U.S. patent application number 14/117406 was filed with the patent office on 2014-07-17 for protection for fibre optic access networks.
This patent application is currently assigned to TELEFONAKTIEBOLAGET L M ERICSSON (PUBL). The applicant listed for this patent is Stefan Dahlfort, David Hood, Einar In De Betou, Peter Ohlen. Invention is credited to Stefan Dahlfort, David Hood, Einar In De Betou, Peter Ohlen.
Application Number | 20140199062 14/117406 |
Document ID | / |
Family ID | 44675521 |
Filed Date | 2014-07-17 |
United States Patent
Application |
20140199062 |
Kind Code |
A1 |
In De Betou; Einar ; et
al. |
July 17, 2014 |
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.
Inventors: |
In De Betou; Einar;
(Vallingby, SE) ; Dahlfort; Stefan; (Stockholm,
SE) ; Hood; David; (Palo Alto, CA) ; Ohlen;
Peter; (Stockholm, SE) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
In De Betou; Einar
Dahlfort; Stefan
Hood; David
Ohlen; Peter |
Vallingby
Stockholm
Palo Alto
Stockholm |
CA |
SE
SE
US
SE |
|
|
Assignee: |
TELEFONAKTIEBOLAGET L M ERICSSON
(PUBL)
Stockholm
SE
|
Family ID: |
44675521 |
Appl. No.: |
14/117406 |
Filed: |
May 17, 2011 |
PCT Filed: |
May 17, 2011 |
PCT NO: |
PCT/SE2011/050621 |
371 Date: |
November 13, 2013 |
Current U.S.
Class: |
398/5 |
Current CPC
Class: |
H04W 88/085 20130101;
H04B 10/25753 20130101; H04J 14/0287 20130101; H04W 24/04 20130101;
H04B 10/032 20130101 |
Class at
Publication: |
398/5 |
International
Class: |
H04B 10/032 20060101
H04B010/032 |
Claims
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.
Description
TECHNICAL FIELD
[0001] Embodiments herein relate generally to protection for fibre
optic access networks, and in particular to protection of
connection between an Optical Network Unit and an Optical Line
Terminal in a fibre optic access network.
BACKGROUND
[0002] Fibre optic access networks connect users to a switching
equipment of a network operator for processing and further
transport of data signals toward a core part of the network.
[0003] The access network can be either point-to-point (e.g.
Ethernet P2P) or point-to-multipoint fibre topology (e.g. Ethernet
Passive Optical Network, EPON, Gigabit Passive Optical Network,
GPON, or Wavelength Division Multiplexing Passive Optical Network,
WDM-PON). The communicating end terminals are referred to as
Optical Network Unit, ONU, at the customer site and Optical Line
Terminal, OLT, in a Central Office of the network operator.
[0004] To provide services over the access network, even in case of
a failure, a resilience mechanism is often implemented. This is
typically done by protecting a part of the network with a backup
network. Resilience in the fibre optic access network is becoming
increasingly important for at least two reasons. A converged fibre
optic access network needs to support high availability services
such as Voice over IP, Business service, Mobile Backhaul traffic,
etc. Network operators seek to achieve node consolidation, where
the network switching equipment is to a higher degree localized in
centralized nodes, to save on operational expenditures. This means
that more and more customers are served over the access network
infrastructure that connects the end user to the switching
equipment. This also means that potentially more and more end
customers could be affected by a single failure.
[0005] A way of protecting the central parts of the access network
is referred to as "dual homing". In this scenario, a main fibre
path between end users and the central office splits into a
protection fibre path that leads to a central office in an adjacent
service area.
[0006] When communication cannot be executed on the main fibre
path, the communication is instead executed on the protection fibre
path. However, the protection fibre path may not be capable of
supporting the same transmission rate as the main fibre path,
thereby requiring active equipment such as amplifiers along the
fibre link in order to amplify and restore the signal as it travels
along the fibre link such that it may be received by a receiving
end terminal. However, such active equipment is relatively costly
to operate and maintain. Further, the main fibre path and the
protection fibre path may not be of the same length, thereby
imposing different requirements on the main path and the protection
path.
[0007] In the case the protection fibre path is much longer than
the main fibre path, excessive requirements may be imposed on the
optical transceivers. Up to 100 km transmission distances may need
to be supported. Such distances are difficult to achieve with low
cost optics. Moreover, the link budget of access networks may be
impacted by additional losses such as connectors and impairments
such as bends etc. Thus, a fibre link may just be slightly too long
or associated with losses slightly too high for the optical
transceivers to handle. This may result in a hard stop where the
optical transceivers simply do not get the link up for
communication between the two end terminals, the ONU and the
OLT.
SUMMARY
[0008] It is an object of the exemplifying embodiments to address
at least some of the problems outlined above. In particular, it is
an object of the exemplifying embodiments to provide an Optical
Network Unit, ONU, an Optical Line Terminal, OLT, a method an ONU
and a method in an OLT for enabling the ONU to communicate over a
fibre optic access network comprising the ONU and the OLT. These
objects and others may be obtained by providing an ONU and an OLT
and a method in an ONU and an OLT according to the independent
claims attached below.
[0009] According to an aspect a method in an Optical Network Unit,
ONU, in a fibre optic access network, the fibre optic access
network comprising at least one Optical Line Terminal, OLT, and two
fibre paths through the fibre optic network, a main path and a
back-up path, connecting the ONU with the OLT for enabling the ONU
to communicate over the fibre optic access network is provided. The
method comprises detecting a fault in the main path between the ONU
and the OLT, during ongoing communication. The method also
comprises performing a transmission rate negotiation with the OLT
over the back-up path. When a transmission rate is agreed upon
between the ONU and the OLT during the transmission rate
negotiation with regard to communication over the back-up path, the
method comprises executing communication with the OLT using the
agreed transmission rate over the back-up path.
[0010] According to an aspect, a method in an Optical Line
Terminal, OLT, in a fibre optic access network, the fibre optic
access network comprising at least two fibre paths between the OLT
and an Optical Network Unit, ONU, a main fibre path and a back-up
fibre path, for enabling the ONU to communicate over the fibre
optic access network is provided. The method comprises detecting a
fault in the main fibre path between the OLT and the ONU, during
ongoing communication. The method also comprises performing a
transmission rate negotiation with the ONU over the back-up path
upon detecting the fault in the main fibre path. When a
transmission rate is agreed upon between the OLT and the ONU,
during the transmission rate negotiation with regard to
communication over the back-up fibre path, the method comprises
executing communication with the ONU using the agreed transmission
rate over the back-up fibre path.
[0011] According to an aspect, an Optical Network Unit, ONU, in a
fibre optic access network, the fibre optic access network
comprising at least one Optical Line Terminal, OLT, and two fibre
paths through the fibre optic network, a main path and a back-up
path, connecting the ONU with the OLT, the ONU being adapted to
enable the ONU to communicate over the fibre optic access network
is provided. The ONU comprises a processing unit adapted to detect
a fault in the main path between the ONU and the OLT during ongoing
communication. The processing unit is also adapted to perform a
transmission rate negotiation with the OLT over the back-up path.
