UPC unit and UPC controlling method

A UPC unit 1 includes a congestion detecting circuit 4 for detecting a congesting status of a network 3 from a flow of cells in the backward direction and calculating or determining a parameter required for UPC based on the congestion status, a rewritable parameter memory 5 for storing the parameter, and a DGCRA circuit 6 for checking a conformance of cells in the forward direction on the basis of the information of the parameter memory 5 and the specified information.

BACKGROUND OF THE INVENTION 
The present invention relates to a communications network of a packet 
switching system, and more particularly to technology of a UPC unit which 
is subject to a feedback limitation such as an ABR traffic. 
As regulated in Shirish S. Sathaye, "The ATM Forum Traffic Management 
Specification Version 4.0", ATM Forum/95-0013R13, April, 1996 (TM4.0), the 
ABR service used in the ATM network is executed to report an allowable 
cell rate (ACR) from the network to a terminal so that the terminal can 
send out data at the ACR or lower rate. In general, the network for 
supporting the ABR service is operated to report a smaller ACR to the 
terminal if a traffic congestion takes place in the network or a larger 
ACR to the terminal if the traffic congestion does not take place. This is 
because the reduction of the traffic flown to the network leads to 
overcoming the congestion if the network is in congestion or the network 
may accept more traffics if the network is not in congestion. 
The traffic direction from the network to the terminal is called a 
backward. The traffic direction from the terminal to the network is called 
a forward. The network operates to monitor the forward traffic for 
checking if the rate is the ACR or lower. If the traffic at the ACR or 
more is sent to the network, the network is executed to impose a penalty 
on the traffic of the ACR or more (non-conformance cell) at the network 
gate. The penalty contains an action of lowering a priority of the 
non-conformance cell or abandoning the cell itself. 
This traffic monitoring and penalty handling are called a conformance check 
as described in TM 4.0. This conformance check is executed at the inlet of 
the unit called a UPC (simply called a UPC unit) based on the proper 
traffic parameter. Some of the UPC units treat a CBR or VBR. Herein, the 
description has been concerned with the UPC unit for treating the ABR. The 
traffic is abandoned if the nonconformance cell is sent out, so the 
terminal cannot keep the communications quality. To avoid this, the 
terminal tries to keep the ACR. 
On the other hand, the network guarantees the regulated communications 
quality against the traffic at the ACR or lower (conformance cell) in the 
forward direction. The terminals termed herein contain a general terminal 
of an information source, a VSVD regulated in TM 4.0, and the other 
general sources viewed from the network such as a router and a LAN, which 
are all called a terminal. If the information source belongs to a network 
promoted by another mother body, the UPC function is called NPC. Since the 
NPC is substantially identical to the UPC, herein, the NPC and the UPC are 
both called a UPC or UPC's. 
The ACR in the backward from the network to the terminal is temporarily 
stored in the UPC when the ACR passes through the UPC. The stored ACR 
reaches the terminal, where the ACR is effective as a monitoring rate for 
the UPC on the timing when the data reaches the UPC. The time taken in the 
process of UPC's receipt of the new ACR, passage of the ACR to the 
terminal, and arrival of the data at the ACR from the terminal to the UPC 
through the network is called .tau..sub.2. For example, it is assumed that 
the reciprocation of data between the UPC and the terminal has a delay of 
2 msec, the ACR of the UPC is set as 10 Mbps, and the traffic sent from 
the terminal is monitored if it is 10 Mbps or lower. When receiving the 
new ACR=5 Mbps from the network, the UPC operates to set the ACR as 5 Mbps 
2 msec later than the receipt and then monitor if the traffic from the 
terminal is 5 Mbps or lower. 
In actual, however, the delay between the UPC and the terminal is not 
always constant. It may be a statistical queuing delay. For example, it is 
assumed that the statistical delay minimum is .tau..sub.3 and the maximum 
is .tau..sub.5. The adoption of .tau..sub.5 as .tau..sub.2 permits the UPC 
to let the nonconformance cell pass if the queuing delay is zero. 
