CA2322794C - Method for determining the required bit rate for a number of communications connections which can be statistically multiplexed - Google Patents
Method for determining the required bit rate for a number of communications connections which can be statistically multiplexed Download PDFInfo
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- CA2322794C CA2322794C CA002322794A CA2322794A CA2322794C CA 2322794 C CA2322794 C CA 2322794C CA 002322794 A CA002322794 A CA 002322794A CA 2322794 A CA2322794 A CA 2322794A CA 2322794 C CA2322794 C CA 2322794C
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L12/00—Data switching networks
- H04L12/54—Store-and-forward switching systems
- H04L12/56—Packet switching systems
- H04L12/5601—Transfer mode dependent, e.g. ATM
- H04L12/5602—Bandwidth control in ATM Networks, e.g. leaky bucket
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04Q—SELECTING
- H04Q11/00—Selecting arrangements for multiplex systems
- H04Q11/04—Selecting arrangements for multiplex systems for time-division multiplexing
- H04Q11/0428—Integrated services digital network, i.e. systems for transmission of different types of digitised signals, e.g. speech, data, telecentral, television signals
- H04Q11/0478—Provisions for broadband connections
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
- H04L12/00—Data switching networks
- H04L12/54—Store-and-forward switching systems
- H04L12/56—Packet switching systems
- H04L12/5601—Transfer mode dependent, e.g. ATM
- H04L2012/5629—Admission control
- H04L2012/5631—Resource management and allocation
- H04L2012/5632—Bandwidth allocation
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- Signal Processing (AREA)
- Data Exchanges In Wide-Area Networks (AREA)
- Time-Division Multiplex Systems (AREA)
Abstract
The invention relates to a method for controlling the acceptance or refusal of a new connection on an ATM communications device having a maximal capacity Rmax which already handles a plurality M of connections that can be statistically multiplexed, whereby the new connection has a peak cell rate P CR and a sustainable average cell rate SCR. The inventive method comprises the following steps: Determining the sum PM+1=.SIGMA.PCRi of the peak cell rate PCR, the sum SM+1=.SIGMA.SCRi of the sustainable cell rate SCR of the M existing connections, and the new connection; determining the variance V of the cell rates of the M+1 connections; determining the required capacity loadM+1 for the M connections according to PM, SM and V, and; accepting the connection in the case when loadM+1 is less than or equal to Rmax. The connection acceptance control can be carried out faster, more effectively an d independent of the sequence of accepted connections by the exact calculation of the required capacity of the communications connections.
Description
METHOD FOR DETERMINING THE REQUIRED BIT RATE
FOR A NUMBER OF COMMUNICTIONS CONNECTIONS
WHICH CA_N BE STATTST_.CALLY MUTIPLEXED
Technical Field The invention relates to a method for calculating the required bit rate of a number of communication connections which can be statistically multiplexed and to a method for controlling the acceptance or refusal of a new connection on an ATM
communication device with a capacity Rma, which is already handling a number M of connections which can be statistically multiplexed.
Background In the Asynchronous Transfer Mode (ATM), data are transmitted independe.ntly of the information represented by them (voice communication, data communication, multimedia) in cells of 53 bytes (48 bytes of useful data and 5 bytes of control data). The network resources of a communication device, such as v5 for example a multiplexer, a line or a switching matrix, are in this case shared by connections with different grade-of-service and bit-rate requirements.
At the same time, it must be ensured by a so-called traffic control that, in spite of the joint transmission of data cells of various origin, various bit rates and various bit rate statistics, the required grade of transmission performance of the ATM layer is ensured. In particular, it must be ensured that the probability of cell loss is very low, for example less than 10-10, and the transmission time variations of the cells do not exceed a certain value.
- la -In an ATM network, various types of connection are possible, distinguished by their bit rate statistics. A connection with a constant bit rate or deterministic bit rate has a fixed transmission bit rate (cell rate) over the entire duration of the connection. This bit rate must be constantly provided by the network. This type of connection is particularly suitable for real-time applications, such as voice communication for example, in which strict requirements are imposed on the cell delay variations and which have a virtually constant transmission rate.
A further type of connection is the available bit rate, the data being transmitted according to the network capacity available at a given time. This type of connection is not suitable for real-time applications, but for example as a low-cost data transmission, such as e-mail for example.
With the statistical bit rate type of connection, the data to be transmitted are transmitted on a virtual connection with a transmission rate varying over time. Examples of such a type of connection are video connections in which the video signals are encoded with a variable bit rate and voice communication with pause suppression and certain data transmission services. Connections with a statistical bit rate, in which the average bit rate is significantly below the maximum bit rate are suitable for statistical multiplexing. In this case, many connections are carried with a statistical bit rate over a common line or a common switching matrix, it not being necessary for each individual connection to reserve the maximum bit rate, since many uncorrelated connections with a low average bit rate in comparison with the maximum bit rate share the available transmission capacity on average. It is thus possible to "overbook" the line to a certain extent. The network infrastructure can be better utilized overall in this way.
To enable the network operator to provide adequate capacity for a number of communication connections with a statistical bit rate that are independent of one another, the maintenance of certain traffic parameters must be ensured by technical precautionary measures at the terminal devices or the like in a so-called traffic agreement. The traffic - 2a -agreement regulates among other things the maximum bit rate (or peak cell rate, PCR) and the average bit rate or corresponding average sustainable cell rate (SCR). The peak cell rate PCR in this case gives the maximum number of ATM cells per unit of time taken up by the connection and the average sustainable cell rate SCR gives the average number of ATM cells per unit of time permissible over a prolonged period of time.
