Multiplexer demultiplexer switching device and network adapter

Claims

What is claimed is:

1. A multiplexer in an asynchronous transfer mode network for multiplexing a plurality of demultiplexed virtual channels transmitting voice signals to a multiplexed virtual channel, said multiplexer comprising:

(a) a table capable of registering correspondences between virtual channel identifiers of said plurality of demultiplexed virtual channels transmitting voice signals among virtual channels being set on an incoming line and positions in an information field of a multiplexed cell belonging to said multiplexed virtual channel among virtual channels being set on an outgoing line; and

(b) cell multiplexing means for receiving demultiplexed cells being inputted from said incoming line and storing signals being stored in information fields of said demultiplexed cells belonging to a plurality of said demultiplexed virtual channels in prescribed positions of said information field of said multiplexed cell on the basis of said correspondence being register in said table for transmitting said multiplexed cell to said outgoing line.

2. The multiplexer in accordance with claim 1, wherein

said cell multiplexing means comprises:

(b-1) a first line,

(b-2) a plurality of second lines, and

(b-3) a third line,

said table being capable of further registering correspondences between said virtual channel identifiers of said plurality of demultiplexed virtual channels transmitting voice signals and said second lines,

said cell multiplexing means further comprising:

(b-4) distribution means receiving cells from said incoming line and comparing virtual channel identifiers of said cells with registered contents in said table for transmitting said cells to said first line when said cells belong to none of said demultiplexed virtual channels transmitting voice signals while distributing signals being stored in said information fields of said demultiplexed cells to any ones of said second lines on the basis of said correspondences being registered in said table when said cells are demultiplexed cells belonging to said demultiplexed virtual channels transmitting voice signals,

(b-5) multiplexed cell generation means for storing said signals being distributed to said plurality of second lines in prescribed positions in said information field of said multiplexed cell on the basis of said correspondences being registered in said table and transmitting said multiplexed cell to said third line, and

(b-6) integration means for transmitting said cells being transmitted to said first line and said multiplexed cell being transmitted to said third line to said outgoing line.

3. The multiplexer in accordance with claim 2, wherein

said cell multiplexing means further comprises:

(b-7) FIFO memory means being interposed in each of said plurality of second lines,

said multiplexed cell generation means successively reading said signals being stored in said FIFO memory means every constant period.

4. The multiplexer in accordance with claim 3, wherein

a display field is provided in a prescribed position of said information field of said multiplexed cell,

said multiplexed cell generation means further comprises:

(b-6-1) means for storing a signal expressing the fact of occurrence of an overflow or an underrun in said FIFO memory means, and a signal specifying one of said second lines causing said fact in said display field.

5. The multiplexer in accordance with claim 2, wherein

said cell multiplexing means further comprises:

(b-8) FIFO memory means being interposed in said third line,

said integration means transmitting said cells being transmitted on said first line to said outgoing line, while reading said multiplexed cell being stored in said FIFO memory means in coincidence with timing causing a vacant cell in said first line as well as inserting said multiplexed cell in said vacant cell and transmitting the same to said outgoing line.

6. The multiplexer in accordance with claim 2, further comprising:

(b-9) FIFO memory means being interposed in said first line,

said integration means transmitting said multiplexed cell being transmitted on said third line to said outgoing line, while reading said cell being stored in said FIFO memory means in coincidence with timing causing a vacant cell in said third line as well as inserting said cell from FIFO memory in said vacant cell and transmitting the same to said outgoing line.

7. A demultiplexer in an asynchronous transfer mode network for demultiplexing a multiplexed virtual channel transmitting voice signals to a plurality of demultiplexed virtual channels, said demultiplexer comprising:

(a) a table capable of registering correspondences between virtual channel identifiers of said plurality of demultiplexed virtual channels transmitting voice signals being set on an outgoing line and positions in an information field of a multiplexed cell belonging to said multiplexed virtual channel transmitting voice signals among virtual channels being set on an incoming line; and

(b) cell demultiplexing means for receiving said multiplexed cell being inputted from said incoming line and distributing signals in an information field of received said multiplexed cell to information fields of a plurality of demultiplexed cells respectively belonging to said plurality of demultiplexed virtual channels on the basis of said correspondences being registered in said table for transmitting said plurality of demultiplexed virtual channels to said outgoing line.

