1. Field of the Invention
Generally, the present invention relates to a passive optical network (PON). More specifically, the present invention relates to a system and method of using optical line terminator (OLT) system time during optical network terminal (ONT) performance monitoring (PM) on the PON.
2. Description of the Related Art
Most networks in the telecommunications networks of today are based on active components at the serving office exchange and termination points at the customer premises as well as in the repeaters, relays and other devices in the transmission path between the exchange and the customer. In this context, active components are devices that require power of some sort, and generally comprise processors, memory chips and other devices that are active and processing information within and along the transmission path.
In contrast, within a typical passive optical network (PON), all active components between the central office exchange and the customers' premises are eliminated, and passive optical components are put into the network to guide traffic based on splitting the power of optical wavelengths to endpoints along the way. This replacement of active components with passive components provides a cost-savings to service providers by eliminating the need to power and service active components in the transmission loop. The passive splitters or couplers are merely devices working to pass or restrict light, and as such, have no power or processing requirements.
In general, a typical PON consists of an optical line terminator (OLT), which is located at a central office (CO), and a set of associated optical network terminals (ONTs), which are located at customers' premises. Between the OLT and the ONTs lies optical distribution networks (ODNs), which includes fibers and one or more of passive splitters and passive couplers. An exemplary PON is described in the International Telecommunication Union Recommendation, ITU-T Recommendation G.983.1, which is incorporated by reference in its entirety and for all purposes.
FIG. 1 illustrates a typical PON. As shown in FIG. 1, in a PON network, fiber can be run from the CO exchange, via an OLT, to an ODN, and then individual fiber strands to each ONT at a building, home or other serving equipment. Each fiber from the OLT can be can be split from the using passive splitters and/or couplers. This allows for an expensive piece of fiber cable from the CO exchange to be shared among many customers, thereby dramatically lowering the overall costs of deployment for fiber to the business (FTTB), fiber to the home (FTTH), and fiber to the curb (FTTC) applications. The alternative would be to run individual fiber or copper strands from the exchange to each customer, which results in a much higher serving cost per customer.
The main fiber run on a PON network can operate at 155 Mps, 622 Mbps, 1.25 Gbps or 2.5 Gbps the various PON standards. Bandwidth allocated to each customer from this aggregate bandwidth can be static or dynamically assigned in order to support voice, data and/or video applications. With PON, a single fiber from the CO exchange can service 16, 32 or more buildings through the use of both passive devices to split the optical signal, and PON protocols to control the sending and transmission of signals across the shared access facility.
In the typical PON, the process of transporting data downstream to the customer premises is different from transporting data upstream from the customer premises. Downstream data is broadcasted from the OLT to each ONT, and each ONT processes the data destined to it by matching the address at the protocol transmission unit header. Upstream traffic is more complicated due to the shared media nature of the ODN. There is a need to coordinate between the transmissions of each of the ONTs to the OLT in order to avoid collisions. Upstream data is transmitted according to control mechanisms in the OLT, in which dedicated transmission time slots are granted to each individual ONT. The time slots are synchronized so that transmission bursts from different ONTs do not collide.
FIG. 2 illustrates a typical ONT at a customer's location within the PON of today. In the example of FIG. 2, the ONT is active and decouples the access network delivery mechanism, at the core shell, from the in-house distribution, at the service shell. The ONT core shell consists of ODN interface, User Port, Transmission, Services and Customers Multiplexing (MUX)/de-multiplexing functions. The ONT common shell includes power and Operations, Administration and Maintenance (OAM).
FIG. 3 illustrates an exemplary OLT of the typical PON of today. As shown in FIG. 3, the OLT service shell is connected to the switched networks via standardized interfaces at the exchange. At the distribution side, the OLT core shell presents optical accesses according to the agreed requirements, in terms of bit rate, power budget, and the like. The OLT common shell, much like the ONT, includes power and Operations, Administration and Maintenance (OAM).
In general, the Optical Distribution Network (ODN) provides the optical transmission medium for the physical connection of the ONTs to the OLTs. Individual ODNs may be combined and extended through the use of optical amplifiers. FIG. 4 illustrates a typical ODN connection between the OLT and one or more ONTs of the typical PON of today.
Part of the OAM function of the OLTs and ONTs of the typical PON includes an element management system (EMS), which includes performance management (or, performance monitoring). Specifically, OAM of the ONT includes the ONT management and control interface (OMCI) functions. An exemplary OMCI for a typical PON is described in the International Telecommunication Union Recommendation, ITU-T Recommendation G.983.2, which is incorporated by reference in its entirety and for all purposes. However, existing OMCI standards (such as, for example, G.983.2) do not communicate system time to an ONT, do not provide the ability to send an OLT's system time to the ONT and ultimately, do not provide the ability to associate a time with the performance monitoring bins (e.g. 15-minute collection time periods) collected and reported by the ONTs.
Thus, what is needed is a method and system that provides the ability to send an OLT's system time to an ONT, and then associate this system time with PM bins collected and reported by the ONT to the OLT within a PON.