Multiplex communications – Pathfinding or routing – Switching a message which includes an address header
Reexamination Certificate
1997-08-11
2001-11-06
Hsu, Alpus H. (Department: 2662)
Multiplex communications
Pathfinding or routing
Switching a message which includes an address header
C370S395430, C359S199200
Reexamination Certificate
active
06314097
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to an optical transmission device used in an optical communication network, and more particularly to an optical transmission device used in an optical communication network which employs a synchronous digital hierarchy.
An optical communication network has been practically used as means for providing broadband services in which a variety of data on telephone, facsimile, images and so on is integrated. The user
etwork interface in the optical communication network has been internationally standardized, and is known as a Synchronous Digital Hierarchy (SDH), as defined in the CCITT recommendations G
707
, G
708
and G
709
, the disclosure of which is hereby incorporated by reference. A network which conforms to the SDH has been practically used as SONET (Synchronous Optical NETwork) in the North America.
2. Description of the Prior Art
First, a description will be briefly given of the SONET. The SONET is described in, for example, William Stallings, “ISDN and Broadband ISDN, Macmillan Publishing Company, 1992, pp. 546-558.
In the SONET, a multiplexed optical carrier (OC) is transmitted. The transmission device converts the optical signal (carrier) into an electric signal and vice versa. The electric signal is called a synchronous transport signal (STS). The basic bit rate of the SONET is 51.84 Mbps. The optical carrier having the above basic bit rate is expressed as OC-
1
. Generally, an optical carrier or signal is expressed as OC-N where N (optical carrier level N) is an integer, and a corresponding electric signal is expressed as STS-N (synchronous transport carrier level N). For example, the optical carrier OC-
12
is an optical carrier or signal having a bit rate of 622.080 Mbps (=12×51.84 Mbps). In the SONET, signals having bit rates which are integer multiples of the basic bit rate. The optical carrier OC-
12
is obtained by multiplexing 12 STS-
1
signals at the byte level to thereby generate an STS-
12
signal and by converting the STS-
12
signal into an optical signal. Generally, the multiplexing of STS-N signals employs a byte-level interleave process.
It will be noted that the STS-
3
in the SONET corresponds to a synchronous transport module STM-
1
in the SDH. Similarly, the STS-
12
corresponds to the STM-
4
.
The signal STS can be obtained by, for example, sequentially multiplexing digital signals having lower bit rates, such as DS-
0
(64 Kbps), DS-
1
(1.5 Mbps), DS-
2
(6.3 Mbps) and DS-
3
(45 Mbps).
FIG. 1
is a block diagram showing the outline of a network of the SONET. Electric signals from terminals
1
and
2
are respectively multiplexed by transmission devices
3
and
7
, and resultant multiplexed signals are converted into light signals, which are then sent to transmission paths
8
formed of optical fiber cables. Repeaters
4
,
5
and
6
are provided in the transmission paths
8
. Particularly, the repeater
5
has a function of terminating the optical signals (the above function is called an add/drop function). As shown in
FIG. 1
, terms “section”, “line” and “path” are defined in the SONET. The section corresponds to an optical transmission part between transmission devices, between repeaters or between a transmission device and a repeater. The line corresponds to an optical transmission part between transmission devices, between repeaters or between a transmission device and a repeater, each having the terminating function. The path indicates the end-to-end optical transmission part.
FIG. 2A
is a diagram showing the frame format of the signal STS-
1
. As shown in
FIG. 2A
, the signal STS-
1
consists of 810 octets, and is transferred every 125 &mgr;s. The 810 octets consists of nine rows arranged in a matrix formation, each of the rows consisting of 90 octets. In other words, the signal STS-
1
has a 9×9 matrix formation. The first three columns (three octets×nine rows) forms an overhead in which a variety of control information concerning transmissions. The first three rows of the overhead forms a section overhead, and the remaining six rows forms a line overhead. The control information forming the overheads is also referred to as overhead information.
FIG. 2B
is a diagram showing the frame format of the signal STS-
3
. In the SDH, a new format is not created during the hierarchically multiplexing operation. That is, the signal STS-
3
can be formed by simply byte-multiplexing the signals STS-
1
including the headers thereof without forming a new header specifically directed to the signal STS-
3
.
FIG. 3A
shows the section overhead and the line overhead, and
FIG. 3B
shows the path overhead. The bytes forming these overheads are well known, and a description thereof will be omitted here.
FIG. 4
is a block diagram of an example of the SONET. The SONET shown in
FIG. 4
includes transmission devices
10
A,
10
B,
10
C and
10
D, each of which has a higher bit rate of the bit rates of other transmission devices provided in the SONET. The transmission devices
10
A-
10
D are coupled by means of optical fiber cables
11
1
and
11
2
in a dual loop (ring) formation. Transmission devices having bit rates equal to or lower than the transmission devices
10
A-
10
D can be coupled to the transmission devices
10
A-
10
D. For example, transmission devices
12
a
,
12
b
,
12
c
,
12
d
, . . . are connected to the transmission device
10
A. The transmission device
10
A multiplexes signals transmitted from the transmission devices
12
a
,
12
b
,
12
c
,
12
d
and so on via optical fiber cables
13
a
,
13
b
,
13
c
,
13
d
and so on. Then, the transmission device
10
A sends a resultant multiplexed signal to either the transmission device
10
B or
10
D or both thereof. For the sake of convenience, the terms “east” and “west” can be used to describe the directions in which the signals are transferred. In
FIG. 4
, the transmission device
10
D is located at the east side of the transmission device
10
A, and the transmission device
10
B is located at the west side thereof.
Although not shown in
FIG. 4
, transmission devices having bit rates lower than those of the transmission devices
12
a
,
12
b
,
12
c
and
12
d
are coupled thereto via optical fiber cables. That is, the system shown in
FIG. 4
has a hierarchical structure in which signals from various terminals such as telephone sets, facsimile machines and personal computers are sequentially multiplexed in accordance with the given hierarchy, and the multiplexed light signals are transferred via the transmission devices
10
A-
10
D. In practice, the transmission devices
10
B and
10
D may be repeaters (regenerators).
FIG. 5
is a block diagram of the transmission device
10
A shown in FIG.
4
. The transmission device
10
A includes a plurality of line termination parts
21
1
,
21
2
, . . . ,
21
n
(n is an arbitrary integer), a multiplexer/demultiplexer (MUX/DMUX)
22
, a time slot assignment part
23
(hereinafter, simply referred to as a TSA part), a DCC relay/broadcast part
24
and a CPU
25
. The working side optical carriers OC-N(W) of the line termination unit
21
1
are connected to the optical fiber cables
11
1
and
11
2
in the east direction. The protection side optical carriers OC-N(P) of the lien termination unit
21
1
are connected to the optical fiber cables
1
and
11
2
in the west direction. The line termination part
21
2
is connected to the optical fiber cable
13
a
(which is illustrated as a single line for the sake of convenience in FIG.
4
). The optical fiber cables
11
1
and
11
2
carry, for example, the light signals OC-
48
, and the optical fiber cable
13
a
carries the light signal OC-
12
.
Each of the line termination parts
21
1
-
21
n
is equipped with a line terminator
25
w
on the working line side, a line terminator
25
p
, and an overhead terminator
26
. Each of the line terminators
25
w
and
25
p
has the function of terminating the overheads, that is, the function of adding the overheads to the signals to be
Fujitsu Limited
Hsu Alpus H.
Rosenman & Colin LLP
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