The problem with the connection acceptance control of connections which can be statistically multiplexed, i.e. connections with a statistical bit rate for which the ratio of the maximum bit rate to the average bit rate is above a certain value, is that on the one hand it is necessary to avoid cell losses, which may occur due to the simultaneous transmission of many connections at a high bit rate, and on the other hand it is necessary to make it possible for the ATM
connection or the ATM communication device to be utilized to the greatest possible extent. Various connection acceptance methods of this kind are known.
One possibility is to reserve the peak cell rate PCR for each communication connection.
Consequently, cell losses caused by overloading of the communication connection cannot occur, but the advantages of statistical multiplexing, i.e. the better utilization of the communication device by connections with a varying cell rate that are independent of one another cannot be exploited.
If, on the other hand, only the average sustainable cell rate SCR is reserved for each connection, intolerable cell losses occur even when there are small variations in the overall cell rate.
Only when there is a very high number of connections that are independent of one another does the capacity required for transmission of the connections without any cell loss come close to the sum of the average sustainable cell rates of the individual connections.
One known method for controlling the acceptance of connections which can be statistically multiplexed is the so-called sigma rule, - d -which is described in European Patent EP 0 433 699 Bl.
In this method, an additional connection is still accepted along with a number M of already existing connections if an upper estimate of the transmission bit rate necessary for the transmission of the M+l connections is less than or equal to the maximum bit rate Rmax of the communication device.
The estimate of the required capacity in the case of the sigma rule is given by the addition of the sum SM+1='7SCP.;, of the average sustainable cell rates of the M+1 connections which can be statistically multiplexed to a factor Q(R) *~VM+1, where Q(R) is a quantile function which indicates the statistical behavior of the connections in dependence on the required bit rate, and V is an estimate of the variance of the bit rates of the M+1 connections.
If the capacity of a transmission device is shared with other types of traffic, for example traffic at an unspecified bit rate or available bit rate, the capacity R available for the traffic to be multiplexed is no longer known.
Until now, the sigma rule has been extended to cope with this problem and the capacity of the M
already reserved connections used as the decision parameter for the acceptance of the M+lth connection.
This capacity is iteratively increased when setting up further connections, to be precise by the average sustainable cell rate of the connection to be added if the sigma rule will accept the connection for this capacity, otherwise by the peak cell rate. By this procedure, the capacity determined is dependent on the setting-up, sequence.
Summary of Invention Embodiments of the invention are therefore based on the object of proposing a method for controlling the acceptance or refusal of a new connection of an ATM
communication device with a given capacity Rmax which is independent of the sequence of the acceptance of the connections of the communication device.
The object is achieved in one aspect by a method for determining a required capacity loadM on an ATM
5(Asynchronous Transfer Mode) communication device by which a plurality M of connections which can be statistically multiplexed is being handled, according to which the capacity loadM required for the M existing connections is determined by resolving an equation Gz: 1oadZ = SZ + Q(1oadZ) *qVZ for Z = M, where the following applies: loadM is a capacity of the M connections, SM =Z [ SCRi ] with 1 <= i <= M, Q(loadM) is a fixed function of loadM, VM =I [ SCRi * ( PCRi - SCRi ) ] with 1 <= i <= M, PCR; is a peak cell rate and SCRi is an average sustainable cell rate of the connection with index i.
The new connection is characterized by its peak cell rate PCR and its average sustainable cell rate SCR. By the method according to the invention, the sum PM+1=Y-PCRi of the peak cell rates and the sum SM+1=Y_SCRi of the average sustainable cell rates of the existing and new connections and the variance V of the cell rates are determined. In dependence on these variables, the required capacity loadM+l of the M+1 connections is determined and the new connection is accepted if the required capacity loadM+l is less than or equal to the maximum capacity RmaX of the ATM communication device.
By contrast with the known sigma rule, in the method according to the invention the overall required capacity loadM+l is calculated exactly. It is not just determined whether or not a new connection can be set up.
Consequently, the result achieved by the method according to the invention is independent of the sequence in which the connections are set up.
Since the required capacity is calculated, and consequently also the free capacity available at a given time, users or management centers of the communication device can be notified of this, making it possible for the network to be utilized more effect;Ively.
In a variant of the method, the connection is accepted if the minimum of the variables loadM+1 and PM+1 is less than or equal to the maximum capacity Rmax= If the calculated capacity loadM+1 is greater than the sum of the maximum bit rates P,.,+I, it is sufficient to reserve the sum of the maximum bit rates pM+1 .
The required bit rate loadM for M connections can be calculated with the assumpti-on of a fictitious bit rate R=SMxQ(R)x~V, where Q(R) is a fixed, empirically determined so-called quantile function of R. The required bit rate loadM is that fictitious bit rate R for which the relationship R = SM + Q (R) = ~V) is satisfied.
The solution to this equation can be determined iteratively by suitable methods of approximation.
The quantile function Q(R) can be chosen to be ql+q2/R, the h erbolic YP quantile ql and the hyperbolic iactor q, of the associated sigma class being empirically determined by simulation calculati.ons.
