Multiplex communications – Communication techniques for information carried in plural... – Combining or distributing information via time channels
Reexamination Certificate
1998-02-18
2001-03-06
Vincent, David R. (Department: 2732)
Multiplex communications
Communication techniques for information carried in plural...
Combining or distributing information via time channels
C370S544000
Reexamination Certificate
active
06198754
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a network system, a transmitting device and a receiving device, which are used for transmitting a plurality of cells forming a broad band cell string generated in, e.g., a broad band rate network by use of a plurality of narrow band rate lines.
In a network using an ATM (Asynchronous Transfer Mode), if there exists no line having a capacity enough to transmit ATM cells (a broad band cell string) of a broad band cell rate, it is required that the broad band cell string be demultiplexed into narrow band cell strings corresponding to a plurality of low-speed lines and thus be transmitted. There is known a network system incorporating a line demultiplexing cell communication function. Herein, the line dividing the cell communicating function is defined as a function of demultiplexing the broad band cell string into a plurality of narrow band cell strings, and transmitting and receiving the respective narrow band cell strings.
As the network system incorporating the line demultiplexing cell communication function, for example, there exists (1) a network system including a band demultiplexer for demultiplexing a broad band cell string received via a high-speed UNI (User Network Interface) such as (1) OC3C etc into low-speed UNIs and thus transmitting these UNIs and a band multiplexer for generating a broad band cell string by multiplexing narrow band cell strings received from the low-speed UNIs, or (2) a network system including a low-speed line broad band device for generating the broad band cell string, allocating each of a plurality of cells forming this broad band cell string to a plurality of low-speed UNIs and thus transmitting the cells and a low-speed line broad band device for restoring the plurality of cells received via the plurality of low-speed UNIs into the broad band cell string and thus transmitting the broad band cell string.
FIG. 25
is a diagram illustrating an example of the network system including a band demultiplexer
5
and a band multiplexer
6
. The network system shown in
FIG. 25
is a network system in which a low-speed ATM network is connected as a relay network between high-speed ATM networks. Shown therein is such a construction that the data (cells) are transmitted from a left side to a right side on the sheet surface in FIG.
25
.
Referring again to
FIG. 25
, each of the band demultiplexer
5
and the band multiplexer
6
is connected via the low-speed UNI to the low-speed ATM network
7
having a plurality of low-speed lines (three low-speed lines &agr;
1
-&agr;
3
in FIG.
25
). A customer premises Equipment (CPE)
2
a
to which data terminal equipments (DTES)
1
a
,
1
b
are respectively connected, is connected via the high UNI to the band demultiplexer
5
. A CPE
2
b
to which DTEs
1
c
,
1
d
are respectively connected, is connected via the high UNI to the band multiplexer
6
.
In the above-described network system, for example, the DTE
1
a
transmits the data to the DTE
1
c
, and the DTE
1
b
transmits the data to the DTE
1
d
. In this case, cells X
1
, X
2
, . . . , Xn stored with the data are transmitted from the DTE a to the DTE
1
c
defined as a transmitting destination. Cells Y
1
, Y
2
, . . . , Yn held with the data are transmitted from the DTE
1
b
to the DTE id defined as a transmitting destination.
Thereupon, the CPE
2
a
multiplexes the plurality of cells received from the DTE a, DTE
1
b
in order of being received, and transmits the cells to the band demultiplexer
5
. At this time, the plurality of cells transmitted from the CPE
2
a
are form one broad band cell string having order of, e.g., the cell X
1
, the cell X
2
, the cell Y
1
, the cell Y
2
,
The band demultiplexer
5
, upon receiving the plurality of cells forming the above broad band cell string from the CPE
2
a
, cyclically allocates the respective cells to the low-speed lines &agr;
1
-&agr;
3
in the order of being received. For instance, the band demultiplexer
5
transmits the cell X
1
to the low-speed line &agr;
1
, the cell X
2
to the low-speed line &agr;
2
, the cell Y
1
to the low-speed line &agr;
3
, and the cell Y
2
to the low-speed line &agr;
1
. With this transmission, the broad band cell string is demultiplexed into three narrow band cell strings transmitted via the low-speed lines &agr;
1
-&agr;
3
. The three narrow band cell strings thus formed are transferred to the band multiplexer
6
via the low-speed lines &agr;
1
-&agr;
3
.