8. The demultiplexer in accordance with claim 7, wherein

said cell demultiplexing means comprises:

(b-1) a first line,

(b-2) a plurality of second lines, and

(b-3) a third line,

said table being capable of further registering correspondences between a virtual channel identifier of said multiplexed virtual channel transmitting voice signals and said second lines,

said cell demultiplexing means further comprising:

(b-4) distribution means receiving a cell from said incoming line and comparing a virtual channel identifier of said cell with registered contents in said table for transmitting said cell to said first line when said cell belongs to no said multiplexed virtual channel transmitting voice signals while distributing said information field of said multiplexed cell to any ones of said second lines on the basis of said correspondences being registered in said table when said cell is a multiplexed cell belonging to a multiplexed virtual channel transmitting voice signals,

(b-5) demultiplexed cell generation means for storing signals in respective said information fields being distributed to said plurality of second lines to said information fields of said plurality of demultiplexed cells on the basis of said correspondences being registered in said table and transmitting said demultiplexed cells to said third line, and

(b-6) integration means for transmitting said cell being transmitted to said first line and said demultiplexed cells being transmitted to said third line to said outgoing line.

9. The demultiplexer in accordance with claim 8, wherein

said cell demultiplexing means further comprises:

(b-8) FIFO memory means being interposed in said third line,

said integration means transmitting said cell being transmitted on said first line to said outgoing line, while reading said demultiplexed cells being stored in said FIFO memory means in coincidence with timing causing a vacant cell in said first line as well as inserting said demultiplexed cells in said vacant cell and transmitting the same to said outgoing line.

10. The demultiplexer in accordance with claim 8, further comprising:

(b-9) FIFO memory means being interposed in said first line,

said integration means transmitting said demultiplexed cells being transmitted on said third line to said outgoing line, while reading said cell being stored in said FIFO memory means in coincidence with timing causing a vacant cell in said third line as well as inserting said cell from FIFO memory in said vacant cell and transmitting the same to said outgoing line.

11. A switching device for relaying a plurality of subscriber's lines and a plurality of internode transmission paths in an asynchronous transfer mode network, said switching device comprising:

(a) switching means for switching cells being transmitted from said plurality of subscriber's lines at virtual channel levels and outputting said cells to any ones of output lines of the same number as said internode transmission paths; and

(b) a plurality of multiplexers, each employing each of said output lines of said switching means as an incoming line thereof while employing each of said internode transmission paths as an outgoing line thereof respectively,

each of said plurality of multiplexers being a multiplexer in said asynchronous transfer mode network for multiplexing a plurality of demultiplexed virtual channels transmitting voice signals to a multiplexed virtual channel,

each of said plurality of multiplexers comprising:

(b-1) a table capable of registering correspondences between virtual channel identifiers of said plurality of demultiplexed virtual channels transmitting voice signals among virtual channels being set on said incoming line and positions in an information field of a multiplexed cell belonging to said multiplexed virtual channel being set on said outgoing line, and

(b-2) cell multiplexing means for receiving demultiplexed cells being inputted from said incoming line and storing signals in information fields of said demultiplexed cells belonging to a plurality of said demultiplexed virtual channels in prescribed positions of said information field of said multiplexed cell on the basis of said correspondences being registered in said table for transmitting said multiplexed cell to said outgoing line.

12. A switching device for relaying a plurality of subscriber's lines and a plurality of internode transmission paths in an asynchronous transfer mode network, said switching device comprising:

(a) a plurality of demultiplexers, each having an incoming line being connected to each of said internode transmission paths respectively,

each of said plurality of demultiplexers being a demultiplexer in said asynchronous transfer mode network for demultiplexing a multiplexed virtual channel transmitting voice signals to a plurality of demultiplexed virtual channels, each of said plurality of demultiplexers comprising:

(a-1) a table capable of registering correspondences between virtual channel identifiers of said plurality of demultiplexed virtual channels transmitting voice signals being set on an outgoing line and positions in an information field of a multiplexed cell belonging to said multiplexed virtual channel transmitting voice signals among virtual channels being set on said incoming line, and

(a-2) cell demultiplexing means for receiving said multiplexed cell being inputted from said incoming line and distributing signals in said information field of received said multiplexed cell to information fields of a plurality of demultiplexed cells respectively belonging to said plurality of demultiplexed virtual channels on the basis of said correspondences being registered in said table for transmitting said plurality of demultiplexed virtual channels to said outgoing line, and

said switching device further comprising:

(b) switching means for switching cells outputted on said outgoing line of each of said plurality of demultiplexers at virtual channel levels and outputting said cells to any ones of said plurality of subscribers' lines.