Then, loadM can be determined by numerical extraction of the root load = xf)/2 + 4q2 = qV + x02 where xO is equal to ql =~V, - 6a -In another aspect of the invention, there is provided a method for determining a still transmissible average sustainable cell rate SCRc and a still transmissible peak cell rate PCRc for a new connection with an average sustainable cell rate SCRM4I, a peak cell rate PCRM+,, an average minimum sustainable cell rate SCRMIN and a minimum peak cell rate PCRMIN on an ATM communication device, by which a plurality M of connections which can be statistically multiplexed is being handled, according to which the still transmissible average sustainable cell rate SCR, and the still transmissible peak cell rate PCRc are determined by resolving an equation GZ: 1oadZ = SZ + Q(loadz) *~VZ for Z = C, where the following applies loade = SCRc, Sc = SM + SCRc with SM =Y- [ SCRi ] and 1 <= i <= M, Q(loade) is a fixed function of load,, Vc = VM + (SCRc) * (PCRc - SCRc) with VM =2: [ SCRi * ( PCRi - SCRi ) ] and 1 <= i<= M, SCRc = SCRMIN + a*x, PCRc = PCRMIN + x, a=( SCRM+1 - SCRMIN )/
PCRM+I - PCRMIN ), x = PCRc - PCRMIN, PCRi is the peak cell rate and SCRi is the average sustainable cell rate of the connection with index i.
In another aspect of the invention, there is provided an ATM communication device with a maximum capacity Rmaxr with a device for indicating a still available residual capacity Rrest of the ATM communication device, where Rrest = Rmax - loadM and loadM is determined according to the method described herein.
Brief Description of the Drawings The invention is described below with reference to the drawing, in which - 6b -Figure 1 is a graph to explain the calculation of the required capacity of a number of connections which can be statistically multiplexed;
Figure 2 is a graph to illustrate an iteration method for calculating the required capacity; and Figure 3 is a graph to explain application of the method according to the invention.
Detailed Description A communication device, such as for example a communication line, a switching matrix or the like, has an overall available capacity Rmax, i.e. a connection with a constant bit rate Rmax can be accepted.
A number M of communication connections which can be statistically multiplexed are transmitted via the communication devices, characterized by a peak cell rate PCR and an average sustainable cell rate SCR. PM=
Z"'PCRi then denotes the sum of the peak cell rates of the M connections and SM=ESCR;, denotes the sum of the average sustainable cell rates of the connections.
V = ESCRi ( PCRi-SCRi ) is the estimate of the variance of the cell rates of the M connections.
If SM + 4V = Q(R) <_ R (1) is satisfied for a bit rate, this capacity is sufficient for all M connections to be accepted. In this case, Q(R) is an empirically determined quantile function. For Q(R) , the function ql+q2/R is known as a good approximation, the factors ql and q2 being determined by simulations and depending on the ratio of the peak cell rate to the average sustainable cell rate of the connections. ql is, for example, of the order of magnitude of 10, q2 is of the order of magnitude of I05. Inequation 1 can then be written as:
(q, + q2/R) = 4V + SM < R (2) The right and left sides of the inequation are graphically represented in Figure 1. The function y(R)=R is a linear, monotonously rising function, while the function y=ql+q2/R4V+SM falls hyperbolically with higher values of R. The intersection point of the two graphs is the value R=load, which gives the required capacity exactly (within the accuracy of the assumptions made) By determining this intersection R=load, the capacity required by the M connections which can be statistically multiplexed can consequently be determined exactly, while in the case of the sigma rule it is just determined whether or not a new connection can be accepted at a given time. The exact calculation of the overall capacity has the advantage that it does not depend on the sequence in which the connections are accepted. Furthermore, the required capacity, and consequently also the free capacity available at a given time, can be indicated and users of the communication device can be notified of it.
For the calculation of load, there are the following possibilities. On the one hand, the equation (ql + q2/load) = ~V + SM = load (3) can be resolved for load if x0:=q14V is defined:
load = xo/2 + ~q2 = ~V + x02 ( 4 ) Alternatively, R=load can also be determined iteratively. The method is schematically represented in Figure 2. From the starting point loado=q14V+SM, load is determined iteratively as loadn+i = (qi + q2/loadn) = 4V + SM (5).
A C program for executing this algorithm is enclosed with the patent application as an annex. In 10' calculations for the acceptance of a connection, the - 8a -relative error of load in three iterations was below 3x10-4. An odd number of iteration steps ensures that the required capacity is overestimated and not underestimated.
The exactly calculated capacity loadM at a given time for M connections of the communication device can in turn be used for effective acceptance control of the communication device. Since the capacity loadM required for M existing connections is continuously available, when there is a new request for a connection with a peak cell rate PCR and an average sustainable cell rate SCR, the connection can be accepted without further calculation if the free capacity Rmax-loadM is greater than PCR and can be refused without further calculation if Rmax-loadM is less than SCR. Only if the load of the communication device is in the range lying in between is a new calculation of the load loadM+l of the M+l connections required before acceptance. As soon as the connection has been set up, the load calculation is extended to all the existing connections.
A further application of the present invention is explained with reference to Figure 3.
In the case of a connection with a variable bit rate, it may be characterized not only by the peak cell rate F and average sustainable cell rate G but also by a peak cell rate required as a minimum Hmin and an average sustainable cell rate required as a minimum I. An example of this is a video telephone service, which requires a minimum transmission bandwidth of, for example, 64 KB per second to be able to build up a picture at all. A high bandwidth is desirable, but not absolutely necessary, for real-time transmission of the mimic or the like.
