Multiplex communications – Data flow congestion prevention or control – Control of data admission to the network
Reexamination Certificate
1998-11-09
2002-10-15
Kizou, Hassan (Department: 2662)
Multiplex communications
Data flow congestion prevention or control
Control of data admission to the network
C370S253000, C370S395100
Reexamination Certificate
active
06466545
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the way how the transmission rate of packets is controlled in a packet transmitting system. More particularly, it relates to an apparatus and a method in which the control parameters of the transmission rate of cells, such as an “initial cell rate” (ICR), a “rate increase factor” (RIF) and a “rate decrease factor” (RDF), are dynamically altered in the ABR (Available Bit Rate) service of an ATM (Asynchronous Transfer Mode) network, thereby to control the transmission rate of the cells of a transmission terminal.
2. Description of the Related Art
At present, in the ATM Forum and the ITU-T (International Telecommunication Union-Telecommunication Standardization Sector), a service called “ABR (Available Bit Rate) service” is under study as a method in which data exchange technology based on the ATM is applied to high-speed data communication networks such as LANs (Local Area Networks) and WANs (Wide Area Networks).
In communications which utilize the ABR service, resource management cells (RM cells) are used for notifying the information items of the resources of the network to terminals. The transmission terminal sends out the RM cell each time it sends out a predetermined number of user data cells. The RM cell arrives via the network at the reception terminal, at which it is looped back to return to the transmission terminal again.
Meanwhile, an ATM switch or exchange included in the network writes the resource information items (bandwidth information, congestion information) from the ATM switch itself, into the RM cell passing therethrough, thereby to notify the information of the network side to the transmission terminal. The transmission terminal which has received the RM cell bearing the bandwidth information and the congestion information, recalculates an “allowed cell rate” (ACR) in accordance with these information items and sends out the cells at a transmission rate not exceeding the ACR.
Besides, in establishing an ABR connection at the start of the communications, the transmission terminal reports to the network a “peak cell rate” (PCR) being the maximum transmission rate, and a “minimum cell rate” (MCR) being the lowest transmission rate, and it negotiates about the values of these rates. Herein, the transmission terminal cannot send out the cells at a rate which is higher than the PCR determined as the result of the negotiations. On the other hand, the network guarantees the transmission terminal that transmission rate of the cells which is not lower than the MCR obtained by the negotiations. In the ABR service, accordingly, the ACR of the transmission terminal fluctuates within a range of the MCR to the PCR both inclusive (MCR≦ACR≦PCR).
Owing to the above operations, the utilization of the ABR service permits the network side to avoid congestion and to recover from congestion, and it also permits the terminal side to transmit the cells at a high transmission rate in a case where the resource of the network is idle.
At present, the operations of the transmission terminal and reception terminal which communicate by utilizing the ABR service are subjects for standardization in the ATM Forum. The main operations of the terminals will be outlined below.
FIG. 1
is a conceptual diagram of a flow control in the ABR service.
Referring to the figure, as indicated by a forward flow A, an ABR transmission terminal
1
sends out cells in a forward direction (from a transmission side to a reception side) at a rate of or below an ACR each time. On that occasion, the ABR transmission terminal
1
sends out one RM cell
4
F to a switch (or ATM exchange)
3
each time it sends out a predetermined number of user data cells
2
. Besides, in a case where the ABR transmission terminal
1
has received an RM cell
4
B from the switch
3
, it increases the value of the ACR to the amount of a predetermined constant magnitude (for example, a magnitude of RIF×PCR) by utilizing the RIF, on condition that a “congestion indicator” (CI) bit and a “no increase” (NI) bit, not shown, contained in the RM cell
4
B are respectively set at “0” (not congested) and “0” (increase not allowed). In contrast, on condition that the CI bit is set at “1” (congested), the ABR transmission terminal
1
decreases the value of the ACR to the amount of a predetermined constant magnitude (for example, a magnitude of RDF×PCR) by utilizing the RDF. Further, after the above operation, the ABR transmission terminal
1
makes a comparison between the magnitudes of the value of an “explicit cell rate” (ER) written in the RM cell
4
B and the value of the ACR obtained by the above calculation, and it sets the value of smaller magnitude as a new ACR. On this occasion, the value of the ACR must fall within a range of MCR≦ACR≦PCR.
As indicated by a backward flow B in
FIG. 1
, an ABR reception terminal
5
terminates the user data cells
2
sent in from the transmission side. Also, the ABR reception terminal
5
loops back the received RM cell
4
F and sends it out toward the ABR transmission terminal
1
in a backward direction (from a reception side to a transmission side). In this case, on condition that an “explicit forward congestion indication” (EFCI) bit expressive of “being congested” is set at “1” in the user data cell
2
A received immediately before the reception of the RM cell
4
F, the ABR reception terminal
5
sets “1” at the CI bit contained in the RM cell
4
F to-be-looped-back, and it sends out the RM cell
4
after the setting, as the RM cell
4
B in the backward direction.
Next, the functions of the ATM exchange or switch
3
in the ABR service will be explained.
The operations of the network side or the ATM exchange
3
for implementing the ABR service are broadly divided into two categories, which are respectively called the “EFCI mode” and “ER mode”.
In the EFCI mode, subject to the congestion of the network, the ATM exchange
3
sets “1” at an EFCI bit in a user data cell
2
which is to pass through the ATM exchange
3
, and it causes this cell
2
to pass therethrough.
In the ER mode, the ATM exchange
3
calculates an ER being an explicit rate which is used for limiting the ACR on the side of the transmission terminal
1
, to a specified value in accordance with the internal resources and congested situation of the network, and it writes the calculated value into a forward or backward RM cell
4
which is to pass through the ATM exchange
3
. Herein, the ATM exchange
3
compares an ER value already contained in the RM cell
4
, with the ER value calculated by itself, and it sets the calculated ER value in the ER field of the pertinent RM cell
4
on condition that this calculated ER value is smaller.
Further, it is possible that the ATM exchange
3
or the reception terminal
5
generates an RM cell separately from an RM cell
4
F sent out of the transmission terminal
1
, whereupon it sends out the generated RM cell to the side of the transmission terminal
1
.
As stated before, the transmission terminal
1
increases or decreases the value of the ACR with reference to the set value of the CI bit or NI bit contained in the RM cell
4
B, by utilizing the parameter RIF or RDF. In this regard, it has heretofore been the actual circumstances that the values of the parameters RIF and RDF are determined when a call is set (that is, when an ABR connection is established), and that they cannot be thereafter altered.
Accordingly, the decremental or incremental magnitude of the ACR is constant irrespective of the degree of congestion of the network for the reason that the parameters RIF and RDF are constant. In other words, the decremental magnitudes of the ACR become equal in both a case where the network is excessively congested and a case where it is lightly congested. Likewise, the incremental magnitudes of the ACR are equal without regard to the degrees of non-congestion of the network.
However, the decremental width of the ACR should preferably be made larger in the case of the excessively c
Fujitsu Limited
Katten Muchin Zavis & Rosenman
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