13. A switching device for relaying a plurality of subscriber's lines and a plurality of internode transmission paths in an asynchronous transfer mode network, said switching device comprising:

(a) first switching means for switching cells being transmitted from said plurality of subscriber's lines at virtual channel levels and outputting said cells to any ones of output lines of the same number as said internode transmission paths; and

(b) a plurality of multiplexers, each employing each of said output lines of said switching means as first incoming line thereof while employing each of said internode transmission paths as first outgoing lines thereof respectively,

each of said plurality of multiplexers being a multiplexer in said asynchronous transfer mode network for multiplexing a plurality of demultiplexed virtual channels transmitting voice signals to a multiplexed virtual channel,

each of said plurality of multiplexers comprising:

(b-1) a table capable of registering correspondences between virtual channel identifiers of said plurality of demultiplexed virtual channels transmitting voice signals among virtual channels being set on said first incoming line and positions in an information field of a multiplexed cell belonging to said multiplexed virtual channel being set on said first outgoing line, and

(b-2) cell multiplexing means for receiving demultiplexed cells being inputted from said first incoming line and storing signals in information fields of said demultiplexed cells belonging to a plurality of said demultiplexed virtual channels in prescribed positions of said information field of said multiplexed cell on the basis of said correspondences being registered in said table for transmitting said multiplexed cell to said first outgoing line, said switching device further comprising:

(d) a plurality of demultiplexers, each having second incoming line being connected to each of said internode transmission paths respectively,

each of said plurality of demultiplexers being a demultiplexer in said asynchronous transfer mode network for demultiplexing a multiplexed virtual channel transmitting voice signals to a plurality of demultiplexed virtual channels,

each of said plurality of demultiplexers comprising:

(d-1) a table capable of registering correspondences between virtual channel identifiers of said plurality of demultiplexed virtual channels being set on a second outgoing line and positions in an information field of a multiplexed cell belonging to said multiplexed virtual channel transmitting voice signals among virtual channels being set on said second incoming line, and

(d-2) cell demultiplexing means for receiving said multiplexed cell being inputted from said second incoming line and distributing signals in said information field of received said multiplexed cell to information fields of a plurality of demultiplexed cells respectively belonging to said plurality of demultiplexed virtual channels on the basis of said correspondences being registered in said table for transmitting said plurality of demultiplexed cells to said second outgoing line,

said switching device further comprising:

(e) second switching means for switching said cells being outputted on said second outgoing line of each of said plurality of demultiplexers at virtual channel levels and outputting said cells to any ones of said plurality of subscriber's lines.

14. A switching device for relaying a plurality of first internode transmission paths and a plurality of second internode transmission paths in an asynchronous transfer mode network, said switching device comprising:

(a) a plurality of demultiplexers, each having first incoming line being connected to each of said first internode transmission paths respectively,

each of said plurality of demultiplexers being a demultiplexer in said asynchronous transfer mode network for demultiplexing a multiplexed virtual channel transmitting voice signals to a plurality of demultiplexed virtual channels, each of said plurality of demultiplexers comprising:

(a-1) a table capable of registering correspondences between virtual channel identifiers of said plurality of demultiplexed virtual channels being set on a first outgoing line and positions in an information field of a multiplexed cell belonging to said multiplexed virtual channel transmitting voice signals among virtual channels being set on said first incoming line, and

(a-2) cell demultiplexing means for receiving said multiplexed cell being inputted from said first incoming line and distributing signals in said information field of received said multiplexed cell to information fields of a plurality of demultiplexed cells respectively belonging to said plurality of demultiplexed cells on the basis of said correspondences being registered in said table and transmitting said plurality of demultiplexed cells to said first outgoing line,

said switching device further comprising:

