1. Field of the Invention
The present invention relates to a communication system where a single subscriber line terminal (SLT) unit on a network side and a plurality of terminal units on a user side share a single transmission line and transfers information by time division multiplexing through polling.
As a typical example of such a type of communication system, there is an asynchronous transfer mode-passive optical network (ATM-PON) communication system. The present invention will be explained below with reference to the example of this ATM-PON communication system. In particular, the present invention provides an improved technique for dynamic bandwidth allocation for handling variable rate traffic in such an ATM-PON communication system.
2. Description of the Related Art
As will be explained in detail later with reference to the drawings, in a conventional communication system handling variable rate traffic, no consideration at all is given to parameters such as the peak cell rate (PCR), sustainable cell rate (SCR), and burst tolerance (BT). Therefore, the problem arose of allocating large bandwidths continuously without limit to virtual connections (VC) in which large numbers of cells are accumulated in buffers of the terminal units on the user side. Therefore, the subscriber line terminal (SLT) unit at the network side could no longer make effective use of the communication resources as planned.
An object of the present invention is to provide a method and apparatus for dynamic bandwidth allocation designed to improve the efficiency of transfer of information in a communication system handling variable rate traffic and simultaneously ensure that the peak cell rate (PCR), sustainable cell rate (SCR), burst tolerance (BT), and other contracted parameters are observed by shaping the allocated bandwidths.
To attain the above object, the communication system according to the present invention is comprised of a queue length extracting function unit (41) extracting from information stored for each connection, a parameter setting function unit (42) for setting the contracted parameters of a sustainable cell rate (SCR) and peak cell rate (PCR) and contracted parameters of fluctuation values allowed in these bandwidths for each connection, a parameter managing memory (43) for storing the queue length information and the contracted parameter information, a bandwidth calculating function unit(44) for re-storing in the memory (43) results of periodic calculation of the cell rates allocated to connection so that the contracted parameters are observed, and a transfer polling information generating function unit (45) determining timings of transfer of information in accordance with the calculated allocated cell rates and outputting them as the polling information. Due to this, it is possible to improve the efficiency of allocation of bandwidth in a transmission line between a plurality of terminal units such as optical network units (ONU) and a subscriber line terminal (SLT) in an ATM-PON communication system while observing the contracted parameters.
These and other objects and features of the present invention will become clearer from the following description of the preferred embodiments given with reference to the attached drawings, wherein:
Before describing the embodiments of the present invention, the related art and the disadvantages therein will be described with reference to the related figures.
The communication system 1, as illustrated, is roughly comprised of a user side, a network side, and a transmission line connecting the two.
First, looking at the user side, this includes personal computers (PCs) 2, telephones (TEL) 3, and other apparatuses owned by the users. Each user apparatus transfers information with other user apparatuses (not shown) through an ATM switch (ATM-SW) 9 on the network side.
One characterizing feature of the ATM-PON communication system 1 is that, in order to achieve the above the transfer of information, a plurality of terminal units (optical network units (ONU)) 4 for each user and a single subscriber line terminal (SLT) 8 are provided, a single transmission line (optical fiber) 7 on the network side is shared by the plurality of terminal units 4 by polling, and thereby the information is transferred over that transmission line 7 by a time division multiplexing. For this, the plurality of user side transmission lines (optical fibers) 5 directly connected to the terminal units 4 are connected to a single network side transmission line 7 through a single photocoupler 6. This photocoupler 6 functions as a splitting/multiplexing apparatus.
The operation of the communication system of
Referring to
On the other hand, in an upward frame (uplink frame) from the terminal unit (ONU) 4 to the subscriber line terminal (SLT) 8, the terminal unit (ONU) 4 uses a time slot designated by the subscriber line terminal (SLT) unit 8 by polling information (
Note that in
The polling information manages transmission permission IDs for each terminal unit (ONU) 4. That is, the subscriber line terminal (SLT) unit 8 assigns one or more transmission permission IDs to each terminal unit (ONU) 4 in advance. In this case, each terminal unit (ONU) 4 obtains a grasp of the correspondence between the transmission permission ID and at least one buffer in the terminal unit (ONU) storing user information.
The subscriber line terminal (SLT) unit 8 determines the number of cells to be read from each buffer of the terminal units (ONU) 4 based on the amount of information stored in the buffer (queue length) notified from each terminal unit (ONU) 4 by an uplink frame at a fixed interval. That is, the subscriber line terminal (SLT) unit 8 determines the bandwidth to be assigned to each buffer in the terminal units (ONU) 4 (allocated bandwidth). The subscriber line terminal (SLT) unit 8 further determines the timing to read information from each buffer according to the amount of bandwidth assigned to each buffer. This read timing information is the above polling information.
