Multiplex communications – Fault recovery – Bypass an inoperative channel
Reexamination Certificate
1999-07-12
2004-01-20
Chin, Wellington (Department: 2664)
Multiplex communications
Fault recovery
Bypass an inoperative channel
C370S225000
Reexamination Certificate
active
06680905
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a transfer path control system comprising two transfer devices connected to each other through two transfer paths consisting of a main transfer path (working line) and a sub-transfer path (protection line).
A dual transfer system has hither to been proposed in order to ensure a reliability of data transfer paths. The dual transfer system has an architecture, which will hereinafter roughly be explained. To be specific, as shown in FIG.
13
(
a
), two transfer devices
101
,
102
are connected to each other through two transfer paths P
1
, P
2
. For example, the transfer path P
1
is used as a main transfer path, while the transfer path P
2
is used sub-transfer path. The transfer device
101
on a transmitting side transmits the same data substantially simultaneously from the transfer paths P
1
, P
2
. The transfer device
102
on a receiving side, when receiving through the transfer paths P
1
, P
2
the communications data transmitted from the transfer device
101
, transfers only the data received through the transfer path P
1
used as the main transfer path toward still another transfer device (not shown) disposed downstream, and discards the data received through the transfer path P
2
.
For instance, if an accident happens on the transfer path P
1
, the transfer device
102
is unable to receive the data through the transfer path P
1
from the transfer device
101
. Then the transfer device
102
, as shown in FIG.
13
(
b
), switches the main transfer path from the transfer path P
1
to the transfer path P
2
. The transfer device thereafter, transfers to another transfer device the data received through the transfer path P
2
. The reliability of the data transfer paths is thereby ensured.
In the example given above, for instance, if the accident occurs on the transfer path P
1
, the main transfer path is instantaneously switched over from the transfer path P
1
to the transfer path P
2
. It is therefore required that each piece of data transferred through the transfer path P
1
and the transfer path P
2
be synchronized.
More specifically, if the data transferred through the transfer path P
2
is received earlier by the transfer device
102
than the data transferred through the transfer path P
1
, missing of data might happen when the transfer path P
2
becomes the main transfer path instead of the transfer path P
1
. On the other hand, if the data transferred through the transfer path P
2
is received later by the transfer device
102
than the data transferred through the transfer path P
1
, duplication of data might happen when the transfer path P
2
becomes the main transfer path instead of the transfer path P
1
. The missing of data and the duplication of data must be strictly avoided because of inducing a decline of quality of communications.
A data delay difference is, however, to occur depending on a difference in terms of transfer path length between the transfer paths P
1
and P
2
, and a difference in status between the transfer paths P
1
and P
2
. Such being the case, there are proposed some systems for obviating the data delay difference.
FIG. 14
is a diagram showing a structure of the prior art transfer path control system containing a structural contrivance for obviating the data delay difference.
FIG. 15
is an explanatory diagram of the transfer path control system shown in FIG.
14
.
Referring to
FIG. 14
, the transfer devices
101
,
102
are connected to each other through the transfer paths P
1
, P
2
, in which case the transfer device
101
stores a predetermined sequence number in a field called a J
1
byte of an overhead of communications data (e.g., an SDH frame) transmitted through the transfer paths P
1
, P
2
to the transfer device
102
. Thereafter, the transfer device
102
through the transfer paths P
1
, P
2
, receives the data.
In the transfer device
102
, each of detectors
105
,
106
detects the content (the sequence number) of the J
1
byte from the data transferred through the transfer paths P
1
, P
2
, and notifies a phase controller
107
of this sequence number. At this time, if a delay difference t (a difference between the sequence numbers) as shown in FIG.
15
(
a
) occurs with respect to the same communications data between the transfer path P
1
and the transfer path P
2
, the communications data are stored in a memory
108
and a memory
109
, respectively. Then, the phase controller
107
reads the communications data simultaneously from the memories
108
,
109
and transmits the data, whereby the same communications data are substantially simultaneously given to a selector
110
. The delay difference t is thereby obviated. Thereafter, the selector
110
transmits only the communications data corresponding to the transfer path selected by the selector
110
itself. For example, if the transfer path P
1
is selected, the selector
110
transmits only the data given from the memory
108
.
There has existed in recent years a case where complicated transfer paths must be set in constructing the network system. For example, a new transfer path is build up in some cases for enhancing the reliability of the transfer paths, which have already been built up and operated. Alternatively, a new transfer path is build up as the case may be for altering the transfer paths that have already been built up and operated. In the case of building up the new transfer path, it must be necessary to try to see whether or not an accident happens when switching over the transfer path from the old one to the new.
There arise, however, the following problems inherent in the prior art of the transfer path control system illustrated in FIG.
14
. That is, if a delay difference (a phase difference) between the transfer path P
1
and the transfer path P
2
is small, the communications data are stored in the memories
108
,
109
, and the same communications data are read therefrom simultaneous, thus obviating the delay difference (the phase difference). By contrast, if the delay difference (the phase difference) is large, capacities of the memories
108
,
109
are limited, and hence one of the memories is saturated with the communications data before the same data are stored in the respective memories
108
,
109
, with the result that the missing of data occurs due to an overflow from the memory in some cases.
The prior art transfer path control system does not, however, have a construction for recognizing a result of switching over the main transfer path before the main transfer path is in fact switched over (before executing a switching operation of the selector
110
shown in FIG.
14
). The operation of building up the new transfer path must be therefore conducted with great prudence in order not to cause the above problem, which is a troublesome part of the operation.
SUMMARY OF THE INVENTION
It is a primary object of the present invention to provide a transfer path control system capable of recognizing a result of switching before switching over a transfer path from a first transfer path to a second transfer path, and of, with this recognition, facilitating an operation of building up a new transfer path.
To accomplish the above object, the present invention adopts the constructions that follow.
According to a first aspect of the present invention, a transfer path control system comprises a first transfer device, and a second transfer device connected to the first transfer device through a first transfer path and a second transfer path for transferring the same data. The first transfer device comprises an index data adding unit adding index data to each piece of data transmitted to the first transfer path and the second transfer path. The second transfer device comprises a selection unit selecting one of the first transfer path and the second transfer path and, when receiving the same data through the first transfer path and the second transfer path, transmitting only the communications data corresponding to the selected transfer path, a first detecting unit detecting the index da
Katten Muchin Zavis & Rosenman
Schaltz William
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