(b) switching means for switching cells being outputted on said first outgoing line of each of said demultiplexers at virtual channel levels and outputting said cells to any ones of output lines of the same number as said second internode transmission paths, and

(c) a plurality of multiplexers, each employing each of said output lines of said switching means as second incoming line thereof while employing each of said second internode transmission paths as second outgoing line thereof respectively,

each of said plurality of multiplexers being a multiplexer in said asynchronous transfer mode network for multiplexing a plurality of demultiplexed virtual channels transmitting voice signals to a multiplexed virtual channel,

each of said plurality of multiplexers comprising:

(c-1) a table capable of registering correspondences between virtual channel identifiers of said plurality of demultiplexed virtual channels transmitting voice signals among virtual channels being set on said second incoming line and positions in an information field of a multiplexed cell belonging to said multiplexed virtual channel being set on said second outgoing line, and

(c-2) cell multiplexing means for receiving a plurality of demultiplexed cells respectively belonging to said plurality of demultiplexed virtual channels being inputted from said second incoming line and storing signals in information fields of said demultiplexed cells belonging to a plurality of said demultiplexed virtual channels in prescribed positions of said information field of said multiplexed cell on the basis of said correspondences being registered in said table and transmitting said multiplexed cell to said second outgoing line.

15. A switching device for relaying a plurality of first internode transmission paths and a plurality of second internode transmission paths in an asynchronous transfer mode network, said switching device comprising:

(a) a plurality of first demultiplexers, each having first incoming line being connected to each of said first internode transmission paths respectively,

each of said plurality of first demultiplexers being a demultiplexer in said asynchronous transfer mode network for demultiplexing a multiplexed virtual channel transmitting voice signals to a plurality of demultiplexed virtual channels,

each of said plurality of first demultiplexers comprising:

(a-1) a table capable of registering correspondences between virtual channel identifiers of said plurality of demultiplexed virtual channels being set on a first outgoing line and positions in an information field of a multiplexed cell belonging to said multiplexed virtual channel transmitting voice signals among virtual channels being set on said first incoming line, and

(a-2) cell demultiplexing means for receiving said multiplexed cell being inputted from said first incoming line and distributing signals in an information field of received said multiplexed cell to information fields of a plurality of demultiplexed cells respectively belonging to said plurality of demultiplexed virtual channels on the basis of said correspondences being registered in said table for transmitting said plurality of demultiplexed cells to said first outgoing line,

said switching device further comprising:

(b) first switching means for switching cells being outputted on said first outgoing line of each of said first demultiplexers at virtual channel levels and outputting said cells to any ones of first output lines of the same number as said second internode transmission paths, and

(c) a plurality of first multiplexers, each employing each of said first output lines of said first switching means as second incoming line thereof while employing each of said second internode transmission paths as second outgoing line thereof respectively,

each of said plurality of first multiplexers being a multiplexer in said asynchronous transfer mode network for multiplexing a plurality of demultiplexed virtual channels transmitting voice signals to a multiplexed virtual channel,

each of said plurality of first multiplexers comprising:

(c-1) a table capable of registering correspondences between virtual channel identifiers of said plurality of demultiplexed virtual channels transmitting voice signals among virtual channels being set on said second incoming line and positions in an information field of a multiplexed cell belonging to said multiplexed virtual channel being set on said second outgoing line, and

(c-2) cell multiplexing means for receiving demultiplexed cells being inputted from said second incoming line and storing signals in information fields of said demultiplexed cells belonging to a plurality of said demultiplexed virtual channels in prescribed positions of said information field of said multiplexed cell on the basis of said correspondences being registered in said table for transmitting said multiplexed cell to said second outgoing line,

said switching device further comprising:

(d) a plurality of second demultiplexers, each having third incoming line being connected to each of said second internode transmission paths respectively,

each of said plurality of second demultiplexers being a demultiplexer in said asynchronous transfer mode network for demultiplexing a multiplexed virtual channel transmitting voice signals to a plurality of demultiplexed virtual channels,

each of said plurality of second demultiplexers comprising:

(d-1) a table capable of registering correspondences between virtual channel identifiers of said plurality of demultiplexed virtual channels being set on a third outgoing line and positions in an information field of a multiplexed cell belonging to said multiplexed virtual channel transmitting voice signals among virtual channels being set on said third incoming line, and

