Multiplex communications – Fault recovery – Bypass an inoperative channel
Reexamination Certificate
1998-09-01
2002-07-02
Yao, Kwang Bin (Department: 2664)
Multiplex communications
Fault recovery
Bypass an inoperative channel
C370S236100
Reexamination Certificate
active
06414937
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention claims priority from Japanese Patent Application No.9-238338 filed Sep. 3, 1997, which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to a self-healing for improving the reliability of ABR (Available Bit Rate) communication services in an ATM (Asynchronous Transfer Mode) transmission.
2. Description of Related Art
As a technique for improving the reliability of communication services in an ATM transmission, the self healing process for automatically setting a new communication route by preparing a bypass of an original communication route in which a failure occurs has been known. A conventional ATM cell switch device which can perform such processing is shown in FIG.
1
.
FIG. 1
is a block diagram showing a construction of the conventional ATM cell switch device
11
together with two ATM terminals, in which one of the ATM terminals transmits data cell as a source terminal
21
and the other ATM terminal receives the data cell as a destination terminal
22
. Only portions of the ATM cell switch device
11
which are related to the data cell transfer from the source terminal
21
to the destination terminal
22
are shown in FIG.
1
.
The ATM cell switch device
11
includes a receiver circuit
13
a
which receives a cell including data cell and RM (Resource Management) cell for network control in relation to the data cell, a source terminal transmission rate measuring circuit
14
and a switch (SW) circuit
15
which receives the cell transmitted from the receiving circuit
13
a
through the source terminal transmission rate measuring circuit
14
. In the SW circuit
15
, a routing is performed on the basis of a VPI and VCI of a cell header of the cell and the cell is transmitted to the destination terminal
22
through a transmitter circuit
16
a
which is also included in the ATM cell switch device
11
. The RM cell aliased by the destination terminal
22
is transmitted to the source terminal
21
through a receiving circuit
16
b
, the SW circuit
15
and a transmitter circuit
13
b.
The source terminal transmission rate measuring circuit
14
counts the ATM cells on the receiving side and outputs the count to a control circuit
12
as a measured source terminal transmission rate signal. The measured source terminal transmission rate signal is used during a time period in which self healing is being executed as a source terminal transmission rate of a path to be monitored when the path to be monitored is a failure path and as an amount of use of frequency band of a bypass route when the path to be monitored is on a bypass route.
The control circuit
12
compares “source terminal transmission rate of an original route” with “amount of idle frequency band” calculated on the basis of the amount of use of frequency band in the bypass route to determine whether or not the original path can assure a frequency band therefor on the bypass route. When it is possible to assure the frequency band on the bypass route, the control circuit
12
outputs a self healing switch instruction signal to the SW circuit
15
to switch the original path to a path on the bypass route.
FIG. 2
is an illustration for explaining an example of frequency band assuring. When the amount of idle frequency band of the bypass route, that is, a value of the physical circuit capacity subtracted by the amount of use of frequency band of the bypass route, exceeds the source terminal transmission rate of the original route, it can be determined that the frequency band assuring is possible.
A problem in this case is that, in order to perform the self healing process, it is generally necessary to perform frequency band calculations of the original and the bypass routes and to rewrite a routing table and, therefore, there is a difference produced in time between a time when a frequency band is assured in the bypass route and a time when the switching of the original path to the bypass route is completed. Particularly, in the case of the ABR communication services, the source terminal transmits data at a rate corresponding to the state of network without preliminarily reserving a frequency band therefor. Therefore, when the self healing is to be performed, there is. a possibility that the transmission rate of the source terminal of the original path (failure path) or the transmission rate of the source terminal of the bypass path at the completion of the switching is increased compared with that at the band assuring time of the bypass route, that is, the start time of the self healing execution.
FIGS. 3 and 4
show examples of such case.
FIGS. 3 and 4
show cases where the source terminal transmission rates of the original route and the bypass route are increased at the completion of the switching to the bypass route compared with those at the band assuring time of the bypass route, respectively. As shown in
FIG. 3
, when the source terminal transmission rate of the original route at the switching time is increased compared with that at the band assuring time, a frequency band for the increment of the rate can not be assured necessarily. Therefore, a portion of cell, which corresponds to the increment of transmission rate, exceeds the physical circuit capacity of the bypass route and loss of the cell portion may occur. Further, as shown in
FIG. 4
, when the source terminal transmission rate of the bypass route at the time of switching is increased compared with that at the band assuring time, a sum of a frequency band therefor and an assured frequency band for the source terminal transmission rate to be switched from the original route may exceed the physical circuit capacity. Therefore, there is a possibility of loss of cell on the bypass route immediately after the switching thereto by the self healing even in such case.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a self healing method for continuing a cell transfer between a source terminal and a destination terminal when a failure occurs in an original path by assuring a frequency band on a bypass route and switching the original path to the bypass route without loss of cell and an ATM cell switch device for use in the same method.
According to a first aspect of the present invention, a self healing method for use in the ABR communication service in which, when a failure occurs in a path in which a cell transfer from a source terminal to a destination terminal is being performed at a variable rate, the cell transfer is maintained by assuring a frequency band in a bypass route different from the path in which the failure occurs and switching the path to the route, is featured by comprising the step of fixing upper limits of the cell sending rate at respective source terminals in both the path in which the failure occurs and the bypass route, during a time period from a time when a frequency band is assured in the bypass route to a time of completion of path switching.
In order to fix the upper limit of cell sending rate, an ATM cell switch device which performs the path switching and an ATM cell switch device on the bypass route set contents of ER (Explicit Rate) fields of BRM (Backward Resource Management) cells (referred to as “ER-in-BRM fields”, hereinafter) to be transferred to the respective source terminals to a value of the sending rate of one of the source terminals which is used at the time when the frequency band is assured in the bypass route during the time period from a time when the frequency band is assured in the bypass route to a time of completion of path switching. The respective source terminals set sending rates thereof according to the contents of the ER-in-BRM fields. Further, contents of ER fields of FRM (Forward Resource Management) cells (referred to as “ER-in-FRM cells”, hereinafter) to be transferred to the respective destination terminals are preferably set to the same value. The FRM cell is aliased by the destination terminal as a BRM cell. Since there is a possibility of loss of cell due to the failure o
Harper Kevin C.
Yao Kwang Bin
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