ATM cell multiplexer

Details ATM cell multiplexer ATM cell multiplexer

1998-03-11

2001-05-01

Ngo, Ricky Q. (Department: 2664)

Multiplex communications

Data flow congestion prevention or control

Control of data admission to the network

C370S395430, C370S474000, C370S535000

Reexamination Certificate

active

06226264

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an ATM cell multiplexer, and in particular to an ATM cell multiplexer connected between terminal equipments and an ATM switchboard. “ATM (Asynchronous Transfer Mode)” technology is expected as a communication technology for realizing a multi-media society, and has been developed for fast data used in an inter-computer communication etc.
However, as seen from a recent ATM forum, a network is demanded in the market where the communication protocols of the prior art such as for voices, HDLC (High level Data Link) and FR (frame relay) can also be interworked with the ATM technology.
When such a network is constructed, it is useful to set up an ATM cell multiplexer as an apparatus in branch circuit or line system in order to construct an ATM switchboard (ATM switch) as a key network and to increase the accommodation efficiency of circuits with terminal equipments.
2. Description of the Related Art
FIG. 1
shows a general arrangement of such an ATM cell multiplexer. An ATM cell multiplexer generally designated by reference numeral
2
is adapted to assemble data received from a terminal equipment generally designated by reference numeral
1
in form of an ATM cell, to send the data to an ATM switchboard generally designated by reference numeral
3
through a trunk circuit, and to disassemble the ATM cell (hereinafter simply referred to as the cell) which is received through the trunk circuit from the ATM switchboard
3
and transmitted to the terminal equipment
1
.
In this ATM cell multiplexer, although strict traffic control (QoS control) proper to the ATM protocol is demanded, the prior art ATM switchboard and ATM cell multiplexer installed an ATM switch (not shown) to perform the traffic control.
However, the ATM switch is disadvantageous in that the manufacturing cost is highly expensive and the control of the software/hardware is complicated, requiring a large-sized unit.
Moreover, in a system where cells are simply multiplexed, when the cells through plural connections mutually compete in the ATM cell multiplexer, some of the cells must be delayed or stood by to make the cells communicate without colliding in each of service categories such as CBR (Constant Bit Rate), VBR (Variable Bit Rate), and UBR (Unspecific Bit Rate).
This is not particularly allowed in a service category like CBR in which a time delay is strictly prohibited.
SUMMARY OF THE INVENTION
It is accordingly an object of the present invention to provide an ATM cell multiplexer which can simply and inexpensively assemble or disassemble cells without causing a time delay between terminal equipments and an ATM switchboard.
Namely, the ATM cell multiplexer according to the present invention is connected between terminal equipments
1
and an ATM switchboard
3
in the same manner as
FIG. 1
, and formed of an ATM bus scheduler
11
, an ATM bus
12
, and plural CLAD units
13
-
1
to
13
-
4
(represented by reference numeral
13
), as schematically shown in FIG.
2
.
The CLAD units
13
are connected in parallel on the ATM bus
12
and enable the cells to be transmitted to the ATM switchboard (see
FIG. 1
) through trunk circuit(line). Moreover, the ATM bus scheduler
11
serves to provide an opportunity when the cells out of the CLAD units
13
are transmitted. This ATM bus scheduler
11
achieves cell multiplexing operations and traffic controls without installing any ATM switch by controlling the transmission/reception of the cells on the ATM bus
12
.
In this case, the schedule means that the ATM bus scheduler
11
gives a transmission right of the cells to each of the CLAD units
13
. The ATM bus
12
transmits and receives the cell between the trunk circuit or backup circuit and the CLAD units
13
.
The CLAD units
13
accommodate terminal circuits connected to the terminal equipments (see FIG.
1
), and assemble data received from the terminal equipments in the form of cell which is to be transmitted to the ATM bus
12
. The cells received from the ATM switchboard through the trunk circuit are also transmitted to the ATM bus
12
and each of the CLAD units
13
.
The ATM bus scheduler
11
controls the ATM bus
12
as follows.
{circle around (1)} When the cells are transmitted to the ATM bus
12
from a plurality of the CLAD units
13
, the ATM bus scheduler
11
avoids the competition of the cells on the ATM bus
12
.
{circle around (2)} In order to transmit the cells to the ATM switchboard through the trunk circuit from the CLAD units
13
according to the service categories (CBR, rt (real time)-VBR, nrt (non-real time)-VBR, UBR) provided by the ATM forum, the ATM bus scheduler
11
gives the transmission right to each of the CLAD units
13
based on the service categories. Only when being given a transmission right by the ATM bus scheduler
11
, the CLAD units
13
transmit the cell to the ATM bus
12
.
{circle around (3)} The ATM bus scheduler
11
controls the cell transmission in agreement with the traffic quantity so that the transmission rate should not exceed a predetermined maximum cell rate (PCR) and average cell rate (SCR) when CLAD unit
13
transmit the cells.
It is to be noted that the above-mentioned ATM bus scheduler can control the transmission/reception of the cells by allocating the cells in the up and down directions equally on the ATM bus in case that a single trunk circuit is connected to the ATM switchboard.
Alternatively, the ATM bus scheduler can also control the reception of plural cells within a single time slot in the down direction while a single cell in the up direction in case that plural trunk circuits are connected to the ATM switchboard.
When there are a plurality of the above-mentioned trunk circuits and the physical speeds are mutually different, the ATM bus scheduler can select the detour or non-detour per each CLAD unit by thinning out a set interval in a memory table which determines the order of the transmission right given by the ATM bus.
It is possible that the ATM bus scheduler can extend the number of the trunk circuits by allocating the reception right per each CLAD unit in accordance with a preset schedule table by the traffic control which complies with a predetermined service category or the traffic quantity with respect to the cells not only in the up direction but also in the down direction.
It is also possible that an SVC call setting controller is provided besides the CLAD units to control the call set protocol, and to set in the CLAD units a connection ID determined on the trunk circuit, thereby connecting to the ATM switchboard.
The SVC call setting controller may set a virtual connection ID and have an SOFT-PVC function prescribed by the PNNI.
The above service categories may comprise CVR, rt-VBR, nrt-VBR, and UBR. The schedule table may be composed of a main table including all service categories except UBR and a sub-table including service categories with a lower priority for the transmission right. The ATM bus scheduler may assign the transmission right on the basis of the sub-table only when the CLAD units in the main table have abandoned the transmission rights.
The main table may be prepared so that the transmission rights for the CLAD units are equally allocated to every time slot in a frame in the order of CBR, rt-VBR and nrt-VBR and in the registration order of the CLAD units.
Alternatively, an ATM cell multiplexer according to the present invention may comprise plural CLAD units connected in parallel on an ATM bus so that ATM cells are assembled and disassembled between ATM cell interfaces equipments and an ATM switchboard, and an ATM bus scheduler for an ATM bus control connected to the CLAD units through the ATM bus, the ATM bus scheduler allocating a transmission right for each CLAD unit in accordance with a preset schedule table based on at least one of predetermined service categories and a traffic control corresponding to a traffic quantity for cell transmission in the up direction from the ATM cell interfaces to the ATM switchboard, and broadcasting t

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