Multiplex communications – Pathfinding or routing – Switching a message which includes an address header
Reexamination Certificate
1998-03-23
2002-10-15
Yoa, Kwang Bin (Department: 2664)
Multiplex communications
Pathfinding or routing
Switching a message which includes an address header
C370S217000, C370S225000
Reexamination Certificate
active
06466576
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an ATM switching unit, and more specifically, to an ATM switching unit for accommodating a duplicated ATM cell transfer line.
In an ATM (Asynchronous Transfer Mode) network, ATM switching unit (ATM switching units) are provided as nodes (switching points) for constituting the ATM network. The ATM switching unit connects a plurality of lines for constituting the ATM network (a plurality of reception lines and a plurality of transmission lines). Then, when a cell transmitted from another transfer apparatus (another ATM switching unit, etc.) is received from the reception line, the ATM switching unit transmits the cell from the transmission line functioning as an output path by using transfer path information stored in a header of this received cell.
As transfer path information of a cell, a VPI (virtual path identifier)/VCI (virtual channel identifier) are stored in a header of a cell. The ATM switching unit contains a line processing unit for converting a VPI/VCI into address information about a counter party (transfer destination), and an ATM switch for switching a cell to any one of plural transfer lines based on this address information. Then, when the line processing unit and the switch are actuated, a plurality of cells which are received by the same ATM switching unit and contain the same VPIs/VCIs are transmitted from the same transfer line in this same ATM switching unit.
By the way, a memory capacity employed in the ATM switching unit is limited. For this reason, in the line processing unit and the switch, the above-explained address converting process and routing process cannot be carried out while directly using a VPI (12 bits) and a VCI (16 bits) of a received cell. Therefore, the line processing unit converts the VPI/VCI of the received cell into 13-bit reduced information (path identifier) called as an ICID-A, and executes the above-explained address converting process and routing process with employment of this ICID-A.
Also, there are duplicated lines connected in the ATM switching unit in view of important factors of transferred data. In other words, lines connected in the ATM switching unit are constructed of a working line for a presently operable system and a protection line for a spare operation system, and cell transmission is carried out by employing this working line under normal condition, whereas when a failure happens to occur in this working line, this troubled working line is switched to the protection line so as to perform the cell transmission.
FIG. 12
is a functional block diagram for showing an arrangement of a line processing unit (input line processing unit)
1
containing a duplicated line in a conventional ATM switching unit. In this drawing, the line processing unit
1
is arranged by an individual unit, a VCC table (common unit)
3
, and an address converting unit
4
provided in the VCC table
3
. The individual unit is constituted by a reducing unit ACT (action) connected to a working line WL, and a reducing unit SBY (standby) connected to a protection line PL. The VCC table (common unit)
3
is connected to the reducing unit ACT and the reducing unit SBY, respectively. Then, the VCC table
3
of the line processing unit
1
is connected to a switch
5
.
Both the working line WL and the protection line PL transfer the same cell, and the same cell is entered via either the working line WL or the protection line PL to the reducing unit ACT and the reducing unit SBY. When a cell is inputted, both the reducing unit ACT and the reducing unit SBY convert a VPI/VCI stored in a header of this inputted cell into an ICID-A, and thereafter transmit the cell toward the VCC table
3
.
In this case, the cell entered into the reducing unit SBY corresponds to a spare cell, and therefore is not required unless a failure happens to occur in the working line WL. As a result, the cell sent out from the reducing unit SBY is forcibly discarded before being entered into the VCC table
3
under such an initial condition that no failure happens to occur in the working line WL. Accordingly, only the cell sent out from the reducing unit ACT is inputted into the VCC table
3
. As a result, the following problem can be avoided. That is, the spare cell will flow into the ATM switching unit, and thus may give the unnecessary processing workload to this ATM sustaining apparatus.
On the other hand, the cell sent out from the reducing unit ACT is entered into the address converting unit
4
of the VCC table. Upon receipt of the cell sent out from the reducing unit ACT, the address converting unit
4
converts the ICID-A saved in the header of this cell into address information about a counter party, and then transfers the cell to the switch
5
. Then, when the switch
5
receives the cell from the VCC table
3
, this switch
5
performs the switching operation in accordance with the address information stored in the header of this cell.
However, the above-described line processing unit
1
of the conventional ATM switching unit owns the following problems. That is, the presently available ATM switching unit is capable of connecting, for instance,
16
sets of lines at maximum, and is provided with the reducing units, the total number of which is selected in accordance with a total number of lines to be connected in order to house the respective lines. The respective reducing units are connected to the VCC table
3
. To simplify the structure of the presently available ATM switching unit, the duplicated line are set as follows: Only when the reducing unit SBY for connecting the protection line PL is installed adjacent to the reducing unit ACT for connecting the working line WL, the cell transferred to the protection line PL is forcibly discarded. In other words, the discarding process of the cell transferred to the spare cell line is carried out based upon the connecting position of the duplicated lines.
For that reason, in such a case that the protection line PL is connected in such a reducing unit located apart from namely not located adjacent to the reducing unit for connecting the working line WL, the cell transferred via the protection line PL is not discarded before being entered into the VCC table
3
, but would flow into the ATM switching unit.
As a consequence, in the case that a user who presently uses a single cell line wants to duplicate the cell lines in the conventional ATM switching unit, such a reducing unit must be empty which is located adjacent to the reducing unit into which this single cell line has been connected. Also, when duplicated lines are newly set in the conventional ATM switching unit, two sets of reducing units located adjacent to each other should be empty.
SUMMARY OF THE INVENTION
In view of the above-mentioned problems, the present invention has been made, and therefore, it is an object of the present invention to provide an ATM switching unit capable of discarding a cell transferred to a spare cell line irrespective of connecting positions of duplicated lines, and thus capable of more properly duplicating lines.
To solve the above-described problems, an ATM switching unit of the present invention may employ the following arrangements:
That is, an ATM switching unit according to a first aspect of the present invention is comprised of: cell receiving means for receiving the same cells from two lines through which the same cells are transferred; cell information storing means for storing specific information indicative of a cell of a presently operable system into only the cell received from one line among the cells received by the cell receiving means, and for storing the specific information into only the cell received from the other line when a failure happens to occur in the one line; discarding means for receiving the cells from the cell information storing means to discard such a cell into which the specific information is not stored; and transferring means for specifying an output path of such a cell which is not discarded by the discarding means, and for transferring the
Ishioka Eiji
Odaka Hiromi
Sekine Shigeru
Duong Frank
Fujitsu Limited
Katten Muchin Zavis & Rosenman
Yoa Kwang Bin
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