Protection for Fibre Optic Access Networks

Abstract

An Optical Network Unit, ONU, and an Optical Line Terminal, OLT, as well as a respective method therein, are provided for enabling the ONU to communicate with the OLT. The ONU and at least one OLT are comprised in a passive fibre optic access network. The passive fibre optic access network comprises two fibre paths through the network, a main fibre path and a back-up fibre path, connecting the ONU with the OLT. When a fault is detected in the main fibre path is detected, transmission rate negotiation is performed between the ONU and the OLT over the back-up path. When a transmission rate is agreed upon between the ONU and the OLT during said transmission rate negotiation with regard to communication over the back-up path, the communication between the ONU and the OLT is executed using the agreed transmission rate over the back-up path.

1 - 56 . (canceled) 
     
     
         57 . A method in an Optical Network Unit (ONU) in a fiber optic access network, the fiber optic access network comprising at least one Optical Line Terminal (OLT) and two fiber paths through the fiber optic access network, a main fiber path and a back-up path, connecting said ONU with said OLT for enabling the ONU to communicate over the fiber optic access network, the method comprising:
 detecting a fault in the main fiber path between said ONU and said OLT, during ongoing communication;   performing a transmission rate negotiation with said OLT over the back-up path; and   when a transmission rate is agreed upon between said ONU and said OLT during the transmission rate negotiation with regard to communication over the back-up path, executing communication with said OLT using the agreed upon transmission rate over the back-up path.   
     
     
         58 . The method according to  claim 57 , wherein detecting the fault in the main fiber path between said ONU and said OLT comprises receiving an alarm indicating the fault. 
     
     
         59 . The method according to  claim 58 , wherein the alarm comprises one of a “loss of signal” alarm, a “loss of synchronization” alarm, a “low signal level” alarm, a “loss of data structure” alarm, and a “high bit error rate” alarm. 
     
     
         60 . The method according to  claim 57 , further comprising negotiating one or more further parameters to be used for communication on the back-up path between said ONU and said OLT. 
     
     
         61 . The method according to  claim 57 , wherein performing the transmission rate negotiation with said OLT comprises confirming use of a pre-negotiated transmission rate with regard to communication over the back-up path. 
     
     
         62 . The method according to  claim 57 , wherein upon detecting the fault in the main fiber path between said ONU and said OLT, the method further comprises, before performing the transmission rate negotiation with said OLT over the back-up path:
 performing a first transmission rate negotiation with said OLT over the main fiber path;   if a first transmission rate is agreed upon between said ONU and said OLT during the first transmission rate negotiation, executing communication with said OLT using the first transmission rate over the main fiber path;   if the first transmission rate is not agreed upon between said ONU and said OLT during the first transmission rate negotiation, performing a second transmission rate negotiation with said OLT over the back-up path; and   when a second transmission rate is agreed upon between said ONU and said OLT during the second transmission rate negotiation, executing communication with said OLT using the second transmission rate over the back-up path.   
     
     
         63 . The method according to  claim 62 , wherein performing the first transmission rate negotiation with said OLT over the main fiber path results in the first transmission rate, which is lower than the transmission rate used before the detection of the fault in the main fiber path between said ONU and said OLT, the method further comprising:
 comparing the first transmission rate between said ONU and said OLT over the main fiber path with a pre-negotiated transmission rate between said ONU and said OLT over the back-up path;   if the first transmission rate over the main fiber path is lower than the pre-negotiated transmission rate over the back-up path, executing communication to said OLT over the back-up path using the pre-negotiated transmission rate; and   if the first transmission rate over the main fiber path is higher than the pre-negotiated transmission rate over the back-up path, executing communication to said OLT over the main fiber path using the first transmission rate.   
     
     
         64 . The method according to  claim 57 , wherein the ONU communicates with two separate OLTs over the fiber optic access network: a main OLT connected to the ONU via the main fiber path and a back-up OLT connected to the ONU via the back-up fiber path. 
     
     
         65 . The method according to  claim 64 , further comprising wherein all negotiation messages sent to said main OLT during the transmission rate negotiation with said ONU over the main fiber path are also sent to the back-up OLT. 
     
