Method of changing over path switch in optical transmission device

• US 5,446,725 A
• Filed: 11/28/1994
• Issued: 08/29/1995
• Est. Priority Date: 08/29/1991
• Status: Expired due to Term

• Current Assignee: Fujitsu Limited
• Original Assignee: Fujitsu Limited
• Inventors: Ishiwatari, Junichi
• Primary Examiner(s): MARCELO, MELVIN C
• Application Number:
  US08/348,181
• Time in Patent Office: 274 Days
• Field of Search: 370/13, 370/15, 370/16, 370/16.1, 370/54, 370/55, 370/85.12, 370/85.15, 371/8.2, 371/11.2, 371/20.6, 371/68.2, 340/825.02, 340/825.03, 340/825.05, 340/827, 359/110, 359/119, 359/161, 359/173
• US Class Current: 370/222
• CPC Class Codes: H04B 1/74 for increasing reliability, e.g. using redundant or spare channels or apparatus replacing by standby devices for amplifiers H03F1/52, H03F1/542
• CPC Class Codes: H04J 2203/0042 Ring
• CPC Class Codes: H04J 2203/006 Fault tolerance and recovery
• CPC Class Codes: H04J 3/085 for ring networks, e.g. SDH/SONET rings, self-healing rings, meashed SDH/SONET networks
• CPC Class Codes: H04L 1/22 using redundant apparatus to increase reliability

Abstract

An optical transmission device for transmitting and receiving SONET signals has a path switch controlled in operation depending on the states of signals received bidirectionally over optical transmission lines. The optical transmission device generates one of a plurality of path switch alarms indicative of respective faults of the signals, based on the states of the signals transmitted to the path switch, and actuates the path switch depending on the generated path switch alarm to output one of the signals from two line terminal equipment units to a lower-level receiver. When SONET signals are transmitted and received in an A/B ring mode, the path switch is actuated in at least one of five control modes to output one of the signals from the two line terminal equipment unit to the lower-level receiver. When SONET signals are transmitted and received in a linear mode, a tributary path function added to the path switch is activated to meet a requirement for the reception of an optical signal transmitted over a unidirectional one of the optical transmission lines.

Claims

1. A method of changing over a path switch in an optical transmission device having a first line terminal equipment unit and a second line terminal equipment unit for receiving optical signals transmitted bidirectionally over optical transmission lines, the path switch being connected to respective paths to said first line terminal equipment unit and said second line terminal equipment unit, and selectively outputting respective output signals from said first line terminal equipment unit and said second line terminal equipment unit to a lower-level receiver, said method comprising the steps of:

receiving the optical signals, transmitted bidirectionally over the optical transmission lines, by said first line terminal equipment unit and said second line terminal equipment unit;

generating by said first line terminal equipment unit and said second line terminal equipment unit the respective output signals responsive to the optical signals;

monitoring, with said path switch, the output signals transmitted by said first line terminal equipment unit and said second line terminal equipment unit to said path switch over the respective paths;

generating one of a plurality of path switch alarms indicative of respective faults of the output signals, based on states of the output signals applied to said path switch; and

actuating said path switch depending on the generated path switch alarm to output a selected one of the respective output signals from said first line terminal equipment unit and said second line terminal equipment unit to said lower-level receiver.

2. A method of changing over a path switch in an optical transmission device having two line terminal equipment units for receiving optical signals transmitted bidirectionally over optical transmission lines, and the path switch being connected to respective paths to the line terminal equipment units, for selectively outputting respective output signals from the line terminal equipment units to a lower-level receiver, said method comprising the steps of:

monitoring, with said path switch, the respective output signals transmitted by said two line terminal equipment units to said path switch over the respective paths;

generating one of a plurality of path switch alarms indicative of respective faults of the output signals, based on states of the respective output signals applied to said path switch; and

actuating said path switch depending on the generated path switch alarm to output a selected one of the respective output signals from said two line terminal equipment units to said lower-level receiver;

transmitting SONET signals from said optical transmission lines arranged in a ring shape to said two line terminal equipment units in an A/B ring mode;

classifying said path switch alarms in different ranks depending on the degree of signal faults indicated thereby;

generating path switch alarms based on the states of two of the respective output signals that are supplied simultaneously to said path switch over said paths; and

connecting the path transmitting the signal with respect to which a path switch alarm in a lower rank is generated, to said lower-level receiver with said path switch.