In Figure 3, the average sustainable cell rate SCR is plotted against the peak cell rate PCR in a diagram. The peak cell rate F and the average sustainable cell rate G form the point (F, G) which characterizes the ideal state of the connection. The point (H, I) formed by the minimum cell rates Hmin and Imin gives the minimum requirements for the connection.
The task of the connection acceptance control is to accept the connection with a variable (as great as possible) bandwidth if it is ensured that the minimum conditions Hmin. Imin are always satisfied. This acceptance control can be realized on the basis of the exact calculation of the available capacity loadM.
If the combination of parameters at the edge of the gray area with the straight-line through (H, I) and (F, G) is assumed, the capacity available is fully utilized and the prescribed rates are taken well into account. a is the slope of the straight-line (H, I)-(F, G) and x is the difference between the peak cell rate sought and Hmin= Then, the sought average sustainable cell rate c is obtained as the sum of the minimum cell rate and a=x:
c = (ql+q2/c) JV+(I+a=x) ~H+x-(I+a=x) ) + SM + I + a = x (6) where x corresponds to the required capacity load and can be calculated from equations (3) and (5). Equation (6) is equivalent to a quadratic equation in x and can be calculated by suitable numerical iteration methods.
The invention makes possible for the first time an exact calculation of the required capacity loadM of a number M of connections which can be statistically multiplexed, characterized by a peak cell rate PCR and an average sustainable cell rate SCR.
FOR A NUMBER OF COMMUNICTIONS CONNECTIONS
WHICH CA_N BE STATTST_.CALLY MUTIPLEXED
Technical Field The invention relates to a method for calculating the required bit rate of a number of communication connections which can be statistically multiplexed and to a method for controlling the acceptance or refusal of a new connection on an ATM
communication device with a capacity Rma, which is already handling a number M of connections which can be statistically multiplexed.
Background In the Asynchronous Transfer Mode (ATM), data are transmitted independe.ntly of the information represented by them (voice communication, data communication, multimedia) in cells of 53 bytes (48 bytes of useful data and 5 bytes of control data). The network resources of a communication device, such as v5 for example a multiplexer, a line or a switching matrix, are in this case shared by connections with different grade-of-service and bit-rate requirements.
At the same time, it must be ensured by a so-called traffic control that, in spite of the joint transmission of data cells of various origin, various bit rates and various bit rate statistics, the required grade of transmission performance of the ATM layer is ensured. In particular, it must be ensured that the probability of cell loss is very low, for example less than 10-10, and the transmission time variations of the cells do not exceed a certain value.
- la -In an ATM network, various types of connection are possible, distinguished by their bit rate statistics. A connection with a constant bit rate or deterministic bit rate has a fixed transmission bit rate (cell rate) over the entire duration of the connection. This bit rate must be constantly provided by the network. This type of connection is particularly suitable for real-time applications, such as voice communication for example, in which strict requirements are imposed on the cell delay variations and which have a virtually constant transmission rate.
A further type of connection is the available bit rate, the data being transmitted according to the network capacity available at a given time. This type of connection is not suitable for real-time applications, but for example as a low-cost data transmission, such as e-mail for example.
With the statistical bit rate type of connection, the data to be transmitted are transmitted on a virtual connection with a transmission rate varying over time. Examples of such a type of connection are video connections in which the video signals are encoded with a variable bit rate and voice communication with pause suppression and certain data transmission services. Connections with a statistical bit rate, in which the average bit rate is significantly below the maximum bit rate are suitable for statistical multiplexing. In this case, many connections are carried with a statistical bit rate over a common line or a common switching matrix, it not being necessary for each individual connection to reserve the maximum bit rate, since many uncorrelated connections with a low average bit rate in comparison with the maximum bit rate share the available transmission capacity on average. It is thus possible to "overbook" the line to a certain extent. The network infrastructure can be better utilized overall in this way.
To enable the network operator to provide adequate capacity for a number of communication connections with a statistical bit rate that are independent of one another, the maintenance of certain traffic parameters must be ensured by technical precautionary measures at the terminal devices or the like in a so-called traffic agreement. The traffic - 2a -agreement regulates among other things the maximum bit rate (or peak cell rate, PCR) and the average bit rate or corresponding average sustainable cell rate (SCR). The peak cell rate PCR in this case gives the maximum number of ATM cells per unit of time taken up by the connection and the average sustainable cell rate SCR gives the average number of ATM cells per unit of time permissible over a prolonged period of time.
The problem with the connection acceptance control of connections which can be statistically multiplexed, i.e. connections with a statistical bit rate for which the ratio of the maximum bit rate to the average bit rate is above a certain value, is that on the one hand it is necessary to avoid cell losses, which may occur due to the simultaneous transmission of many connections at a high bit rate, and on the other hand it is necessary to make it possible for the ATM
connection or the ATM communication device to be utilized to the greatest possible extent. Various connection acceptance methods of this kind are known.
One possibility is to reserve the peak cell rate PCR for each communication connection.
Consequently, cell losses caused by overloading of the communication connection cannot occur, but the advantages of statistical multiplexing, i.e. the better utilization of the communication device by connections with a varying cell rate that are independent of one another cannot be exploited.
