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Fairness in broadband ISDNs
Computers ind. Engng Vol. 21, Nos 1-4, pp. 325-327, 1991 Printed in Great Britain. All rights reserved
0360-8352/91 $3.00+0.00 Copyright © 1991 PergamonPress plc
FAIRNESS IN BROADBAND ISDNs
Mr. Dawei Yu and Dr. Mohammad Ilyas Department of Computer Engineering Florida Atlantic University Boca Raton, Florida, USA 33431
since no global synchronization is needed, it is easier to manage and maintain the network.
ABSTRACT In order to achieve satisfactory performance in broadband Integrated Services Digital Networks (ISDNs), some techniques to control flow of information traffic, are necessary. Bandwidth allocation, bandwidth enforcement, and load balancing, are some of the examples of these techniques. Unfortunately, some of these techniques result in unfair distribution of resources among users. Recently, fairness in resource sharing systems has received significant attention among researchers. In this paper, we discuss, in comparative terms, several resource allocation techniques along with their fairness aspects in broadband ISDNs. We will also propose a threshold-based scheme to minimize the blocking probability and improve fairness.
Many of the services supported by BISDNs are expected to exhibit bursty traffic characteristics. Due to this bursty nature of services, sometimes demands for the network resources may exceed the quantity of the resources. If this happens and no steps are taken to avoid it, the network may experience congestion [2], which may eventually lead to a deadlock. It is, therefore, of paramount importance that in high speed communication networks such as BISDNs, resources must be allocated to users with great care. Due to this reason, resource allocation and congestion control techniques have received significant attention among telecommunication professionals.
flexibility to support various kinds of services with different requirements,
Although proper allocation of resources and use of appropriate congestion control techniques reduce the possibility of any unpleasant experience to its users, they do not eliminate the possibility of being fair to some users and not to the others. Fairness, therefore, is also an important consideration in design and implementation of resource allocation and congestion control techniques. Fairness considerations pose a tedious problem. The biggest of those problems is how to define fairness and from whose point of view. Generally, fairness is defined as the ability to provide equal satisfaction to all the network users. This definition raises more problems that it resolves. For instance, how do we define satisfaction? Are we going to involve behavioral sciences to quantify satisfaction and hence fairness? The second aspect of fairness is even more involved than the first one i.e. from whose point of view the fairness should be considered. Should it be considered from users' point of view, or should it be from the network manager's point of view, or should it be considered form the designer's point of view. All of these have different approaches to fairness and usually they contradict each other [5].
by using the multiplexing technique for the bursty type of traffic or variable bit rate (VBR) type of traffic, one can achieve better efficiency and better utilization of the network resources such as bandwidth and buffer memory etc.,
In this paper, we will discuss several approaches to implement fairness and discuss their merits and demerits. Finally, we will discuss some additional approaches to ensure a greater degree of fairness in Broadband ISDNs. In the next section, we discuss
INTRODUCTION Broadband Integrated Service Digital Networks (BISDNs) provide end-to-end digital, efficient, and costeffective means of information transfer for a large variety of information services including voice, data, and video. The mode of transportation in BISDNs as recommended by CCI'I~I", is referred to as Asynchronous Transfer Mode (ATM). ATM is a fast form of packet switching technique that can be used for a broad spectrum of services ranging from low speed to high speed, from constant bit rate traffic to bursty traffic, and from connection oriented to connectionless applications. ATM technique uses small packets of information called "cells". Each cell has its own header that contains information related to the routing, and error control etc. The advantages of the ATM technique include:
325
326
Proceedings of the 13th Annual Conference on Computers and Industrial Engineering
various fairness approaches used in communication networks. In the following section, we propose another approach to fairness problem. Finally we give some conclusions in the last section. FAIRNESS METHODS The fairness schemes as applicable to BISDNs can be broadly categorized into the following three groups [11: • • •
schemes that result is fair resource sharing among users schemes that result in equal performance level for all users schemes that result in balanced interference among users.
