Connection setting method in ATM network

Details Connection setting method in ATM network Connection setting method in ATM network

1999-08-31

2004-10-26

Qureshi, Afsar (Department: 2667)

Multiplex communications

Fault recovery

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

C370S238100, C370S242000, C370S395100

Reexamination Certificate

active

06810009

ABSTRACT:

BACKGROUND OF THE INVENTION
Field of the Invention
The present invention relates to the technology of reconnecting the connection in failures of a line/failures of an apparatus in an ATM switched network, particularly in an ATM swiched network in which terminals are connected through software PVCs.
A P-NNI (Private—Network Node Interface) is one of service interfaces of an ATM (Asynchronous Transfer Mode) switched network, and is the convention for connecting between the public networks and the private networks in order to switch the address information or the routing information.
In the P-NNI, it is possible to establish a software PVC (software Permanent Virtual Connection: hereinafter, referred to as “an SPVC” or “a software PVC” for short, when applicable). In this case, the PVC is established only between a UNI (User Network Information) of a source and the UNI of a destination, and ATM nodes (ATM switching equipment) which are arranged in the middle of the UNI of the source and the UNI of the destination are connected through an SVC (Switched Virtual connection). As a result, it is said that the P-NNI is the technology which is capable of realizing the dynamic routing between the ATM switching equipment.
Now, the description will hereinafter be given with respect to the system configuration of the ATM network with reference to FIG.
1
.
In the figure, a terminal
101
a
(#A) and ATM switching equipment
102
, and ATM switching equipment
104
and a terminal
101
b
(#b) are respectively connected through PVCs (Permanent Virtual Connections), and interchange routes (between ATM switching equipment) are connected through the SVCs.
Now, when the SPVC is set in the ATM switching equipment
102
, for the SVC part of the interchange routes, the ATM switching equipment
102
,
103
and
104
automatically sets the connections to maintain the connections. The features of this system are the following two points.
(1) Automatic Alternate Function of PVC
Since the ATM switching network has the SVCs set therein, if a VC (Virtual Connection) is, in occurrence of the failures, released due to the failures or the like (e.g., occurs between the ATM switching equipment
103
and
104
), then the ATM switching equipment
102
on the transmission side recalls the ATM switching equipment
104
on the reception side, thereby ensuring the alternate route (the ATM switching equipment
102
→
105
→
104
).
(2) Simplified Function of PVC Setting
By only setting the terminal information of the both of the terminals (an ATM address of the terminal
101
a
(#A), VPI/VCI=a, an ATM address of the terminal
101
b
(#b), and VPI/VCI=b) and the like in both of the ATM switching equipment
102
on the transmission side and the ATM switching equipment
104
on the reception side, the PVC over the overall of the ATM network can be set.
FIG. 2
shows a hierarchy structure in the ATM. In occurrence of the failures in the above-mentioned paragraph (1), the alternate route is determined in the ATM layer shown in FIG.
2
.
FIG. 3
shows the procedure of this failure recovery in the form of a flow chart.
When the failures occur in the location between the switching equipment
103
and
104
as shown in
FIG. 1
(Step
301
), in order that the processing may proceed to the alternate operation in the ATM switching network, the following processings are required.
First of all, the VC (Virtual Connection) needs to be disconnected in the ATM switching network (Step
302
).
In this connection, in the data link monitoring timer installed in each of the ATM switching equipment, it takes normally about 17 seconds to disconnect the VC. This numeric value is obtained by summing 7 seconds defined for Timer No Response and 10 seconds of a L
3
timer T
309
.
If the contents of a routing table are updated in recalling made from the terminal
101
a
(#A)(an Owner switching equipment in the case of the SPVC, but in this case, the ATM switching equipment
102
), the alternate route is ensured.
Now, in order to make a recall, it becomes the prerequisite that any of the prior calls is already released. The data link monitoring timer for confirming the disconnection of the VC is arranged in the ATM layer in the hierarchy structure shown in FIG.
2
.
Secondly, it is required that the contents of the routing table are already updated (Step
303
).
Now, the numeric value which is obtained by multiplying “Hello packet sending time interval” by “the number of Hello packet sendings” becomes the update time of the routing table. Then, if the interval value is 15 seconds×5 times, then the update time is 75 seconds in total.
This results from the function wherein “It is defined that the Hello packets are transmitted at intervals of 15 seconds from the adjacent node. If the Hello packet has not arrived,though the time period for the five times has elapsed for which the corresponding Hello packet is expected to essentially arrive, then the ATM switching equipment judges that the route to the adjacent node can not be used to update the contents of the routing table.”
The reception sequence of the Hello packet between the nodes in occurrence of the failures in the prior art is shown in the form of a diagram in FIG.
6
.
The route changing processing is only started when both of the steps
302
and
303
as described above have been confirmed (Step
305
).
By the way, as apparent from the above-mentioned description, the time period required to update the contents of the routing table in the ATM switching equipment must be made longer than the time period required to disconnect the VC.
Now, in order that the alternate route may be set as speedily as possible, the time period required to update the contents of the routing table has only to be made slightly longer than the time period required to disconnect the VC.
The example associated therewith will be shown as follows.
Time intervals of sending Hello packets=15 seconds (setable range is a to b seconds).
The number of Hello packet sendings=2 times (setable range is c to d times).
If the values as described above are adopted, then the contents of the routing table are updated with the following conditions.
Minimum: 15 seconds×2 times=30 seconds
Maximum: 14 seconds+15 seconds×2 times=44 seconds
(The maximum time period required for the case where the failures occur on the line right after the Hello packet has been received from the adjacent node).
Now, with respect to the reconnection of the alternative connection in failures due to the SPVC, when making a detour to avoid the failure route, even if the route is restored from the failures to its former state, the terminal
101
a
(#A) and the ATM switching equipment
102
are connected to each other through the PVC, and hence no recall is made from the terminal
101
a
(#A). Therefore, since the ATM switching equipment
102
continues to maintain the SVC connection, no return of the state is made automatically back to the original route (the route in which the failures are recovered: the ATM switching equipment
102
→
103
→
104
).
For this reason, there arises the problem that the connections for which the alternate route is selected are concentrated on some intervals and hence the network performance is continued to be pressed to induce the overcrowding.
In order to use the original route which has been restored from the failures to its former state, the definition in the table needs to be once released to carry out the registration again.
In this connection, there is known an OAM (Operation Administration and Maintenance) cell for reporting the failures between the nodes (between the ATM switching equipment) within the ATM network. As shown in
FIG. 4
, however, while after having recognized the node failures (Step
401
), the failure report is made every connection (Step
402
), the OAM cell has only the function of reporting in which direction the failures have occurred in the connection and hence does not contain therein the informat

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