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US 6,618,358 B2Granted
Method and apparatus for switching a clock source from among multiple T1/E1 lines with user defined priority
AssigneeCisco Technology, Inc.
InventorsSanjeev A. Mahajan, Venkaiah Dukkipati
Life of this patent
Estimating the term…
Abstract
A clock selection controller is shown which allows a user to assign a priority scheme to recovered clock signals obtained from communication facilities. The clock selection controller also receives a plurality of alarm signals corresponding to the communications facilities for each of the recovered clock signals. The clock selection controller then automatically selects, for output as a reference clock signal, the highest priority clock input available for which the corresponding alarm signals are inactive. In the absence of an available clock input in the priority scheme, the processor selects a free running clock input.
Claims24
A clock selection controller, the controller comprising:
- a plurality of clock inputs, each configured to receive a clock signal from a line interface controller;
- a clock output configured to output an internal clock signal;
- a first plurality of alarm inputs each corresponding to one of the plurality of clock inputs and configured to receive a first alarm signal from the line interface controller;
- a clock signal switch coupled to each of the plurality of clock inputs and the clock output, the clock signal switch configured to receive a clock selection signal at a control input and, responsive thereto, switch the clock signal from one of the plurality of clock inputs to the clock output;
- a user interface configured to receive user configuration commands for selecting different user configurable priority schemes each identifying different orders of priority for the plurality of clock inputs independently of physical connections of the clock inputs on the clock signal switch;
- and
- a clock selection processor configured to identify when the clock input currently used as the clock output has an active alarm and then automatically and without manual user selection selecting a next one of the multiple clock inputs having an inactive alarm signal and a highest priority according to the user configured priority schemes, the clock selection processor further configured to automatically generate the clock selection signal for configuring the clock signal switch to output the selected next one of the multiple clock inputs.
4 more elements
A method for selecting an internal clock source from among a plurality of clock signals recovered from a plurality of incoming transmission lines, the method comprising:
- assigning a programmable priority scheme to the clock signals from the plurality of incoming transmission lines, the programmable priority scheme providing a programmable priority order for automatically selecting one of the plurality of clock signals;
- automatically selecting a first one of the plurality of clock signals as the internal clock source having a highest priority in the programmable priority scheme;
- monitoring up to k alarm signals from each of the plurality of incoming transmission lines, where each group of k alarm signals corresponds to the clock signal from the incoming transmission line;
- placing each clock signal in an available state when each of the corresponding k alarm signals is inactive;
- placing each recovered clock signal in an unavailable state when any of the corresponding k alarm signals are active;
- automatically identifying when the first one of the clock signals is placed in the unavailable state;
- and
- automatically and without user intervention selecting a second one of the clock signals in the available state having a next highest priority in the programmable priority scheme as the internal clock source.
5 more elements
A clock source selection system for a network access server, the system comprising:
- a plurality of line interface controllers each configured to generate a clock signal and k different alarm signals from data received on a transmission line;
- a user interface configured to receive user configuration commands;
- a clock selection controller coupled to each one of the plurality of line interface controllers and the user interface, the clock selection controller maintaining a configurable and programmable priority scheme among the clock signals responsive to the user configuration commands and independently of physical interfaces on the clock selection controller receiving the line interface controllers and automatically selecting a first one of the clock signals according to the configurable priority scheme and automatically selecting a second one of the clock signals having a second highest priority in the configurable priority scheme when the first one of the clock signals has at least one active alarm signal, the clock selection controller automatically reselecting the first one of the clock signals when the alarm signals for the first one of the clock signals are no longer active.
A clock source selection system for a network access server, the system comprising:
- means for generating a plurality of clock signals and k multiple different alarm signals for each clock signal from data received on a transmission line;
- means for receiving user configuration commands;
- means for maintaining a programmable priority scheme among the clock signals responsive to the user configuration commands independent of physical connections receiving the clock signals;
- means for automatically selecting a first one of the clock signals according to the programmable priority scheme;
- means for automatically monitoring the k multiple different alarm signals for each clock signal;
- means for automatically selecting a second one of the clock signals having a next highest priority in the programmable priority scheme when any one of the k different alarm signals for the first one of the clocks signals is active;
- means for reprogramming the priority scheme;
- and
- means for automatically selecting a third one of the clock signals having a new highest priority in the reprogrammed priority scheme when any one of the k different alarm signals for the second one of the clocks signals is active.
6 more elements
A computer-readable medium, which, when read, causes a clock source selection system for a network access server to perform functions comprising:
- generating a plurality of clock signals and k different alarm signals for each clock signal from data received on a transmission line;
- receiving user configuration commands;
- programming a configurable priority scheme among the clock signals responsive to the user configuration commands and automatically selecting a first one of the clock signals according to the configurable priority scheme;
- automatically monitoring the different alarm signals and automatically selecting a second one of the clock signals having a next highest priority in the priority scheme when any of the alarm signals for the first one of the clock signals is active;
- reprogramming the configurable priority scheme among the clock signals responsive to the user configuration commands and automatically selecting a third one of the clock signals according to the reprogrammed priority scheme;
- and
- automatically monitoring the different alarm signals and automatically selecting a fourth one of the clock signals having a next highest priority in the reprogrammed priority scheme when any of the alarm signals for the third one of the clock signals is active.
4 more elements
Dependencies are inferred from the claim text.