If, on the other hand, only the average sustainable cell rate SCR is reserved for each connection, intolerable cell losses occur even when there are small variations in the overall cell rate.
Only when there is a very high number of connections that are independent of one another does the capacity required for transmission of the connections without any cell loss come close to the sum of the average sustainable cell rates of the individual connections.
One known method for controlling the acceptance of connections which can be statistically multiplexed is the so-called sigma rule, - d -which is described in European Patent EP 0 433 699 Bl.
In this method, an additional connection is still accepted along with a number M of already existing connections if an upper estimate of the transmission bit rate necessary for the transmission of the M+l connections is less than or equal to the maximum bit rate Rmax of the communication device.
The estimate of the required capacity in the case of the sigma rule is given by the addition of the sum SM+1='7SCP.;, of the average sustainable cell rates of the M+1 connections which can be statistically multiplexed to a factor Q(R) *~VM+1, where Q(R) is a quantile function which indicates the statistical behavior of the connections in dependence on the required bit rate, and V is an estimate of the variance of the bit rates of the M+1 connections.
If the capacity of a transmission device is shared with other types of traffic, for example traffic at an unspecified bit rate or available bit rate, the capacity R available for the traffic to be multiplexed is no longer known.
Until now, the sigma rule has been extended to cope with this problem and the capacity of the M
already reserved connections used as the decision parameter for the acceptance of the M+lth connection.
This capacity is iteratively increased when setting up further connections, to be precise by the average sustainable cell rate of the connection to be added if the sigma rule will accept the connection for this capacity, otherwise by the peak cell rate. By this procedure, the capacity determined is dependent on the setting-up, sequence.
Summary of Invention Embodiments of the invention are therefore based on the object of proposing a method for controlling the acceptance or refusal of a new connection of an ATM
communication device with a given capacity Rmax which is independent of the sequence of the acceptance of the connections of the communication device.
The object is achieved in one aspect by a method for determining a required capacity loadM on an ATM
5(Asynchronous Transfer Mode) communication device by which a plurality M of connections which can be statistically multiplexed is being handled, according to which the capacity loadM required for the M existing connections is determined by resolving an equation Gz: 1oadZ = SZ + Q(1oadZ) *qVZ for Z = M, where the following applies: loadM is a capacity of the M connections, SM =Z [ SCRi ] with 1 <= i <= M, Q(loadM) is a fixed function of loadM, VM =I [ SCRi * ( PCRi - SCRi ) ] with 1 <= i <= M, PCR; is a peak cell rate and SCRi is an average sustainable cell rate of the connection with index i.
The new connection is characterized by its peak cell rate PCR and its average sustainable cell rate SCR. By the method according to the invention, the sum PM+1=Y-PCRi of the peak cell rates and the sum SM+1=Y_SCRi of the average sustainable cell rates of the existing and new connections and the variance V of the cell rates are determined. In dependence on these variables, the required capacity loadM+l of the M+1 connections is determined and the new connection is accepted if the required capacity loadM+l is less than or equal to the maximum capacity RmaX of the ATM communication device.
By contrast with the known sigma rule, in the method according to the invention the overall required capacity loadM+l is calculated exactly. It is not just determined whether or not a new connection can be set up.
Consequently, the result achieved by the method according to the invention is independent of the sequence in which the connections are set up.
Since the required capacity is calculated, and consequently also the free capacity available at a given time, users or management centers of the communication device can be notified of this, making it possible for the network to be utilized more effect;Ively.
In a variant of the method, the connection is accepted if the minimum of the variables loadM+1 and PM+1 is less than or equal to the maximum capacity Rmax= If the calculated capacity loadM+1 is greater than the sum of the maximum bit rates P,.,+I, it is sufficient to reserve the sum of the maximum bit rates pM+1 .
The required bit rate loadM for M connections can be calculated with the assumpti-on of a fictitious bit rate R=SMxQ(R)x~V, where Q(R) is a fixed, empirically determined so-called quantile function of R. The required bit rate loadM is that fictitious bit rate R for which the relationship R = SM + Q (R) = ~V) is satisfied.
The solution to this equation can be determined iteratively by suitable methods of approximation.
The quantile function Q(R) can be chosen to be ql+q2/R, the h erbolic YP quantile ql and the hyperbolic iactor q, of the associated sigma class being empirically determined by simulation calculati.ons.
Then, loadM can be determined by numerical extraction of the root load = xf)/2 + 4q2 = qV + x02 where xO is equal to ql =~V, - 6a -In another aspect of the invention, there is provided a method for determining a still transmissible average sustainable cell rate SCRc and a still transmissible peak cell rate PCRc for a new connection with an average sustainable cell rate SCRM4I, a peak cell rate PCRM+,, an average minimum sustainable cell rate SCRMIN and a minimum peak cell rate PCRMIN on an ATM communication device, by which a plurality M of connections which can be statistically multiplexed is being handled, according to which the still transmissible average sustainable cell rate SCR, and the still transmissible peak cell rate PCRc are determined by resolving an equation GZ: 1oadZ = SZ + Q(loadz) *~VZ for Z = C, where the following applies loade = SCRc, Sc = SM + SCRc with SM =Y- [ SCRi ] and 1 <= i <= M, Q(loade) is a fixed function of load,, Vc = VM + (SCRc) * (PCRc - SCRc) with VM =2: [ SCRi * ( PCRi - SCRi ) ] and 1 <= i<= M, SCRc = SCRMIN + a*x, PCRc = PCRMIN + x, a=( SCRM+1 - SCRMIN )/
PCRM+I - PCRMIN ), x = PCRc - PCRMIN, PCRi is the peak cell rate and SCRi is the average sustainable cell rate of the connection with index i.
