Multiplex communications – Fault recovery
Reexamination Certificate
1999-11-12
2003-10-14
Chin, Wellington (Department: 2664)
Multiplex communications
Fault recovery
C370S242000
Reexamination Certificate
active
06633537
ABSTRACT:
BACKGROUND OF THE INVENTION
(1) Field of the Invention
The present invention relates to a hitless path switching ring network, a hitless path switching transmission system, a node device for a hitless path switching ring network, and a failure occurrence-time hitless path switching transmission method in a ring network, which are capable of transmitting a signal without instantaneous hitting of the signal in a ring network where a plurality of node devices are interconnected in ring form through a work transmission line and a protection transmission line, even when switching of the transmission line is performed at the time of failure occurrence.
(2) Description of the Related Art
The ring network is constructed by a plurality of node devices interconnected through high-speed transmission lines (work and protection transmission lines).
Each node device in this ring network receives a signal sent from another network that is in a lower hierarchy, through a low-speed transmission line an d outputs the received signal onto the high-speed transmission line (work transmission line) toward another node.
Note that as an example, consider the case where a synchronous digital hierarchy (SDH) frame is transmitted along the high-speed transmission line within the ring network and each signal in each node device sent from a lower hierarchy is added to the payload of this SDH frame (high-group frame).
As a typical example of this ring network, a uni-directional protection switched ring (UPSR) has been proposed. If there is a failure in a transmission line along which a signal sent out from a certain node device is transmitted, the transmission line can be switched with no means so that the signal is transmitted to another node device, as if there were no failure.
FIG. 35
is a diagram showing a ring network
1
-x
1
of this UPSR type. The ring network
1
-x
1
shown in this diagram is constituted by node devices
10
A-x~
10
D-x. In the node device
10
A-x on the side of transmitting a signal (path
1
), the signal is sent out onto a work transmission line (arrow x
1
in
FIG. 35
) and is also previously sent out onto a protection transmission n line (arrow a x
2
in
FIG. 35
) In the node device
10
C-x on the receiving side, the signals received through the work and protection transmission lines are held in a work memory
20
-x and a protection memory
30
-x, respectively.
At the time of normal operation, for the signals read out from the work and protection memories
20
-x and
30
-x, the signal with better quality is selected and output by a path selecting section
40
-x. Also, when a failure occurs in the work transmission line, the signal from the protection transmission line (i.e., the signal output from the protection memory
30
-x) is automatically selected.
Thus, in the UPSR, the same signal is sent out onto the work transmission line and the protection transmission line, so when a failure occurs in the work transmission line, the output signal can be switched without instantaneous hitting by the path selecting section
40
-x. However, the line (transmission line) capacity within the network is employed more than 1.5 times the case where a signal is sent out on either the work-transmission line or the protection transmission line (three or more nodes are employed).
On the other hand, compared with the aforementioned UPSR, another technique (bi-directional line switched ring (BLSR)) of effectively utilizing transmission lines has been proposed.
FIG. 36
is a schematic diagram showing a ring network of this BLSR type. In this ring network (hereinafter also referred to as simply a “ring”)
1
-x
2
shown in the diagram,
4
node devices
10
A-x
2
~
10
D-x
2
respectively connected to other networks are connected and constructed in ring form through transmission lines.
In this ring network
1
-x
2
, one-half its transmission line capacity within in the ring
1
-x
2
is employed in the work transmission line and the remaining half is employed in the protection transmission line. The ring network
1
-x
2
performs communication in the form of sending out a SDH frame in the east and west directions by the node devices (node devices on the transmitting side)
10
A-x
2
~
10
D-x
2
. Also, if the node devices
10
A-x
2
~
10
D-x
2
detect a signal, which is output to another network, from the signals (added to the SDH frame) received through the trunk transmission line (between node devices), the node devices
10
A-x
2
~
10
D-x
2
will drop the detected signal to the other network. On the other hand, if a signal is received from another network, the node devices
10
A-x
2
~
10
D-x
2
will add the received signal to the SDH frame and send out the SDH frame onto the transmission line between the node devices.
Incidentally, if a section failure occurs in the work transmission line between the node devices
10
B-x
2
and
10
C-x
2
, the ring network
1
-x
2
will loop back the signal, which is sent onto the work transmission line, at the node device,
10
B-
2
and send out the signal onto the protection transmission line on the side of the node device
10
A-x
2
, after failure occurrence, as shown in FIG.
37
. The signal, looped back and sent out onto the protection transmission line, is sent through the node devices
10
A-x
2
and
10
D-x
2
to the node device
10
C-x
2
.
Note that the process of looping back a signal onto the protection transmission line at the time of section failure occurrence is controlled by the bytes K
1
and K
2
added to the section overhead (SOH) of a SDH frame.
Also, when the node device
10
C-x
2
detects a failure in the work transmission line, it instructs a loop back instruction to the node device
10
B-x
2
through a long path (i.e., via the node devices
10
D-x
2
and
10
A-x
2
) with the bytes K
1
and K
2
.
As mentioned above, in the ring network
1
-x
2
, the node device
10
B-x
2
outputs a signal toward the node device
10
A-x
2
, after receiving the bytes K
1
and K
2
.
For instance, in the node device
10
B-x
2
, a signal (path
3
) coming in along a low-speed transmission line is sent out toward the node device
10
C-x
2
with the work transmission line at the time of normal operation. However, when a section failure occurs, the signal (path
3
) coming in along the low-speed transmission line after failure occurrence is sent out toward the node device
10
A-x
2
with the protection transmission line. And in the node device
10
C-x
2
, the signal (path
1
) is output onto a low-speed transmission line.
Thus, in the BLSR, after failure occurrence, a section signal is sent out onto the protection transmission line in the opposite direction from the direction in which a signal is transmitted before failure occurrence, so that there is a possibility that the signal received at the node device
10
C-x
2
on the receiving side will be partially chopped. As a result, it becomes difficult to switch a transmission line without causing instantaneous hitting of a signal.
SUMMARY OF THE INVENTION
The present invention has been made in view of the aforementioned problems. Accordingly, it is the object of the present invention to enable switching from work transmission line to the protection transmission line without causing the occurrence of instantaneous hitting of a signal, when a failure occurs in the work transmission line in a ring network such as the aforementioned BLSR.
To achieve the aforementioned object of the present invention, there is provided a hitless path switching ring network comprising at least two node devices connected in ring form through a work-transmission line and a protection transmission line, wherein at the time of normal operation a signal, is transmitted with the work transmission line and at the time of failure occurrence in the work transmission line the signal can be transmitted with the protection transmission line in the opposite direction from the direction in which the signal was transmitted before failure occurrence. In order to cause the signal to be received from one of the node devices to the other of the node devices without
Chin Wellington
Pham Brenda
LandOfFree
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