The polling information (
A specific example of the polling information is given in
For example, when terminal unit (ONU) 4 set as above receives the polling information of
By changing the transmission bandwidth of the cells dynamically in accordance with the communication state of each terminal unit (ONU) 4 in this way, the subscriber line terminal (SLT) unit 8 can efficiently handle IP data traffic or other strongy burst-like traffic. This is the dynamic bandwidth allocation system for handling variable rate traffic.
Next, the hardware configuration for realizing this dynamic bandwidth allocation system will be explained.
The terminal unit (ONU) 4 at the left side of the figure is comprised of a polling information extracting unit 11 for receiving user directed information comprised of the polling information from the subscriber line terminal (SLT) 8 by a downlink frame and downlink information from another party and extracting the polling information from it; a plurality of buffers 12 momentarily storing the uplink information from existing user apparatuses for respective connections (VC1, VC2, . . . VCn); a buffer reading unit 13 for reading the user information stored in the buffers 12; a buffer status monitoring unit 15 for monitoring the fullness (buffer status) of the amounts of information in the buffers 12 (that is, the queue lengths); a queue length information generating unit 16 for generating information relating to the queue lengths in the buffers 12 based on the results of monitoring by the buffer status monitoring unit 15; and a multiplexing unit 14 for multiplexing the queue length information and the user information from the buffer reading unit 13 and transmitting the same to the transmission line 5.
On the other hand, the subscriber line terminal (SLT) unit 8 at the right side of
Therefore, the series of operations of the communication system 1 as a whole shown in
The cells including the user information sent from the user side are stored in any of the buffers 12, that is, the Buffer 1 to Buffer n, in accordance with the connection information (VC identifier). The buffer reading unit 13 reads the cells from the buffers 12 using the time slots of the timings designated by the polling information sent from the subscriber line terminal (SLT) 8 and transfers the same to the subscriber line terminal (SLT) unit 8.
Further, the queue length generating unit 16 in the terminal unit (ONU) 4 sends the queue lengths in the buffers 12 monitored by the buffer status monitoring unit 15 to the subscriber line terminal (SLT) unit 8 through the multiplexing unit 14. At this time, the user information from the user side and the above queue length information are multiplexed by the multiplexing unit 14 as explained above.
The subscriber line terminal (SLT) unit 8 extracts the queue length information transferred from each terminal unit (ONU) 4 through the transmission lines 5 and 7 by the queue length information extracting unit 21 inside it. Further, the bandwidth calculating unit 23 determines the bandwidth to allocate to each buffer (for each connection VC) based on the queue length of each buffer 12 notified every bandwidth update period. Next, the polling information generating unit 24 assigns the timings of the time slots to be used in accordance with the bandwidth size allocated to each connection (VCi) and generates polling information for instructing that allocation. This polling information is inserted into the monitor/control cells of the downlink frames and delivered to each terminal unit (ONU) 4.
Here, the framework of the above polling and the fluctuation occurring due to the polling will be briefly explained.
First, referring to
The first and second terminal units (ONU) 4 read from their respective buffers 12 the user information using the time slots (shown by 1 and 2) designated in accordance with the already explained transmission permission IDs shown by the received polling information. The signals are shown at the right sides of the row (b) and row (c) (uplink signals). They are multiplexed at the photocoupler 6 and reach the subscriber line terminal (SLT) unit 8 as shown at the right side in row (a) of the figure as uplink frames. Note that uplink signals and downlink signals are optical signals of different wavelengths from each other, so full duplex communication where information is simultaneously transferred up and down over the same optical fiber becomes possible.
Next, referring to
Further, in the timing charts of the figure, only the first to seventh time slots #1 to #7 among the 53 time slots are shown for simplification.
As the allocated bandwidth for the transfer of the cells from each terminal unit (ONU) 4 to the subscriber line terminal (SLT) unit 8, often a predetermined sustainable cell rate (SCR) is given. Timing charts for the case of transmitting cells from a terminal unit (ONU) 4 to the subscriber line terminal (SLT) unit 8 while strictly observing the sustainable cell rate (SCR) are given in row (b) and row (d) of the figure. That is, as shown in row (b) of the figure, the uplink cells arrive at the subscriber line terminal (SLT) 8 at predetermined intervals of 1/SCR. Therefore, no fluctuation occurs.