In the first category, we identify critical resources in a communication network such as bandwidth, and buffers etc. and implement schemes that ensure availability of these resources to all competing users on equal basis. However, if we let these resources to be shared among users on an equal basis, that will be unfair to users who have a larger traffic volume and will be wasteful for those users who have relatively less traffic volume. To avoid this problem, we can let users share system resources according to traffic volume that they have: a heavy user receives a larger share and a sluggish user receives proportionally less share of resources. Even this scheme has some drawbacks because their may not be a linear relationship between the traffic volume that a user generates and the amount of resources needed to support that traffic volume. Finding an exact relationship between the traffic volume and resources requirements may not be a simple one and extensive simulations or mathematical models may be required to find an optimal resource allocation mechanism. In BISDNs, as a call for a service originates from a user, resources have to be allocated before the call can proceed through the network. This implies that potentially a few calls may use up all the resources of the network and may hold these for a longer duration of time. In this situation several calls may not be accepted simply due to the non-availability of the resources. However, if we always keep some of the resources in reserve, we may be able to support a relatively larger number of service calls [6]. The second category deals with equal performance level instead of equal share of resources. This approach feels better to the users, however, may not be fair to the service provider i.e. network managers. The techniques in this category make an effort to provide a uniform quality of service to all network users. Note that the performance level or quality of service is not attached to the level of traffic that a user generates. However, in this approach the biggest problem is that different users view performance in different terms. Some users view performance in terms of delay, some users view performance in terms of throughput, while some users take a middle approach
and combine delay and throughput together as one performance measure. A combined performance measure of delay and throughput takes several forms. One combination of these measures is obtained by multiplying delay and throughput with two multipliers and adding them up. The values of these multipliers depend upon their relative importance. If delay is more important to a user, the delay multiplier will be larger in value as compared to that for throughput and vice versa. This is usually referred to as reward function. Another combination is obtained by taking a ratio of throughput and delay. This combination is called power. This performance measure is important in situations where we intend to optimize network's performance in terms of delay as well as throughput. As mentioned earlier, for the purpose of fairness, we like to provide the same level of performance to all users irrespective of the performance parameters in use. In this situation, delay itself may not be an ideal parameter to work with. In most cases, it is the variance in delay that is used for measuring fairness. In a perfectly fair system, the variance would be zero. In general, we like to minimize the delay variance. In BISDNs, the performance parameters are quite different as compared to those traditionally used in computer communication networks. In BISDNs, call blocking probability is one of the key performance measure that is used. Cell loss rate is another important performance measure in BISDNs. As mentioned earlier, in BISDNs, we use fixed size packets that are called cells. Before a call can use network resources, a virtual circuit has to be established between source and destination, in response to a call request that originates from the source user. The call is established in accordance with the parameters passed onto the network through the call setup message. These parameters contain information related to burstiness of the information, bandwidth requirements, call holding time, and buffer requirement etc. Once a call is established, the information is transmitted to its destination in the form of fixed size cells. If the network cannot provide resources for a call as indicated through the call setup message, the virtual circuit for that call cannot be established and the call is said to be blocked. In order to achieve fairness, each user must be subject to the same blocking probability. If the resource allocation process is not properly implemented, this may lead to a situation that calls from some users may have a very small blocking probability while others may face call blocking most of the time [6]. There has to be a strategy that does not allocate resources simply on the basis of first-come-first-served but takes into consideration the amount of resources being requested. Generally, as a call request arrives, it is accepted as long there are resources to support it. This implies that if a few calls with larger requirement occupy the resources, calls with lesser resource requirement may be blocked. However, if we allocate resources to calls according to a policy that a call can only be accepted if
Yu and Ilyas: Broadband ISDNs it does not take more than a ceratin percentage of the available resources, then there will always be a good possibility that calls with lesser requirement will be accepted. Such a scheme will be a fair to most of the users rather than being generous to only a few [6]. In the third category, a network tends to provide a mechanism to inflict a penalty for users that cause discomfort in a network. For instance, if a user pours too much traffic, its direct effect is that the delay increases, and this may lead to an increased level of congestion as well. Such a user should pay a penalty in terms of limiting its throughput or in terms of limiting the availability of resources to such a user. In such schemes, exact relationship between traffic and congestion level needs to be worked out which is not a simple task.