3. A method of changing over a path switch in an optical transmission device having two line terminal equipment units for receiving optical signals transmitted bidirectionally over optical transmission lines, and the path switch being connected to respective paths to the line terminal equipment units, for selectively outputting respective output signals from the line terminal equipment units to a lower-level receiver, said method comprising the steps of:

monitoring, with said path switch, the respective output signals transmitted by said two line terminal equipment units to said path switch over the respective paths;

generating one of a plurality of path switch alarms indicative of respective faults of the respective output signals, based on states of the respective output signals applied to said path switch; and

actuating said path switch depending on the generated path switch alarm to output a selected one of the respective output signals from said two line terminal equipment units to said lower-level receiver;

transmitting SONET signals from said optical transmission lines arranged in a ring shape to said two line terminal equipment units in an A/B ring mode;

counting the number of times which said path switch is changed over from the connection between one of said paths and said lower-level receiver to the connection between the other of said paths and said lower-level receiver to the connection between the other of said paths and said lower-level receiver, and vice versa; and

locking said path switch against further change-overs when the counted number of times reaches a predetermined value.

4. A method of changing over a path switch in an optical transmission device having two line terminal equipment units for receiving optical signals transmitted bidirectionally over optical transmission lines, and the path switch being connected to respective paths to the line terminal equipment units, for selectively outputting respective output signals from the line terminal equipment units to a lower-level receiver, said method comprising the steps of:

monitoring with said path switch, the respective output signals transmitted by said two line terminal equipment units to said path switch over the respective paths;

generating one of a plurality of path switch alarms indicative of respective faults of the respective output signals, based on states of the respective output signals applied to said path switch; and

actuating said path switch depending on the generated path switch alarm to output a selected one of the respective output signals from said two line terminal equipment units to said lower-level receiver;

transmitting SONET signals from said optical transmission lines arranged in a ring shape to said two line terminal equipment units in an A/B ring mode;

providing said path switch with a manual change-over function to manually change over from the connection between one of said paths and said lower-level receiver to the connection between the other of said paths and said lower-level receiver, and vice versa; and

activating said manual changeover function only when said path switch alarms are not produced.

5. A method of changing over a path switch in an optical transmission device having two line terminal equipment units receiving optical signals transmitted bidirectional by over optical transmission lines, and the path switch being connected to respective paths to the line terminal equipment units, for selectively outputting respective output signals from the line terminal equipment units to a lower-level receiver, said method comprising the steps of:

monitoring, with said path switch, the respective output signals transmitted by said two line terminal equipment units to said path switch over the respective paths;

generating one of a plurality of path switch alarms indicative of respective faults of the respective output signals, based on states of the respective output signals applied to said path switch; and

actuating said path switch depending on the generated path switch alarm to output a selected one of the respective output signals from said two line terminal equipment units to said lower-level receiver;

transmitting SONET signals from said optical transmission lines arranged in a ring shape to said two line terminal equipment units in an A/B ring mode;

providing said path switch with a tributary path function to select and lock the connection between one of said paths and said lower-level receiver or the connection between the other of said paths and said lower-level receiver; and

activating said tributary path function when said optical transmission device is required to receive an optical signal from a unidirectional one of said optical transmission lines.

6. A method of changing over a path switch in an optical transmission device having two line terminal equipment units for receiving optical signals transmitted bidirectionally over optical transmission lines, and the path switch being connected to respective paths to the line terminal equipment units, for selectively outputting respective output signals from the line terminal equipment units to a lower-level receiver, said method comprising the steps of:

monitoring, with said path switch, the respective output signals transmitted by said two line terminal equipment units to said path switch over the respective paths;

generating one of a plurality of path switch alarms indicative of respective faults of the respective output signals, based on states of the respective output signals applied to said path switch; and

actuating said path switch depending on the generated path switch alarm to output a selected one of the respective output signals from said two line terminal equipment units to said lower-level receiver;

transmitting SONET signals from said optical transmission lines arranged in a ring shape to said two line terminal equipment units in an A/B ring mode;

providing said path switch with a forcible changeover function to forcibly change over from the connection between one of said paths and said lower-level receiver to the connection between the other of said paths and said lower-level receiver, and vice versa; and

forcibly changing over said path switch irrespective of whether path switch alarms are generated when said forcible changeover function is activated.

7. A method of changing over a path switch in an optical transmission device having two line terminal equipment units for receiving optical signals transmitted bidirectionally over optical transmission lines, and the path switch being connected to respective paths to the line terminal equipment units, for selectively outputting respective output signals from the line terminal equipment units toga lower-level receiver, said method comprising the steps of:

monitoring with said path switch, the respective output signals transmitted from said two line terminal equipment units to said path switch over the respective paths;

generating one of a plurality of path switch alarms indicative of respective faults of the respective output signals, based on states of the respective output signals applied to said path switch; and

actuating said path switch depending on the generated path switch alarm to output a selected one of the respective output signals from said two line terminal equipment units to said lower-level receiver;

transmitting SONET signals from said optical transmission lines to said two line terminal equipment units in a linear mode;

providing said path switch with a tributary path function to select and lock the connection between one of said paths and said lower-level receiver or the connection between the other of said paths and said lower-level receiver; and

activating said tributary path function when said optical transmission device is required to receive an optical signal from a unidirectional one of said optical transmission lines.