If the amount of information to be transmitted from the terminal unit (ONU) 4 increases, however, the interval of transmission of the uplink cells from the terminal unit (ONU) 4 becomes shorter than 1/SCR. That is, originally speaking the uplink cells from the terminal unit (ONU) 4 should reach the subscriber line terminal (SLT) 8 by the timing shown in row (b) of the figure (#1→#2→#3→ . . . ), but in fact they arrive at the subscriber line terminal (SLT) unit 8 by the timing shown in row (a) of the figure (#1→#2→#3→ . . . )
Here, a deviation in timing of arrival of the uplink cells arises between row (a) and row (b). This deviation is the above-mentioned “fluctuation”. In this figure, only the fluctuation when taking note of one time slot #4 is shown. This fluctuation accumulates along with the time slots #1, #2, #3, . . . The fluctuation at the time of the end of one uplink frame therefore becomes considerably large in size. This accumulated fluctuation must be kept less than the burst tolerance (BT) predetermined by the protocol.
In the dynamic bandwidth allocation system for handling variable rate traffic, the above fluctuation is one of the important factors determining the quality of communication. Further, it is deeply related to the present invention. Therefore, some additional explanation will be given here of the above variable traffic rate while referring to the drawings.
Along with the rapid spread of the Internet, a technique for efficiently handling data traffic has become necessary even in ATM-PON communication systems. This data traffic is variable rate traffic of a strong burst nature. In an ATM-PON communication system, in general it is handled by the VBR (variable bit rate) class.
The specifications of the variable bit rate (VBR) class are defined in ATM-Forum Traffic Management 4.1. The variable bit rate (VBR) class is managed by the parameters of the peak cell rate (PCR) (that is, maximum bandwidth), cell delay variance tolerance (CDVT) (that is, fluctuation with respect to maximum bandwidth), sustainable cell rate (SCR) (sustainable cell rate), and burst tolerance (BT) (value of fluctuation allowable with respect to SCR).
The network normally guarantees transfer of data by the sustainable cell rate (SCR) to all connections handled by the network. If there is further unused capacity in the network to handle traffic, the data can be transferred by the maximum bandwidth (PCR) in the range where the fluctuation does not exceed the burst tolerance (BT). Therefore, at the time of new registration of a connection, the carrier decides whether it is possible to guarantee the sustainable cell rate for a new connection based on the parameters reported from the user and the network resource information. When deciding that it is not possible, it rejects the new registration. When all variable bit rate (VBR) connections are allowed according to their reported parameters, this means the quality can be guaranteed for the reported parameters.
Row (a) and row (b) of
On the other hand, referring to
Showing the conventional bandwidth allocation system for cells in more detail based on the general summary of the ATM-PON communication system given above, in a conventional ATM-PON communication system, when handling variable bit rate (VBR) traffic, roughly speaking, either of the fixed bandwidth allocation system or the dynamic bandwidth allocation system has been applied. More specifically, these include the fixed sustainable cell rate (SCR) allocation system (System 1), the fixed peak cell rate (PCR) allocation system (System 2), and the dynamic bandwidth allocation system (System 3).
The above System 1 and System 2, however, each have their own disadvantages. Further, System 3 has the problems explained later. This will be explained in detail below.
In the following explanation, a connection accommodating a buffer i (see Buffer 1, Buffer 2, . . . Buffer n of buffers 12 in
System 1: Fixed Sustainable Cell Rate (SCR) Allocation System
The subscriber line terminal (SLT) unit 8 allocates a fixed sustainable cell rate (SCR) parameter Si to each connection VCi. That is, the allocated bandwidth Bi and the sustainable cell rate SCRi are in the following relationship:
Bi=SCRi
In this model, there are six connections (VC1 to VC6) overall. Each is allocated a fixed sustainable cell rate (SCR) of 10 Mbps.
In System 1, when a user transmits cells by more than the sustainable cell rate (SCR), the queue length and the delay time in queue increase. Therefore, there are the disadvantages that it is not possible to handle real time traffic sensitive to delay such as TV conferences, that a large buffer capacity is required to prevent overflow of cells in the buffers 12 in each terminal unit (ONU) 4, and that unused bandwidth cannot be used, so the efficiency of data transfer is poor.