REFERENCES
[11
Gerla, M. and Chan, H.W., "Fairness in Computer Networks", Conference Record of IEEE ICC '85, June 1985, pp. 1384-1389.
[2]
Gerla, M., and Kleinrock, M., "Flow Control: A Comparative Survey", IEEE Transactions on Communications", Vol. COM-28, No. 4, April 1980, pp. 553-573.
[3]
Gersht, A., and Lee, K.J., "Virtual-Circuit Load Control in Fast Packet-Switched Broadband Networks", Conference Record of IEEE GLOBECOM '88, December 1988, pp. 214-220.
[4]
Hui, J.Y., "Resource Allocation for Broadband ISDNs", IEEE Journal on Selected Areas in Communications, Vol. 6, No. 9, December 1988, pp. 1598-1608.
[5]
Ilyas, M. and Mouftah, H.T., "Performance Evaluation of Computer Communication networks", IEEE Communications Magazine, Vol. 23, No. 4, April 1985, pp. 18-29.
[6]
Ilyas, M., and Mouftah, H.T., "A Comparative Simulation of Congestion Avoidance Techniques in Broadband ISDNs", Conference Record of IEEE GLOBECOM '90, December 1990. pp. 584-588.
[7]
Katevenis, M.G.H., "Fast Switching and Fair Control of Congested Flow in Broadband Networks", IEEE Journal on Selected Areas in Communications, Vol. SAC-5, No. 8, October 1987, pp. 1315-1326.
[8]
Minzer, S.E., Broadband ISDN and Asynchronous Transfer Mode (ATM)", IEEE Communications Magazine, Vol. 27, No. 9, September 1989, pp. 17-24.
[9]
Wong, F., and De Marca, J.R.B., "Fairness in Window Flow Controlled Computer Networks", IEEE Transactions on Communications, Vol. 37, No. 5, May 1989, pp. 475-480.
[I0]
Wong, J.W., Sauve, J.P., and Field, J.A., "A Study of Fairness in Packet-Switched Networks", IEEE Transactions on Communications, Vol. COM-30, No. 2, February 1982, pp. 346-353.
[11]
Woodruff, G.M., Rogers, R.G.H., and Richards, P.S., "A Congestion Control Framework for High Speed Integrated Packetized Transport", Conference Record of IEEE GLOBECOM '88, December 1988, pp. 203-207.
HYBRID METHODS FOR FAIRNESS As one may have noted from previous section that fairness in computer communication networks is a complicated issue and it is even more complex in BISDNs simply because there are so many variables involved and usually they have conflicting requirements. In order to develop simple and effective means of achieving fairness, one may have to look into possibility of combining a few of the fairness schemes into one and implement it in simplest possible terms. It may also be better to relate resource allocation mechanism with fairness considerations. One such scheme of resource allocation in BISDNs is proposed in [6]. In this scheme, the authors suggest that the allocation of resources should be on the basis of a threshold and the scheme has been shown to give an overall fair share of resources to all types of traffic and at the same time reduces overall call blocking probability. In order to be more comprehensive, this resource allocation scheme may be merged with other schemes i.e. resource utilization and having balanced performance in terms of delay and throughput. All one has to do is to define a combined performance metric that quantifies fairness or unfairness. If we are dealing with just one parameter that may be easy and simple to implement as compared to dealing with several parameters that may be contradictory at times.
327
CONCLUSIONS In this paper, we have presented some issues related to fairness in computer communication networks, in general, and Broadband Integrated Services Digital Networks, in particular. We have identified three categories of classifying fairness and have pointed out that in order to achieve fairness in a network one may have to combine various fairness schemes into one for the sake of simplicity. We have also some possible schemes for achieving fairness in BISDNs.
