PDF of this tutorialThe ATM–PON system offers a number of benefits for carriers and end users.
Because fiber is less costly to maintain than copper based systems, carriers benefit by being able to reduce costs and thereby increase profit margins or simply lower prices to end users to ward off competitive threats.
ATM–PON transmission is conducted through a single strand and thereby conserves fiber. Using a single fiber strand for up to 64 end users provides great cost savings over the current point-to-point architecture.
ATM PON conserves optical interfaces at the OLT because a single fiber is used to service as many as 64 end-user locations. Thus, a 64 to 1 reduction in optical interfaces is achieved in comparison to point-to-point optical systems.
Another advantage of the ATM–PON system is the aggregation and concentration of ATM cells in the OLT. This concentration allows the carriers to serve many more customers than if only TDM–based techniques are used. At the same time, QoS benefits of ATM allow the carriers to provide service-level agreements (SLAs) and rest assured that service is guaranteed. It is estimated that ATM–PON technology can achieve savings of 20 to 40 percent over circuit-based access systems. ATM PON realizes these savings through the use of ATM concentration and statistical multiplexing in addition to sharing active opto-electronic components through the splitter elements.
Because the ONTs share the same fiber and optical splitter, the bandwidth can also be shared. In the future, dynamic bandwidth-allocation protocols will allow the carriers to serve more users by allocating bandwidth on an as-needed basis. These protocols are already part of the FSAN specification as an optional requirement. Therefore, more users can be served with a smaller number of OLTs, leading to additional savings.
Operational and maintenance savings will be derived from ATM PON. Because the system is based on ATM, a single management system can completely provision the bandwidth end to end. Also, if the service interface is a high-speed local-area network (LAN) such as 10/100Base–T, where the carrier's ATM circuit rather than the physical interface bit rate is the limiting factor to the bandwidth, then bandwidth can be incrementally provisioned over time as needed, up to the limitations of the physical interface. For example, if a small business needs only 1 Mbps capacity at first but will require 2 Mbps a year from now, then the carrier must only provision greater ATM PVC rate, rather than having to do a truck roll to wire more T1 lines (as is currently done).
Because the PON system will be ATM–based, it can adapt to virtually any service desired. Telco operators, for instance, can deliver all of their legacy services, such as T1 and T3 lines, or deliver new services, such as transparent LAN service (TLS) over the optical network (see Figure 4). This future-proofs the architecture. New revenue streams are derived by being able to provide transparent LAN services to end users quickly and easily.
Figure 4. Transparent LAN over the Optical Network
The ONT is proportioned for small- to medium-sized businesses and costs little. This low cost is achieved because there are more small businesses than large ones. Currently, service providers serve small businesses from synchronous optical network (SONET) ring nodes, and these are costly elements when compared to small ATM–PON ONTs. ATM PONs will mean new business for carriers and services providers, as they can eliminate the need to place small- and medium-sized businesses on SONET rings that exist in most metropolitan area networks.
Active components of the ATM–PON system are located at the customer premises or CO, rather than at remote outside plant terminals. Thus, costs associated with outside plant–battery backup systems and active electronics that must incur severe temperature variations are eliminated. Battery backup systems can be placed indoors at the customer premises and thus last much longer between maintenance intervals. In addition, the option of having the end user provide the battery backup from low-cost computer UPC systems can be offered on a per-user basis. With typical outside-plant systems (such as DLC or FTTCab) that are shared between many users, this option is simply not available.
As ATM–PON architecture and processes mature, end users will benefit by being able to provision their own services, whenever they are needed, through an automated process. This process will either link the carriers' service management system (SMS) with the customers' network management system or allow the customer access to the SMS through a secured Web-browser interface. The CO then updates network elements and provisions the new bandwidth.
