication delivery in which an optical fiber is run directly onto customers' premises. This contrasts with other fiber optic communication delivery strategies such as fiber to the node (FTTN), fiber to the curb (FTTC) or hybrid fibre-coaxial (HFC), all of which depend upon more traditional methods such as copper wires or coaxial cable for "last mile" delivery.
Fiber to the premises can be further categorized according to where the optical fiber ends:
- FTTH (fiber to the home) is a form of fiber optic communication delivery in which the optical signal reaches the end user's living or office space.
- An optical signal is distributed from the central office over an optical distribution network (ODN). At the endpoints of this network, devices called optical network terminals (ONTs) convert the optical signal into an electrical signal. (For FTTP architectures, these ONTs are located on private property.) The signal usually travels electrically between the ONT and the end-users' devices.
- A passive optical network (PON) is a point-to-multipoint, fiber to the premises network architecture in which un-powered optical splitters are used to enable a single optical fiber to serve multiple premises, typically 32-128. A PON consists of an Optical Line Termination (OLT) at the service provider's central office and a number of Optical Network Units (ONUs) near end users as shown in figure1 below. A PON configuration reduces the amount of fiber strands and central office equipment required compared with point to point architectures.
Figure 1. Optical Network Unit (ONU), point-to-multi-point fiber
The standards of PON are varied and have improved over the years. In the United States, a majority of PON deployments until recently were BPON; however, the trend has been toward GPON in the recent years. Below is a list of different PON standards showing their application and data rates:
- APON (ATM Passive Optical Network). This was the first Passive optical network standard. It was used primarily for business applications, and was based on ATM.
- BPON (Broadband PON) is a standard based on APON. It adds support for WDM, dynamic and higher upstream bandwidth allocation, and survivability. It also created a standard management interface, called OMCI, between the OLT and ONU/ONT, enabling mixed-vendor networks.
- GPON (Gigabit PON) is an evolution of the BPON standard. It supports higher rates, enhanced security, and choice of Layer 2 protocol (ATM, GEM, Ethernet). In early 2008, Verizon is in the process of installing millions of lines, while British Telecom and AT&T are in advanced trials.
- EPON or GEPON (Ethernet PON) is an IEEE/EFM standard for using Ethernet for packet data.
- 10GEPON (10 Gigabit Ethernet PON) is an IEEE Task Force for 10Gbit/s backwards compatible with 802.3ah EPON. 10GigEPON will likely multi-lamda downstream and continue to use a single lamda with ATDMA for upstream. It will also be WDM-PON compatible.