CAIE 21:1-4-V
0360-8352/91 $3.00+0.00 Copyright © 1991 PergamonPress plc
FAIRNESS IN BROADBAND ISDNs
Mr. Dawei Yu and Dr. Mohammad Ilyas Department of Computer Engineering Florida Atlantic University Boca Raton, Florida, USA 33431
since no global synchronization is needed, it is easier to manage and maintain the network.
ABSTRACT In order to achieve satisfactory performance in broadband Integrated Services Digital Networks (ISDNs), some techniques to control flow of information traffic, are necessary. Bandwidth allocation, bandwidth enforcement, and load balancing, are some of the examples of these techniques. Unfortunately, some of these techniques result in unfair distribution of resources among users. Recently, fairness in resource sharing systems has received significant attention among researchers. In this paper, we discuss, in comparative terms, several resource allocation techniques along with their fairness aspects in broadband ISDNs. We will also propose a threshold-based scheme to minimize the blocking probability and improve fairness.
Many of the services supported by BISDNs are expected to exhibit bursty traffic characteristics. Due to this bursty nature of services, sometimes demands for the network resources may exceed the quantity of the resources. If this happens and no steps are taken to avoid it, the network may experience congestion [2], which may eventually lead to a deadlock. It is, therefore, of paramount importance that in high speed communication networks such as BISDNs, resources must be allocated to users with great care. Due to this reason, resource allocation and congestion control techniques have received significant attention among telecommunication professionals.
flexibility to support various kinds of services with different requirements,
Although proper allocation of resources and use of appropriate congestion control techniques reduce the possibility of any unpleasant experience to its users, they do not eliminate the possibility of being fair to some users and not to the others. Fairness, therefore, is also an important consideration in design and implementation of resource allocation and congestion control techniques. Fairness considerations pose a tedious problem. The biggest of those problems is how to define fairness and from whose point of view. Generally, fairness is defined as the ability to provide equal satisfaction to all the network users. This definition raises more problems that it resolves. For instance, how do we define satisfaction? Are we going to involve behavioral sciences to quantify satisfaction and hence fairness? The second aspect of fairness is even more involved than the first one i.e. from whose point of view the fairness should be considered. Should it be considered from users' point of view, or should it be from the network manager's point of view, or should it be considered form the designer's point of view. All of these have different approaches to fairness and usually they contradict each other [5].
by using the multiplexing technique for the bursty type of traffic or variable bit rate (VBR) type of traffic, one can achieve better efficiency and better utilization of the network resources such as bandwidth and buffer memory etc.,
In this paper, we will discuss several approaches to implement fairness and discuss their merits and demerits. Finally, we will discuss some additional approaches to ensure a greater degree of fairness in Broadband ISDNs. In the next section, we discuss
INTRODUCTION Broadband Integrated Service Digital Networks (BISDNs) provide end-to-end digital, efficient, and costeffective means of information transfer for a large variety of information services including voice, data, and video. The mode of transportation in BISDNs as recommended by CCI'I~I", is referred to as Asynchronous Transfer Mode (ATM). ATM is a fast form of packet switching technique that can be used for a broad spectrum of services ranging from low speed to high speed, from constant bit rate traffic to bursty traffic, and from connection oriented to connectionless applications. ATM technique uses small packets of information called "cells". Each cell has its own header that contains information related to the routing, and error control etc. The advantages of the ATM technique include:
325
326
Proceedings of the 13th Annual Conference on Computers and Industrial Engineering
various fairness approaches used in communication networks. In the following section, we propose another approach to fairness problem. Finally we give some conclusions in the last section. FAIRNESS METHODS The fairness schemes as applicable to BISDNs can be broadly categorized into the following three groups [11: • • •
schemes that result is fair resource sharing among users schemes that result in equal performance level for all users schemes that result in balanced interference among users.