When a transmission rate is agreed upon between the ONU and the OLT
during the transmission rate negotiation with regard to
communication over the back-up path, the processing unit is adapted
to execute communication with the OLT using the agreed transmission
rate over the back-up path.
[0012] According to an aspect, an Optical Line Terminal, OLT, in a
fibre optic access network, the fibre optic access network
comprising at least two fibre paths between the OLT and an Optical
Network Unit, ONU, a main fibre path and a back-up fibre path, the
OLT being adapted to enable the ONU to communicate over the fibre
optic access network is provided. The OLT comprises a processing
unit adapted to detect a fault in the main fibre path between the
OLT and the ONU, during ongoing communication. The processing unit
is also adapted to perform a transmission rate negotiation with the
ONU over the back-up path upon detecting the fault in the main
fibre path. When a transmission rate is agreed upon between the OLT
and the ONU, during the transmission rate negotiation with regard
to communication over the back-up fibre path, the processing unit
is adapted to execute communication with the ONU using the agreed
transmission rate over the back-up fibre path.
BRIEF DESCRIPTION OF DRAWINGS
[0013] Embodiments will now be described in more detail in relation
to the accompanying drawings, in which:
[0014] FIG. 1a is a flowchart of an exemplifying embodiment of a
method in ONU for enabling the ONU to communicate over the optic
fibre access network.
[0015] FIG. 1b is a flowchart of an exemplifying embodiment of a
method in an ONU for enabling the ONU to communicate over the optic
fibre access network
[0016] FIG. 2a is a flowchart of an exemplifying embodiment of a
method in an OLT enabling an ONU to communicate over the fibre
optic access network.
[0017] FIG. 2b is a flowchart of an exemplifying embodiment of a
method in an OLT for enabling the ONU to communicate over the optic
fibre access network.
[0018] FIG. 2c is a flowchart of an exemplifying embodiment of a
method in an OLT, wherein the OLT is a back-up OLT.
[0019] FIG. 2d is a flowchart of an exemplifying embodiment of a
method in an OLT, wherein the OLT is a back-up OLT.
[0020] FIG. 3a is a block diagram schematically illustrating an
exemplifying embodiment of an ONU and an OLT connected by two fibre
link paths.
[0021] FIG. 3b is a block diagram schematically illustrating an
exemplifying embodiment of an ONU, a main OLT connected to the ONU
via a main fibre link path, and a back-up OLT connected to the ONU
via a back-up fibre link path.
[0022] FIG. 3c schematically illustrates several ONUs connected to
an OLT via two fibre path links, a main fibre link and a back-up
fibre link.
[0023] FIG. 3d schematically illustrates several ONUs connected to
a main OLT via a main fibre link and connected to a back-up OLT via
a back-up fibre link.
[0024] FIG. 4 is a block diagram schematically illustrating an
exemplifying embodiment of a part of a passive optical network.
DETAILED DESCRIPTION
[0025] Briefly described, exemplifying embodiments of a method in
an Optical Network Unit, ONU, and a method in an Optical Line
Terminal, OLT, as well as an ONU and an OLT, are provided in a
fibre optic access network, the fibre optic access network
comprising at least one OLT and two fibre paths or links through
the fibre optic access network, a main fibre path and a back-up
fibre path, connecting the ONU with the at least one OLT for
enabling the ONU to communicate over the fibre optic access
network. The enabling of the ONU to communicate, over the fibre
optic access network, with the at least one OLT is ensured by, in
case a fault in the main fibre path or link between the ONU and the
OLT is detected, performing a transmission rate negotiation with
the OLT over the back-up path.
[0026] It shall be noted that the expression "fibre path" or simply
"path" will be used herein to refer to a fibre link or a fibre path
link.
[0027] An exemplifying embodiment of a method in an ONU in a fibre
optic access network, the fibre optic access network comprising at
least one OLT and two fibre paths or links through the fibre optic
access network, a main fibre path and a back-up fibre path,
connecting the ONU with the OLT for enabling the ONU to communicate
over the fibre optic access network will now be described with
reference to FIG. 1a. FIG. 1a is a flowchart of an exemplifying
embodiment of a method in ONU for enabling the ONU to communicate
over the optic fibre access network.
[0028] In this example, the method 100 in an ONU for enabling the
ONU to communicate over the optic fibre access network comprises
detecting 110 a fault in the main path between the ONU and the OLT,
during ongoing communication. The method also comprises performing
120 a transmission rate negotiation with the OLT over the back-up
path. When a transmission rate is agreed upon between the ONU and
the OLT during the transmission rate negotiation with regard to
communication over the back-up path, the method comprises executing
150 communications with the OLT using the agreed transmission rate
over the back-up path.
[0029] This exemplifying method has several advantages. By
providing a back-up path between the ONU and the at least one OLT,
a cost effective way to protect the optic fibre access network is
achieved. By providing a negotiation procedure, the back-up link
may be of lower "standard" and thus less expensive. By lower
standard is meant that it may not be capable of supporting the same
transmission rates as the main fibre link. By providing the
negotiation procedure, communication may still be possible, but at
a reduced rate. In an example the two fibre links are not of the
same length, e.g. due to running between the ONU and the OLT along
different routes or paths. Consequently, they may not be able to
support the same transmission rates even though the fibre links
themselves may be of the same quality, since the longer fibre path
may typically not be capable of supporting transmission rates as
high as the shorter fibre path. It may be desirable to make the two
fibre paths run along different routes in order to further increase
robustness. In case one fibre link should be broken due to a cut,
the other fibre cable will not be subject to the same cut if it
runs along a different path. In such cases, the negotiation of
transmission rates enables communication to be executed on the
back-up fibre path in case the back-up fibre path does not support
communication at the same transmission rate as the main fibre
path.
[0030] According to an embodiment, the detecting of a fault in the
main fibre path between the ONU and the OLT comprises receiving an
alarm indicating the fault.
[0031] In another example, the detection of a fault in the path
between the ONU and the OLT comprises receiving statistical
information from an FEC decoder block from which the ONU determines
that a fault has occurred.
[0032] This means that in one example, the ONU receives an alarm,
e.g. from the OLT and the performing 120 of a transmission rate
negotiation with the OLT over the back-up path is initiated by the
OLT. In another example, the ONU detects the fault in the main path
between the ONU and the OLT and initiates the performing 120 of a
transmission rate negotiation with the OLT over the back-up
path.
[0033] According to an embodiment, the alarm is one of "loss of
signal", "loss of synchronization", "low signal level", "loss of
data structure" and "high bit error rate".
[0034] An example of "loss of data structure" is loss of bytes,
loss of words, loss of blocks or loss of frames. All of these
alarms described above will indicate to the ONU a fault has
occurred on the main fibre path toward the OLT and will trigger the
ONU to perform a transmission rate negotiation with the OLT over
the back-up path.