System 2: Fixed Peak Cell Rate (PCR) Allocation System
The subscriber line terminal (SLT) unit 8 allocates a fixed peak cell rate (PCR) parameter Pi to each connection VCi. That is, the allocated bandwidth size Bi and the peak cell rate PCRi are in the following relationship:
Bi=PCRi
In this model, there are the restrictions that the sustainable cell rate (SCR) is 10 Mbps and the peak cell rate (PCR) is 30 Mbps. Looking at the connection VC1, it occupies a bandwidth up to the peak cell rate (PCR) over the limit of SCR=10 Mbps, so it is not desirable for the other connection VC3 to further occupy bandwidth simultaneously.
In System 2, the peak cell rate (PCR) is allocated to each connection VCi regardless of the amount of traffic. Therefore, there are the disadvantages that the number of connections which can be handled is limited and the efficiency of service is poor and that even the sustainable cell rate (SCR) and burst tolerance (BT) parameters cannot be satisfied.
Further, at the variable bit rate (VBR) class, it is assumed that the data is transmitted while each connection VCi observes the parameters. Therefore, if handling a connection not observing the parameters, the flow of traffic cannot be maintained with the buffer capacity or transmission line capacity prepared in advance and the disadvantages of cell discard, cell delay, or other serious deteriorations in quality arise.
System 3: Dynamic Bandwidth Allocation System
There are various types of System 3, but here the explanation will be made of the typical queue length proportional allocation system (Japanese Unexamined Patent Publication (Kokai) No. 10-242981).
In System 3, the allocated bandwidth Bi is changed in accordance with the queue length information Qi of a buffer i handling a connection VCi. That is, the following relationship stands between Bi and Qi:
Bi=SH·Qi/ΣQi
where, SH is the sharable bandwidth (total bandwidth)
In this model, in the same way as
In System 3, efficient handling of data traffic becomes possible by sharing the unused network resources among the connections VCi. However, the parameters of the burst tolerance (BT), peak cell rate (PCR), and sustainable cell rate (SCR) cannot be satisfied. Therefore, the same disadvantages arise as with the above System 2.
A specific example of the operation will be explained next. For simplification, the number of connections VCi for the dynamic bandwidth allocation will be limited to four (VC1 to VC4). Each terminal unit (ONU) 4 notifies the subscriber line terminal (SLT) unit 8 of the queue lengths of the buffers 12 for each connection VCi at predetermined intervals. The parameters at this time are assumed to be as in the following Table 1 and Table 2:
Note that in Table 2, PCRi, SCRi, and BTi are values preset by contract, while Qi is the actual value of the queue length of a buffer i at a certain time.
Continuing with the explanation of the example of operation, first, the subscriber line terminal (SLT) unit 8 determines the bandwidth size Bi allocated to each connection VCi by the following equation from the queue length information Qi:
Bi=C*Qi/ΣQi:
An example of the results of calculation by this equation is shown in the following Table 3:
Comparing Table 3 with Table 2, in the end, no consideration is taken at all of the peak cell rate (PCR), sustainable cell rate (SCR), burst tolerance (BT), and other parameters. Therefore, the problem is caused that a large bandwidth is continuously allocated without end to connections VCi with large numbers of cells accumulated in the buffers. Therefore, the subscriber line terminal (SLT) unit 8 can no longer effectively utilize the communication resources as scheduled.
Therefore, the present invention provides a dynamic bandwidth allocation method and apparatus designed to improve the efficiency of transfer of information in a communication system handling variable rate traffic and simultaneously ensure that the peak cell rate (PCR), sustainable cell rate (SCR), burst tolerance (BT), and other contracted parameters are observed by shaping the allocated bandwidths.
The network side transmission apparatus 30 of this figure forms a repeater between the user side and network side in a general communication system. In the already explained ATM-PON communication system, however, the network side transmission apparatus 30 corresponds to the already explained subscriber line terminal (SLT) 8.
The basic configuration of this figure covers three embodiments. In each embodiment, the network side transmission apparatus 30 designates the timings of transfer of information for a plurality of terminal units (ONU) 4 on the user side and receives information transferred from these terminal units 4 by time division multiplexing at the designated transfer timings. It controls the variable rate traffic by dynamic bandwidth allocation.
The network side transmission apparatus 30 of the present invention, as shown in the figure, include an allocating means 31 and a computing means 32.
The allocating means 31 assigns allocated bandwidth (Bi) for transfer to the connection VCi periodically according to the amounts of information to be transferred for the connection stored in the terminal unit 4.