Conversely, the adoption of .tau..sub.3 as .tau..sub.2 permits the UPC to 
erroneously treat the conformance cell if the cell suffers from the 
queuing delay on the way to the UPC. 
The foregoing conventional UPC unit has a constant value of .tau..sub.2 set 
independently of the congestion. If .tau..sub.2 takes a large value, 
therefore, the UPC unit lets the nonconformance cell pass to the network 
if the network is in congestion, thereby increasing the congestion and 
lowering the communications quality. Conversely, if .tau..sub.2 takes a 
small value, the UPC unit lets even the doubtful cells be forcibly 
abandoned if the network is in congestion, thereby lowering the 
communication quality. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide a UPC unit and a method 
for controlling data through a UPC which enable to solve the foregoing 
problems. 
It is another object of the present invention to provide a UPC unit and a 
method for controlling data through a UPC which are arranged to prevent 
improper traffic flown to a network if the network is in congestion or 
prevent erroneous abandonment of doubtful cells if the network is not in 
congestion. 
The objects of the present invention are achieved by a UPC unit for 
controlling a traffic that is subject to feedback control, which 
comprises: congestion detecting means for detecting a congesting status of 
a network on flow of cells in backward direction and calculating 
parameters for UPC based on the detected congestion status; a rewritable 
parameter memory for storing the parameters; and checking means for 
checking a conformance of cells in forward direction based on information 
of the parameter memory and traffic information. 
The objects of the present invention are achieved by a method for 
controlling a traffic that is subject to feedback control for a UPC, which 
comprises the steps of: detecting a congesting status of a network from 
the flow of cells in backward direction and calculating a parameter for 
UPC control based on the detected congesting status; and checking a 
conformance of cells coming to a UPC unit in forward direction, based on 
the calculated parameter. 
According to an aspect of the invention, the UPC unit enables to grasp the 
congesting status of the network and adjust the value of .tau..sub.2 
according to the congesting status. If the network is in congestion, the 
UPC unit operates to prevent improper inflow of a traffic to the network 
by inhibiting as many non-conformance cells as possible. Conversely, if 
the network is in congestion, the UPC unit operates to prevent erroneous 
abandonment of doubtful cells to the network by flowing the doubtful cells 
to the network. 
It is preferable that the means for checking a conformance of cells 
utilizes the algorithm A contained in the DGCRA algorithm regulated in the 
appendix of TM 4.0. 
The parameter is 2, which indicates a timing on which the data sent at the 
ACR from the terminal reaches the UPC. 
The congestion detecting circuit operates to extract ER (Explicit Rate) 
information from a BRM (Background Resource Management) cell. If the new 
ER value is lower than the immediately previous ER value, the congestion 
detecting circuit operates to lower .tau..sub.2 by a decrement. If the 
lowered result is smaller than the minimum value .tau..sub.3, .tau..sub.2 
is replaced with .tau..sub.3. Conversely, if the new ER value is the same 
or greater than the immediately previous ER value, the congestion 
detecting circuit operates to increase .tau..sub.2 If the increased result 
is larger than the maximum value .tau..sub.5, .tau..sub.2 is replaced with 
.tau..sub.5. 
Further, the congestion detecting circuit operates to check if the 
operation regulations of the sending terminal regulated in TM 4.0 can 
trigger the action of decreasing or increasing the ACR. If the checking 
result reveals the change of the ACR, the new ACR is assumed as the 
extracted ER and is used for defining the value of .tau..sub.2.

DESCRIPTION OF THE EMBODIMENTS 
The present invention will be described along the embodiments with 
reference to the appended drawing. 
FIG. 1 is a block diagram showing a UPC unit according to an embodiment of 
the present invention. 
The present adaptive control UPC unit is installed in an UNI (User Network 
Interface) provided in a packet switching network as described in TM 4.0. 