     
         66 . The method according to  claim 57 , further comprising first synchronizing said ONU and said OLT before performing the transmission rate negotiation. 
     
     
         67 . A method in an Optical Line Terminal (OLT) in a fiber optic access network, the fiber optic access network comprising at least two fiber paths between the OLT and an Optical Network Unit (ONU), a main fiber path and a back-up fiber path, for enabling the ONU to communicate over the fiber optic access network, the method comprising:
 detecting a fault in the main fiber path between said OLT and said ONU during ongoing communication;   performing a transmission rate negotiation with said ONU over the back-up path upon detecting the fault in the main fiber path;   when a transmission rate is agreed upon between said OLT and said ONU during the transmission rate negotiation with regard to communication over the back-up fiber path, executing communication with said ONU using the agreed upon transmission rate over the back-up fiber path.   
     
     
         68 . The method according to  claim 67 , wherein detecting the fault in the main fiber path between said OLT and said ONU comprises receiving an alarm indicating the fault. 
     
     
         69 . The method according to  claim 68 , wherein the alarm comprises one of a “loss of signal” alarm, a “loss of synchronization” alarm, a low signal level” alarm, a “loss of data structure” alarm, and a “high bit error rate” alarm. 
     
     
         70 . The method according to  claim 67 , further comprising negotiating one or more further parameters to be used for communication on the back-up fiber path between said OLT and said ONU. 
     
     
         71 . The method according to  claim 67 , wherein performing the transmission rate negotiation with said ONU comprises confirming use of a pre-negotiated transmission rate with regard to communication over the back-up path. 
     
     
         72 . The method according to  claim 67 , wherein upon detecting the fault in the main link between said ONU and said OLT, the method further comprises, before performing the transmission rate negotiation with the OLT over the back-up path:
 performing a first transmission rate negotiation with said ONU over the main fiber path;   if a first transmission rate is agreed upon between said ONU and said OLT during the first transmission rate negotiation, executing communication with said ONU using the first transmission rate over the main fiber path;   if the first transmission rate is not agreed upon between said ONU and said OLT during the first transmission rate negotiation, performing a second transmission rate negotiation with said ONU over the back-up fiber path; and   when a second transmission rate is agreed upon between said ONU and said OLT during the second transmission rate negotiation, executing communication with said ONU using the second transmission rate over the back-up fiber path.   
     
     
         73 . The method according to  claim 72 , wherein performing the first transmission rate negotiation with said ONU over the main fiber path results in the first transmission rate, which is lower than the transmission rate used before the detection of the fault in the main fiber path between said ONU and said OLT, the method further comprising:
 comparing the first transmission rate between said ONU and said OLT over the main fiber path with a pre-negotiated transmission rate between said ONU and said OLT over the back-up fiber path;   if the first transmission rate over the main fiber path is lower than the pre-negotiated transmission rate over the back-up fiber path, executing communication to said ONU over the back-up fiber path using the pre-negotiated transmission rate; and   if the first transmission rate over the main fiber path is higher than the pre-negotiated transmission rate over the back-up fiber path, executing communication to said ONU over the main fiber path using the first transmission rate.   
     
     
         74 . The method according to  claim 67 , wherein said OLT comprises a main OLT connected to said ONU via the main fiber path, and wherein the back-up fiber path connects said ONU to a back-up OLT. 
     
     
         75 . The method according to  claim 74 , wherein when the back-up fiber path is to be used, the method comprises sending an instruction to the back-up OLT instructing the back-up OLT to initiate the transmission rate negotiation with said ONU over the back-up fiber path. 
     
     
         76 . The method according to  claim 74 , wherein all negotiation messages sent to said ONU in during the transmission rate negotiation with said ONU over the main fiber path are also sent to the back-up OLT. 
     
     
         77 . The method according to  claim 74 , further comprising receiving a request from said ONU to establish communication with the back-up OLT, wherein the main OLT sends a request to the back-up OLT to execute communication to said ONU over the back-up fiber path. 
     