The computing means 32 computes the allocated bandwidth Bi so that the contracted parameter (Si) relating to the sustainable cell rate (SCR) and the contracted parameter relating to the fluctuation value (BT) allowed for the sustainable cell rate (SCR) preset for each connection VCi are observed.
The allocating means 31, in the same way as above, assigns allocated bandwidth Bi for transfer to the connection VCi periodically according to the amounts of information to be transferred for the connection stored in the terminal unit 4.
The computing means 32, unlike the above, compute the allocated bandwidth Bi so that the contracted parameter (Pi) relating to the peak cell rate (PCR) and the contracted parameter relating to the fluctuation value (CDVT) allowed for the peak cell rate (PCR) preset in each connection VCi are observed.
The allocating means 31, in the same way as above, assigns allocated bandwidth Bi for transfer to the connection VCi periodically according to the amounts of information to be transferred for the connection stored in the terminal unit 4.
The computing means 32, unlike the above, computes the allocated bandwidth Bi so that the contracted parameters (Si/Pi) relating to the sustainable cell rate (SCR) and peak cell rate (PCR) and the contracted parameters (Si/Pi) relating to the fluctuation values (BT/CDVT) allowed for the sustainable cell rate (SCR) and peak cell rate (PCR) preset for each connection VCi are observed.
Among the three embodiments, the third embodiment enables the contracted parameters to be observed most strictly.
This method is applied, as mentioned above, to a network side transmission apparatus 30 which designates the timings of transfer of information for a plurality of terminal units on the user side, receives information transferred from these terminal units by time division multiplexing at the designated transfer timings, and controls the variable rate traffic by dynamic bandwidth allocation.
Here, the method of the present invention includes steps S11, S12, and S13 shown in
At step S11, the apparatus receives the amounts of information to be transferred to the connection VCi stored in the terminal unit 4.
At step S12, the apparatus computes the allocated bandwidth based on the received amounts of information to be transferred so that at least the contracted parameter (Si) relating to the sustainable cell rate (SCR) and the contracted parameter relating to the fluctuation value (burst tolerance (BT)) allowed for the sustainable cell rate (SCR) are observed among the contracted parameters (Si/Pi) relating to the sustainable cell rate (SCR) and peak cell rate (PCR) and contracted parameters relating to the fluctuation values (BT/CDVT) allowed for the sustainable cell rate (SCR) and peak cell rate (PCR) preset for each connection VCi.
At step S13, the apparatus assigns the computed allocated bandwidth to the connection (VCi) and notifies the terminal unit 4.
The communication system 1 has, at the user side, a plurality of terminal units 4 for reading and transferring information by time division multiplexing from internal buffers set to respective connections VCi at the designated timings for transfer of the information.
On the other hand, the system 1 has, at the network side, a network side transmission apparatus 30 (SLT 8) which designates the timings of transfer of information for the terminal units 4, receives information read and transferred from the buffers in these terminal units 4, and controls the variable rate traffic by dynamic bandwidth allocation.
Between the network side transmission apparatus 30 and the plurality of terminal units 4, the system has a time division multiplex transmission line which transfers polling information designating the transfer timings to the plurality of terminal units 4 and transfers the information from the buffers to the network side transmission apparatus 30 at the designated transfer timings. Further, the network side transmission apparatus 30 includes an allocating means 31 for assigning allocated bandwidth for transfer to the connection VCi periodically in accordance with the amounts of information to be transferred for the connection VCi stored in each of the buffers and a computing means 32 for computing the allocated bandwidth so that at least the contracted parameter (Si) relating to the sustainable cell rate (SCR) and the contracted parameter relating to the fluctuation value (burst tolerance (BT)) allowed for the sustainable cell rate (SCR) are observed among the contracted parameters (Si/Pi) relating to the sustainable cell rate (SCR) and peak cell rate (PCR) and contracted parameters relating to the fluctuation values (BT/CDVT) allowed for the sustainable cell rate (SCR) and peak cell rate (PCR) preset for the connection VCi.
Therefore, according to the present invention, the network side transmission apparatus 30 can observe the traffic parameters of the sustainable cell rate (SCR) and burst tolerance (BT) and further the peak cell rate (PCR) and cell delay variance tolerance (CDVT) to the extent possible and effectively utilize the system resources.
Next, the communication system 1 according to the present invention, in particular the network side transmission apparatus 30 (
The subscriber line terminal (SLT) unit 8, as illustrated, is provided with a queue length extracting function unit 41, a parameter setting function unit 42, a parameter managing memory 43, a bandwidth calculating function unit 44, and a polling information generating function unit 45.