[0035] According to still an embodiment, the method in the ONU
further comprises negotiating 140 one or more further parameters to
be used for communication on the back-up fibre path between the ONU
and the OLT.
[0036] There are other parameters, which when used for
communication on a fibre path will affect the transmission rate or
the probability of being able to successfully communicate at a
certain transmission rate without excess bit error rate. Some
examples of such parameters are Forward Error Correction, FEC,
cryptographic capabilities and usage, modulation format and
parameters.
[0037] According to an embodiment, the transmission rate
negotiation with the OLT comprises confirming use of a
pre-negotiated transmission rate with regard to communication over
the back-up path.
[0038] In an example, the ONU performs the transmission rate
negotiation with the OLT over the back-up path before any fault is
detected in the main fibre path. This means that in case a failure
occurs in the main fibre path, the ONU is able to quickly switch
over to the back-up path. In one example, the transmission rate
over the back-up fibre path is negotiated before any session is
ongoing between the ONU and the OLT over the main fibre path and
stored within the ONU. In another example, the transmission rate is
negotiated over the back-up fibre path when communication is
ongoing over the main fibre path.
[0039] FIG. 1b is a flowchart of an exemplifying embodiment of a
method in ONU for enabling the ONU to communicate over the optic
fibre access network.
[0040] According to an exemplifying embodiment, wherein upon
detecting 110 a fault in the main link between the ONU and the OLT,
the method further comprises, before performing 120 a transmission
rate negotiation with the OLT over the back-up fibre path:
performing 111 a first transmission rate negotiation with the OLT
over the main path. If a transmission rate is agreed upon between
the ONU and the OLT during the first transmission rate negotiation
111, the method comprises executing 155 communications with the OLT
using the agreed transmission rate over the main path. If a
transmission rate is not agreed upon between the ONU and the OLT
during the first transmission rate negotiation 111, the method
comprises performing 120 a second transmission rate negotiation
with the OLT over the back-up path. When a transmission rate is
agreed upon between the ONU and the OLT during the second
transmission rate negotiation, the method comprises executing 150
communications with the OLT using the agreed transmission rate over
the backup path.
[0041] In this embodiment, it is preferred to use the main fibre
path for executing communication with the OLT. In such a case, the
ONU first attempts to re-establish connection with the OLT via the
main fibre path and tries to negotiate a transmission rate with the
OLT over the main fibre path. This is illustrated in FIG. 1b by
step 111. If the negotiation with the OLT over the main fibre path
is not successful, then the method continues to step 120 which is
described in FIG. 1a. In this exemplifying embodiment, if the
negotiation is successful then communication is executed with the
OLT over the main fibre path as indicated in step 155.
[0042] In an example, the method comprises determining the severity
of the fault indicated in the alarm. For example, "loss of signal"
will cause the ONU to directly initiate transmission rate
negotiation with the OLT over the back-up path, whereas for example
"low signal level" or "high bit error rate" will cause the ONU to
first negotiate a new transmission rate over the main fibre, which
transmission rate probably will be lower than the currently used
transmission rate, before initiating transmission rate negotiation
with the OLT over the back-up fibre path. In this example, in case
the transmission rate negotiation with the OLT over the main fibre
path is successful, the ONU compares the negotiated transmission
rate over the main fibre path to a pre-negotiated transmission rate
over the back-up fibre path, and depending on the result of this
comparison the ONU decides to either execute communication to the
OLT over the main fibre path using the negotiated transmission rate
or to execute communication to the OLT over the back-up fibre path
using the pre-negotiated transmission rate
[0043] According to still an embodiment, the first transmission
rate negotiation 111 with the OLT over the main path results in a
transmission rate which is lower than the transmission rate used
before the detection of the fault in the main fibre path between
the ONU and the OLT. The method then further comprises comparing
114 the negotiated transmission rate between the ONU and the OLT
over the main path with the pre-negotiated transmission rate
between the ONU and the OLT over the backup path. If the negotiated
transmission rate over the main path is lower than the
pre-negotiated transmission rate over the back-up path, the method
comprises executing 116 communications to the OLT over the backup
path using the pre-negotiated transmission rate. If the negotiated
transmission rate over the main path is higher than the
pre-negotiated transmission rate over the back-up path, then the
method comprises executing 155 communications to the OLT over the
main path using the negotiated transmission rate.
[0044] If the first transmission rate negotiation 111 with the OLT
over the main path is successful, then the negotiated transmission
rate can be the same, higher or lower than the transmission rate
used before the detection of the fault in the main fibre path. If
the negotiated transmission rate is the same or higher than the
transmission rate used before the detection of the fault in the
main fibre path, then this negotiated transmission rate is used
when executing 155 communication to the OLT over the main fibre
path. This is illustrated in FIG. 1b by step 113, i.e. checking if
the negotiated transmission rate is lower than the transmission
rate used before the detection of the fault in the main fibre
path.
[0045] If the negotiated transmission rate is lower than the
transmission rate used before the detection of the fault in the
main fibre path, then it might be advantageous to execute
communication over the back-up fibre path. It may be that the
negotiated transmission rate over the main fibre path is lower than
the transmission rate used before the detection of the fault in the
main fibre path but still higher than the pre-negotiated
transmission rate over the back-up path.
[0046] To find this out, the method comprises comparing 114 the
negotiated rate to a pre-negotiated transmission rate over the
back-up path. As was described above, the transmission rate over
the back-up path is in an example negotiated beforehand with the
OLT.
[0047] If the negotiated transmission rate over the main path is
lower than the pre-negotiated transmission rate over the back-up
path, the method comprises executing 116 communications to the OLT
over the backup path using the pre-negotiated transmission rate.
If, on the other hand, the negotiated transmission rate over the
main path is higher than the pre-negotiated transmission rate over
the back-up fibre path, the method comprises executing 155
communications to the OLT over the main path using the negotiated
transmission rate.
[0048] According to an embodiment, the ONU communicates with two
physically distinct OLTs over the fibre optic network, a main OLT
connected to the ONU via the main fibre path and a back-up OLT
connected to the ONU via the back-up fibre path.
[0049] According to still an embodiment, all negotiation messages
which are sent to the main OLT in the transmission rate negotiation
with the ONU over the main fibre path are also sent to the back-up
OLT over the back-up fibre path.
[0050] In case the ONU communicates with two separate OLTs over the
fibre optic network, a main OLT connected to the ONU via the main
fibre path and a back-up OLT connected to the ONU via the back-up
fibre path, sending all transmission rate negotiation messages also
to the back-up OLT, which transmission rate negotiation messages
are destined to the main OLT, enables the back-up OLT to "monitor"
the main OLT. In other words, the back-up OLT can deduce from the
transmission negotiation messages sent from the ONU to the main
OLT, if the transmission rate negotiation is successful. In case
the transmission rate negotiation is not successful, the back-up
OLT is in this way enabled to take action as will be described
below.
[0051] According to still an embodiment of the method in the ONU,
the transmission rate negotiation comprises first synchronising the
ONU and the backup OLT before the negotiation of transmission rate
is performed.
