Short cell multiplexer

Details Short cell multiplexer Short cell multiplexer

1998-03-17

2002-10-22

Chin, Wellington (Department: 2664)

Multiplex communications

Pathfinding or routing

Switching a message which includes an address header

C370S537000

Reexamination Certificate

active

06470014

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to a multiplexer for multiplexing a plurality of short cells containing low-bit rate information on an ATM connection in communications involving the use of an ATM (Asynchronous Transfer Mode) network.
Generally, communications using an ATM network are carried out by transmitting ATM cells from a transmitting station to a receiving station. The ATM cell consists of a 5-byte header and a payload defined as a 48-byte fixed length data storage area. The payload is stored with user data. The ATM cell is, when transmitted within the ATM network, allocated with one destination (VPI/VCI: Virtual Path Identifier/Virtual Channel Identifier) per connection. Therefore, the header of one ATM cell is stored with information about only one connection.
Incidentally, in the field of mobile communications utilizing a radio system, the information to be transmitted is embedded (cell assembled) in a compression-coded status in the payload of the ATM cell in order to effectively utilize communication bands. The compression-coded information is several bps to several tens of bps, and has an extremely lower bit rate than a transmission speed of the ATM cell. The low-bit rate information takes a relatively long time till it occurs (arrives). Hence, pieces of compression-coded information sequentially occurred are stored directly in the payload of the ATM cell, and, when the payload becomes full of the compression-coded information, the ATM cell is transmitted to the ATM network. If this method is taken, a cellulating process is delayed, i.e., the data transmission is delayed. This delay of data transmission is undesirable because of causing a decline in quality of the communications.
Thus being the case, a transmission method capable of restraining the delay of data transmission due to the delay of the cellulating process and effectively utilizing the transmission bands, is examined in an ATM forum and ITU-T etc. As one of the transmission methods under the examination, there is proposed a method by which the payload of the ATM cell is stored with a plurality of variable-length short cells having a short data length.
FIG. 15
is a conceptual diagram showing a process of multiplexing the short cell in the payload of the ATM cell. Referring to
FIG. 15
, a short cell
1
consists of a short cell header
2
and a short cell payload
3
. The short cell header
2
contains a CID (short cell connection identifier) for identifying a connection of the short cell, and a length indicator (LI) for indicating a payload length of the short cell.
Then, as shown in
FIG. 15
, the plurality of short cells
1
are multiplexed in the payload
7
of the ATM cell
5
and then transmitted. At this time, one short cell
1
is mapped extending in two ATM cells
5
(which is called an overlap), depending on a position where the short cell
1
is embedded in the payload
7
.
Thus, if the plurality of short cells
1
are multiplexed within the ATM cell
5
transmitted on the same connection, a time for which the payload
7
of the ATM cell
5
becomes full of the data can be reduced by the CID attached to each short cell, and hence the delay of the cellulating process, i.e., the delay of data transmission can be restrained.
By the way, there is a CLAD (Cell Assembly and Disassembly) as a technique for storing the payload of the ATM cell
5
with data given from one information source.
FIG. 16
is a diagram showing a structure of the CLAD. Referring to
FIG. 16
, a CLAD
8
is constructed of a data storage buffer
9
, a data quantity monitoring unit
10
, a reading control unit
11
, and an ATM cell header generating unit
12
.
The data storage buffer
9
accumulates data inputted from an information source. The data quantity monitoring unit
10
monitors whether or not a quantity of the data stored in the data storage buffer
9
exceeds one cell. When the data exceeding one cell are accumulated, the reading control unit
11
is notified of this fact. The reading control unit
11
, upon receiving the notification from the data quantity monitoring unit
10
, reads the data for one cell from the data storage buffer
9
, and supplies the data to the ATM cell header generating unit
12
. The ATM cell header generating unit
12
attaches the ATM cell header
6
to the one-cell data (embedded in the payload
7
) read from the data storage buffer
9
, thereby generating the ATM cell
5
. Then, the thus generated ATM cell
5
is transmitted to the ATM network
13
.
The above-described CLAD
8
is, however, structured on the premise that the data stored in the payload
7
of the ATM cell
5
be transmitted on the same connection. Therefore, in the case of the multiplexing the above short cells
1
by use of the CLAD
8
, the respective short cells
1
are required to have the same connection information (which are required to be transmitted on the same connection). Accordingly, it was impossible to multiplex the plurality of short cell
1
having different connection data.
Obviation of this problem entails the short cell multiplexer in which the plurality of short cells
1
having the different connection data are multiplexed and stored in the payload
7
of the ATM cell
5
, and this ATM cell is transmitted on the same connection. Herein, for example, the above short cell multiplexer can be actualized by providing buffers corresponding to QOS classes classified according to QOS conditions containing connection statuses (types), designating a reading band for each QOS class, designating a sequence of the buffers for reading the short cells in accordance with the above designation, reading the short cells
1
one by one from the designated buffer, and multiplexing the short cells.
FIG. 17
is a conceptual diagram illustrating the short cell multiplexer having the construction described above. Referring to
FIG. 17
, the short cell multiplexer is constructed of an identifying unit
16
, a writing unit
17
, a storage unit
18
, a reading unit
19
, and a reading sequence control unit
20
. The short cell arriving is inputted to the identifying unit
16
.
The identifying unit
16
confirms a process of identifying the connection (such as confirming whether or not the connection is set an, if there is, e.g., “no setting”, disposing of the relevant short cell
1
and so on) on the basis of the CID stored in the short cell header
2
of the short cell
1
inputted to the identifying unit
16
itself. Further, on the basis of the CID of the short cell
1
, the identifying unit
16
executes a process of identifying which QOS class the short cell
1
belongs to.
The storage unit
18
is constructed of a plurality of FIFOs (First-In First-Out)
22
(
22
a
-
22
n
). Each of the FIFOs
22
a
-
22
n
constitutes a storage area of the short cell
1
, which correspond to the above-described QOS class. Each of the FIFOs
22
a
-
22
n
is stored with the short cell
1
having the same CID on the basis of a result of the identification by the identifying unit
16
.
The writing unit
17
receives the short cell
1
from the identifying unit
16
via a signal line
16
a
, and also receives the result of the identification (e.g., a QOS class number of the short cell
1
arriving at the identifying unit
16
) by the identifying unit
16
via a signal line
16
b
. Thereupon, the writing unit
17
switches over its own output in accordance with the QOS class number. The short cell
1
transmitted from the identifying unit
16
is stored in the FIFO
22
of the relevant QOS class by the writing unit
17
.
The reading sequence control unit
20
supplies the reading unit
19
with a sequence of reading the short cells
1
stored in the FIFOs
22
a
-
22
n
in accordance with a predetermined algorithm. for instance, the reading sequence control unit
20
gives to the reading unit
19
an indication of designating the QOS class of the short cells
1
in accordance with the reading sequence corresponding to a sending band preset per QOS class.
The reading unit
19
, upon receiving the indication of designat

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