Multiplex communications – Fault recovery – Bypass an inoperative switch or inoperative element of a...
Reexamination Certificate
1998-03-17
2002-01-08
Yao, Kwang B. (Department: 2664)
Multiplex communications
Fault recovery
Bypass an inoperative switch or inoperative element of a...
C370S244000
Reexamination Certificate
active
06337848
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a technology for processing alarms in a transmission apparatus such as an ADM apparatus with a path switch ring function by means of a path switch, and a bi-directional line switch ring function by means of a service selector, etc.
2. Description of the Related Art
These days, with the advent of large-scale and urbanized networks composing optical transmission systems, the implementation of an add drop multiplexer (ADM) apparatus is required in order to construct a ring type network which can cope with large-scale networks and the urbanization of networks.
When the ring type network implemented by an ADM apparatus is classified by a transmission form and a form of failure prevention, a path switch ring (uni-directional path switch ring)(hereinafter called PSR) and a bi-directional line switch ring (BLSR) are publicly known. However, both rings are required to be implemented by means of one ADM apparatus so that customers may construct an optimal network.
FIG. 1
shows the configuration of both an ADM apparatus and a general-purpose optical transmission network constructed using an ADM apparatus.
To implement this network ITU-T established an SDH transmission system, and in North America a transmission interface based on this transmission system and called a synchronous optical network (SONET) is used.
In the SONET interface a signal OC-N (or STS-N) is used which is based on a signal with a transmission rate of 51.84 Mbit/second called a synchronous transport signal-level 1(STS-1) or an optical carrier-level 1(OC-1), and has a transmission rate N (integer) times as fast as the STS-1 or OC-1 signal. In the example shown in
FIG. 1
, OC-3 (or STS-3), OC-12 (or STS-12) and OC-48 (or STS-48) with transmission rates 3, 12 and 48 times as fast as the STS-1 (OC-1) signal, respectively, are shown.
FIG. 2
shows the frame format of an STS-1 signal. The STS-N (OC-N) signal has a structure in which N pieces of STS-1 (OC-1) signals shown in
FIG. 2
are multiplexed by way of byte multiplication.
As shown in
FIG. 2
, the STS-1 frame is divided into two areas, one area is called a transport overhead for transmitting overhead information, and the other area is called a synchronous payload envelope for transmitting payload information. Besides the information payload being user information, the synchronous payload envelope transmits overhead information called a path overhead. The transport overhead comprises an area called a section overhead and an area called a line overhead. The overhead area is used to transmit various kinds of control information and alarms between transmission apparatuses (ADM apparatus, etc.) composing a network.
The STS-1 frame shown in
FIG. 2
is transmitted byte by byte in order from the top line to the bottom line, and from the left to the right.
In the information payload, digital signals of a plurality of users are multiplexed.
On the other hand, section, line and path overhead areas for classifying the overhead are concepts for identifying communication spans composing the SONET network.
The path specifies end-to-end connection between a transmission apparatus for generating one STS-1 frame and a transmission apparatus for terminating the frame, and the path overhead transmits overhead information communicated between both above-mentioned transmission apparatuses using the end-to-end connection. Although one STS-1 frame is transmitted via various kinds of physical media (OC-1, OC-3, OC-12 and OC-48) on the way, a path corresponding to the STS-1 signal is specified independently of those media.
The line specifies connection in which physical characteristics are continuous, more specifically connection between optical fiber spans with the same transmission rate, and the line overhead transmits overhead information communicated between transmission apparatuses at both ends of the physically continuous connection.
The section specifies connection between network elements such as a lightwave regenerator inserted between the above-mentioned lines, and the section overhead transmits overhead information communicated between the network elements.
As described above, since in the STS-1 frame, overhead information is layered and stored in an overhead area corresponding to both communication range and communication characteristics, and transmitted, and thereby, since it is sufficient for each network apparatus to process only overhead information related to itself, an efficient communication control can be implemented.
FIG. 3
shows the structure of the section overhead and line overhead in the transport overhead, and each overhead byte of a path overhead in a synchronous payload envelope. Out of these, overhead bytes particularly related to the present invention are described later.
Returning to the explanation of
FIG. 1
, ADM apparatuses
101
are apparatuses with a function to mutually connect optical fibers for ADD/DROP-transmitting OC (STS) signals with different transmission rates. The ADM apparatus
101
shown in
FIG. 1
, for example, connects an optical fiber for transmitting an OC-48 signal with an optical fiber for transmitting an OC-12 signal.
To implement the above-mentioned signal switching function, the ADM apparatus
101
comprises a time slot assigning (TSA) unit
102
and a multiplexer unit (THRU/ADD unit)
103
.
The TSA unit
102
has a function to multiplex an arbitrary STS-1 frame multiplexed in the OC (STS) signal of the input side, to a signal with an arbitrary STS-1 frame timing in the OC signal of the output side, and has a configuration, for example, as shown in FIG.
4
.
FIG. 4
shows the case where an input side main signal is an OC-48 main signal consisting of 48 channels, and where an output side main signal is an OC-N signal consisting of N channels.
Channels 1 to 48 (each channel corresponds to one STS-1 signal) of the input side main signal are inputted to N switches
401
#1 to #N. Each switch
401
is designated which channel to select and to output by a TSA control signal, and sends the channel at the STS-1 frame timing of the output side main signal to which the switch
401
is assigned.
In
FIG. 1
the TSA unit
102
(DROP) multiplexes (drops) an arbitrary STS-1 frame multiplexed in the OC-48 signal being a higher order group side, to a signal with an arbitrary STS-1 frame timing in the OC-12 signal being a lower order group side.
On the other hand, the TSA unit
102
(ADD) multiplexes (adds) an arbitrary STS-1 frame multiplexed in the OC-12 signal being a lower order group side, to a signal with an arbitrary STS-1 frame timing in the OC-48 signal being a higher order group side, and an ADD signal obtained as this result is mixed with the OC-48 signal by the THRU/ADD unit
103
.
Next, the PSR is described below.
FIG. 5
shows the configuration of the PSR.
An ADM apparatus
501
used in a PSR configuration comprises TSA units
502
(E-ADD) and
502
(W-ADD) and THRU/ADD (T/A) units
503
(E) and
503
(W) for multiplexing (adding) an ADM signal
505
from a lower order group side optical fiber, to a higher order group optical fiber, TSA units
502
(E-DROP) and
502
(W-DROP) for multiplexing (dropping) a DROP signal
506
from a higher order group side optical fiber, to a lower order group side optical fiber, and a path switch (PSW)
504
.
Then, in an ADM apparatus
501
(#1) an ADD signal
505
(#1) from a lower order group side optical fiber is added to an outer optical fiber
507
(OUTER) by the operation of both TSA unit
502
(E-ADD) and THRU/ADD unit
503
(E), and is added to an inner optical fiber
507
(INNER) by the operation of both TSA unit
502
(W-ADD) and THRU/ADD unit
503
(W). In this way, over both optical fiber
507
(OUTER) and optical fiber
507
(INNER) the same optical signal is transmitted.
The optical signal added from the ADM apparatus
501
#1 and redundantly transmitted on dual rings, for example, is dropped at the ADM apparatus
501
#2.
That is, in the ADM apparatus
501
#2, an optical signal from t
Takatsu Kazuo
Taniguchi Atsuki
Fujitsu Limited
Rosenman & Colin LLP
Yao Kwang B.
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