8. A method according to claim 7, further including the steps of:

monitoring clock pulses contained in the respective output signals transmitted from said two line terminal equipment units to said path switch over the respective paths; and

when no clock pulses are supplied from one of said line terminal equipment units while said tributary path function is inactivated, actuating said path switch to output the other of the respective output signals generated by the other line terminal equipment unit to said lower-level receiver.

9. A method of changing over a path switch in an optical transmission device for transmitting and receiving SONET signals in an A/B ring mode, said optical transmission device having two line terminal equipment for receiving optical signals transmitted bidirectionally over ring-shaped optical transmission lines, and the path switch being connected to respective paths to the line terminal equipment, said optical transmission device being operable to generate one of a plurality of path switch alarms indicative of respective faults of the signals, based on the states of the signals transmitted from said line terminal equipment over said respective paths to said path switch, and to actuate said path switch to connect the path other than the path transmitting a signal with respect to which a path switch alarm is generated, to a lower-level receiver, said method comprising the steps of:

providing a first mode for classifying said path switch alarms in different ranks depending on the degree of signal faults indicated thereby, generating path switch alarms based on the states of two signals that are supplied simultaneously to said path switch over said paths, and connecting the path transmitting the signal with respect to which a path switch alarm in a lower rank is generated, to said lower-level receiver with said path switch;

providing a second mode for counting the number of times which said path switch is changed over from the connection between one of said paths and said lower-level receiver to the connection between the other of said paths and said lower-level receiver, and vice versa, and locking said path switch against further changeovers when the counted number of times reaches a predetermined value;

providing a third mode for providing said path switch with a manual changeover function to manually change over from the connection between;

one of said paths and said lower-level receiver to the connection between the other of said paths and said lower-level receiver, and vice versa, and activating said manual changeover function only when said path switch alarms are not produced;

providing a fourth mode for providing said path switch with a tributary path function to select and lock the connection between one of said paths and said lower-level receiver or the connection between the other of said paths and said lower-level receiver, and activating said tributary path function when said optical transmission device is required to receive an optical signal from a unidirectional one of said optical transmission lines;

providing a fifth mode for providing said path switch with a forcible changeover function to forcibly change over from the connection between one of said paths and said lower-level receiver to the connection between the other of said paths and said lower-level receiver, and vice versa, and forcibly changing over said path switch irrespective of whether path switch alarms are generated when said forcible changeover function is activated; and

controlling said path switch to operate successively in said fifth mode, said fourth mode, said third mode, said second mode, and said first mode in the order named when at least two of said first, second, third, fourth, and fifth modes are to be simultaneously performed.

10. A method of changing over a path switch in an optical transmission device having two line terminal equipment units for receiving optical signals transmitted bidirectionally over optical transmission lines, and the path switch being connected to respective paths to the line terminal equipment units, for selectively outputting respective output signals from the line terminal equipment units to a lower-level receiver, said method comprising the steps of:

monitoring, with said path switch, the respective output signals transmitted by said two line terminal equipment units to said path switch over the respective paths;

generating one of a plurality of path switch alarms indicative of respective faults of the output signals, based on states of the respective output signals applied to said path switch; and

actuating said path switch depending on the generated path switch alarm to output a selected one of the respective output signals from said two line terminal equipment units to said lower-level receiver;

transmitting the optical signals from said optical transmission lines arranged in a ring shape to said two line terminal equipment units;

classifying said path switch alarms in different ranks depending on a kind of signal faults indicated thereby;

generating path switch alarms based on the states of two of the respective output signals that are supplied simultaneously to said path switch over said paths; and

connecting the path transmitting the signal with respect to which a path switch alarm in a lower rank is generated, to said lower-level receiver with said path switch.

11. A method of changing over a path switch in an optical transmission device having two line terminal equipment units for receiving optical signals transmitted bidirectionally over optical transmission lines, and the path switch being connected to respective paths to the line terminal equipment units, for selectively outputting respective output signals from the line terminal equipment units toga lower-level receiver, said method comprising the steps of:

monitoring, with said path switch, the respective output signals transmitted by said two line terminal equipment units to said path switch over the respective paths;

generating one of a plurality of path switch alarms indicative of respective faults of the respective output signals, based on states of the respective output signals applied to said path switch; and

actuating said path switch depending on the generated path switch alarm to output a selected one of the respective output signals from said two line terminal equipment units to said lower-level receiver;

transmitting the optical signals from said optical transmission lines arranged in a ring shape to said two line terminal equipment units;

counting the number of times which said path switch is changed over from the connection between one of said paths and said lower-level receiver to the connection between the other of said paths and said lower-level receiver to the connection between the other of said paths and said lower-level receiver, and vice versa; and

locking said path switch against further change-overs when the counted number of times reaches a predetermined value.