In the first category, we identify critical resources in a communication network such as bandwidth, and buffers etc. and implement schemes that ensure availability of these resources to all competing users on equal basis. However, if we let these resources to be shared among users on an equal basis, that will be unfair to users who have a larger traffic volume and will be wasteful for those users who have relatively less traffic volume. To avoid this problem, we can let users share system resources according to traffic volume that they have: a heavy user receives a larger share and a sluggish user receives proportionally less share of resources. Even this scheme has some drawbacks because their may not be a linear relationship between the traffic volume that a user generates and the amount of resources needed to support that traffic volume. Finding an exact relationship between the traffic volume and resources requirements may not be a simple one and extensive simulations or mathematical models may be required to find an optimal resource allocation mechanism. In BISDNs, as a call for a service originates from a user, resources have to be allocated before the call can proceed through the network. This implies that potentially a few calls may use up all the resources of the network and may hold these for a longer duration of time. In this situation several calls may not be accepted simply due to the non-availability of the resources. However, if we always keep some of the resources in reserve, we may be able to support a relatively larger number of service calls [6]. The second category deals with equal performance level instead of equal share of resources. This approach feels better to the users, however, may not be fair to the service provider i.e. network managers. The techniques in this category make an effort to provide a uniform quality of service to all network users. Note that the performance level or quality of service is not attached to the level of traffic that a user generates. However, in this approach the biggest problem is that different users view performance in different terms. Some users view performance in terms of delay, some users view performance in terms of throughput, while some users take a middle approach
and combine delay and throughput together as one performance measure. A combined performance measure of delay and throughput takes several forms. One combination of these measures is obtained by multiplying delay and throughput with two multipliers and adding them up. The values of these multipliers depend upon their relative importance. If delay is more important to a user, the delay multiplier will be larger in value as compared to that for throughput and vice versa. This is usually referred to as reward function. Another combination is obtained by taking a ratio of throughput and delay. This combination is called power. This performance measure is important in situations where we intend to optimize network's performance in terms of delay as well as throughput. As mentioned earlier, for the purpose of fairness, we like to provide the same level of performance to all users irrespective of the performance parameters in use. In this situation, delay itself may not be an ideal parameter to work with. In most cases, it is the variance in delay that is used for measuring fairness. In a perfectly fair system, the variance would be zero. In general, we like to minimize the delay variance. In BISDNs, the performance parameters are quite different as compared to those traditionally used in computer communication networks. In BISDNs, call blocking probability is one of the key performance measure that is used. Cell loss rate is another important performance measure in BISDNs. As mentioned earlier, in BISDNs, we use fixed size packets that are called cells. Before a call can use network resources, a virtual circuit has to be established between source and destination, in response to a call request that originates from the source user. The call is established in accordance with the parameters passed onto the network through the call setup message. These parameters contain information related to burstiness of the information, bandwidth requirements, call holding time, and buffer requirement etc. Once a call is established, the information is transmitted to its destination in the form of fixed size cells. If the network cannot provide resources for a call as indicated through the call setup message, the virtual circuit for that call cannot be established and the call is said to be blocked. In order to achieve fairness, each user must be subject to the same blocking probability. If the resource allocation process is not properly implemented, this may lead to a situation that calls from some users may have a very small blocking probability while others may face call blocking most of the time [6]. There has to be a strategy that does not allocate resources simply on the basis of first-come-first-served but takes into consideration the amount of resources being requested. Generally, as a call request arrives, it is accepted as long there are resources to support it. This implies that if a few calls with larger requirement occupy the resources, calls with lesser resource requirement may be blocked. However, if we allocate resources to calls according to a policy that a call can only be accepted if
Yu and Ilyas: Broadband ISDNs it does not take more than a ceratin percentage of the available resources, then there will always be a good possibility that calls with lesser requirement will be accepted. Such a scheme will be a fair to most of the users rather than being generous to only a few [6]. In the third category, a network tends to provide a mechanism to inflict a penalty for users that cause discomfort in a network. For instance, if a user pours too much traffic, its direct effect is that the delay increases, and this may lead to an increased level of congestion as well. Such a user should pay a penalty in terms of limiting its throughput or in terms of limiting the availability of resources to such a user. In such schemes, exact relationship between traffic and congestion level needs to be worked out which is not a simple task.