     
         78 . The method according to  claim 67 , wherein the OLT comprises a back-up OLT connected to said ONU via the back-up fiber path and the main fiber path connects said ONU to a main OLT. 
     
     
         79 . The method according to  claim 78 , further comprising:
 receiving an indication that communication needs to be executed on a link between said back-up OLT and said ONU;   performing the transmission rate negotiation between said back-up OLT and said ONU over the back-up fiber path;   if the transmission rate negotiation does not result in the agreed upon transmission rate to be used for executing communication between said ONU and said back-up OLT over the back-up fiber path, generating a link failure message; and   if the transmission rate is agreed upon between said ONU and said back-up OLT, executing communication with the back-up OLT using the agreed upon transmission rate over the back-up fiber path.   
     
     
         80 . The method according to  claim 79 , wherein receiving the indication comprises receiving a request, from said main OLT, to initiate the transmission rate negotiation with said ONU over the back-up fiber path. 
     
     
         81 . The method according to  claim 79 , wherein receiving the indication comprises receiving transmission rate negotiation messages from said ONU destined for said main OLT. 
     
     
         82 . The method according to  claim 79 , wherein performing the transmission rate negotiation between said back-up OLT and said ONU over the back-up fiber path comprises confirming use of a pre-negotiated transmission rate between said ONU and said back-up OLT over the back-up fiber path. 
     
     
         83 . The method according to  claim 81 , further comprising determining, from the transmission rate negotiation messages received from said ONU, that an un-recoverable link failure has occurred on the main fiber path between said ONU and said main OLT. 
     
     
         84 . The method according to  claim 83 , wherein determining that the un-recoverable link failure has occurred on the main fiber comprises:
 starting a preset timer when one of the transmission rate negotiation messages is received from said ONU destined for said main OLT; and   if the preset timer expires before a receiving an expected follow-up transmission rate negotiation message from said ONU destined for said main OLT, performing the transmission rate negotiation with said ONU over the back-up fiber path.   
     
     
         85 . An Optical Network Unit (ONU) in a fiber optic access network, the fiber optic access network comprising at least one Optical Line Terminal (OLT) and two fiber paths through the fiber optic access network, a main fiber path and a back-up fiber path, connecting said ONU with said OLT, the ONU configured to enable the ONU to communicate over the fiber optic access network, the ONU comprising a processing circuit configured to:
 detect a fault in the main fiber path between said ONU and said OLT during ongoing communication;   perform a transmission rate negotiation with said OLT over the back-up fiber path; and   when a transmission rate is agreed upon between said ONU and said OLT during the transmission rate negotiation with regard to communication over the back-up fiber path, execute communication with said OLT using the agreed upon transmission rate over the back-up fiber path.   
     
     
         86 . The ONU according to  claim 85 , wherein the processing circuit detects the fault in the main fiber path between said ONU and said OLT by receiving an alarm indicating the fault. 
     
     
         87 . The ONU according to  claim 86 , wherein the alarm comprises one of a “loss of signal” alarm, a “loss of synchronization” alarm, a low signal level” alarm, a “loss of data structure” alarm, and a “high bit error rate” alarm. 
     
     
         88 . The ONU according to  claim 85 , wherein the processing circuit is further configured to negotiate one or more further parameters to be used for communication on the back-up fiber path between said ONU and said OLT. 
     
     
         89 . The ONU according to  claim 85 , wherein the processing circuit performs the transmission rate negotiation with said OLT by confirming use of a pre-negotiated transmission rate with regard to communication over the back-up fiber path. 
     
     
         90 . The ONU according to  claim 85 , wherein the processing circuit, upon detecting the fault in the main fiber path between said ONU and said OLT, is further configured to, before performing the transmission rate negotiation with said OLT over the back-up fiber path:
 perform a first transmission rate negotiation with said OLT over the main fiber path;   if a first transmission rate is agreed upon between said ONU and said OLT during the first transmission rate negotiation, execute communication with said OLT using the first transmission rate over the main fiber path;   if the first transmission rate is not agreed upon between said ONU and said OLT during the first transmission rate negotiation, perform a second transmission rate negotiation with said OLT over the back-up fiber path; and   when a second transmission rate is agreed upon between said ONU and said OLT during the second transmission rate negotiation, execute communication with said OLT using the second transmission rate over the back-up fiber path.   
     