[0052] An exemplifying embodiment in an Optical Line Terminal, OLT,
in a fibre optic access network, the fibre optic access network
comprising at least two fibre paths between the OLT and an Optical
Network Unit, ONU, a main fibre path and a back-up fibre path, for
enabling the ONU to communicate over the fibre optic access network
will now be described with reference to FIG. 2a.
[0053] FIG. 2a is a flowchart of an exemplifying embodiment of a
method in an OLT enabling an ONU to communicate over the fibre
optic access network.
[0054] According to an exemplifying embodiment of the method 200 in
the OLT, the method comprises detecting 210 a fault in the main
fibre path between the OLT and the ONU, during ongoing
communication. The method also comprises performing 220 a
transmission rate negotiation with the ONU over the back-up path
upon detecting the fault in the main fibre path. When a
transmission rate is agreed upon between the OLT and the ONU,
during the transmission rate negotiation with regard to
communication over the back-up fibre path, the method comprises
executing 231 communications with the ONU using the agreed
transmission rate over the back-up fibre path.
[0055] This exemplifying method has several advantages. By
providing a back-up path between the ONU and the OLT, a cost
effective way to protect the optic fibre access network is
achieved. By providing a negotiation procedure, the back-up link
may be of lower "standard" and thus less expensive. By lower
standard is meant that it may not be capable of supporting the same
transmission rates as the main fibre link. By providing the
negotiation procedure, communication may still be possible, but at
a reduced rate. In an example the two fibre links are not of the
same length, e.g. due to running between the ONU and the OLT along
different routes or paths or e.g. due to being connected to
separate physical OLTs. Consequently, they may not be able to
support the same transmission rates even though the fibre links
themselves may be of the same quality, since the longer fibre path
may typically not be capable of supporting transmission rates as
high as the shorter fibre path. It may be desirable to make the two
fibre paths run along different routes in order to further increase
robustness. In case one fibre link should be broken due to a cut,
the other fibre cable will not be subject to the same cut if it
runs along a different route. In such cases, the negotiation of
transmission rates enables communication to be executed on the
back-up fibre path in case the back-up fibre path does not support
communication at the same transmission rate as the main fibre
path.
[0056] According to an embodiment, the detection of a fault in the
main fibre path between the OLT and the ONU comprises receiving an
alarm indicating the fault.
[0057] This means that in one example, the OLT receives an alarm,
e.g. from the ONU and the performing 220 of a transmission rate
negotiation with the ONU over the back-up path is initiated by the
ONU. In another example, the OLT detects the fault in the main path
between the OLT and the ONU and initiates the performing 220 of a
transmission rate negotiation with the OLT over the back-up
path.
[0058] In another example, the detection of a fault in the path
between the OLT and the ONU comprises receiving statistical
information from an FEC decoder block from which the OLT determines
that link performance has degraded to unacceptable levels.
[0059] According to an embodiment, the alarm is one of "loss of
signal", "loss of synchronization", "low signal level", "loss of
data structure" and "high bit error rate".
[0060] An example of "loss of data structure" is loss of bytes,
loss of words, loss of blocks or loss of frames. All of these
alarms described above will indicate to the OLT a fault has
occurred on the main fibre path toward the ONU and will trigger the
OLT to perform a transmission rate negotiation with the ONU over
the back-up path. It is understood that, in the event that main and
backup OLTs are physically separate equipment, a communications
link between them enables them to exchange the necessary status and
event information.
[0061] According to an embodiment, the method in the OLT further
comprises negotiating 230 one or more further parameters to be used
for communication on the back-up fibre path between the OLT and the
ONU.
[0062] There are other parameters, which when used for
communication on a fibre path will affect the transmission rate or
the probability of being able to successfully communicate at a
certain transmission rate without excess bit error rate. Some
examples of such parameters are Forward Error Correction, FEC,
cryptographic capabilities and usage, modulation format and
parameters.
[0063] According to an embodiment, the transmission rate
negotiation with the ONU comprises confirming use of a
pre-negotiated transmission rate with regard to communication over
the back-up path.
[0064] FIG. 2b is a flowchart of an exemplifying embodiment of a
method in an OLT for enabling the ONU to communicate over the optic
fibre access network.
[0065] According to an exemplifying embodiment, wherein upon
detecting a fault in the main link between the OLT and the ONU, the
method further comprises before performing 210 a first transmission
rate negotiation with the ONU over the backup path, performing 211
a first transmission rate negotiation with the ONU over the main
fibre path. If a transmission rate is agreed upon between the ONU
and the OLT during the first transmission rate negotiation, the
method comprises executing 232 communications with the ONU using
the agreed transmission rate over the main path. If a transmission
rate is not agreed upon between the ONU and the OLT during the
first transmission rate negotiation, the method comprises
performing 210 a second transmission rate negotiation with the ONU
over the back-up path. When a transmission rate is agreed upon
between the ONU and the OLT during the second transmission rate
negotiation, the method comprises executing 231 communications with
the ONU using the agreed transmission rate over the backup
path.
[0066] In this embodiment, it is preferred to use the main fibre
path for executing communication with the ONU. In such a case, the
OLT first attempts to re-establish connection with the ONU via the
main fibre path and tries to negotiate a transmission rate with the
ONU over the main fibre path. This is illustrated in FIG. 2b by
step 211. If the negotiation with the ONU over the main fibre path
is not successful, then the method continues to step 220 which is
described in FIG. 2a. In this exemplifying embodiment, if the
negotiation is successful then communication is executed with the
ONU over the main fibre path as indicated in step 232.
[0067] According to an embodiment, the first transmission rate
negotiation 211 with the ONU over the main path results in a
transmission rate which is lower than the transmission rate used
before the detection of the fault in the fibre path between the ONU
and the OLT, the method further comprising comparing 214 the
negotiated transmission rate between the ONU and the OLT over the
main path with the pre-negotiated transmission rate between the ONU
and the OLT over the backup path. If the negotiated transmission
rate over the main path is lower than the pre-negotiated
transmission rate over the back-up path, the method comprises
executing 216 communications to the ONU over the backup path using
the pre-negotiated transmission rate. If the negotiated
transmission rate over the main path is higher than the
pre-negotiated transmission rate over the back-up path, the method
comprises executing 232 communications to the ONU over the main
path using the negotiated transmission rate.
[0068] If the first transmission rate negotiation 211 with the ONU
over the main path is successful, then the negotiated transmission
rate can be the same, higher or lower than the transmission rate
used before the detection of the fault in the main fibre path. If
the negotiated transmission rate is the same or higher than the
transmission rate used before the detection of the fault in the
main fibre path, then this negotiated transmission rate is used
when executing 232 communication to the ONU over the main fibre
path. This is illustrated in FIG. 2b by step 213, i.e. checking if
the negotiated transmission rate is lower than the transmission
rate used before the detection of the fault in the main fibre
path
[0069] If the negotiated transmission rate is lower than the
transmission rate used before the detection of the fault in the
main fibre path, then it might be advantageous to execute
communication over the back-up fibre path. It may be that the
negotiated transmission rate over the main fibre path is lower than
the transmission rate used before the detection of the fault in the
main fibre path but still higher than the pre-negotiated
transmission rate over the back-up path.
