Multiplex communications – Pathfinding or routing – Switching a message which includes an address header
Reexamination Certificate
1999-08-04
2004-05-04
Duong, Frank (Department: 2666)
Multiplex communications
Pathfinding or routing
Switching a message which includes an address header
Reexamination Certificate
active
06731637
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a method of and an apparatus for releasing a cut-through connection.
Network services provided for data transmission can be classified into a connection type and a connection-less type.
In the connection-type network service, communication data is transmitted through a communication channel which has been established exclusively between a sender terminal and a receiver terminal according to a telephone number, for example, designated by the sender terminal.
On the other hand, communication data is transmitted being divided into packets, such as IP (Internet Protocol) packets, each added with a header having destination information, in the connection-less-type network service. The packet received by a node of the network is relayed to a next node retrieved by referring to routing information prepared in the node according to the destination information described in the header. Being thus relayed node by node, each packet finally arrives to a destination node which accommodates the receiver terminal of the packet.
In the connection-less-type network service, communication channels between the sender terminal and the receiver terminal can be shared by packets having various destinations, enabling a good use of the network resources.
However, in view of transmission speed, the connection-type network service is advantageous, and substantially the same efficiency of the network resources can be obtained even in the connection-type network service when there are many packets to be transmitted continuously from a specific sender terminal to a specific receiver terminal.
Recently, a network node device called the IP switch is developed, wherein an ATM (Asynchronous Transfer Mode) switch is employed together with an IP controller which takes charge of routing the IP packets by controlling the ATM switch.
In the IP switch, continuous flows of IP packets, such as a flow of multi-media data or burst data, are taken in consideration, and a VC (Virtual Channel) is assigned to each distinct continuous flow of the IP packets, so that ATM cells of the concerning flows can be relayed promptly by way of “cell-switching”, that is, can be relayed directly by the ATM switch without reassembled into packet data.
In the IP switch, ATM cells of the IP packet arrived to the node for the first of each continuous flow are reassembled into packet data and transferred to the IP controller. When the IP packet is detected by the IP controller to belong to a continuous flow, such as a flow according to the FTP (File Transfer Protocol) or the HTTP (Hyper Text Transfer Protocol), a VC connection exclusively assigned to the flow is established in the ATM switch for performing a high-speed switching of the ATM cells of the flow, at the cell-level without passing the IP controller. This connection is called the cut-through connection.
The cut-through connection should be released when the concerning flow has been over, that is, when it is detected that any ATM cell of the concerning flow does not arrive for a predetermined time period.
Besides the IP switch, several network node devices, such as those called the LANE (LAN Emulation over ATM), the MPOA (Multi-Protocol Over ATM) or the IPOA (IP Over ATM), are proposed or developed in the ATM Forum or the IETF (Internet Engineering Task Force) by integrating the ATM and the IP technology.
In these network node devices, also, the cut-through connection is established for each continuous flow of the packet traffic, similarly to the IP switch, and established cut-through connections are monitored always individually for releasing them in the absence of their traffic for a certain time period.
For detecting the absence of the packet arrival for a certain period, a traffic monitoring means, which is realized conventionally with software and cell counters for counting cell arrivals on each cut-through connection, has been provided in any of the IP switch, the LANE, the MPOA and the IPOA.
FIG. 5
is a block diagram illustrating a configuration example of a conventional traffic monitoring means for detecting the absence of the cell arrival, and
FIG. 6
is a flowchart illustrating operational steps performed in the software for controlling the monitoring means of FIG.
5
.
A cell detecting unit
41
detects passage of ATM cells of each cut-through connection, which is notified to a cell counter
42
and the count value of the cell counter
42
is incremented by one with passage of one ATM cell.
In the software implemented in the IP controller, for example, initialization is performed (at step S
20
of
FIG. 6
) when a cut-through connection is newly established. A register A for storing the preceding count value of the cell counter
42
and a soft counter, both provided in the software, are reset to ‘0’, together with the cell counter
42
, and a timing clock, which indicates a timing periodically to read out the cell counter
42
, is started.
Every time the timing to read out the cell counter
42
arrives (YES at step S
21
), the count value of the cell counter
42
is read out (at step S
22
) and compared to the preceding count value of the cell counter
42
stored in the register A (at step S
23
).
When the count value is not equal to the preceding value, it means that at least one ATM cell of the cut-through connection is arrived and so, the concerning traffic is determined to be flowing normally. The preceding value stored in the register A is revised with the count value newly read out (at step S
24
), and the operational step returns to S
21
for repeating steps S
21
to S
24
.
When the count value of the cell counter
42
is detected to be equal to the preceding value (at step S
23
), the software counter is incremented by one (at step S
25
) as no ATM cell has arrived from the preceding read-out timing. Until the software counter counts a threshold value, the operational steps S
21
to S
26
are repeated. When the count value of the software counter attains to the threshold value, it is determined (at step S
27
) that the traffic of the corresponding cut-through connection has terminated, and the concerning cut-through connection is released.
However, a problem of the conventional traffic monitoring means as above described is that there must be performed many software processings, such as reading out the cell counter
42
(step S
22
), comparing the count value to the preceding value (steps S
23
and S
24
), or revising the software counter (step S
25
). Therefore, when the number of established cut-through connections becomes large, load of the software to be executed in the IP controller, for example, becomes too much increased.
Another problem of the conventional traffic monitoring means is that a large memory space is required because the software counter and the register A should be provided for each cut-through connection.
SUMMARY OF THE INVENTION
Therefore, a primary object of the present invention is to provide a method of and an apparatus for releasing a cut-through connection which is applicable to such network node devices and able to reduce load to be charged on software processings.
In order to achieve the object, in an apparatus according to an aspect of the invention for releasing a cut-through connection in a network node when traffic on the cut-through connection becomes smaller than a fixed value by monitoring traffic of each of cut-through connections established in the network node, there are comprised:
a timer having a time counter assigned to the cut-through connection and outputting a time-out notification signal when a count value of the time counter has attained to a time-out threshold value determined corresponding to the cut-through connection, the time counter being incremented along with time passage and being reset when the cut-through connection is established and when a cell of the cut-through connection arrives to the network node;
a time-out threshold memory wherein the time-out threshold value is registered;
a connection-release control unit for controlling a cell proce
Ikeda Hiroshi
Isoyama Kazuhiko
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