REFERENCES
[11
Gerla, M. and Chan, H.W., "Fairness in Computer Networks", Conference Record of IEEE ICC '85, June 1985, pp. 1384-1389.
[2]
Gerla, M., and Kleinrock, M., "Flow Control: A Comparative Survey", IEEE Transactions on Communications", Vol. COM-28, No. 4, April 1980, pp. 553-573.
[3]
Gersht, A., and Lee, K.J., "Virtual-Circuit Load Control in Fast Packet-Switched Broadband Networks", Conference Record of IEEE GLOBECOM '88, December 1988, pp. 214-220.
[4]
Hui, J.Y., "Resource Allocation for Broadband ISDNs", IEEE Journal on Selected Areas in Communications, Vol. 6, No. 9, December 1988, pp. 1598-1608.
[5]
Ilyas, M. and Mouftah, H.T., "Performance Evaluation of Computer Communication networks", IEEE Communications Magazine, Vol. 23, No. 4, April 1985, pp. 18-29.
[6]
Ilyas, M., and Mouftah, H.T., "A Comparative Simulation of Congestion Avoidance Techniques in Broadband ISDNs", Conference Record of IEEE GLOBECOM '90, December 1990. pp. 584-588.
[7]
Katevenis, M.G.H., "Fast Switching and Fair Control of Congested Flow in Broadband Networks", IEEE Journal on Selected Areas in Communications, Vol. SAC-5, No. 8, October 1987, pp. 1315-1326.
[8]
Minzer, S.E., Broadband ISDN and Asynchronous Transfer Mode (ATM)", IEEE Communications Magazine, Vol. 27, No. 9, September 1989, pp. 17-24.
[9]
Wong, F., and De Marca, J.R.B., "Fairness in Window Flow Controlled Computer Networks", IEEE Transactions on Communications, Vol. 37, No. 5, May 1989, pp. 475-480.
[I0]
Wong, J.W., Sauve, J.P., and Field, J.A., "A Study of Fairness in Packet-Switched Networks", IEEE Transactions on Communications, Vol. COM-30, No. 2, February 1982, pp. 346-353.
[11]
Woodruff, G.M., Rogers, R.G.H., and Richards, P.S., "A Congestion Control Framework for High Speed Integrated Packetized Transport", Conference Record of IEEE GLOBECOM '88, December 1988, pp. 203-207.
HYBRID METHODS FOR FAIRNESS As one may have noted from previous section that fairness in computer communication networks is a complicated issue and it is even more complex in BISDNs simply because there are so many variables involved and usually they have conflicting requirements. In order to develop simple and effective means of achieving fairness, one may have to look into possibility of combining a few of the fairness schemes into one and implement it in simplest possible terms. It may also be better to relate resource allocation mechanism with fairness considerations. One such scheme of resource allocation in BISDNs is proposed in [6]. In this scheme, the authors suggest that the allocation of resources should be on the basis of a threshold and the scheme has been shown to give an overall fair share of resources to all types of traffic and at the same time reduces overall call blocking probability. In order to be more comprehensive, this resource allocation scheme may be merged with other schemes i.e. resource utilization and having balanced performance in terms of delay and throughput. All one has to do is to define a combined performance metric that quantifies fairness or unfairness. If we are dealing with just one parameter that may be easy and simple to implement as compared to dealing with several parameters that may be contradictory at times.
327
CONCLUSIONS In this paper, we have presented some issues related to fairness in computer communication networks, in general, and Broadband Integrated Services Digital Networks, in particular. We have identified three categories of classifying fairness and have pointed out that in order to achieve fairness in a network one may have to combine various fairness schemes into one for the sake of simplicity. We have also some possible schemes for achieving fairness in BISDNs.
CAIE 21:1-4-V