Patent Application
20110069954
The present invention relates generally to optical systems, and more particularly, to protection of an optical line terminal in a passive optical network.
Service resilience has always been an area of critical focus for the carriers. Carrier grade equipments require “Five nines” (99.999%) of availability, i.e., about 5 minutes of outage per year. This takes into account all the incidents that could disrupt communications services—hardware failures, fiber cuts, or software failures. So far different solutions have been applied from various aspects: the system is designed with enough redundancy, including key modules redundancy (e.g., control, switching and power supply modules) and operating environment redundancy (e.g., temperature range and electromagnetic interference); the network is deployed with certain protecting schemes, such as ring topology or backup path. Besides the system and network robustness, the recovery time is also critical. The normally required network recovery time is within 50 milliseconds.
Yet for passive optical networks PON and other access systems, most of the research/product efforts for reliable network are generally focused on the network topology and the protect-switching with the specific topology. Though the network-level protection usually provides enough redundancy and enables traffic re-route, in access networks, the proposed solutions are usually not economic, which is a big concern for the carriers. Moreover, with the existing network protection schemes, usually a 1:1 redundancy for the optical line terminal OLT is necessary to enable the protection. So practically there is strong demand to enable the line card protection to improve the access network reliability.
Accordingly, there is a need for a 1-to-N protecting solution from the system level, to improve the system (and thus the network) robustness. Moreover, a “seamless service recovery” scheme is also needed to reduce the recovery time.
In accordance with the invention, there is provided an optical network apparatus having interconnected processing gigabit passive optical network G-PON blades, a protection blade, and controller blade, the regular blades and protecting blade having a higher layer processing and switching interface to a G-PON media access control MAC coupled to PHY including serializer and de-serializer modules that are connected to respective interface modules, the improvement including a protecting 1:N signal driver and a protecting N:1 signal select driver (multiplexer) coupled between the interface module and serializer and de-serializer modules of the protecting blade, respectively, for protecting connection to the interface module of the protecting blade. The improvement further includes a processing 1:N signal driver and a processing N:1 signal select driver coupled between the interface module and serializer and de-serializer modules of the processing G-PON blade, respectively, for protecting connection to the interface module of the processing G-PON blade and a 1:2 signal driver and 2:1 signal select driver in the interface module for providing an alternative connection to the protection blade.
These and other advantages of the invention will be apparent to those of ordinary skill in the art by reference to the following detailed description and the accompanying drawings.
The invention is directed to, for a system architecture, physically separating interface modules from the passive optical network (PON) optical line terminal (OLT) blade, and connecting to the corresponding OLT blade through either the backplane or the midplane. The protection blade has a serial signal connection to all the interface modules. For the interface modules, one serial data connection is to its regular OLT blade and the other is to the protection blade. The signal selection is controlled by the controller blade to select either the regular OLT blade or the protection blade.
For seamless service recovery, besides the OLT's local buffer for the necessary information (e.g., ONU serial number and ONU-ID, security encryption key), the backup copy is saved onto the controller blade. In case an OLT blade failure is encountered, the protection blade will be invoked and connected to the interface module under protection. To enable immediate service recovery the operation state and other necessary information are retrieved from the controller blade. Moreover, to eliminate the ranging process, the whole system uses the same slot synchronization signal provided by the controller blade.
Error! Reference source not found. shows the system external architecture supporting 1-to-N protection for the present invention, using a Gigabit-passive-optical-network G-PON, as an example. The architecture includes G-PON blades 10, protecting blades 11, an interface blade 12, interface modules 13 either on dedicated interface blade 12 (FIG. 1(1)) or in the same slot as G-PON blades 10 (
Two different mechanical approaches are illustrated in Error! Reference source not found.: (a) gives the architecture with dedicated interface slot that accepts the pluggable interface modules; (b) gives the architecture using mid-plane 15, that the interface modules are plugged on the other side of the mid-plane than the OLT processing modules. The differences of Error! Reference source not found. (a) and (b) are only mechanical.
