Network system

Details Network system Network system

2000-11-15

2004-07-20

Chin, Wellington (Department: 2664)

Multiplex communications

Fault recovery

Bypass an inoperative switch or inoperative element of a...

C370S225000, C370S228000, C714S002000, C714S004110, C714S005110

Reexamination Certificate

active

06765863

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a network system, and in particular to a network system composed of a master network synchronization device and a slave network synchronization device.
In recent years, a multimedia network system for the communication of a variety of data has been remarkable. Transmitting/receiving devices composing such a multimedia network system, like transmitting/receiving devices composing a conventional network, cannot receive information such as voice data from opposite devices if the devices are not operating at the same clock frequency as the opposite devices. Therefore, it is important to achieve a network synchronization which makes all of the devices composing the network system have a unified clock.
2. Description of the Related Art
FIG. 21
shows an arrangement of a conventional network system in which ATM switches
11
-
14
are connected in the form of a ring with routes
61
-
64
. Among the ATM switches, the ATM switch
11
is a network synchronization master device, which performs a transmitting/receiving operation based on a clock
31
based on a clock
30
extracted from a signal from a route
60
connected to another network system (not shown), or based on a clock of a clock generator (not shown) of its own, i.e. the ATM switch
11
itself.
If no failure has occurred in any of the routes
61
-
64
, the ATM switches
12
-
14
respectively extract the clocks
31
_
1
,
32
, and
31
_
2
from the routes
61
,
62
, and
64
, which are first routes, to perform the transmitting/receiving operation in synchronization with the clock
31
of the ATM switch
11
. Thus, a network synchronization is established for the entire network system.
Each of the ATM switches
12
-
14
has a second route set in lieu of the first route in case of a failure occurrence therein.
For example, if a failure occurs in the first route
61
(see timing T
11
of FIG.
21
), the ATM switch
12
which has detected this failure performs switchover of the clock extracting route (see timing T
12
of
FIG. 21
) in order to extract the clock
33
from the route
62
which is the second route. Since the ATM switch
13
is extracting the clock from the ATM switch
12
at this time, a competition state occurs where the ATM switches
12
and
13
mutually extract their clocks from each other so that the synchronization is disturbed. As a result, the clocks of the ATM switches
12
and
13
run away or drive recklessly (see timings T
13
and T
14
of FIG.
21
).
FIG. 22
shows a case where a failure occurs, not in the route
61
in the network system shown in
FIG. 21
, but in the ATM switch
11
itself which is the network synchronization master and causes the stoppage of the system (see timing T
21
of FIG.
22
).
The ATM switches
12
and
14
respectively detect the failure and perform the clock switchover from the clocks
31
_
1
and
31
_
2
of the first routes
61
and
64
to the clocks
33
_
1
and
33
_
2
of the second routes
62
and
63
(see timings T
2
and T
23
of FIG.
22
).
Thus, the clocks of the ATM switches
12
and
13
run away (see timings T
24
and T
25
of
FIG. 22
) as is the case with a failure occurrence in the route
61
shown in
FIG. 21
(see timings T
13
and T
14
of FIG.
21
).
Moreover, when the clock of the ATM switch
13
runs away, the clock of the ATM switch
14
which has switched over to the clock of the ATM switch
13
also runs away (see timing T
26
of FIG.
22
), so that the network synchronization of the entire network system cannot be established.
For example, recent technologies of ATM (Asynchronous Transfer Mode) include a PNNI (Private Network Node Interface) in which two network interface functions called routing and signaling are defined.
Although this PNNI enables the data to be detoured in case a circuit (route) failure occurs, there is a possibility that the communication is interrupted since the clock is not detoured systematically.
Also, such a case where the data communication is interrupted due to the clock not being detoured systematically is not limited to ATM.
In the conventional network system, the above-mentioned problems have been dealt with the methods explained as follows:
(1)In case a failure occurs in the route
61
between the ATM switches
11
and
12
in
FIG. 21
, a maintenance operator of the ATM switch
12
switches over the route (port) for extracting the clock from the current second route to the third route
66
without problems to extract the clock
36
.
At this time, the maintenance operator has to recognize the clock extraction status of not only the ATM switch
12
but also all of the adjoining ATM switches in order to select the port without problems. Therefore, the operation becomes extremely complicated.
(2)In case a failure occurs in the ATM switch
11
which is the network synchronization master in
FIG. 22
, and the master clock can not be extracted, the maintenance operator of the ATM switch
12
is required to review the clock of the entire network by making the clock of the ATM switch
12
the master clock after changing the clock extracting route to the third route
66
, and to change the route from which the clock is extracted if there is an ATM switch requiring the change of the clock extracting route.
Thus, with the conventional methods, the maintenance operator has been greatly burdened when a failure occurs in the circuit or the own device.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a network system composed of a master network synchronization device and a slave network synchronization device wherein a network synchronization of the entire network system is established by selecting the clock extracting route without requiring a maintenance manual work when a failure occurs in the circuit or the master network synchronization device.
For the achievement of the above object, a master network synchronization device of a network system according to claim
1
of the present invention has clock routing means for repeatedly transmitting hop count information set to a predetermined initial value at a predetermined timing, and the slave network synchronization device has clock routing means for receiving the hop count information from an adjoining network synchronization device and for transmitting a minimum hop count between the slave and the master network synchronization device as the hop count information, a clock determination table for determining the minimum hop count between the slave and the master network synchronization device based on the received hop count information and for saving the minimum hop count and a route from which the minimum hop count is received as a clock extracting route, and a clock extractor for extracting a clock from the clock extracting route.
Namely, the network system is composed of the master network synchronization device and the slave network synchronization device, the network synchronization devices mutually transmitting the hop count information to adjoining network synchronization devices.
Therefore, this hop count information increases every time it is relayed by the network synchronization device.
The clock routing means of the master network synchronization device transmit the hop count information set to the initial value to the adjoining slave network synchronization device, for example, periodically.
The clock routing means of the slave network synchronization device provide the clock determination table with the received hop count information. The clock determination table sequentially determines the minimum hop count between its own device and the master network synchronization device from the received hop count information, and saves the minimum hop count and the route from which the minimum hop count is received as the clock extracting route.
The clock extractor extracts the clock from the signal on the clock extracting route saved to the clock determination table to establish the network synchronization.
Thus, the routes are systematically formed for seq

Affiliated with

Also associated with

Rating

Network system does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Network system, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Network system will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-3185934