The queue length extracting function unit 41 receives notifications relating to the queue lengths of information stored for the connections VCi in the buffers 12 (
The parameter setting function unit 42 sets at least one of the contracted parameter (Si) relating to the sustainable cell rate (SCR), the contracted parameter (Pi) relating to the peak cell rate (PCR), and the contracted parameters relating to the fluctuation values (BT/CDVT) allowed for the sustainable cell rate (SCR) and peak cell rate (PCR) for the connections contracted for with each terminal unit 4.
The parameter managing memory 43 stores at least the queue length information and contracted parameter information input from the queue length extracting function unit 41 and the parameter setting function unit 42.
The bandwidth calculating function unit 44 periodically calculates the allocated bandwidths Bi for the connections VCi so that the contracted parameters are observed and re-stores the results of the calculation in the parameter managing memory 43.
Further, with an ATM-PON communication system, the polling information generating function unit 45 is essential. This polling information generating function unit 45 determines the timings of transfer of information to be designated for the terminal units (ONU) 4 in accordance with the allocated bandwidths Bi of the results of calculation re-stored in the parameter managing memory 43 and transfers them as polling information to the terminal units (ONU) 4 through the transmission lines 7 and 5.
This will be explained in further detail below. To speed understanding, first the meanings of the abbreviations used in the explanation will be listed.
[Meaning of Abbreviations]
The bandwidth calculating function unit 44 of the subscriber line terminal (SLT) unit 8 reads the amounts of information in the buffers 12 transmitted from the terminal units (ONU) 4 through the transmission lines 5 and 7 at each bandwidth update period (Tupdate (slots)) and parameter information in the parameter managing memory 43 to calculate the allocated bandwidths Bi for the connections VCi.
The polling information generating function unit 45 generates polling information from the allocated bandwidths Bi for the connections VCi. All of the information required for the calculation of bandwidth is managed in the parameter managing memory 43.
The parameter managing memory 43 stores the setting information of the system required for bandwidth calculation (bandwidth update period Tupdate, transmission line capacity C, etc.), the contracted parameter information for each connection VCi (PCR, SCR, BT, CVDT, etc.), and the variables required for the bandwidth calculation (ideal arrival time Ti etc.) The variable information is updated for every calculation. The basic operation of the bandwidth calculating function unit 44 will be explained below.
Assume here that for all of the allocated time slots, the cells of the uplink frames return to the subscriber line terminal (SLT) unit 8 without being discarded. Since the arrival times of the cells can be predicted from the allocated times of the time slots, the allocated times of the time slots are called the scheduled arrival times of the cells here.
First, the unit calculates the queue length converted bandwidths B′i (B′i being the provisional values of Bi found by initial calculation) from the queue lengths of the connections VCi. When allocating these bandwidths B′i to the connections VCi, the time slots of
N′i=T update*B′i/C
are allocated in the bandwidth update period (Tupdate).
Assuming that the time slots addressed to the connections VCi are assigned at equal intervals in this bandwidth update period, the interval of allocated time slots becomes
C/B′i (slots)
This being the case, the last allocated time slot time (last scheduled arrival time) A-HEAD′i in the bandwidth update period becomes
A.HEAD′i=A+(N′i−1)*C/Bi
where, A is the start time of the bandwidth update period.
The arrival times at the subscriber line terminal (SLT) unit 8 of cells from a terminal unit (ONU) 4 assuming that the cells of the connection VCi arrive at not more than the sustainable cell rate (Si) at all times are the ideal arrival times Ti. The time interval of the ideal arrival times Ti is
C/Si (slots)
When allocating N′i number of cells in the bandwidth update period Tupdate, the ideal arrival times Ti are newly advanced by exactly N′i*C/Si (slots). The ideal arrival time T-HEAD′i of the last cell becomes
T.HEAD′i=T-LASTi+N′i*C/Si
The fluctuation value (BT′) accompanying the last cell in one uplink frame can be calculated by the following equation:
BT′=T.HEAD′i−A.HEAD′i
The above will become clearer by reference to
A′i shown at the left in the figure shows the scheduled arrival times in the case of allocating the provisional bandwidth B′i. Similarly, Ti shows the ideal arrival times.
The numerical figures for the concrete example shown in
In the above bandwidth calculation, it is predicted that if this amount of bandwidth is allocated to a certain connection, the last value of the fluctuation accumulated with each time slot becomes just this.
For example, in
Therefore, the allocated bandwidth is reduced (increased) under this prediction.