In another aspect of the invention, there is provided an ATM communication device with a maximum capacity Rmaxr with a device for indicating a still available residual capacity Rrest of the ATM communication device, where Rrest = Rmax - loadM and loadM is determined according to the method described herein.
Brief Description of the Drawings The invention is described below with reference to the drawing, in which - 6b -Figure 1 is a graph to explain the calculation of the required capacity of a number of connections which can be statistically multiplexed;
Figure 2 is a graph to illustrate an iteration method for calculating the required capacity; and Figure 3 is a graph to explain application of the method according to the invention.
Detailed Description A communication device, such as for example a communication line, a switching matrix or the like, has an overall available capacity Rmax, i.e. a connection with a constant bit rate Rmax can be accepted.
A number M of communication connections which can be statistically multiplexed are transmitted via the communication devices, characterized by a peak cell rate PCR and an average sustainable cell rate SCR. PM=
Z"'PCRi then denotes the sum of the peak cell rates of the M connections and SM=ESCR;, denotes the sum of the average sustainable cell rates of the connections.
V = ESCRi ( PCRi-SCRi ) is the estimate of the variance of the cell rates of the M connections.
If SM + 4V = Q(R) <_ R (1) is satisfied for a bit rate, this capacity is sufficient for all M connections to be accepted. In this case, Q(R) is an empirically determined quantile function. For Q(R) , the function ql+q2/R is known as a good approximation, the factors ql and q2 being determined by simulations and depending on the ratio of the peak cell rate to the average sustainable cell rate of the connections. ql is, for example, of the order of magnitude of 10, q2 is of the order of magnitude of I05. Inequation 1 can then be written as:
(q, + q2/R) = 4V + SM < R (2) The right and left sides of the inequation are graphically represented in Figure 1. The function y(R)=R is a linear, monotonously rising function, while the function y=ql+q2/R4V+SM falls hyperbolically with higher values of R. The intersection point of the two graphs is the value R=load, which gives the required capacity exactly (within the accuracy of the assumptions made) By determining this intersection R=load, the capacity required by the M connections which can be statistically multiplexed can consequently be determined exactly, while in the case of the sigma rule it is just determined whether or not a new connection can be accepted at a given time. The exact calculation of the overall capacity has the advantage that it does not depend on the sequence in which the connections are accepted. Furthermore, the required capacity, and consequently also the free capacity available at a given time, can be indicated and users of the communication device can be notified of it.
For the calculation of load, there are the following possibilities. On the one hand, the equation (ql + q2/load) = ~V + SM = load (3) can be resolved for load if x0:=q14V is defined:
load = xo/2 + ~q2 = ~V + x02 ( 4 ) Alternatively, R=load can also be determined iteratively. The method is schematically represented in Figure 2. From the starting point loado=q14V+SM, load is determined iteratively as loadn+i = (qi + q2/loadn) = 4V + SM (5).
A C program for executing this algorithm is enclosed with the patent application as an annex. In 10' calculations for the acceptance of a connection, the - 8a -relative error of load in three iterations was below 3x10-4. An odd number of iteration steps ensures that the required capacity is overestimated and not underestimated.
The exactly calculated capacity loadM at a given time for M connections of the communication device can in turn be used for effective acceptance control of the communication device. Since the capacity loadM required for M existing connections is continuously available, when there is a new request for a connection with a peak cell rate PCR and an average sustainable cell rate SCR, the connection can be accepted without further calculation if the free capacity Rmax-loadM is greater than PCR and can be refused without further calculation if Rmax-loadM is less than SCR. Only if the load of the communication device is in the range lying in between is a new calculation of the load loadM+l of the M+l connections required before acceptance. As soon as the connection has been set up, the load calculation is extended to all the existing connections.
A further application of the present invention is explained with reference to Figure 3.
In the case of a connection with a variable bit rate, it may be characterized not only by the peak cell rate F and average sustainable cell rate G but also by a peak cell rate required as a minimum Hmin and an average sustainable cell rate required as a minimum I. An example of this is a video telephone service, which requires a minimum transmission bandwidth of, for example, 64 KB per second to be able to build up a picture at all. A high bandwidth is desirable, but not absolutely necessary, for real-time transmission of the mimic or the like.
In Figure 3, the average sustainable cell rate SCR is plotted against the peak cell rate PCR in a diagram. The peak cell rate F and the average sustainable cell rate G form the point (F, G) which characterizes the ideal state of the connection. The point (H, I) formed by the minimum cell rates Hmin and Imin gives the minimum requirements for the connection.
The task of the connection acceptance control is to accept the connection with a variable (as great as possible) bandwidth if it is ensured that the minimum conditions Hmin. Imin are always satisfied. This acceptance control can be realized on the basis of the exact calculation of the available capacity loadM.