[0070] To find this out, the method comprises comparing 214 the
negotiated rate to a pre-negotiated transmission rate over the
back-up path. As was described above, the transmission rate over
the back-up path is in an example negotiated beforehand with the
ONU.
[0071] If the negotiated transmission rate over the main path is
lower than the pre-negotiated transmission rate over the back-up
path, the method comprises executing 216 communications to the ONU
over the backup path using the pre-negotiated transmission rate.
If, on the other hand, the negotiated transmission rate over the
main path is higher than the pre-negotiated transmission rate over
the back-up fibre path, the method comprises executing 232
communications to the ONU over the main path using the negotiated
transmission rate.
[0072] According to still an embodiment, the OLT is a main OLT
connected to the ONU via the main fibre path and the back-up fibre
path connects the ONU and a back-up OLT.
[0073] In this case, the main OLT and the back-up OLT are
physically different entities. In an example, they are located in
the same geographical location and in another example, they are
located at two different geographical locations.
[0074] In an example of the method in a main OLT, wherein in case
the back-up fibre path is to be used, the method comprises sending
an instruction to the back-up OLT, the instruction instructing the
back-up OLT to initiate transmission rate negotiation with the ONU
over the back-up fibre path.
[0075] In this example, the main OLT determines, e.g. as explained
above in step 216 that the communication is to be executed over the
back-up fibre path. The main OLT then sends a signal or otherwise
instructs the back-up OLT that it should execute communication to
the ONU over the back-up fibre path.
[0076] In still an example of the method in a main OLT, all
negotiation messages which are sent to the ONU in the transmission
rate negotiation with the ONU over the main fibre path are also
sent to the back-up OLT.
[0077] In yet an example of the method in a main OLT, the method
further comprises receiving a request from the 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 the ONU over
the back-up fibre path.
[0078] This situation may arise when it is the ONU that determines
that the back-up fibre path is to be used to execute communication
to an OLT, in this case the back-up OLT. Then the ONU sends a
request to the main OLT where the ONU requests the communication to
be executed over the back-up path with the back-up OLT. Then the
main OLT in turn sends a request to the back-up OLT to execute
communication to the ONU over the back-up fibre path.
[0079] FIG. 2c is a flowchart of an exemplifying embodiment of a
method in an OLT, wherein the OLT is a back-up OLT.
[0080] According to an embodiment of the method in the OLT, the OLT
is a back-up OLT connected to the ONU via the back-up fibre path
and the main fibre path connects the ONU and a main OLT (not shown
in FIG. 2c).
[0081] In an example of the method in a back-up OLT, the method
comprises receiving 240 an indication that communication needs to
be executed on a link between the back-up OLT and the ONU, and
performing 250 transmission rate negotiation with the ONU over the
back-up fibre path. If the transmission rate negotiation does not
result in an agreed transmission rate to be used for executing
communication between the ONU and the back-up OLT over the back-up
fibre path, then the method comprises generating 257 a link failure
message. If a transmission rate is agreed upon between the ONU and
the back-up OLT, then the method comprises executing 256
communication with the back-up OLT using the agreed transmission
rate over the back-up fibre path.
[0082] In case the transmission rate negotiation fails, it is not
possible to execute communication at any transmission rate that is
supported by both the ONU and the OLT. In such a case a link
failure message is generated 257.
[0083] In yet an example of the method in a back-up OLT, the method
comprises receiving 240 the indication comprises receiving a
request, from the main OLT, to initiate transmission rate
negotiation with the ONU over the back-up fibre path.
[0084] As has been described above, in case it is the ONU that
determines that the back-up fibre path is to be used to execute
communication to an OLT, in this case the back-up OLT, then the ONU
sends a request to the main OLT where the ONU requests the
communication to be executed over the back-up path with the back-up
OLT. Then the main OLT in turn sends a request to the back-up OLT
to execute communication to the ONU over the back-up fibre
path.
[0085] FIG. 2d is a flowchart of an exemplifying embodiment of a
method in an OLT, wherein the OLT is a back-up OLT.
[0086] In yet an example of the method in a back-up OLT, wherein
receiving 240 the indication comprises receiving 241 transmission
rate negotiation messages from the ONU destined for the main
OLT.
[0087] This means that the indication which is received 240 to
establish communication with the ONU comprises receiving a copy of
all transmission rate negotiations messages which are sent to the
main OLT.
[0088] In still an example, of the method in a back-up OLT, the
method further comprises determining, from the received
transmission rate negotiation messages from the ONU, that an
un-recoverable link failure has occurred on the main fibre path
between the ONU and the main OLT.
[0089] This means that since the back-up OLT receives a copy of all
transmission rate negotiations messages which are sent to the main
OLT, the back-up OLT can deduce from the received messages if the
transmission rate negotiation between the ONU and the main OLT is
being successful or not.
[0090] In a further example, of the method in a back-up OLT, the
transmission rate negotiation between the back-up OLT and the ONU
over the back-up fibre path comprises confirming use of a
pre-negotiated transmission rate between the ONU and the back-up
OLT over the back-up fibre path
[0091] In a further example, of the method in a back-up OLT,
wherein the determining from the received transmission rate
negotiation messages from the ONU or the main OLT that an
un-recoverable link failure has occurred on the main fibre path
comprises starting 242 a preset timer when a transmission rate
negotiation message is received 241 from the ONU destined for the
main OLT; and if the timer expires before receiving an expected
follow-up transmission rate negotiation message from the ONU
destined for the main OLT, then performing 250 transmission rate
negotiation with the ONU over the back-up path.
[0092] As transmission rate negotiation messages from the ONU
destined for the main OLT are also received by the back-up OLT, the
back-up OLT starts a preset timer 242 as it receives a transmission
rate negotiation message. If the timer expires before any other
transmission rate negotiation message is received then the back-OLT
determines that the transmission rate negotiation was unsuccessful.
Likewise, if the back-up OLT can deduce that communication cannot
be executed on the main fibre path due to an un-recoverable link
failure has occurred on the main fibre path between the ONU and the
main OLT, the back-up OLT performs 250 transmission rate
negotiation with the ONU over the back-up fibre path.
[0093] However, if a subsequent transmission negotiation message
from the ONU destined for the main OLT is received 244 by the
back-up OLT or a transmission negotiation message from the main OLT
destined for the ONU is received 244 by the back-up OLT before the
timer expires, then the back-up OLT can determine if the main link
is not up but transmission rate negotiation is still ongoing on the
main fibre path and the back-up OLT again starts 242 the preset
timer.
[0094] The back-up OLT can detect 244 that communication is
executed on the main fibre path between the ONU and the main OLT,
e.g. by receiving a confirmation message from either the ONU or the
main OLT. If this is the case, the method is ended 246, meaning
that the back-up OLT will go back to a stand-by mode.