In the previously explained first embodiment of the present invention, the bandwidths Bi allocated to the connections VCi were determined so that the fluctuation value does not exceed the burst tolerance (BT).
If adding the second embodiment of the present invention explained above, since there is the restriction that an allocated bandwidth Bi may not exceed the peak cell rate parameter (Pi), the arrival interval of the cells becomes not more than C/Pi. Therefore, it is possible to ignore the fluctuation with respect to the peak cell rate (PCR) (CDVT) (third embodiment). Note that details of the steps for calculating the allocated bandwidth Bi are given in
Models of bandwidth allocation to connections VCi according to the first embodiment and third embodiment become for example as shown in
According to
Further, according to
Next, a detailed example of the present invention will be explained.
Before starting the dynamic bandwidth allocation, the manager (subscriber line terminal (SLT) unit 8) sets the bandwidth update period (Tupdate), sharable bandwidth (SH), contracted parameter information of the connections VCi (PCR/SCR/BT), etc. in the parameter managing memory 43. The bandwidth calculating function unit 44 reads the parameter information necessary for bandwidth calculation from the parameter managing memory 43 at each bandwidth update period and determines the bandwidths Bi allocated to the connections VCi. The bandwidth update period Tupdate and the burst tolerance BTi are converted to times of time slot increments. Further, the ideal arrival times Ti and scheduled arrival times Ai show the times in time slot increments.
(i) First Embodiment of Present Invention
This first embodiment is a system for observing the prescribed sustainable cell rate (SCR) and burst tolerance (BT) of the variable rate traffic in the dynamic bandwidth allocation system and performs the following processes (1) to (7):
(1) The subscriber line terminal (SLT) unit 8 converts the queue lengths Qi (cells) notified from the terminal units (ONU) 4 to provisional allocated bandwidths B′i (step S21 in FIG. 8).
B′i=Qi*C/T update
where, C is the transmission line capacity
When the total of the provisional allocated bandwidths B′i exceeds the sharable bandwidth SH, all of the provisional allocated bandwidths B′i are equally compressed (S22 and S23):
if ΣB′i>SH
B′i=B′i*SH/ΣB′i
(2) When the pre-update ideal arrival time (Ti before update) is less than the bandwidth update period start time (A), the pre-update ideal arrival time Ti is set to the bandwidth update period start time A (S26, S27).
(3) The number N′i of allocated time slots in the bandwidth update period when allocating the provisional allocated bandwidths B′i to the connections VCi is calculated (S25). The number N′i of allocated time slots calculated here is called the provisional number of allocated slots.
N′i=T update*B′i/C
(4) The provisional last scheduled arrival time A′i is then calculated. Here, A′i has the same meaning as the above A.HEAD′i.
The scheduled arrival time of the last time slot (provisional scheduled arrival time) A′i when allocating the provisional allocated bandwidths B′i to the connections VCi is calculated at step S28.
A′i=A+(N′i−1)*C/B′i
where, C/B′ is the allocated time slots, that is, the interval of the scheduled arrival times
(5) The provisional ideal arrival time T′i is calculated. Here, T′i is the same in meaning as the above T.HEAD′i. When allocating bandwidths B′i to the connections VCi, N′i number of slots are allocated in the bandwidth update period. The ideal arrival time (provisional ideal arrival time) T′i of the last cell is calculated at the above step S28.
T′i=Ti+N′i*C/Si
where, C/Si is the interval of the ideal arrival times.
(6) The actual bandwidths Bi allocated to the connections VCi are determined.
When
T′i≦A′i+BT (a)
(NO at S29), the burst tolerance (BT) parameter is not violated even if allocating the provisional allocated bandwidths B′i to the connections VCi as they are. Therefore, the provisional allocated bandwidths B′i are set for the allocated bandwidths Bi (S30).
When
T′i>A′i+BT (b)
(YES at S29), the burst tolerance (BT) parameter would be violated if the provisional allocated bandwidths B′i were allocated to the connections VCi as they were.
To solve this problem, the above computing means 32 (
First, giving several related conditional equations:
Ti+N′i*C/Si=A+(N′i−1)*C/Bi+BTi and
N′i=T update*B′i/C,
so the following is obtained:
Ti+T update*B′i/Si=A+(T update*B′i/C−1)*C/B′i+BTi
If B′i and Si are multiplied with at the two sides of the equation to clean it up and the following quadratic equation is solved, the allocated bandwidths Bi to be sought are found (S31). “f” at step S31 expresses the quadratic function:
T update·Bi2+(Si·Ti−A·Si−T update·Si−Si·BTi)·Bi+C·Si=0
The solution to the above quadratic equation is
(7) The ideal arrival times Ti are updated.
