Multiplex communications – Data flow congestion prevention or control – Flow control of data transmission through a network
Reexamination Certificate
1996-07-08
2001-05-01
Nguyen, Chau (Department: 2663)
Multiplex communications
Data flow congestion prevention or control
Flow control of data transmission through a network
C370S395430
Reexamination Certificate
active
06226265
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a system for monitoring a flow of packets in a network, and particularly relates to a system for monitoring a flow of cells of an ABR communication in an ATM network.
2. Description of the Related Arts
In recent years, a service handling various types of communications, including image data which requires a higher transmission speed, in addition to voice data, text data, etc., has become more and more essential. The core technique of such a service is an ATM (Asynchronous Transfer Mode) method.
The ATM method takes advantage of a cell where control information called a header is added to its payload, divided into a fixed length of 48 octets, as a data transmission unit (data exchange unit).
Currently, discussions about an ABR (Available Bit Rate) service class are frequently made as a method for applying the ATM technique to a high-speed data communication network such as a LAN, a WAN, etc. In the ABR service class, congestion control is performed between a network and a terminal for each connection.
A CBR (Constant Bit Rate) service which allocates a fixed transmission band for each connection, monitors a maximum request band PCR, while a VBR (Variable Bit Rate) service which dynamically allocates a transmission band for each connection according to band information managed by a CAC (Call Admission Control), monitors the maximum request band PCR and an average request band SCR (Sustainable Cell Rate), in order to perform a congestion control using respective results of monitoring the above described bands.
For the ABR communication, a minimum available band MCR (Minimum Cell Rate) and the maximum request band PCR (Peak Cell Rate), are set by a negotiation between a user and a network, when a call is established. These settings are made by the CAC for each connection.
Also for the ABR communication, a data transmitting terminal transmits a cell called an RM (Resource Management) cell for each predetermined number of transmission data cells. The network or a receiving terminal writes control information indicating whether or not resource information or congestion occurs in the network, etc., to the RM cell, and returns that RM cell to the transmitting terminal. When receiving the RM cell to which the control information, etc. is written, the transmitting terminal calculates a transmission allowed band ACR (Allowed Cell Rate) according to the control information. The ACR is a cell rate at which the transmitting terminal is allowed to perform a transmission to a network (cell transfer speed). This cell rate varies between the minimum available band MCR and the maximum request band PCR. The transmitting terminal transmits a cell at a transfer rate within an allowable range of the ACR transfer rate. Thus, for the ABR communication, a cell rate at which a transmitting terminal is allowed to perform a transmission to a network is determined depending on a use state of a network by using feedback control.
If a network is not in congestion state, a transmitting terminal can transmit a cell in the maximum request band PCR. If the network is in congestion state, the transmitting terminal recognizes the congestion state by an RM cell fed back from the network, and progressively reduces a size of an ACR. The minimum value of the ACR is an MCR. Assume that the ACR at a certain transmitting terminal is the MCR. If the transmitting terminal transmits a cell at a transmission rate equal to or higher than the MCR (that is, if the transmitting terminal transmits the cell beyond the transmission-allowable range), the congestion state continues. This is because a large amount of cells flow into the network even though the network is in the congestion state. Even if the network is in a normal state (not in congestion state), the network may often enter a congestion state when the transmitting terminal transmits a cell at a transmission rate equal to or higher than the PCR or the ACR.
To prevent a network from entering congestion state, a process such as monitoring a flow of cells (an amount of data) at an entry point of the network, discarding a cell which violates a predetermined transmission rate (a PCR or an MCR), etc. must be performed. As a method for monitoring the flow of cells, a method for making a comparison between an actual flow of cells and a predetermined transmission rate (a PCR or an MCR) can be considered.
As described above, for the ATM technique which is the basic technique of a B-ISDN (Broadband-Integrated Service Digital Network), a usage parameter control technique (or a polcing technique) for controlling a flow of cells by determining whether or not a flow of user cells from a user terminal into an ATM network exceeds a value set by a user, becomes essential.
With the usage parameter control technique UPC, a flow of user cells is measured for each connection such as a virtual path (VP), a virtual channel (VC), etc., and a comparison between the flow of user cells and an amount of flow set by the user is made. As a result of the comparison, a violation cell is discarded or tagged (attached with a violation tag). As such a congestion control method in an ATM network, the above described ABR (Available Bit Rate) method is known.
A service implemented by the ABR method monitors a congestion caused by a concentration of traffic. If a congestion occurs, the transmission rate at a transmitting terminal must be lowered. To lower the transmission rate, it is currently being discussed to notify the transmitting terminal of a currently allowable transmission rate or a currently occurring congestion, so that the transmitting terminal which receives the notification can voluntarily lower its transmission rate.
With the service implemented by the ABR method, a user terminal reports a minimum cell rate (MCR), a peak cell rate (PCR), etc., when establishing a call, and transmits data based on these parameters. A network instructs the user terminal to vary an ACR (Allowed Cell Rate) according to its congestion state, depending on need. The usage parameter control UPC implemented by the ABR method performs a usage parameter control for the varying ACR.
FIG. 1
is a schematic showing an ATM network.
The ATM network is configured by, for example, interconnecting an arbitrary number of ATM switches (SWs), and arranging a virtual path VP and a virtual channel VC between a transmitting terminal and a receiving terminal as shown in
FIG. 1
, in order to transmit an ATM cell. In this case, a usage parameter control unit UPC monitoring if a user transmits cells as set is positioned at an entry point of the ATM network.
The usage parameter control UPC determines whether or not an arrived cell is a violation cell. If the arrived cell is determined to be a violation cell, it is discarded or tagged. The leaky bucket algorithm, for example, is recommended as a standard algorithm by the ITU-T, etc. The virtual scheduling algorithm equivalent to the leaky bucket algorithm is also well-known.
FIGS. 2A and 2B
are schematics showing a notification process of a congestion.
21
indicates a user transmitting terminal.
22
indicates a user receiving terminal.
23
and
24
indicate switches such as an ATM switch (SW
1
and SW
2
). The ATM network is configured by these switches
23
and
24
.
FIG. 2A
is a schematic diagram showing a congestion notification method implemented by a forward notification, while
FIG. 2B
is a schematic diagram showing a congestion notification method implemented by a backward notification.
User cells are transmitted from the user terminal
21
, and an RM cell is inserted as a control cell for each predetermined number of user cells. When it receives the RM cell, the receiving terminal
22
returns the RM cell. In this case, the RM cell transmitted from the transmitting terminal
21
to the receiving terminal
22
is called an F-RM (Forward RM) cell, while the RM cell transmitted from the receiving terminal
22
to the transmitting terminal
21
is called a B-RM (Backward RM) cell.
FIG. 3
shows
Ishihara Tomohiro
Katoh Masafumi
Kawasaki Takeshi
Kusayanagi Michio
Nakamichi Koji
Fujitsu Limited
Helfgott & Karas, P C.
Lee Chiho Andrew
Nguyen Chau
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