Electrical computers and digital processing systems: multicomput – Computer-to-computer protocol implementing – Computer-to-computer data transfer regulating
Reexamination Certificate
1997-01-29
2001-05-29
Maung, Zarni (Department: 2154)
Electrical computers and digital processing systems: multicomput
Computer-to-computer protocol implementing
Computer-to-computer data transfer regulating
C709S231000, C370S230000
Reexamination Certificate
active
06240460
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a data transmission system and method for performing contention control on data transmission attempts when a plurality of terminals transmit data at an arbitrary time point via a shared network.
DESCRIPTION OF THE RELATED ART
[Transmission Bandwidth Contention]
When a plurality of terminals execute data transmission at an arbitrary time point on a single network, transmission bandwidth contention may occur among data transmission attempts. First, this point will be discussed with reference to FIG.
2
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In general, a network consists of a plurality of transmission media. A plurality of terminals are connected to the network and data transmission is executed among the terminals via transmission media making up the network. The transmission bandwidth is represented by the transmission data amount per unit time. The transmission capability of a transmission medium has a limit and the maximum transmission bandwidth Rmax is a certain finite value.
The bandwidth of a transmission medium is shared by a plurality of data transmission attempts, and in each data transmission a bandwidth is used in accordance with the transmission data amount per unit time. The bandwidth use amount in each data transmission, r(t), changes with time.
If the total of the bandwidth use amounts of data transmission attempts sharing the bandwidth of the same transmission medium, &Sgr;r(t), is greater than the maximum transmission bandwidth of the transmission medium, Rmax, the data transmission attempts contend with each other for the shared bandwidth. This is called contention.
The contention occurs for the following reasons. The nucleus of data transmission is applications operating on the terminals connected to the network. Generally, a plurality of applications operate on each terminal. Of course, a plurality of applications operate when viewed from the entire network. The data transmission conditions of each application are characterized by the start time, the end time, a transmission terminal, a reception terminal, a route, and use bandwidth variation with time. Some applications involving data transmission have the data transmission conditions that cannot be predicted, such as telnet with human being's interaction as a transmission data source.
On the other hand, general data transmission is realized by a functional layered structure typified by the ISO 7-layer reference model. In the general conventional networks, applications operating on the networks are undefined and in the functional layer of data transmission control, control cannot be performed based on information that can be obtained only in a specific application. That is, when viewed from the side of a transmission medium which is a functional layer lower than the application layer, the data transmission conditions from each application sharing the transmission medium for executing data transmission are all handled as information that cannot be acquired.
Thus, it is impossible to grasp all the data transmission conditions such as the start time, the end time, a transmission terminal, a reception terminal, a route, and use bandwidth variation with time of each data transmission in the conventional networks. The information is predicted statistically or in probability.
Applications involving data transmission on the network generally operate separately and execute data transmission independently of the data transmission conditions of other applications. Thus, the data transmission attempts are independent of each other and are controlled plurally at their respective transmission ends.
Paying attention to one data transmission in such conditions, the bandwidth R(t) that can be used in the transmission changes with time because of tradeoffs with the bandwidth use conditions of other data transmission attempts. However, at the transmission end of the data transmission, the bandwidth use conditions of other data transmission attempts cannot be grasped, and other data transmission attempts are controlled separately at their respective transmission ends.
Thus, at the transmission end of the data transmission, the bandwidth use conditions of other data transmission attempts must be predicted to control the bandwidth use amount of the data transmission. If the prediction is erroneous, the total of the bandwidth use amounts of data transmission attempts sharing the same transmission medium, &Sgr;r(t), may sometimes exceed the maximum transmission bandwidth of the transmission medium, Rmax.
Such contention lowers the bandwidth use efficiency and should be avoided. That is, if a bandwidth required for transmission is not obtained because of bandwidth contention, data to be transmitted is lost. Generally, if data is lost, it is resent, whereby the effective bandwidth use efficiency (i.e., (data amount resulting in success in transmission)/(bandwidth amount used for transmission)) lowers. To suppress contention and efficiently use the maximum transmission bandwidth of each transmission medium limited, it is necessary to equally control the current bandwidth R(t) that can be used for data transmission and the bandwidth r(t) used by the data transmission at the sending end of the data transmission.
[Conventional Contention Avoidance Schemes]
Next, contention avoidance schemes in the conventional transmission technologies will be discussed. To share a single transmission medium for executing a plurality of data transmission attempts, switching technologies for allocating bandwidths among the data transmission attempts. The switching technologies are roughly classified into packet switching and circuit switching.
(1) Packet Switching
Data is divided into small units called packets for transmission. A bandwidth is allocated to a packet each time arriving at each transmission medium on the transmission route of the packet. This means that the bandwidth of each transmission medium is dynamically allocated in packet units among the data transmission attempts sharing the bandwidth at each point in time in the packet switching.
(2) Circuit Switching
Before data transmission, a bandwidth required for the transmission is previously allocated at each transmission medium on the route of the data transmission. This is called line connection. In contrast, releasing the bandwidth allocated at each transmission medium on the route is called line disconnection. Since the bandwidth at each transmission medium on the route of the data transmission is occupied during the period between the line connection and disconnection, the bandwidth that can be used for the transmission, R(t), becomes constant. This means that the bandwidth of each transmission medium is allocated comparatively statically in line units among the data transmission attempts sharing the bandwidth.
The control schemes to avoid bandwidth contention in the respective switching schemes correspond to the following items that are described in terms of control.
(1) Variable Value Control
A controlled variable (i.e., a bandwidth amount used for transmission at time t, r(t)) is manipulated for a changing target value (i.e., a bandwidth amount that can be used for transmission at time t, R(t)) and control is performed so that the difference |R(t)−r(t)| becomes zero.
(2) Constant Value Control
A controlled variable r(t) is manipulated for a constant target value Rconst and control is performed so that the difference |Rconst−r(t)| becomes zero. Control accuracy can be easily enhanced.
The conventional technologies have the following features.
(1) Packet Switching
Since a bandwidth is dynamically allocated to transmission actually using a transmission medium bandwidth, the maximum transmission bandwidth of the transmission medium, Rmax, can be used without waste. On the other hand, however, variable value control of the use bandwidth needs to be performed and at the time, excess or shortage may occur in manipulation of the controlled variable, as shown in FIG.
3
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i) R(t)−r(t)<0 (Controlled Variable
Hayano Takahiko
Hisanaga Takanori
Kamizawa Koh
Kawase Fumiyoshi
Kozawa Yuji
Caldwell Andrew
Fuji Xerox, Ltd.
Maung Zarni
Oliff & Berridg,e PLC
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