Multiplex communications – Data flow congestion prevention or control – Flow control of data transmission through a network
Reexamination Certificate
1998-12-16
2003-04-15
Hsu, Alpus H. (Department: 2665)
Multiplex communications
Data flow congestion prevention or control
Flow control of data transmission through a network
C370S236200, C370S395200
Reexamination Certificate
active
06549518
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a policing apparatus in an ATM (Asynchronous Transfer Mode) network.
2. Description of the Related Art
In an ATM network using an ATM switching apparatus and an ATM local area network (LAN), a communication band which use is predicted is generally declared for every subscriber at the time of the joining contract in the subscriber system in which a subscriber is directly accommodated. The communication band is defined using the values such as a peak transmission rate of ATM cells and an average transmission rate thereof. When communication is started in the subscriber system, the traffic for every subscriber is monitored in accordance with the declaration value for every subscriber. Especially, when the transmission rate of the ATM cells sent out from the subscriber exceeds the declaration value, various processing is accomplished. For example, in a policing process, a part of the ATM cells sent out from the subscriber to exceed the declaration value is discarded. Also, in the tagging process, the priority level of the ATM cells is lowered, and the cell identification data is given to be primarily discarded when traffic jam is caused in the network.
The policing in a user network interface (UNI) as a subscriber interface of the ATM apparatus is also called usage parameter control (UPC). This policing process is the technique, which is necessary to prevent damage from extending to the other general subscriber in the form of cell; loss, when only a specific subscriber sends out ATM cells at the transmission rate more than the declaration value. In addition, the policing process, which is called a network parameter control (NPC), exists in a network node interface (NNI) in the network. This policing process will be explained using the UPC terminology in UNI. Also, various techniques are proposed about the technique, which measures the transmission rate of the specific ATM cells for the policing process.
However, in the conventional policing apparatus of the ATM network which has the conventional transmission rate measurement technique of the ATM cells, the following problems exist. Also, these techniques are not accomplished to the practical use due to various constraints.
The first problem in the conventional example is in the following point. That is, when a policing processing circuit is provided for every cell header identification data, i.e., in units of virtual pass identifier (VPI)/virtual channel identifier (VCI) of the ATM cell, the maximum number of policing processing circuits to be required become a huge value. For example, in case of the ATM cell in UNI, the number of circuits necessary at the maximum structure is 384,000 from the power for the number of bits of (VPI+VCI)=2
8
×2
16
=256×64 k=384,000.
When a memory is common to all ATM cells is used and is processed by a common circuit, the number of times of access to the common memory becomes necessary for the number of cell header identifiers. As a result, it has become a huge value. For example, in case of the ATM cells in UNI, it is necessary that access to the common memory is performed 384,000 times per one cell time, about 2.5 &mgr; second in 155 Mlines at a maximum structure, from the power for the number of bits of (VPI+VCI)=2
8
×2
16
=256×64 k =384,000.
By the way, the conventional policing technique is mainly classified into two groups. That is, one is a cell count method which contains a fixed window system, a sliding window system, and a leaky bucket system, and the other is a time comparing method which contains a reception time (time stamp) comparing system, a cell reception interval comparing system.
In the cell count method, the number of reception cells or the difference between the number of reception cells and a predetermined value for a predetermined time interval (window) or continuously is determined.
FIG. 1
shows a measurement example of ATM cell transmission rate in the fixed window system of the cell count method. In this example, a window size=5. As seen from the
FIG. 1
, there is a problem in that the large difference occurs to the cell count value based on an initial position of the window in case of the fixed window system. In this figure, the maximum value would be seen to be the cell count value=3. However, if the initial position is shifted in a front direction, the maximum value could be understood to be the cell count value=4.
Also, the transmission rate measurement is performed at the same time for a lot of ATM cells having different cell identification data (cell headers) in the fixed window system. In this case, it is necessary to perform the resetting operation of a counter and a reading operation of the count value at a time for all the ATM cells. Therefore, it is necessary that a lot of necessary counters for the number of cell identifiers are arranged and operated. Or, it is necessary that a counter is provided for the common memory, and the common memory is frequently accessed for the number of identifiers every time 1 ATM cell is received.
Next,
FIG. 2
shows a measurement example of a cell transmission rate in the sliding window system. According to this system, in the sliding window system, a window is slid continuously, compared with the case of the fixed window system. Therefore, it could be understood that the number of ATM cells could be correctly counted without influence due to the initial window position.
However, the transmission rate measurement is performed at the same time for a lot of ATM cells having different cell identification data (cell header). In this time, all windows are made to slide at a time, and the reading operation of the count value for each window must be performed at a time. Therefore, the same problem as the case of the fixed window system is caused. In this way, although the correct measurement is possible, the circuit structure and circuit operation become more complicated. For this reason, this system has a larger problem than the above system.
The leaky bucket system is not especially illustrated. Generally, a counter is used which is incremented by “1” each time an ATM cell is received and decremented by “1” for every predetermined time interval. When the count of the counter is balanced, the transmission rate is equal to a defined or predicted rate. When the reception of the cells continues, the counter is counted up. When the count value exceeds a constant value, it is thought of as the policing violation. In this case, the reception cell is subjected to the cell discarding process or the tagging process.
In case of the leaky bucket system, there is a problem in the following point. That is, a lot of up and down counters must be arranged or a common memory must be frequently accessed, when transmission rate measurement is performed at the same time to a lot of ATM cells having different cell identification data (cell headers), like the case of the fixed window system and the sliding window system. Thus, a fundamental problem as this point is left without being solved.
On the other hand, the time comparing system is an influential method, like the cell count method. A reception time (time stamp) is measured for every cell reception in some way and is stored for every cell. A time until the predetermined number of ATM cells is received is compared with a predetermined time. Or, a cell reception time interval is compared with a predetermined value for every ATM cell to determine the existence or non-existence of the policing violation.
FIG. 3
shows a policing example of the ATM cells in the reception time comparing system. In this reception time comparing system, a reception time value of an ATM cell is independently stored in the reception time memory for every cell identifier (cell header). In case of the policing value=3, the reception time of a current ATM cell is compared with the reception time of a cell which has been received before 3 c
Foley & Lardner
Hsu Alpus H.
NEC Corporation
Tran Thien D
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