[0095] Exemplifying embodiments of an ONU and an OLT in a fibre
optic access network, the ONU and the OLT being adapted to enable
the ONU to communicate with the OLT will now be described with
reference to FIGS. 3a-d. The ONU and the OLT have the same objects,
advantages and technical features as the methods therein described
above. Therefore, the ONU and the OLT will be described briefly in
order to avoid unnecessary repetition.
[0096] FIG. 3a is a block diagram schematically illustrating an
exemplifying embodiment of an ONU and an OLT connected by two fibre
link paths.
[0097] It will be appreciated that the OLT in an example is adapted
to comprise two roles, a main role and a backup role, and that
these roles may be implemented either in a single OLT equipment or
in two distinct OLT equipments.
[0098] In FIG. 3a, the ONU and the OLT are illustrated having
transceiver arrangements 317 and 327. These are adapted to enable
the ONU 310 and the OLT 320 to communicate with each other via a
main fibre link or fibre path; or a back-up fibre link or fibre
path. A transceiver arrangement may comprise one or more
transmitters and one or more receivers.
[0099] The OLT is adapted to perform a main OLT role or function
and a backup OLT role or function and these roles or functions may
be implemented either in a single OLT equipment or in two distinct
OLT equipments.
[0100] According to an exemplifying embodiment of the Optical
Network Unit, ONU 310, in a fibre optic access network, the fibre
optic access network comprising at least one Optical Line Terminal,
OLT, 320 and two fibre paths through the fibre optic network, a
main path and a back-up path, connecting the ONU 310 with the OLT
320, the ONU being adapted to enable the ONU 310 to communicate
over the fibre optic access network, the ONU 310 comprises a
processing unit 311 adapted to detect a fault in the main path
between the ONU 310 and the OLT 320, during ongoing communication.
The processing unit 311 is also adapted to perform a transmission
rate negotiation with the OLT 320 over the back-up path. When a
transmission rate is agreed upon between the ONU 310 and the OLT
320 during the transmission rate negotiation with regard to
communication over the back-up path, the processing unit 311 is
adapted to execute communication with the OLT 320 using the agreed
transmission rate over the back-up path.
[0101] According to an embodiment of the Optical Network Unit, the
detection of a fault in the main fibre path between the ONU 310 and
the OLT 320 comprises receiving an alarm indicating the fault.
[0102] The ONU is adapted to detect the fault, e.g. by the
transceiver arrangement 317. The transceiver arrangement 317 is
then adapted to generate an alarm which is sent to the processing
unit. Hence, the detection of a fault in the main fibre path
between the ONU 310 and the OLT 320 by reception of an alarm
indicating the fault means that the processing unit 311 receives
the alarm from the transceiver arrangement 317.
[0103] In an example, the transceiver arrangement 317 is adapted to
perform comprises signal recovery, framing alignment, error
checking and correcting functions.
[0104] In yet an embodiment, the alarm is one of "loss of signal",
"loss of synchronization", "low signal level", "loss of data
structure" and "high bit error rate".
[0105] According to still an embodiment, the processing unit 311 is
further adapted to negotiate one or more further parameters to be
used for communication on the back-up fibre path between the ONU
310 and the OLT 320.
[0106] According to an embodiment, the transmission rate
negotiation with the OLT 320 comprises confirming use of a
pre-negotiated transmission rate with regard to communication over
the back-up path.
[0107] In still an embodiment, wherein upon detecting a fault in
the main link between the ONU and the OLT, the processing unit 311
is further adapted to, before performing a transmission rate
negotiation with the OLT 320 over the back-up fibre path, perform a
first transmission rate negotiation with the OLT 320 over the main
path. If a transmission rate is agreed upon between the ONU 310 and
the OLT 320 during the first transmission rate negotiation, the
processing unit 311 is adapted to execute communication with the
OLT 320 using the agreed transmission rate over the main path. If a
transmission rate is not agreed upon between the ONU 310 and the
OLT 320 during the first transmission rate negotiation, the
processing unit 311 is adapted to perform a second transmission
rate negotiation with the OLT 320 over the back-up path. When a
transmission rate is agreed upon between the ONU 310 and the OLT
320 during the second transmission rate negotiation, the processing
unit 311 is adapted to execute communication with the OLT using the
agreed transmission rate over the backup path.
[0108] In yet an embodiment, wherein the first transmission rate
negotiation with the OLT 320 over the main path results in a
transmission rate which is lower than the transmission rate used
before the detection of the fault in the main fibre path between
the ONU 310 and the OLT 320, the processing unit 311 is further
adapted to compare the negotiated transmission rate between the ONU
310 and the OLT 320 over the main path with the pre-negotiated
transmission rate between the ONU 310 and the OLT 320 over the
backup path. If the negotiated transmission rate over the main path
is lower than the pre-negotiated transmission rate over the back-up
path, then the processing unit 311 is adapted to execute
communication to the OLT 320 over the backup path using the
pre-negotiated transmission rate. If the negotiated transmission
rate over the main path is higher than the pre-negotiated
transmission rate over the back-up path, then the processing unit
311 is adapted to execute communication to the OLT 320 over the
main path using the negotiated transmission rate.
[0109] FIGS. 3b and 3d illustrate an example wherein an ONU 310
communicates with two separate OLTs 330 and 340.
[0110] According to an embodiment, the ONU 310 is adapted to
communicate with two separate OLTs over the fibre optic network, a
main OLT 330 connected to the ONU via the main fibre path and a
back-up OLT 340 connected to the ONU via the back-up fibre
path.
[0111] As can be seen in the FIGS. 3b and 3d, the main OLT 330 and
the back-up OLT are each connected to an ONU 310 by means of two
fibre paths, a main fibre path and a back-up fibre path. Typically,
the main OLT 330 serves a first set of ONUs and the back-up OLT
serves other ONUs (not shown) for which ONUs the back-up OLT is a
main OLT. Likewise the main OLT 330 may act as a back-up OLT for
still other ONUs (not shown) being connected to a still further OLT
(not shown).
[0112] FIGS. 3c and 3d also illustrate that the main fibre path and
the back-up fibre path can be shared by a plurality of ONUs 310. In
the embodiment illustrated in FIGS. 3c and 3d, various passive or
semi-passive devices, e.g. power splitters, wavelength filters
and/or optical switches, 350 and 360 could be used to enable
several ONUs 310 sharing the respective main and back-up fibre
paths.
[0113] It shall be pointed out, that in case there should be any
active equipment in points 350 and 360, no active equipment is
present between the point 360 and the respective main OLT 330 or
the back-up OLT 440.
[0114] In yet another example, the redundant links go all the way
to the ONUs 310, such that splitting nodes 350, 360 exist
separately for each of main and backup links. In that
configuration, an ONU 310 is adapted to distinguish and negotiate
main and backup independently.
[0115] In yet another example, not illustrated in FIG. 3d, there
are N number of main fibre links, one for each of the N sets of
ONUs 310 where a set is either a single ONU or multiple ONUs, but
just one back-up fibre running from the point 360 to the back-up
OLT 340.