If it is used as an NPC, it is installed in the NNI. 
As shown in FIG. 1, the UPC unit according to this embodiment is arranged 
to control the traffic that is subject to the feedback control like the 
ABR traffic as described in TM 4.0. The UPC is connected to a sending 
terminal 2 and a network 3 and includes a congestion detecting circuit 4, 
a parameter memory 5, and a DGCRA circuit 6. The congestion detecting 
circuit 4 operates to detect the congesting status of the network from the 
flow of cells in the backward direction and calculate or define parameters 
required for UPC control based on the detected congestion status. The 
parameter memory 5 is rewritable and stores the parameters. The DGCRA 
circuit 6 operates to perform a conformance check for the cells coming to 
the UPC unit in the forward direction by using the information stored in 
the parameter memory 5 and the specified information. 
Herein, the congesting status means a status presumed from the value 
standing for the congesting information of the network such as ER, CI, and 
NI of a RM cell in the backward. When the arrival interval of the RM cells 
is long, the network is likely to be in congestion, while when the arrival 
interval is short, the network is less likely to be in congestion. The 
arrival pattern of the RM cells may be a basis on which the congesting 
status is determined. 
The determined or presumed congesting status is used for determining part 
of a parameter required for UPC control. Herein, the part of the required 
parameter means such parameters such as .tau..sub.2 as changeable 
according to the congesting status of the network for improving the 
communications quality. 
The DGCRA circuit 6 operates to monitor the traffic from the terminal 2 to 
the network 3 on the traffic parameters and detect or extract the 
congesting information and the rate control information such as an arrival 
pattern or a cell type coming from the terminal 2 to the network 3 from 
the traffic or the cell payload. Further, the network congestion 
extracting circuit 4 operates to determine a parameter of .tau..sub.2 from 
the congesting information and the rate control information and write it 
to a .tau..sub.2 memory 5. The parameter .tau..sub.2 is part of the 
regulated traffic parameters. The parameters .tau..sub.2 accumulated in 
the .tau..sub.2 memory 5 is changed by the network congesting detecting 
circuit 4. 
In turn, the description will be oriented to the operation of each circuit. 
The DGCRA circuit 6 performs the conformance check regulated in TM 4.0. 
The UPC unit of this embodiment adopts an algorithm termed the algorithm A 
contained in the DGCRA algorithm regulated in the appendix of TM 4.0. 
Concretely, the DGCRA circuit 6 checks the cells coming from the sending 
terminal 2 to the UPC unit 1 one by one on the basis of the algorithm. 
This algorithm is executed to check if it is conformance. The cell 
determined to be conformance is sent to the network 3 as it is. The cell 
determined to be non-conformance is abandoned or may be sent to the 
network 3 after the priority of the cell is degraded. The algorithm is 
executed by using the traffic parameters as specified in TM 4.0, the part 
of which parameters are dynamic ones and may be changed according to a 
time point, occurrence of an event such as arrival of cells from the 
terminal 2 to the network 3 or from the network 3 to the terminal 2, an 
occurrence interval, and an occurrence sequence. The TM 4.0, however, 
indicates that the parameter .tau..sub.2 is determined when a connection 
is made without changing it. In the prior art, the parameter .tau..sub.2 
is not changed since the connection is made. In this embodiment, however, 
the UPC unit may define the maximum value .tau..sub.5 and the minimum 
value .tau..sub.3 and take any middle value between the maximum value 
.tau..sub.5 and the minimal value .tau..sub.3. The parameter .tau..sub.2 
may be any real value. In place, the set values of .tau..sub.2 may be 
reduced in number and may be discrete values. That is, these three values 
may be taken such as .tau..sub.3, .tau..sub.5, and .tau..sub.4 
(.tau..sub.4 =(.tau..sub.3 =.tau.5)/2). 
