Multiplex communications – Communication techniques for information carried in plural... – Adaptive
Reexamination Certificate
1999-12-27
2003-12-23
Olms, Douglas (Department: 2661)
Multiplex communications
Communication techniques for information carried in plural...
Adaptive
C370S535000, C370S907000, C370S517000, C714S800000
Reexamination Certificate
active
06667990
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a transmission terminal station apparatus for transmitting data received from a low-order group terminal device to a high-order group terminal station device, a transmission terminal station apparatus for transmitting data received from a high-order group terminal station device to a low-order group terminal device, and a network system including these transmission terminal station apparatuses.
2. Prior Art
With an advance in information systems in recent years, line capacities in a communication network increase. In the field of optical communications, optical fibers which are physical resources of optical lines tend to be short. In contrast to this, the shortage of optical fiber are compensated for by replacing a plurality of low-speed lines into high-speed lines by using a high-order group terminal-station device (called “overlay”).
FIGS. 5A and 5B
are diagrams for explaining the overlay of an optical communication network. As shown in
FIG. 5
, the following optical communication network is assumed. That is, the optical communication network is constituted by a plurality of low-order group terminal devices (indicated by blocks in FIG.
5
A), and the low-order group terminal devices are connected to each other through low-speed lines (OC-12 or OC-48).
A site A in
FIG. 5A
has low-order group terminal devices T
1
to T
3
, and a site B has low-order group terminal devices T
4
to T
6
. The low-order group terminal devices T
1
to T
3
are connected to the low-order group terminal devices T
4
to T
6
through low-speed lines (e.g., OC-48) L
1
to L
3
. The low-order group terminal device T
1
and the low-order group terminal device T
4
are transparent to each other, the low-order group terminal device T
2
and the low-order group terminal device T
5
are transparent to each other, and the low-order group terminal device T
3
and the low-order group terminal device T
6
are transparent to each other. Note that OC-12 and OC-48 represent optical carrier levels (optical speed standards) defined by SONET (Synchronous Optical Network) serving as one of SDHs (Synchronous Digital Hierarchies).
In this case, as shown in
FIG. 5B
, high-order group terminal station devices K
1
and K
2
are arranged in the sites A and B. Each of the high-order group terminal station devices K
1
and K
2
accommodates a low-order group terminal device in the site to which the corresponding high-order group terminal station device belongs. The high-order group terminal station device K
1
and the high-order group terminal station device K
2
are connected to each other through a high-speed line (e.g., OC-192) L
4
.
Each of the high-order group terminal station devices K
1
and K
2
makes OC-48×4 lines multiplexed to OC-192 transparent in accordance with the transparent relationships of the low-order group terminal devices T
1
to T
6
. In this manner, the low-speed lines L
1
to L
3
of OC-48 are replaced with the high-speed line L
4
of OC-192 to compensate for the shortage of optical fiber.
At this time, the high-order group terminal station devices K
1
and K
2
are pseudo intermediate repeater device with reference to the low-order group terminal devices T
1
to T
6
. That is, the low-order group terminal devices T
1
to T
6
are arranged such that the low-order group terminal devices T
1
to T
6
can transmit data to the low-order group terminal devices which are transparent to each other in
FIG. 5A
without regarding the presence of the high-order group terminal station devices K
1
and K
2
(low-order group terminal devices T
1
to T
6
can perform transparent transmission).
According to the optical communication network shown in
FIG. 5B
, for example, when data is transmitted from the low-order group terminal device T
1
of the site A to the low-order group terminal device T
4
of the site B, the low-order group terminal device T
1
transmits data to the high-order group terminal station device K
1
.
At this time, the low-order group terminal device T
1
regards only that the data is transmitted to the low-order group terminal device T
4
. the high-order group terminal station device K
1
multiplexes data received from the low-order group terminal devices T
1
to T
3
to transmit the multiplexed data to the high-order group terminal station device K
2
.
The high-order group terminal station device K
2
separates the data received from the high-order group terminal station device K
1
, and transmits, of the separated data, data to be transmitted to the low-order group terminal device T
4
to the low-order group terminal device T
4
. In this manner, the low-order group terminal device T
4
receives the data transmitted from the low-order group terminal device T
1
. The low-order group terminal device T
4
regards only that the data is received from the low-order group terminal device T
1
.
Even if a high-order group terminal station device is inserted between low-order group terminal devices by overlay as described above, it is demanded that the same transmission/reception as that performed when low-order group terminal devices are directly connected through a low-speed line is should be performed between transparent low-order group terminal devices (e.g., the low-order group terminal device T
1
and the low-order group terminal device T
4
, the low-order group terminal device T
2
and the low-order group terminal device T
5
, and the low-order group terminal device T
3
and the low-order group terminal device T
6
which are shown in FIG.
5
A).
With respect to the above demand, in a conventional optical communication network, the following problems are posed.
FIG. 6
is a diagram showing problems in a conventional optical communication network.
FIG. 6
shows the low-order group terminal devices T
1
and T
4
and the high-order group terminal station devices K
1
and K
2
which are shown in FIG.
5
B. In the optical communication network, when data is transmitted between transmission terminal station apparatuses (between low-order group terminal devices or between a low-order group terminal device and a high-order group terminal station device), the data is transmitted while the data is stored in a SONET frame (SDH frame).
The SONET frame (SDH frame) has a payload for storing user data (transmission information) and an overhead in which operation maintenance information of a network is stored. The overhead is constituted by a section overhead (SOH), a line overhead (LOH), or the like.
When the low-order group terminal device or the high-order group terminal station device receives a SONET frame, the corresponding group terminal station terminates the SONET frame, generates a new SONET frame depending on an output port of data stored in the SONET frame, and stores data to be transmitted to the payload of each SONET frame to transmit the data to the corresponding output port. In this process, the contents of the overhead of the new SONET frame are new contents to be inserted by the low-order group terminal device or the high-order group terminal station device.
A byte (called a B2 byte) used for monitoring a code error between transmission terminal station apparatuses is stored in the LOH of the overhead. The B2 byte is inserted into the LOH of a SONET frame in a transmission terminal station apparatus on the transmission side, detected by a transmission terminal station apparatus (transmission terminal station apparatus on the reception side) which terminates the SONET frame, and used for monitoring a code error (calculating the number of parity errors).
A monitor result (the number of parity errors) obtained by monitoring a code error is transmitted to the transmission terminal station apparatus on the transmission side (L-FEBE). The transmission terminal station apparatus on the transmission side switches a line used in data transmission to another line when the number of parity errors exceeds a threshold value. In this manner, the transmission quality of data can be maintained.
In
FIG. 6
, data i
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