     
         91 . The ONU according to  claim 90 , wherein the first transmission rate negotiation with said OLT over the main fiber path results in the first transmission rate, which is lower than the transmission rate used before the detection of the fault in the main fiber path between said ONU and said OLT, and wherein the processing circuit is further configured to:
 compare the first transmission rate between said ONU and said OLT over the main fiber path with a pre-negotiated transmission rate between said ONU and said OLT over the back-up fiber path;   if the first transmission rate over the main fiber path is lower than the pre-negotiated transmission rate over the back-up fiber path, the processing circuit is configured to execute communication to said OLT over the back-up fiber path using the pre-negotiated transmission rate; and   if the first transmission rate over the main fiber path is higher than the pre-negotiated transmission rate over the back-up fiber path, the processing circuit is configured to execute communication to said OLT over the main fiber path using the first transmission rate.   
     
     
         92 . The ONU according to  claim 85 , wherein said ONU is configured to communicate with two separate OLTs over the fiber optic access network, a main OLT connected to said ONU via the main fiber path and a back-up OLT connected to said ONU via the back-up fiber path. 
     
     
         93 . The ONU according to  claim 92 , wherein said ONU is configured to send all negotiation messages, which are sent to said main OLT during the transmission rate negotiation with said ONU over the main fiber path, also to said back-up OLT via the back-up fiber path. 
     
     
         94 . The ONU according to  claim 85 , wherein the processing circuit is configured to synchronize said ONU and said OLT before performing the negotiation of the transmission rate. 
     
     
         95 . An Optical Line Terminal (OLT) in a fiber optic access network, the fiber optic access network comprising at least two fiber paths between the OLT and an Optical Network Unit, ONU, a main fiber path and a back-up fiber path, the OLT being configured to enable the ONU to communicate over the fiber optic access network, the OLT comprising a processing circuit configured to:
 detect a fault in the main fiber path between said OLT and said ONU during ongoing communication;   perform a transmission rate negotiation with said ONU over the back-up fiber path upon detecting the fault in the main fiber path; and   when a transmission rate is agreed upon between said OLT and said ONU during the transmission rate negotiation with regard to communication over the back-up fiber path, the processing circuit is configured to execute communication with said ONU using the agreed upon transmission rate over the back-up fiber path.   
     
     
         96 . The OLT according to  claim 95 , wherein the processing circuit detects the fault in the main fiber path between said OLT and said ONU by receiving an alarm indicating the fault. 
     
     
         97 . The OLT according to  claim 96 , wherein the alarm comprises one of a “loss of signal” alarm, a “loss of synchronization” alarm, a low signal level” alarm, a “loss of data structure” alarm, and a “high bit error rate” alarm. 
     
     
         98 . The OLT according to  claim 95 , wherein the processing circuit is further configured to negotiate one or more further parameters to be used for communication on the back-up fiber path between said OLT and said ONU. 
     
     
         99 . The OLT according to  claim 95 , wherein the processing circuit performs the transmission rate negotiation with said ONU by confirming use of a pre-negotiated transmission rate with regard to communication over the back-up fiber path. 
     
     
         100 . The OLT according to  claim 95 , wherein upon detecting the fault in the main link between said ONU and said OLT, the processing circuit is further configured to, before performing the transmission rate negotiation with said OLT over the back-up fiber path:
 perform a first transmission rate negotiation with said ONU over the main fiber path;   if a first transmission rate is agreed upon between said ONU and said OLT during the first transmission rate negotiation, the processing circuit is configured to execute communication with said ONU using the first transmission rate over the main fiber path;   if the first transmission rate is not agreed upon between said ONU and said OLT during the first transmission rate negotiation, the processing circuit is configured to perform a second transmission rate negotiation with said ONU over the back-up fiber path; and   when a second transmission rate is agreed upon between said ONU and said OLT during the second transmission rate negotiation, the processing circuit is configured to execute communication with said ONU using the second transmission rate over the back-up fiber path.   
     