The network congestion detecting circuit 4 operates to extract the ER 
information from the BRM cell. If the newly extracted ER value is lower 
than the immediately previous ER value by f % or more, .tau..sub.2 is made 
lower by a decrement (1/s). If the value of .tau..sub.2 lowered by 1/s is 
made smaller than .tau..sub.3, the ER value is taken as .tau..sub.3. 
Conversely, if the newly extracted ER value is equal to or greater than 
the immediately previous ER value, the value of .tau..sub.2 is increased 
by delta .tau.. If the increased value is larger than .tau..sub.5, the ER 
value is made to be .tau..sub.5. In this embodiment, the delta 
.tau.=(.tau.5-.tau..sub.3)/10. However, the delta .tau. may be any 
positive value except that or may be experimentally determined on the 
trial-and-error basis. In this embodiment, the newly extracted ER value is 
compared with the immediately previous ER. In place, it may be compared 
with the ER values extracted in the past. Or, the reduction of the ER 
value may be determined to be statistically changed by the statistical 
method using the past average values and discrete values without 
considering the minute ER value fluctuation. 
Further, the network congestion extracting circuit 4 operates to check if 
the following status or condition is established where an action of 
increasing or decreasing the ACR is triggered according to the operating 
regulations of the sending terminal regulated in TM 4.0 such as a longtime 
absence of a BRM cell coming to the UPC unit. The checked result indicates 
the change of the ACR. If the changed ACR is made to be a new ACR, the new 
ACR is assumed as the extracted ER value, on which the parameter 
.tau..sub.2 is determined by the foregoing method. 
The congestion extracting circuit 4 operates to write the parameter 
.tau..sub.2 in the .tau..sub.2 memory 5 a time .tau.s later than the start 
of the process for determining the parameter .tau..sub.2. In this 
embodiment, if it is assumed that the process for determining .tau..sub.2 
consumes a time of .tau.6=100 msec, .tau.set=.tau.6 is established. 
.tau.set may be set as any value except .tau.6. 
The UPC operation is executed at each connection unit. Hence, this 
description has been oriented to one connection, In actual, the physical 
transmission path are shared by plural connections (cell-multiplexed), so 
that two or more connections may be treated by one UPC unit at a time. If 
two or more connections are treated at a time, the required number of the 
.tau..sub.2 memory 5 is equal to the number of the corresponding 
connections and the other circuits such as the network congestion 
detecting circuit 4 are operated at each connection unit. The UPC unit for 
one connection as described above may be easily changed to the UPC unit 
for the network with plural connections by the persons skilled in the art. 
As set forth above, according to the present invention, the UPC unit and 
the control method through the UPC are arranged to speed up the solving of 
the congestion when the network is in congestion and reliably put the 
doubtful cells in the network when the network is not in congestion. 
Hence, the arrangements are effective in keeping the communication quality 
of the doubtful cells constant. 
The ground for the above is as follows. When the network is in congestion, 
the traffic of the non-conformance cells that are not necessary and have 
an adverse effect on the network is inhibited to be flown into the 
network, thereby speeding up the solving of the congestion. In this case, 
the doubtful cells may be abandoned. However, if the doubtful cells are 
allowed to be flown in the network, they are more likely to be abandoned 
in the network when the network is in congestion. Hence, the UPC unit 
operates to abandon the doubtful cells in advance, thereby lowering the 
load of the network and effectively solving the congestion of the network. 
On the other hand, when the network is not in congestion, the traffic of 
the non-conformance cells may be flown into the network. If so, the 
traffic of the nonconformance cells is less likely to lower the 
communications quality of the network. Further, when the network is not in 
congestion, the doubtful cells are allowed to be positively put in the 
network, which does not lead to lowering the communications quality of the 
doubtful cells. 
The entire disclosure of Japanese Patent Application No. 8-221235 filed on 
Aug. 22, 1996 including specification, claims, drawing and summary are 
incorporated herein by reference in its entirety.