That is, the number Ni of allocated time slots is calculated and the ideal arrival times Ti are re-calculated based on the allocated bandwidths Bi (S32).
Ni=T update*Bi/C, so
Ti=Ti+Ni*C/Si=Ti+T update*Bi/Si
This third embodiment is an equation for further ensuring the observation of the parameter of the peak cell rate (PCR) as compared with the first embodiment. The difference from the first embodiment is that the allocated bandwidths Bi are limited to the peak cell rate (PCR) contract values (Pi) of the connections VCi. This being the case, the arrival intervals of the cells become not more than C/Pi (slots), so no fluctuation (CDVT) with respect the peak cell rate (PCR) occurs any longer.
The processes of the third embodiment are actually the same except as the above processes (1), (2), (3) . . . (7) except for the process (6). Therefore, steps S21 to S32 in
In the above first embodiment and third embodiment, the step S31 of solving the quadratic equation was included, so the processing load on the central processing unit (CPU) in the subscriber line terminal (SLT) unit 8 and the specialized hardware became heavier. This is inconvenient when there is no surplus margin in the resources.
Therefore, a method will be proposed for eliminating this inconvenience. That is, under this method, when the allocated bandwidth Bi exceed a predetermined condition, the computing means 32 (
Looking first at
That is, when the burst tolerance BTi is exceeded under the first embodiment, instead of re-calculating the allocated bandwidth Bi, the contracted parameter (Si) relating to the sustainable cell rate (SCR) is set for the allocated bandwidth Bi. Step S51 of
Next, looking at
That is, when the burst tolerance BTi is exceeded under the first embodiment, instead of re-calculating the allocated bandwidth Bi, the contracted parameter (Si) relating to the sustainable cell rate (SCR) is set for the allocated bandwidth Bi (S51). When the contracted parameter (Pi) relating to the peak cell rate (PCR) is exceeded (YES at S61), the contracted parameter (Pi) is set for the allocated bandwidth Bi (S62). The modification of the third embodiment is somewhat inferior to the third embodiment in terms of the effective use of the bandwidth, but there is no problem in practice.
Summarizing the effects of the invention, it is possible to improve the transfer efficiency of variable rate traffic in an ATM-PON system by changing the bandwidth Bi in accordance with the arrival of data.
Further, since the traffic is shaped so as to satisfy the parameters of the sustainable cell rate (SCR) and burst tolerance (BT), the network can predict to a certain extent the properties of the connections handled and therefore when predicting that the network will become overloaded, can refuse to accept new connections.
As a result, it is possible to guarantee the sustainable cell rate (SCR) for the connections VCi handled and possible to eliminate deterioration in performance due to buffer overflow etc. occurring due to the inflow of more than the contracted traffic into the network (first embodiment).
In addition, it is possible to define the parameters of the peak cell rate (PCR) or cell delay variance tolerance (CDVT) as well, so it becomes possible to shape the traffic more strictly (third embodiment).
While the invention has been described with reference to specific embodiments chosen for purpose of illustration, it should be apparent that numerous modifications could be made thereto by those skilled in the art without departing from the basic concept and scope of the invention.
The present disclosure relates to subject matter contained in Japanese Patent Application No. 2002-24424, filed on Jan. 31, 2002, the disclosure of which is expressly incorporated herein by reference in its entirety.
Number | Date | Country | Kind |
---|---|---|---|
2002-024424 | Jan 2002 | JP | national |
Number | Name | Date | Kind |
---|---|---|---|
6072773 | Fichou et al. | Jun 2000 | A |
6141322 | Poretsky | Oct 2000 | A |
6285657 | Lewis et al. | Sep 2001 | B1 |
6442138 | Yin et al. | Aug 2002 | B1 |
6690678 | Basso et al. | Feb 2004 | B1 |
6731605 | Deshpande | May 2004 | B1 |
6757251 | Nakaishi | Jun 2004 | B1 |
20010028633 | Shimada et al. | Oct 2001 | A1 |
Number | Date | Country |
---|---|---|
1 021 058 | Jul 2000 | EP |
10-242981 | Sep 1998 | JP |
9735410 | Sep 1997 | WO |
Number | Date | Country | |
---|---|---|---|
20030142692 A1 | Jul 2003 | US |