(d-2) cell demultiplexing means for receiving said multiplexed cell being inputted from said third incoming line and distributing signals in an information field of received said multiplexed cell to information fields of a plurality of demultiplexed cells respectively belonging to said plurality of demultiplexed virtual channels on the basis of said correspondences being registered in said table for transmitting said plurality of demultiplexed cells to said third outgoing line,

said switching device further comprising:

(e) second switching means for switching cells being outputted on said third outgoing line of each of said plurality of second demultiplexers at virtual channel levels and outputting said cells to any ones of second output lines of the same number as said first internode transmission paths, and

(f) a plurality of second multiplexers, each employing each of said second output lines of said second switching means as fourth incoming line thereof while employing each of said first internode transmission paths as fourth outgoing line thereof respectively,

each of said plurality of second multiplexers being a multiplexer in said asynchronous transfer mode network for multiplexing a plurality of demultiplexed virtual channels transmitting voice signals to a multiplexed virtual channel,

each of said plurality of second multiplexers comprising:

(f-1) a table capable of registering correspondences between virtual channel identifiers of said plurality of demultiplexed virtual channels transmitting voice signals among virtual channels being set on said fourth incoming line and positions in an information field of a multiplexed cell belonging to said multiplexed virtual channel being set on said fourth outgoing line, and

(f-2) cell multiplexing means for receiving said demultiplexed cells being inputted from said fourth incoming line and storing signals in information fields of said demultiplexed cells belonging to a plurality of said demultiplexed virtual channels in prescribed positions of said information field of said multiplexed cell on the basis of said correspondences being registered in said table for transmitting said multiplexed cell to said fourth outgoing line.

16. A network adapter for relaying a synchronous mode transmission path in a synchronous transfer mode network and an asynchronous mode transmission path in an asynchronous transfer mode path, said network adapter comprising:

(a) interface means for demultiplexing a time-division multiplexed signal being transmitted from said synchronous mode transmission path and transmitting the same to a plurality of first output lines;

(b) cell adaptation means for setting virtual channels being varied with said first output lines and storing demultiplexed time-division signals in information fields of cells belonging to said virtual channels, thereby carrying out cellularization to create cellularized signals;

(c) integration means for transmitting cellularized signals to a second output line; and

(d) a multiplexer having said second output line as an incoming line and said asynchronous mode transmission path as an outgoing line,

said multiplexer being a multiplexer in said asynchronous transfer mode network for multiplexing a plurality of demultiplexed virtual channels transmitting voice signals to a multiplexed virtual channel,

said multiplexer comprising:

(d-1) a table capable of registering correspondences between virtual channel identifiers of said plurality of demultiplexed virtual channels transmitting voice signals among virtual channels being set on said incoming line and positions in an information field of a multiplexed cell belonging to said multiplexed virtual channel being set on said outgoing line, and

(d-2) cell multiplexing means for receiving demultiplexed cells being inputted from said incoming line and storing signals in information fields of said demultiplexed cells belonging to a plurality of said demultiplexed virtual channels in prescribed positions of said information field of said multiplexed cell on the basis of said correspondences being registered in said table for transmitting said multiplexed cell to said outgoing line.

17. A network adapter for relaying a synchronous mode transmission path in a synchronous transfer mode network and an asynchronous mode transmission path in an asynchronous transfer mode path, said network adapter comprising:

(a) a demultiplexer having an incoming line being connected to said asynchronous mode transmission path,

said demultiplexer being a demultiplexer in said asynchronous transfer mode network for demultiplexing a multiplexed virtual channel transmitting voice signals to a plurality of demultiplexed virtual channels,

said demultiplexer comprising:

(a-1) a table capable of registering correspondences between virtual channel identifiers of said plurality of demultiplexed virtual channels transmitting voice signals being set on an outgoing line and positions in an information field of a multiplexed cell belonging to said multiplexed virtual channel among virtual channels being set on said incoming line; and

(a-2) cell demultiplexing means for receiving said multiplexed cell being inputted from said incoming line and distributing a signal in an information field of received said multiplexed cell to information fields of a plurality of demultiplexed cells respectively belonging to said plurality of demultiplexed virtual channels on the basis of said correspondences being registered in said table for transmitting said plurality of demultiplexed cells to said outgoing line,

said network adapter further comprising:

(b) distribution means for distributing cells being outputted on said outgoing line of said demultiplexer to output lines being varied with virtual channels and transmitting the same,

(c) adaptation means for taking out said signals from said information fields of said cells being transmitted to said output lines of said distribution means, and (d) interface means for time-division multiplexing said signals as being taken out for transmitting the same to said synchronous mode transmission path.

