Optical waveguides – With optical coupler – Switch
Reexamination Certificate
1999-10-05
2001-12-04
Palmer, Phan T. H. (Department: 2874)
Optical waveguides
With optical coupler
Switch
C385S016000
Reexamination Certificate
active
06327400
ABSTRACT:
FIELD OF THE INVENTION
The invention pertains to passive optical point-to-multipoint optical networks. More particularly, the invention pertains to protection schemes for such networks.
BACKGROUND OF THE INVENTION
A passive optical network (PON) is a point-to-multipoint optical fiber network having no active (i.e., powered) components in the inter-node portion of the network. Fiber optic networks are becoming increasingly common because of the many advantages of optical fiber over standard electrical cables, such as increased bandwidth and low signal degradation.
Many users of such networks require extremely high reliability of the network. That is, the network must be operational an extremely high percentage of the time. Such users requiring very high network reliability might include the military, banks and other financial institutions, and civilian air traffic control systems. In general, communications over a network can be interrupted by two general types of failures, namely, a fiber break failure and an interface failure. As used herein, the term interface failure refers to a failure at the interface equipment of a network terminal of the network.
Of particular interest in the present specification are point-to-multipoint networks. The term “point-to-multipoint” refers to a network architecture in which all communications between nodes are routed through a control node, typically termed the head end. In this specification, the control node is termed the head end and all other network nodes are termed network terminals.
Point-to-multipoint networks may take on various configurations including a tree configuration, a bus configuration, a star configuration, and a ring configuration. They also may use any type of communication protocol, including time division multiple access (TDMA) protocols, code division multiple access (CDMA) protocols, contention protocols (e.g., CSMA-CD used for Ethernet), etc. An example of an ATM passive optical network (APON) using TDMA is described in ITU-T G983.1.
In order to provide extremely high reliability, such networks typically employ redundant architectures. For instance, in order to assure high reliability against fiber breaks, a network would be designed to provide two separate and independent fiber routes between each network terminal and the head end.
To provide protection against interface failures, each node of the network, including the head end, would be provided with redundant interfaces. Thus, if one interface failed, the node could switch to use the other interface.
Generally, it has been believed that, for networks requiring fiber and/or interface protection (i.e., redundancy), a ring architecture is most efficient. However, protected star and other networks are known.
FIGS. 1A
,
1
B and
1
C illustrate unprotected star, tree and bus optical network architectures, respectively.
Commonly, the multiple fibers connecting a network terminal to the head end in a protected network are routed over geographically different routes. This is because the cause of a fiber break frequently is a localized event, such as severe weather, insurrection, accidental human breakage (for instance, due to construction), etc.
Examples of redundancy/protection schemes can be found, for example, in appendix D of ITU-T G983.1. J. L. De Groote, D. A. Buise, H. K. Dedecker, F. M. Louagie and H. F. Slabbinck,
Redundancy and Protection—Switching in APON Systems, Broadband Access and Technology
, W. Faulkner and J. L. Hammer (IDS.), 1999 also discloses several architectures for protected APONs.
FIGS. 2
,
3
and
4
illustrate some of the protected APON architectures disclosed in the aforementioned article. For instance,
FIG. 2
illustrates a partial protection scheme in which the head end and the fibers
28
and
30
between the head end and the splitter
26
is protected. Particularly, the head end
20
includes two interfaces
22
and
24
to the optical network. Each of those interfaces is coupled to a 2:N splitter
26
via a fiber
28
and
30
, respectively, where N is the number of network terminals. The splitter
26
couples to each of the terminals, e.g., terminals
32
-
1
and
32
-N through a fiber, e.g.,
34
-
1
and
34
-N and an interface, e.g.,
36
-
1
and
36
-N, respectively. A failure of one of the interfaces
22
or
24
at head end
20
or in fibers
28
,
30
is non-fatal since the other interface can take over. However, this scheme provides no protection for failure of an interface of one of the network terminals
32
-
1
through
32
-N. Also, it does not provide protection for any fiber breaks other than in fiber portions
28
and
30
.
FIG. 3
illustrates a fully redundant, i.e., fully protected, APON network architecture. In this architecture, the head end
40
includes two optical interfaces
42
and
44
. Each optical interface
42
and
44
is coupled via a fiber
46
and respectively, to a 1:N optical splitter,
50
and
52
respectively. Each optical splitter
50
and
52
is coupled to each network terminal
54
-
1
through
54
-N via a separate fiber
56
-
1
through
56
-N and
57
-
1
through
57
-N and optical interface
58
-
1
through
58
-N and
60
-
1
through
60
-N at the terminal. For instance, splitter
50
is coupled to network terminal
54
-
1
via fiber
56
-
1
and interface
58
-
1
. Splitter
50
is coupled to network terminal
54
-N via fiber
56
-N and interface
58
-N. This configuration provides full redundancy for interface failure at any of the network terminals and the head end as well as for a fiber break anywhere in the network.
FIG. 4
illustrates a third protected network topology. Whereas
FIGS. 2 and 3
illustrate star network topologies,
FIG. 4
discloses a ring network topology.
FIG. 4
shows a route redundant architecture having optical interface protection at the head end and full fiber break protection. It does not have optical interface protection at the terminals. Particularly,
FIG. 4
illustrates a route redundant architecture with different drop sections along a ring network. The head end
80
has redundant optical interfaces
82
and
84
with each of the optical interfaces
92
and
84
coupled to a 1:K splitter
83
,
85
with each output fiber
90
,
92
and
94
forming a ring between the two splitters. K is the number of drop sections and therefore also the number of fibers. Each fiber
90
,
92
and
94
couples to one or more network terminals
96
,
98
or
100
through one of the drop sections. Each drop section includes a 2:M splitter
102
,
104
and
106
, where M is the number of network terminals coupled to the ring via that splitter. Accordingly, each group of network terminals coupled to a 2:M splitter can communicate on the ring in either the clockwise or counterclockwise direction.
In this ring architecture, the network is fully protected against optical interface failure at the head end or fiber failure anywhere between the drop sections (i.e., the 2:M splitters) and the head end. There is no protection, however, for optical interface failure at the network terminals or in the fiber sections between the network terminals and the 2:M splitters, e.g., fiber sections
112
,
114
.
Providing multiple fiber routes between network terminals and the head end is expensive, particularly when the fibers are laid along different routes. Further, providing redundant optical interfaces is expensive since interface equipment costs are doubled. Further, there is additional design and equipment costs associated with the circuitry and software that must be provided for switching between the redundant interfaces.
Accordingly, it is an object of the present invention to provide a low cost protection scheme for a point-to-multipoint optical network.
It is a further object of the present invention to provide a network that is fully protected against fiber breaks without the need for redundant fibers.
SUMMARY OF THE INVENTION
The invention provides circuitry for coupling network nodes to a passive network comprised of a single fiber that provides substantial protection against fiber
Harstead Edward E.
Hazeu Louis Viktor
Lucent Technologies - Inc.
Palmer Phan T. H.
Synnestvedt & Lechner LLP
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