If the combination of parameters at the edge of the gray area with the straight-line through (H, I) and (F, G) is assumed, the capacity available is fully utilized and the prescribed rates are taken well into account. a is the slope of the straight-line (H, I)-(F, G) and x is the difference between the peak cell rate sought and Hmin= Then, the sought average sustainable cell rate c is obtained as the sum of the minimum cell rate and a=x:
c = (ql+q2/c) JV+(I+a=x) ~H+x-(I+a=x) ) + SM + I + a = x (6) where x corresponds to the required capacity load and can be calculated from equations (3) and (5). Equation (6) is equivalent to a quadratic equation in x and can be calculated by suitable numerical iteration methods.
The invention makes possible for the first time an exact calculation of the required capacity loadM of a number M of connections which can be statistically multiplexed, characterized by a peak cell rate PCR and an average sustainable cell rate SCR.
Claims (13)
1. A method for determining a required capacity load M
on an ATM (Asynchronous Transfer Mode) communication device by which a plurality M of connections which can be statistically multiplexed is being handled, according to which the capacity load M required for the M existing connections is determined by resolving an equation G Z: load Z
= S Z + Q(load Z) * .sqroot.V Z for z = M, where the following applies:
- load M is a capacity of the M connections, - S M = .SIGMA. [ SCR i ] with 1 <= i <= M, - Q(load M) is a fixed function of load M, V M = .SIGMA. [ SCR i * ( PCR i - SCR i ) ] with 1 <= i <= M, - PCR i is a peak cell rate and SCR i is an average sustainable cell rate of the connection with index i.
on an ATM (Asynchronous Transfer Mode) communication device by which a plurality M of connections which can be statistically multiplexed is being handled, according to which the capacity load M required for the M existing connections is determined by resolving an equation G Z: load Z
= S Z + Q(load Z) * .sqroot.V Z for z = M, where the following applies:
- load M is a capacity of the M connections, - S M = .SIGMA. [ SCR i ] with 1 <= i <= M, - Q(load M) is a fixed function of load M, V M = .SIGMA. [ SCR i * ( PCR i - SCR i ) ] with 1 <= i <= M, - PCR i is a peak cell rate and SCR i is an average sustainable cell rate of the connection with index i.
2. The method as claimed in claim 1, wherein, given a maximum capacity R max of the ATM communication device, a new connection with an average sustainable cell rate SCR M+1 is accepted if a fictitious capacity load M+l, which is determined for the M existing connections and the new connection by resolving the equation G Z for Z = M+1, satisfies the condition: load M+1 <= R max.
3. The method as claimed in one of claims 1 or 2, wherein P M+1, a sum of the peak cell rates PCR i of the M
existing connections and the new connection, is additionally determined and the new connection is accepted if the following condition is satisfied:
minimum ( P M+1, load M+1 ) <= R max.
existing connections and the new connection, is additionally determined and the new connection is accepted if the following condition is satisfied:
minimum ( P M+1, load M+1 ) <= R max.
4. The method as claimed in any one of claims 1 to 3, wherein the required capacity load M is continuously available, the new connection has a peak cell rate PCR M+1 and the new connection is already accepted before determination of the fictitious capacity load M+1 if the following condition is satisfied:
load M + PCR M+1 <= R max, and the new connection is refused without determination of the fictitious capacity load M+1 if the following condition is satisfied:
load M + SCR M+1 > R max.
load M + PCR M+1 <= R max, and the new connection is refused without determination of the fictitious capacity load M+1 if the following condition is satisfied:
load M + SCR M+1 > R max.
5. A method for determining a still transmissible average sustainable cell rate SCR c and a still transmissible peak cell rate PCR c for a new connection with an average sustainable cell rate SCR M+1, a peak cell rate PCR M+1, an average minimum sustainable cell rate SCR MIN and a minimum peak cell rate PCR MIN on an ATM (Asynchronous Transfer Mode) communication device, by which a plurality M of connections which can be statistically multiplexed is being handled, according to which the still transmissible average sustainable cell rate SCR c and the still transmissible peak cell rate PCR c are determined by resolving an equation G Z:
load Z = S Z + Q(1oad Z) * .sqroot.V2 for Z = C, where the following applies - load c = SCR c, - S c = S M + SCR c with S M =[ SCR i ] and 1 <= i <= M, - Q(load c) is a fixed function of load c, - V c = V M + (SCR c) * (PCR c - SCR c) with V M = .SIGMA. [ SCR i * ( PCR i - SCR i ) ] and 1 <= i <= M, - SCR c = SCR MIN + a*x, - PCR c = PCR MIN + X, - a = ( SCR M+1 - SCR MIN ) / ( PCR M+1 - PCR MIN
- x = PCR c - PCR MIN, - PCR i is the peak cell rate and SCR i is the average sustainable cell rate of the connection with index i.
load Z = S Z + Q(1oad Z) * .sqroot.V2 for Z = C, where the following applies - load c = SCR c, - S c = S M + SCR c with S M =[ SCR i ] and 1 <= i <= M, - Q(load c) is a fixed function of load c, - V c = V M + (SCR c) * (PCR c - SCR c) with V M = .SIGMA. [ SCR i * ( PCR i - SCR i ) ] and 1 <= i <= M, - SCR c = SCR MIN + a*x, - PCR c = PCR MIN + X, - a = ( SCR M+1 - SCR MIN ) / ( PCR M+1 - PCR MIN
- x = PCR c - PCR MIN, - PCR i is the peak cell rate and SCR i is the average sustainable cell rate of the connection with index i.