18. A network adapter for relaying a synchronous mode transmission path in a synchronous transfer mode network and an asynchronous mode transmission path in an asynchronous transfer mode path, said network adapter comprising:

(a) first interface means for demultiplexing a time-division multiplexed signal being transmitted from said synchronous mode transmission path and transmitting the same to a plurality of first output lines;

(b) first adaptation means for setting virtual channels being varied with said first output lines and storing demultiplexed time-division signals in information fields of cells belonging to said virtual channels, thereby carrying out cellularization;

(c) integration means for transmitting cellularized signals to a second output line; and

(d) a first multiplexer having said second output line as a first incoming line and said asynchronous mode transmission path as a first outgoing line,

said first multiplexer being a multiplexer in said asynchronous transfer mode network for multiplexing a plurality of demultiplexed virtual channels transmitting voice signals to a multiplexed virtual channel,

said multiplexer comprising:

(d-1) a table capable of registering correspondences between virtual channel identifiers of said plurality of demultiplexed virtual channels transmitting voice signals among virtual channels being set on said first incoming line and positions in an information field of a multiplexed cell belonging to said multiplexed virtual channel being set on said first outgoing line, and

(d-2) cell multiplexing means for receiving demultiplexed cells being inputted from said first incoming line and storing signals in information fields of said demultiplexed cells belonging to a plurality of said demultiplexed virtual channels in prescribed positions of said information field of said multiplexed cell on the basis of said correspondences being registered in said table for transmitting said multiplexed cell to said first outgoing line,

said network adapter further comprising:

(e) a demultiplexer having a second incoming line being connected to said asynchronous mode transmission path,

said demultiplexer being a demultiplexer in said asynchronous transfer mode network for demultiplexing a multiplexed virtual channel transmitting voice signals to a plurality of demultiplexed virtual channels,

said demultiplexer comprising:

(e-1) a table capable of registering correspondences between virtual channel identifiers of said plurality of demultiplexed virtual channels transmitting voice signals being set on said demultiplexed virtual channels and positions in an information field of a multiplexed cell belonging to said multiplexed virtual channel among virtual channels being set on said second incoming line; and

(e-2) cell demultiplexing means for receiving said multiplexed cell being inputted from said second incoming line and distributing a signal in an information field of received said multiplexed cell to information fields of said demultiplexed virtual channels on the basis of said correspondences being registered in said table for transmitting said multiplexed cell to said demultiplexed virtual channels,

said network adapter further comprising:

(f) distribution means for distributing cells being outputted on said second outgoing line of said demultiplexer to third output lines being varied with virtual channels and transmitting the same,

(g) second adaptation means for taking out said signals in said information fields of said cells being transmitted to said third output lines of said distribution means, and

(h) second interface means for time-division multiplexing said signals as being taken out for transmitting the same to said synchronous mode transmission path.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a switching device and a network adapter for efficiently transmitting voice-band signals on an ATM network, and a multiplexer and a demultiplexer forming principal parts thereof.

2. Background of the Invention

<Background of ATM>

ISDN (integrated service digital network) is a communication network for integratedly providing various communication services such as voice communication and data communication through generic user-network interfaces. This ISDN is now developing to B-ISDN (broadband aspects of ISDN) aimed at providing high-speed communication services such as a visual telephone, a picturephone meeting and a cable television and simultaneously and efficiently providing a number of services which are varied with media. An ATM (asynchronous transfer mode) is a key technique supporting the B-ISDN. A network generally employing the ATM technique including the B-ISDN is generally called an ATM network.