[0116] According to still an embodiment, the ONU 310 is adapted to
send all negotiation messages, which are sent to the main OLT 330
in the transmission rate negotiation with the ONU 310 over the main
fibre path, also to the back-up OLT 340 via the back-up fibre
path.
[0117] In yet an embodiment, the processing unit 311 is adapted to
synchronise the ONU 310 and the OLT 320, 330, 340 before performing
negotiation of transmission rate.
[0118] According to an exemplifying embodiment of an Optical Line
Terminal, OLT 320, in a fibre optic access network, the fibre optic
access network comprising at least two fibre paths between the OLT
and an Optical Network Unit, ONU, (310) a main fibre path and a
back-up fibre path, the OLT being adapted to enable the ONU to
communicate over the fibre optic access network, the OLT comprises
a processing unit 321 adapted to detect a fault in the main fibre
path between the OLT 320 and the ONU 310, during ongoing
communication. The processing unit 321 is also adapted to perform a
transmission rate negotiation with the ONU 310 over the back-up
path upon detecting the fault in the main fibre path. When a
transmission rate is agreed upon between the OLT 320 and the ONU
310, during the transmission rate negotiation with regard to
communication over the back-up fibre path, the processing unit 321
is adapted to execute communication with the ONU 310 using the
agreed transmission rate over the back-up fibre path.
[0119] According to an embodiment of the OLT 320, the detection of
a fault in the main fibre path between the OLT 320 and the ONU 310
comprises receiving an alarm indicating the fault.
[0120] According to still an embodiment, the alarm is one of "loss
of signal", "loss of synchronization", "low signal level", "loss of
data structure" and "high bit error rate".
[0121] In yet an embodiment, the processing unit 321 is further
adapted to negotiate one or more further parameters to be used for
communication on the back-up fibre path between the OLT 320 and the
ONU 310.
[0122] In a further embodiment, the transmission rate negotiation
with the ONU 310 comprises confirming use of a pre-negotiated
transmission rate with regard to communication over the back-up
path.
[0123] According to an embodiment, wherein upon detecting a fault
in the main link between the ONU 310 and the OLT 320, the
processing unit 321 is further adapted to, before performing a
first transmission rate negotiation with the OLT 320 over the
back-up path, perform a first transmission rate negotiation with
the ONU 310 over the main fibre path. If a transmission rate is
agreed upon between the ONU 310 and the OLT 320 during the first
transmission rate negotiation, the processing unit 321 is adapted
to execute communication with the ONU 310 using the agreed
transmission rate over the main path. If a transmission rate is not
agreed upon between the ONU 310 and the OLT 320 during the first
transmission rate negotiation, the processing unit 321 is adapted
to perform a second transmission rate negotiation with the ONU 310
over the back-up path. When a transmission rate is agreed upon
between the ONU 310 and the OLT 320 during the second transmission
rate negotiation, the processing unit 321 is adapted to execute
communication with the ONU 310 using the agreed transmission rate
over the backup path.
[0124] According to still an embodiment, of the OLT 320, the first
transmission rate negotiation with the ONU 310 over the main path
results in a transmission rate which is lower than the transmission
rate used before the detection of the fault in the link between the
ONU 310 and the OLT 320, the processing unit 321 is further adapted
to compare the negotiated transmission rate between the ONU 310 and
the OLT 320 over the main path with the pre-negotiated transmission
rate between the ONU 310 and the OLT 320 over the backup path. If
the negotiated transmission rate over the main path is lower than
the pre-negotiated transmission rate over the back-up path, then
the processing unit 321 is adapted to execute communication to the
ONU 310 over the backup path using the pre-negotiated transmission
rate. If the negotiated transmission rate over the main path is
higher than the pre-negotiated transmission rate over the back-up
path, then the processing unit 321 is adapted to execute
communication to the ONU 310 over the main path using the
negotiated transmission rate.
[0125] In still a further embodiment, the OLT 330 is a main OLT 330
connected to the ONU 310 via the main fibre path and the back-up
fibre path connects the ONU 310 and a back-up OLT 340.
[0126] In this case, the main OLT and the back-up OLT are
physically different entities. In an example, they are located in
the same geographical location and in another example, they are
located at two different geographical locations.
[0127] In an example of the main OLT 330, wherein in case the
back-up fibre path is to be used, the processing unit 331 is
adapted to send an instruction to the back-up OLT 340, the
instruction instructing the back-up OLT 340 to initiate
transmission rate negotiation with the ONU 310 over the back-up
fibre path.
[0128] In yet an example of the main OLT 330, the processing unit
331 is adapted to send all negotiation messages, which are sent to
the ONU 310 in the transmission rate negotiation with the ONU 310
over the main fibre path, also to the back-up OLT 340 over the
back-up fibre path.
[0129] In still an example of the main OLT 330, the processing unit
331 is adapted to receive an alarm indicating a severe failure,
wherein communication will not be able to be restored on the main
fibre path at any transmission rate. Then the processing unit 331
is adapted to order to the back-up OLT 340 to initiate transmission
rate negotiation with the ONU over the back-up path.
[0130] In still a further example of the main OLT 330, the
processing unit 331 is further adapted to receive a request from
the ONU 310 to establish communication with the back-up OLT 340,
wherein the processing unit 331 is adapted to send a request to the
back-up OLT 340 to execute communication to the ONU 310 over the
back-up fibre path.
[0131] According to an embodiment, the OLT 340 is a back-up OLT 340
connected to the ONU 310 via the back-up fibre path and the main
fibre path connects the ONU 310 and a main OLT 330.
[0132] In an example of the back-up OLT 340, the processing unit
341 is further adapted to receive an indication that communication
needs to be executed on a link between the back-up OLT 340 and the
ONU (310), and to perform transmission rate negotiation with the
ONU 310 over the back-up fibre path. If the transmission rate
negotiation does not results in an agreed transmission rate to be
used for executing communication between the ONU 310 and the
back-up OLT 340 over the back-up fibre path, then the processing
unit 341 is adapted to generate a link failure message. If a
transmission rate is agreed upon between the ONU 310 and the
back-up OLT 340, then the processing unit 341 is adapted to execute
communication with the back-up OLT 340 using the agreed
transmission rate over the back-up fibre path.
[0133] In still an example of the back-up OLT 340, the reception of
the indication comprises receiving a request, from the main OLT
330, to initiate transmission rate negotiation with the ONU 310
over the back-up fibre path.
[0134] In still a further example of the back-up OLT 340, the
reception of the indication comprises receiving transmission rate
negotiation messages from the ONU 310 destined for the main OLT
330.
[0135] In yet an example of the back-up OLT 340, the processing
unit 341 is further adapted to determine, from the received
transmission rate negotiation messages from the ONU 310, that a
un-recoverable link failure has occurred on the main fibre path
between the ONU 310 and the main OLT 330.