     
         101 . The OLT according to  claim 100 , wherein the first transmission rate negotiation with said ONU over the main fiber path results in the first transmission rate, which is lower than the transmission rate used before the detection of the fault in the main fiber path between said ONU and said OLT, and wherein the processing circuit is further configured to:
 compare the first transmission rate between said ONU and said OLT over the main fiber path with a pre-negotiated transmission rate between said ONU and said OLT over the back-up fiber path;   if the first transmission rate over the main fiber path is lower than the pre-negotiated transmission rate over the back-up fiber path, then the processing circuit is configured to execute communication to said ONU over the back-up fiber path using the pre-negotiated transmission rate; and   if the first transmission rate over the main fiber path is higher than the pre-negotiated transmission rate over the back-up fiber path, then the processing circuit is configured to execute communication to said ONU over the main fiber path using the first transmission rate.   
     
     
         102 . The OLT according to  claim 95 , wherein said OLT comprises a main OLT connected to said ONU via the main fiber path and the back-up fiber path connects said ONU to a back-up OLT. 
     
     
         103 . The OLT according to  claim 102 , wherein in case the back-up fiber path is to be used, the processing circuit is configured to send an instruction to said back-up OLT instructing said back-up OLT to initiate the transmission rate negotiation with said ONU over the back-up fiber path. 
     
     
         104 . The OLT according to  claim 102 , wherein the processing circuit is configured to send all negotiation messages, which are sent to said ONU during the transmission rate negotiation with said ONU over the main fiber path, also to said back-up OLT over the back-up fiber path. 
     
     
         105 . The OLT according to  claim 102 , wherein the processing circuit is further configured to receive a request from said ONU to establish communication with said back-up OLT, wherein the processing circuit is configured to send a request to said back-up OLT to execute communication to said ONU over the back-up fiber path. 
     
     
         106 . The OLT according to  claim 95 , wherein said OLT comprises a back-up OLT connected to said ONU via the back-up fiber path, and wherein the main fiber path connects said ONU to a main OLT. 
     
     
         107 . The OLT according to  claim 106 , wherein the processing circuit is further configured to:
 receive an indication that communication needs to be executed on a link between said back-up OLT and said ONU;   perform the transmission rate negotiation with said ONU over the back-up fiber path;   if the transmission rate negotiation does not results in the transmission rate to be used for executing communication between said ONU and said back-up OLT over the back-up fiber path, generate a link failure message; and   if the transmission rate is agreed upon between said ONU and said back-up OLT, then execute communication with said back-up OLT using the agreed upon transmission rate over the back-up fiber path.   
     
     
         108 . The back-up OLT according to  claim 107 , wherein the processing circuit receives the indication by receiving a request, from said main OLT, to initiate the transmission rate negotiation with said ONU over the back-up fiber path. 
     
     
         109 . The OLT according to  claim 107 , wherein the processing circuit receives the indication by receiving transmission rate negotiation messages from said ONU destined for said main OLT. 
     
     
         110 . The OLT according to  claim 107 , wherein the processing circuit performs the transmission rate negotiation between said back-up OLT and said ONU by confirming use of a pre-negotiated transmission rate between said ONU and said back-up OLT over the back-up fiber path. 
     
     
         111 . The OLT according to  claim 109 , wherein the processing circuit is further configured to determine, from the received transmission rate negotiation messages, that an un-recoverable link failure has occurred on the main fiber path between said ONU and said main OLT. 
     
     
         112 . The OLT according to  claim 111 , wherein the processing circuit is configured to, when determining from the received transmission rate negotiation messages that an un-recoverable link failure has occurred on the main fiber path, start a preset timer when one of the transmission rate negotiation messages is received from said ONU destined for said main OLT; and if the timer expires before the processing circuit receives an expected follow-up transmission rate negotiation message from said ONU destined for said main OLT, then the processing circuit is further configured to perform the transmission rate negotiation with said ONU over the back-up fiber path.