In the ATM, blocks (called "ATM cells" or "cells") which are provided with header parts storing labels are transmitted in response to occurrence of information, similarly to a packet mode in ISDN which is precedent to the B-ISDN, i.e., N-ISDN (narrowband aspects of ISDN). Thus, it is possible to cope with arbitrary communication speeds including variable speed communication (service system transmitting burstly generated information at its original variable speed).

In the ATM, further, the cells are at a fixed length, dissimilarly to the packet mode. Therefore, the communication can be made with no inhibition of speed increase by positional detection for the header parts. Further, all data are stored in cells of the same shapes and subjected to processing such as exchange regardless of communication media such as voices, images and data, whereby it is possible to transmit various types of data in a single network in a one-way manner regardless of differences between the media.

In addition, protocols are simplified in the ATM with the background of quality improvement in the transmission media, while the same can be processed in a hardware manner with no software. Namely, the ATM is a technique which is mainly adapted to solve the problem of difficulty in coping with speed increase in the packet mode.

<Principle of ATM>

As hereinabove described, all data are carried on cells in the ATM. FIG. 16 is a structural diagram showing the structure of a cell 13. The data length of the cell 13 is fixed at 53 octets (1 octet=8 bits). The cell 13 is formed by a header part (cell header) 14 of 5 head octets and an information field part (also referred to as a "payload") 10 of 48 octets. The header part 14 stores an identifier indicating the destination, so that the cell 13 is transmitted to the destination through the identifier. Information such as a voice, an image and data is stored in the information field part 10.

FIG. 17 is a block diagram showing an exemplary structure of paths for transmitting cells each having the aforementioned structure, i.e., an ATM network. As shown in FIG. 17, two types of hierarchical information transmission paths (connections) including virtual channels (VC) 23a to 23d and virtual paths (VP) 24a to 24c and 25a to 25h are logically defined in the ATM network. The VCs 23a to 23d are connections forming the basis of ATM services, and a series of cells storing information such as voices and data of subscribers 21a to 21h are identified as those belonging to a single VC. In general, each VC is set between a pair of subscribers, as illustrated in FIG. 17.

The ATM network identifies the VC for a certain cell through a VCI (virtual channel identifier) which is stored in each header part. The values of such VCIs may be reloaded by ATM switching nodes (relay points) 22a to 22c. When a VC is set, a relevant switching node holds a conversion table of the VCI, so that connection is theoretically maintained between end subscribers. In such VC connections, respective segments which are delimited by the switching nodes are called VC links. Therefore, a single VCI value can be regarded as being supplied to a single VC link.

On the other hand, the VPs, each of which is formed by bundling a plurality of VCs, are generally set between the subscribers and the switching nodes (VCPs 25a to 25h in FIG. 17) or pairs of switching nodes (VPs 24a to 24c in FIG. 17). The ATM network identifies a VP for a certain cell through a VPI (virtual path identifier) which is stored in each header part. The values of such VPIs are released by the ATM switching nodes. Namely, the ATM switching nodes are nodes between the VC links, as well as terminating ends of the VP connections.

As to a system of transmitting voice-band signals through the ATM network, currently defined is a method of transmitting a 1 octet voice signal every 125 .mu.sec. with a 1 octet control signal, while storing the same in an information field part of a single cell. FIG. 18 typically shows the principle of this method. Voice signals 12 which are inputted in the unit of 1 octet every 125 .mu.sec. are stored in cells 13 by a cellularizing unit 11, and transmitted every 125 .mu.sec. These cells 13 are transmitted through the ATM network, as hereinabove described.

Each cell 13 stores a 1 octet control signal 15 and a 1 octet voice signal 12 in its information field part 10. In the information field part 10 of 48 octets, therefore, only 2 octets are used with no employment of the remaining 46 octets. Namely, the network bands are disadvantageously used in vain in transmission of voice signals through the ATM network.

In order to solve this problem, it may be possible to store the voice signals of the cells 13 belonging to a single VC by the information field length for simultaneously storing the same in a single cell. However, storage of the voice signals is accompanied with corresponding transmission delay. When 47 octet voice signals and 1 octet control data are stored in a single cell, for example, the delay reaches 5.875 msec. An efficient real-time operation is required for the voice signal transmission service, and the delay caused by this method results in unneglectable reduction in transmission quality.