12. A method of changing over a path switch in an optical transmission device having two line terminal equipment units for receiving optical signals transmitted bidirectionally over optical transmission lines, and the path switch being connected to respective paths to the line terminal equipment units, for selectively outputting respective output signals from the line terminal equipment units to a lower-level receiver, said method comprising the steps of:

monitoring, with said path switch, the respective output signals transmitted by said two line terminal equipment units to said path switch over the respective paths;

generating one of a plurality of path switch alarms indicative of respective faults of the respective output signals, based on states of the respective output signals applied to said path switch; and

actuating said path switch depending on the generated path switch alarm to output a selected one of the respective output signals from said two line terminal equipment units to said lower-level receiver;

transmitting the optical signals from said optical transmission lines arranged in a ring shape to said two line terminal equipment units;

providing said path switch with a manual change-over function to manually change over from the connection between one of said paths and said lower-level receiver to the connection between the other of said paths and said lower-level receiver, and vice versa; and

activating said manual changeover function only when said path switch alarms are not produced.

13. A method of changing over a path switch in an optical transmission device having two line terminal equipment units for receiving optical signals transmitted bidirectionally over optical transmission lines, and the path switch being connected to respective paths to the line terminal equipment units, for selectively outputting respective output signals from the line terminal equipment units to a lower-level receiver, said method comprising the steps of:

monitoring, with said path switch, the respective output signals transmitted by said two line terminal equipment units to said path switch over the respective paths;

generating one of a plurality of path switch alarms indicative of respective faults of the respective output signals, based on states of the respective output signals applied to said path switch; and

actuating said path switch depending on the generated path switch alarm to output a selected one of the respective output signals from said two line terminal equipment units to said lower-level receiver;

transmitting the optical signals from said optical transmission lines arranged in a ring shape to said two line terminal equipment units;

providing said path switch with a tributary path function to select and lock the connection between one of said paths and said lower-level receiver or the connection between the other of said paths and said lower-level receiver; and

activating said tributary path function when said optical transmission device is required to receive an optical signal from a unidirectional one of said optical transmission lines.

14. A method of changing over a path switch in an optical transmission device having two line terminal equipment units for receiving optical signals transmitted bidirectionally over optical transmission lines, and the path switch being connected to respective paths to the line terminal equipment units, for selectively outputting respective output signals from the line terminal equipment units to a lower-level receiver, said method comprising the steps of:

monitoring, with said path switch, the respective output signals transmitted by said two line terminal equipment units to said path switch over the respective paths;

generating one of a plurality of path switch alarms indicative of respective faults of the respective output signals, based on states of the respective output signals applied to said path switch; and

actuating said path switch depending on the generated path switch alarm to output a selected one of the respective output signals from said two line terminal equipment units to said lower-level receiver;

transmitting the optical signals from said optical transmission lines arranged in a ring shape to said two line terminal equipment units;

providing said path switch with a forcible changeover function to forcibly change over from the connection between one of said paths and said lower-level receiver to the connection between the other of said paths and said lower-level receiver, and vice versa; and

forcibly changing over said path switch irrespective of whether path switch alarms are generated when said forcible changeover function is activated.

15. A method of changing over a path switch in an optical transmission device having two line terminal equipment units for receiving optical signals transmitted bidirectionally over optical transmission lines, and the path switch being connected to respective paths to the line terminal equipment units, for selectively outputting respective output signals from the line terminal equipment units to a lower-level receiver, said method comprising the steps of:

monitoring, with said path switch, the respective output signals transmitted from said two line terminal equipment units to said path switch over the respective paths;

generating one of a plurality of path switch alarms indicative of respective faults of the respective output signals, based on states of the respective output signals applied to said path switch; and

actuating said path switch depending on the generated path switch alarm to output a selected one of the respective output signals from said two line terminal equipment units to said lower-level receiver;

transmitting the optical signals from said optical transmission lines to said two line terminal equipment units in a linear mode;

providing said path switch with a tributary path function to select and lock the connection between one of said paths and said lower-level receiver or the connection between the other of said paths and said lower-level receiver; and

activating said tributary path function when said optical transmission device is required to receive an optical signal from a unidirectional one of said optical transmission lines.

16. A method according to claim 15, further including the steps of:

monitoring clock pulses contained in the respective output signals transmitted from said two line terminal equipment units to said path switch over the respective paths; and

when no clock pulses are supplied from one of said line terminal equipment units while said tributary path function is inactivated, actuating said path switch to output the other of the respective output signals generated by the other line terminal equipment unit to said lower-level receiver.