6. The method as claimed in claim 5, wherein the still transmissible average sustainable cell rate SCR c and the still transmissible peak cell rate PCR c are determined if the new connection with the average sustainable cell rate SCR M+1 and the peak cell rate PCR M+1 is refused and would be accepted with the average minimum sustainable cell rate SCR MIN and the minimum peak cell rate PCR MIN.
7. The method as claimed in claim 5 or 6, wherein a variance V Z is chosen as V Z = .SIGMA. [ SCR i * ( PCR i - SCR i ) ]
where PCR i are peak cell rates of the Z connections with 1 <= i <= z.
where PCR i are peak cell rates of the Z connections with 1 <= i <= z.
8. The method as claimed in any one of claims 5 to 7, wherein the fixed function Q(load Z) is chosen as Q (load Z) = q1 + q2 / load Z, where q1 is a hyperbolic quantile and q2 is a hyperbolic factor.
9. The method as claimed in any one of claims 5 to 8, wherein the solution of the equation G z is determined iteratively.
10. The method as claimed in claims 8 and 9, wherein the iteration is begun at a starting point load D = S z + q1 * .sqroot.V z and load i is determined in each iteration step by load i = S z + ( q1 + q2 / load i-1 ) * .sqroot.V z.
11. The method as claimed in claim 10, wherein the iteration is ended after an odd number of iteration steps.
12. The method as claimed in claim 8, wherein the capacity load Z is determined by the solution of a further equation GW z :
load Z = x0/2 + .sqroot.q2 .cndot. .sqroot.V z + x0 2, where x 0 = q1 * .sqroot.V z.
load Z = x0/2 + .sqroot.q2 .cndot. .sqroot.V z + x0 2, where x 0 = q1 * .sqroot.V z.
13. An ATM communication device with a maximum capacity R max, with a device for indicating a still available residual capacity R rest of the ATM communication device, where R rest = R max - load M and load M is determined according to the method as claimed in claim 1.
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DE19808947A DE19808947A1 (en) | 1998-03-03 | 1998-03-03 | Method for determining the required bit rate for a number of statistically multiplexable communication links |
| DE19808947.3 | 1998-03-03 | ||
| PCT/DE1998/003563 WO1999045739A1 (en) | 1998-03-03 | 1998-12-03 | Method for determining the required bit rate for a number of communications connections which can be statistically multiplexed |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA2322794A1 CA2322794A1 (en) | 1999-09-10 |
| CA2322794C true CA2322794C (en) | 2008-07-22 |
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| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA002322794A Expired - Fee Related CA2322794C (en) | 1998-03-03 | 1998-12-03 | Method for determining the required bit rate for a number of communications connections which can be statistically multiplexed |
Country Status (6)
| Country | Link |
|---|---|
| EP (1) | EP1060634B1 (en) |
| AT (1) | ATE290302T1 (en) |
| CA (1) | CA2322794C (en) |
| DE (2) | DE19808947A1 (en) |
| ES (1) | ES2235385T3 (en) |
| WO (1) | WO1999045739A1 (en) |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2000261459A (en) * | 1999-03-10 | 2000-09-22 | Nec Corp | Statistical multiplex transmission system |
| FI20002646A (en) * | 2000-12-01 | 2002-06-02 | Nokia Corp | A method for multiplexing sources with different bit rates |
| DE10108048A1 (en) * | 2001-02-20 | 2002-09-05 | Siemens Ag | Method for switching connections, associated communication arrangement, associated communication device and associated program |
| US8468572B2 (en) * | 2008-03-26 | 2013-06-18 | Cisco Technology, Inc. | Distributing digital video content to multiple end-user devices |
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| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| ATE139396T1 (en) * | 1989-12-22 | 1996-06-15 | Siemens Ag | CIRCUIT ARRANGEMENT FOR COMMUNICATION DEVICES WITH ASYNCHRONOUS TRANSFER MODE |
| US5289462A (en) * | 1992-08-19 | 1994-02-22 | International Business Machines Corp. | Traffic management in packet communications networks |
| US5548581A (en) * | 1994-08-17 | 1996-08-20 | Bellsouth Corporation | System and method for making connection acceptance/rejection decisions in a communication system |
-
1998
- 1998-03-03 DE DE19808947A patent/DE19808947A1/en not_active Withdrawn
- 1998-12-03 CA CA002322794A patent/CA2322794C/en not_active Expired - Fee Related
- 1998-12-03 EP EP98964379A patent/EP1060634B1/en not_active Expired - Lifetime
- 1998-12-03 ES ES98964379T patent/ES2235385T3/en not_active Expired - Lifetime
- 1998-12-03 AT AT98964379T patent/ATE290302T1/en not_active IP Right Cessation
- 1998-12-03 DE DE59812628T patent/DE59812628D1/en not_active Expired - Fee Related
- 1998-12-03 WO PCT/DE1998/003563 patent/WO1999045739A1/en active IP Right Grant
Also Published As
| Publication number | Publication date |
|---|---|
| CA2322794A1 (en) | 1999-09-10 |
| EP1060634A1 (en) | 2000-12-20 |
| DE19808947A1 (en) | 1999-09-09 |
| DE59812628D1 (en) | 2005-04-07 |
| EP1060634B1 (en) | 2005-03-02 |
| ES2235385T3 (en) | 2005-07-01 |
| WO1999045739A1 (en) | 1999-09-10 |
| ATE290302T1 (en) | 2005-03-15 |
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