Multiplex communications – Data flow congestion prevention or control – Flow control of data transmission through a network
Reexamination Certificate
1999-12-28
2004-11-02
Pham, Chi (Department: 2663)
Multiplex communications
Data flow congestion prevention or control
Flow control of data transmission through a network
C370S252000
Reexamination Certificate
active
06813245
ABSTRACT:
BACKGROUND OF THE INVENTION
1) Field of the Invention
The present invention relates to an ATM (Asynchronous Transfer Mode) communication system, and a congestion state detection method and an ATM communication device in the ATM communication system.
2) Description of the Related Art
ATM is a technique of transferring information, which is provided with high-speed switching by hardware processing and provides high quality of services (QOS) which is sufficient for realizing multimedia data communication. The ATM technology has been developed as practicable technology by the efforts of the organizations such as the ITU-T (International Telecommunication Union-Telecommunication Standardization Sector) and the ATM Forum.
In addition, various products and services in accordance with a number of standards for the ATM technology have been provided by manufacturers and carriers, and a large market of the ATM products and services has already been developed. In particular, interworking between high-speed, high-quality ATM communication networks for using the Internet. technology over such ATM communication networks are intensively studied. The study is also conducted by IETF (the Internet Engineering Task Force), in addition to the above organizations.
The ATM technology was first used as a backbone of a LAN (Local Area Network). At that time, a typical LAN used the Ethernet, and the mainly used transmission rate of the Ethernet was 10 Mbps or 100 Mbps. On the other hand, the mainly used rate of interface of ATM communication networks was 156 Mbps. Therefore, the ATM communication networks functioned well as a backbone of the above LAN. Recently, the 100 Mbps Ethernet is dominant, and further the Gigabit Ethernet having the transmission rate of 1 Gbps is supplanting the ATM.
However, faster interfaces for ATM, such as ATM interfaces having the transmission rates of 2.4 Gbps and 10 Gbps, have been standardized, while the speeding up of the Ethernet seems to be near the limit.
Under the above circumstances, the ATM technology was next used in a wide area service in which a plurality of private networks (e.g., LANs) are connected to each other. Although, conventionally, high-speed digital dedicated-line services are mainly used for connections between the private networks in a wide area service, only a small number of predetermined transmission rates are provided by such high-speed digital dedicated-line service, and gaps-between the values of the predetermined transmission rates are great. Therefore, it is necessary to bundle more than one dedicated line or use a dedicated line having excessive bandwidth for satisfying user's requirement.
On the other hand, in the ATM dedicated-line services, virtual channels (VCs) can be set as permanent virtual connection in small unit amounts. For example, in the ATM Mega Link Service, which is currently provided by NTT Communications Corporation in Japan, users can select the transmission rate in 1 Mbps increments in the range of 1 to 135 Mbps. As another example, the Super Relay Service is a virtual channel (VC) service, which is also provided by NTT Communications Corporation in Japan. The Super Relay Service provides a number of options for the transmission rate, such as 16 Kbps, 32 Kbps, 48 Kbps, . . . 1 Mbps, 2 Mbps, . . . 10 Mbps, in the low transmission rate range, and a switched virtual connection (SVC) service.
In addition, due to the statistical multiplexing gain in the ATM technology, network service providers can reduce equipment investment and lower service tariff to reduce users' cost. It is expected that the ATM services are further diversified in the future to provide further options corresponding to various needs of users.
In the ATM services, a plurality of service categories are provided to cope with various traffic characteristics. For example, the ATM Forum Traffic Management Specification Version 4.0 (af-tm-0056.0) provides the following four service categories:
(i) CBR (Constant Bit Rate)
In the CBR service, users' cell transmission rates are completely guaranteed within a range defined by a Peak Cell Rate (PCR). The service category CBR achieves quality corresponding to the conventional dedicated-line service.
(ii) UBR (Unspecified Bit Rate)
The UBR service is a best-effort service, in which users' cell transmission rates are not guaranteed even under the PCR. When congestion occurs in the network, cells may be discarded. In ATM-LANs, traffic is generally controlled in the manner of the UBR service.
(iii) VBR (Variable Bit Rate)
The VBR service guarantees a contracted Sustainable Cell Rate (SCR) as an average of cell transmission rates from a user when congestion does not occur in the network. For cell transmission rates exceeding the Sustainable Cell Rate (SCR) and not exceeding the PCR, the VBR service is a best-effort service like the UBR service. It is generally said that the VBR service is suitable for bursty traffic.
(iv) ABR (Available Bit Rate)
The ABR service guarantees users' cell transmission rates under a Minimum Cell Rate (MCR). In addition, the ABR service includes notification of a state of resources in the network or a receiver-side (destination) endsystem to a transmitter-side (source), endsystem. Therefore, the transmitter-side endsystem can vary a cell transmission rate between the Minimum Cell Rate (MCR) and the Sustainable Cell Rate (SCR) in response to the notified state of resources.
Only three of the above service categories, CBR, UBR, and VBR, are provided in the ATM communication networks currently operating in the world. However, the UBR and VBR services do not include notification of congestion, although cells may be discarded under these services. That is, the currently operating networks do not have a function of notifying an endsystem of occurrence of congestion.
FIG. 24
shows endsystems which transmit cells from one to the other through an ATM communication network. In
FIG. 24
, the endsystems are ATM routers
100
and
200
, and the ATM communication network
300
does not have the function of notifying an endsystem of occurrence of congestion. Therefore, endsystems such as ATM routers
100
and
200
in
FIG. 24
cannot perform, in the ATM layer, control (e.g., reduction) of cell transmission rates corresponding to the occurrence of congestion (i.e., discard of a cell) in the ATM communication network such as the network
300
in
FIG. 24
, and the endsystems using the UBR or VBR service of the conventional ATM communication network usually send cells at the PCR on the premise that cells may be discarded.
As described above, when the UBR or VBR service of the conventional ATM communication network is used, cells may be discarded due to occurrence of congestion. Nevertheless, the current network does not have functions of detecting and notifying the occurrence of congestion. Actually, ATM-exchanges or the like which constitute the ATM communication network do not have the above functions. Thus, endsystems cannot be informed of the occurrence of congestion (and discard of a cell), and therefore cannot perform cell rate control for coping with or avoiding the occurrence of congestion.
If a function of retransmitting a discarded cell is provided in another layer above the ATM layer, it is possible to recover information contained in the discarded cell. However, the congestion per se cannot be avoided unless the cell rate control is performed in the ATM layer.
On the other hand, if the ATM communication network provides the aforementioned ABR service, the ATM communication network has the function of notifying an endsystem of occurrence of congestion. Therefore, endsystems can recognize the occurrence of congestion, and perform the cell rate control. However, in order to implement the ABR service in the conventional ATM communication network, all of the endsystems and the ATM communication network including all the ATM exchanges and other constituents of the ATM communication network need substantial modification. Therefore, considering design, manufacturing, and cost, it
Fujitsu Limited
George Keith M.
Katten Muchin Zavis & Rosenman
Pham Chi
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