The band multiplexer
6
receives the narrow band cell string via each of the low-speed lines &agr;
1
-&agr;
3
, and restores the previous broad band cell string by multiplexing these cell strings. That is, the band width multiplexer
6
, upon receiving the plurality of cells forming the narrow band cell strings, forms the previous high-speed cell string therefrom and transfers the high-speed cell string to the CPE
2
b.
The CPE
2
b
, when receiving the plurality of cells forming the broad band cell string from the band multiplexer
6
, transfers the cells X
1
-Xn the DTE
1
c
in the order of being received from the band multiplexer
6
on the basis of connection address data (address data about of the transmitting destination) stored in each cell. Further, the CPE
2
b
transfers the cells Y
1
-Yn the DTE
1
d
in the order of being received from the band multiplexer
6
. In this way, the DTE
1
c
receives the data transmitted from the DTE
1
a,
and the DTE
1
d
receives the data transmitted from the DTE
1
c.
Incidentally, if a fluctuation of the cells in the low-speed ATM network
7
is 0, and if cell delay times are all the same, the broad band cell string is formed by use of the cells received cyclically by the band multiplexer
6
via the low-speed lines &agr;
1
-&agr;
3
in the order of being received, in which case the broad band cell string is restored in the order (the cell X
1
, the cell X
2
, the cell Y
1
, the cell Y
2
, . . . ) of being transmitted from the band demultiplexer
5
.
In reality, however, the cell delay time becomes different according to the low-speed lines &agr;
1
-&agr;
3
, and the cell fluctuation has a finite value. Therefore, the cells do not arrive at the band multiplexer
6
in the order of being transmitted from the band demultiplexer
5
. Accordingly, when the band multiplexer
6
restores the broad band cell string in the order of receiving the cells, the cell order becomes different from the order of being transmitted from the DTE
1
a
or DTE
1
b.
In this case, the cells do not arrive at the DTE
1
c
or DTE
1
d
defined as a cell receiving equipment in an accurate order. Accordingly, it might happen that an error occurs in the data transmitted to the DTE
1
c
or DTE
1
d.
To cope with this error, the band demultiplexer
5
has a transmitting unit
5
a
, while the band multiplexer
6
has a receiving unit
6
a
. Then, the transmitting unit
5
a
and the receiving unit
6
a
make the band multiplexer
6
generate the broad band cell string from the plurality of narrow band cell strings in a proper cell order.
FIG. 26
is a diagram showing an example of operations of the band demultiplexer
5
(the transmitting unit
5
a
) and the band multiplexer
6
(the receiving unit
6
a
) illustrated in FIG.
25
.
In order to generate the broad band cell string from the narrow band cell strings transmitted via the plurality of low-speed lines &agr;
1
-&agr;
3
in the proper cell order, it is required that a delay in the low-speed ATM network
7
be known beforehand by the band multiplexer
6
. Therefore, the transmitting unit
5
a
of the band demultiplexer
5
transmits training cells TR
1
-TR
3
to the low-speed lines &agr;
1
-&agr;
3
at the same timing. Then, the receiving unit
6
a
of the band multiplexer
6
measures a delay time of each of the low-speed lines &agr;
1
-&agr;
3
from a receiving time of each of the training cells TR
1
-TR
2
.
The receiving unit
6
a
does not, however, grasp a transmitting time of each of the training cells TR
1
-TR
3
, and therefore measures a relative delay time (T
1
, T
Fujitsu Limited
Helfgott & Karas P.C.
Vincent David R.
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