SUMMARY OF THE INVENTION

According to a first aspect of the present invention, a multiplexer in an asynchronous transfer mode network for multiplexing a plurality of demultiplexed virtual channels transmitting voice signals to a multiplexed virtual channel comprises (a) a table capable of registering correspondences between virtual channel identifiers of the plurality of demultiplexed virtual channels transmitting voice signals among virtual channels which are set on an incoming line and positions in an information field of a multiplexed cell belonging to the multiplexed virtual channel among virtual channels which are set on an outgoing line, and (b) cell multiplexing means for receiving demultiplexed cells which are inputted from the incoming line and storing signals which are stored in information fields of the demultiplexed cells belonging to the plurality of demultiplexed virtual channels in prescribed positions of the information field of the multiplexed cell for transmitting the multiplexed cell to the outgoing line.

In the multiplexer according to the first aspect of the present invention, the signals in the information fields of the demultiplexed cells belonging to the plurality of demultiplexed virtual channels transmitting voice signals are stored in the information field of the multiplexed virtual channel. Therefore, it is possible to save the band in the transmission path setting the multiplexed virtual channel while suppressing delay fluctuation.

Preferably, the cell multiplexing means comprises (b-1) a first line, (b-2) a plurality of second lines, and (b-3) a third line, and the table is capable of further registering correspondences between the virtual channel identifiers of the plurality of demultiplexed virtual channels transmitting voice signals and the second lines. Preferably, the cell multiplexing means further comprises (b-4) distribution means receiving cells from the incoming line and comparing virtual channel identifiers of the cells with registered contents in the table for transmitting the cells to the first line when the cells belong to none of the multiplexed virtual channels transmitting voice signals while distributing signals which are stored in the information fields of the demultiplexed cells to any ones of the second lines on the basis of the correspondences which are registered in the table when the cells are demultiplexed cells belonging to the demultiplexed virtual channels transmitting voice signals, (b-5) multiplexed cell generation means for storing the signals which are distributed to the plurality of second lines in prescribed positions in the information field of the multiplexed cell on the basis of the correspondences which are registered in the table and transmitting the multiplexed cell to the third line, and (b-6) integration means for transmitting the cells which are transmitted to the first line and the multiplexed cell which are transmitted to the third line to the outgoing line.

In the multiplexer according to the first aspect of the present invention, the cells transmitted from the incoming line are sorted to those belonging to the plurality of demultiplexed channels transmitting voice signals and other cells, to be handled. Namely, multiplexing is carried out on the cells belonging to the plurality of demultiplexed channels transmitting voice signals, while no multiplexing is carried out on the remaining cells. Every one of the multiplexed and demultiplexed cells is outputted to the outgoing line by the integration means. According to this multiplexer, therefore, the cells transmitted from the incoming line are not restricted to those belonging to the plurality of demultiplexed channels transmitting voice signals to be multiplexed.

Preferably, the cell multiplexing means further comprises (b-7) FIFO type memory means which is interposed in each of the plurality of second lines, and the multiplexed cell generation means successively reads the signals which are stored in the FIFO type memory means every constant period.

The multiplexer according to the first aspect of the present invention comprises the FIFO type memory means interposed in the second line while the signals are periodically read from the respective FIFO type memory means, whereby delay fluctuation of cells inputted from the incoming line is absorbed.

Preferably, a display field is provided in a prescribed position of the information field of the multiplexed cell, and the multiplexed cell generation means further comprises (b-6-1) means for storing a signal expressing the fact of occurrence of an overflow or an underrun in the FIFO memory means, and a signal specifying one of the second lines causes the fact in the display field.

In the multiplexer according to the first aspect of the present invention, information on an overflow or an underrun in the FIFO type memory means is transmitted while being carried on the multiplexed cell. Therefore, it is possible to efficiently process the multiplexed cell in a demultiplexer, for example, on the basis of this information.

Preferably, the cell multiplexing means further comprises (b-8) FIFO type memory means which is interposed in the third line, and the integration means transmits the cells which are transmitted on the first line to the outgoing line, while reading the multiplexed cell which is stored in the FIFO type memory means in coincidence with timing causing a vacant cell in the first line as well as inserting the multiplexed cell in the vacant cell and transmitting the same to the outgoing line.

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