[0136] In a further example of the back-up OLT 340, the
transmission rate negotiation between the back-up OLT 340 and the
ONU 310 comprises the processing unit 341 being adapted to confirm
use of pre-negotiated transmission rate between the ONU 310 and the
back-up OLT 340 over the back-up fibre path.
[0137] In yet an example of the back-up OLT 340, the processing
unit 341 is adapted to, when determining from the received
transmission rate negotiation messages from the ONU 310 or the main
OLT 330 that a un-recoverable link failure has occurred on the main
fibre path, start a preset timer when a transmission rate
negotiation message is received from the ONU 310 destined for the
main OLT 330. If the timer expires before a receiving an expected
follow-up transmission rate negotiation message from the ONU 310
destined for the main OLT 330, then the processing unit 341 is
adapted to perform transmission rate negotiation with the ONU 310
over the back-up path.
[0138] In the case that the main OLT and the back-up OLT are
geographically co-located, the OLT in one example does not
duplicate the full functionality of the main OLT. In one example of
such an OLT, it comprises only a transceiver arrangement and the
back-up OLT is connected to the main OLT, which is located at the
same geographical location, via a separate link.
[0139] The exemplifying embodiments of the ONU, the OLT and the
respective methods therein provides a protection mechanism for the
access network that doesn't require active equipment between the
end user and the back-up OLT over the protection fibre path.
Typically, the OLT is located in a Central Office, CO, of the
network operator. It is cost effective since a part of the capacity
over a link can be protected, avoiding the potential high costs of
providing protection of the full link capacity. The exemplifying
embodiments enable a damaged link to be restored, e.g. the main
fibre path/link may still be used even though it is damaged by
lowering the transmission rate. This way, the main fibre path may
still be capable of supporting communication between the ONU and
the OLT. Alternatively, if the damaged main fibre path is not
capable of supporting communication between the ONU and the OLT,
then the back-up fibre path is used to support communication
between the ONU and the OLT.
[0140] According to an embodiment, when a fault has occurred on the
main fibre path resulting in either lowering the transmission rate
on the main fibre path or switching to the back-up fibre path, the
OLT is adapted to prioritise traffic and selectively discard
traffic which exceeds the capacity of the fibre path used for
communication. In an example, this is done in a manner such that
service level agreements, SLAs, are Quality-of-Service, QoS,
requirements or guarantees are fulfilled.
[0141] FIG. 4 is a block diagram schematically illustrating an
exemplifying embodiment of a part of a passive optical network.
[0142] FIG. 4 illustrates two exemplifying configurations enabling
an ONU 419 to communicate over a main fibre path and a back-up
fibre path. The upper configuration illustrates N number of ONUs
410 being connected to a 2:N multiplexer 470. The multiplexer 470
is e.g. a power splitter, a wavelength splitter or an Arrayed
Waveguide Grating AWG. In case an AWG is used as the multiplexer,
an extra port on the AWG is provided to connection of the back-up
fibre path. If the multiplexer 470 is a 2:N AWG, the user
wavelength will appear differently at the back-up OLT compared to
the main OLT; wavelength 1 in the main OLT will correspond to
wavelength 2 in the back-up OLT.
[0143] The lower configuration illustrates an ONU 410 being
connected to an optical 1:2 splitter 480.
[0144] In the described embodiments, forward error correction (FEC)
may optionally be used. While finding the maximum transmission rate
over specific link, FEC can help to give additional link budget. An
example of such code is the Reed-Solomon (255,239) code which gives
a bandwidth overhead of roughly 7% and increase the link budget
with roughly 3-5 dB. There are multiple FEC codes that can be used.
For example, two different FEC codes could be supported; one
referred to as strong FEC (giving higher link budget increase at
the cost of higher bandwidth overhead), and one referred to as weak
FEC (giving lower link budget increase at the cost of lower
bandwidth overhead). When the end terminals negotiate which
transmission rate to use over a link, according to an embodiment,
several other parameters may be negotiated, both with regard to
communication to the other end terminal and also with regard to
communication received from the other end terminal.
[0145] The ONU, 310 the OLT 320, the main OLT 330 and the back-up
OLT 340 are illustrated in FIGS. 3a and 3b to comprise a respective
processing unit 311, 321, 331 and 341 which in turn are illustrated
comprising dedicated modules adapted to perform different method
steps, e.g. synchronising module, negotiation module, timing module
and communication module. It shall be noted that this is merely an
exemplifying illustration of the respective processing unit 311,
321, 331 and 341. Further FIGS. 3a and 3b illustrate the ONU, 310
the OLT 320, the main OLT 330 and the back-up OLT 340 comprising a
memory 312, 322, 332 and 342. Further, the, 310 the OLT 320, the
main OLT 330 and the back-up OLT 340 are illustrated having
transceiver arrangements 317, 327, 337 and 347 adapted to enable
the ONU 310 to communicate with the other terminals via a main
fibre link or fibre path; or a back-up fibre link or fibre path. A
transceiver arrangement may comprise one or more transmitters and
one or more receivers. Further, FIGS. 3b and 3d illustrate the main
OLT and the back-up OLT being connected by a separate link or path.
This ensures that the main OLT and the back-up OLT are able to
communicate with each other without making use of the main fibre
path/link or the back-up fibre path/link.
[0146] It shall be noted that the main fibre path and the back-up
fibre path may run all the way between the ONU and the OLT, main
OLT or back-up OLT. Alternatively, the main fibre path and the
back-up fibre path may run only along a part of the way between the
ONU and the OLT, main OLT or back-up OLT. Further, in case there is
just one OLT adapted to function as a main OLT and a back-up OLT,
or in case there are a main OLT and a back-up OLT located at the
same geographical location, the main fibre path and the back-up
fibre path are in one example running along the same route and in
another example running along different routes. Further, the fibre
topology can be a tree, a ring or a mixture of the two.
[0147] It should be noted that FIGS. 3a and 3b merely illustrates
various functional modules and units in the ONU, 310 the OLT 320,
the main OLT 330 and the back-up OLT 340 in a logical sense. The
functions in practice may be implemented using any suitable
software and hardware means/circuits etc. Thus, the embodiments are
generally not limited to the shown structures of the ONU, 310 the
OLT 320, the main OLT 330 and the back-up OLT 340 and the
functional modules and units. Hence, the previously described
exemplary embodiments may be realised in many ways. For example,
one embodiment includes a computer-readable medium having
instructions stored thereon that are executable by the respective
processing unit 311, 321, 331 and 341 for performing the method
steps of the exemplifying embodiments as set forth in the claims.
The instructions executable by the computing system and stored on
the computer-readable medium perform the method steps of the
exemplifying embodiments as set forth in the claims.
[0148] While the embodiments have been described in terms of
several embodiments, it is contemplated that alternatives,
modifications, permutations and equivalents thereof will become
apparent upon reading of the specifications and study of the
drawings. It is therefore intended that the following appended
claims include such alternatives, modifications, permutations and
equivalents as fall within the scope of the embodiments and defined
by the pending claims.
* * * * *