Error! Reference source not found. is a diagram schematic of the protecting blade architecture 20. The “higher-layer processing & switching interface” 22, “GPON MAC” 23 and PHY 24 which mainly include serializer/deserializer and other control functions are the well known modules in the PON OLT system. For conventional OLT blade, the serializer and de-serializer are directly connected to the interface module; yet in the present invention, for the protection blade, a 1:N signal driver and N:1 signal Mux is presented 26, for the protecting connection to the interface modules. The 1:N signal driver duplicates one input signal to N outputs, and each output is connected to an interface module; the N:1 signal Mux is controlled by the selection signal 25 from the controller blade, to select the signal from the interface module that is under protection. The regular OLT is identical to the protection OLT, to simplify the design. Error! Reference source not found. is the regular OLT processing blade and its connection to the interface module. Unlike conventional interfaces, the interface module has a 1:2 signal driver and 2:1 signal select module to provide alternative connection to the protection blade. The processing blade 30 is shown with a detail for the interface module that includes optical transceiver and filter, connection from and to the protection blade 32, and the backplane connection and data and direction control 34.
Error! Reference source not found. is the backplane signal illustration diagram to support the interconnection. The types of slot include controller slot 41, GPON slots 42, 43, . . . 44 and the protecting slot 45. The controller slot 41 includes the following interconnections to or from the GPON slots and/or protecting slot:
Sel. Ctrl.: selection control, to enable the interface module select the signal from either regular blade 10 or the protecting blade 11; Sel. Ctrl.: selection control, to enable the interface module select the signal from either the regular blade 10 or the protecting blade 11. The protecting slot 45 includes the following interconnections:
The controller slot 41 is for the controller blade 16; the GPON slots are for the regular OLT blade 10, and the protecting slot is for the protection blade 11. “Sel. Ctrl.” is the selection control signal for the N:1 Mux in the protection blade 11, or for the 2:1 Mux in the interface modules; “Serialized data” is serial signals following 1:N driver (for the protection blade), or N:1 Mux (for the protection blade), or 1:2 driver (for the interface modules), or 2:1 Mux (for the interface modules); “Data Bus”, “Addr Bus”, “Bus Access Req”, and “Bus Access Grant” are the signals for fast system recovery (to be introduced in the next section). Error! Reference source not found. is the system level interconnection based on the architecture of the controller blade 16, regular OLT blade 10, protection OLT blade 11, and the interface modules 13.
The “Clock & Sync.” Signals 50 of the control unit in Error! Reference source not found. are for system-level synchronization. The clock is used as a system clock, and the synchronization signal is used for the OLT blades 10 to align the time slot (which is the basic time unit for PON). The purpose is to eliminate the optical network unit ONU ranging process.
The present invention saves the initial optical network unit ONU registration parameters and the real-time OLT processing states in the controller blade 16, besides the local registers/buffers. The signals between the controller blade 16 and the OLT blades (including both the regular OLT 10 blades and the protection blades 11) include the Data Bus, Addr Bus, Bus Access Req., Bus Access Grant, and other common signals 45. Whenever an OLT blade updates its entry, a corresponding update will be performed in the controller blade 16, through these bus access signals. When OLT blade encounters problem, the protection blade will retrieve the necessary information from the controller blade 16 through these bus signals and continue the normal operation without interrupting the service.
The flow diagrams of
Shown in 8 (b) is the initial waking up procedure for the protection blade to retrieve the processing state information from the controller blade, from the buffer control unit's point of view. Once the controller blade activates the protection blade, the bus access priority for the protection blade is set to the highest. When the protection blade is invoked, it first requests for bus access 801, waits for a bus grant 802, to retrieve the operating state 803. The “operating state” is the operation status (including the necessary state information) of the regular blade 10 (which is now protected) that is saved before the blade fails. The protection retrieves these states to continue from the point when the OLT blade fails. Once the state information is retrieved 804, the protection blade is ready 805 to interact with the ONUs.
Shown in 8 (c) is the protection blade working procedure to retrieve the necessary information from the controller blade, from the buffer control unit's point of view, after that of the procedure shown in
Referring specifically to the flow diagram in
The present invention has been shown and described in what are considered to be the most practical and preferred embodiments. It is anticipated, however, that departures may be made therefrom and that obvious modifications will be implemented by those skilled in the art. It will be appreciated that those skilled in the art will be able to devise numerous arrangements and variations, which although not explicitly shown or described herein, embody the principles of the invention and are within their spirit and scope.
