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SERVICE LEVEL AGREEMENTS AND
FIELD OF THE INVENTION
 The present invention generally relates to information technology, and more particularly relates to managing one or more services for forming and complying with service level agreements.
BACKGROUND OF THE INVENTION
 Recent technological advances combined with market forces have resulted in the creation of new services composed of other services. The term "composite service" is used to describe these new services. Composite service providers pull together a plurality of component services to provide a composite service. Composite services conventionally span several participant organizations. Terms such as "virtual enterprise" and "virtual organization" are conventionally used to describe this type of collection of organizations. A participant organization may provide component services to one or more virtual enterprises. Each component service provider implements a service by executing a process. Implementation of a composite service requires execution of a process that spans multiple organizations. The execution of such multi-organizational processes conventionally involves interaction among participant organizations' computer systems.
 By way of example and not limitation, today there are virtual enterprises reselling web search services. Such virtual enterprises receive a query from a user. This query is then used to query selected web search services offered by component service providers of which this virtual enterprise is a client.
 Referring to the block diagram of FIG. 1, a group of component service providers' computer systems 20 comprise component service providers 20a and 20b. Component service providers 20a and 20b have respective service implementations 19/ and 19k. Service implementations 19/ and 19A: may be put in communication with composite service providers 10a and lOfc of a group of composite service providers' computer systems 10. Each composite service provider 10a and lOfc may have one or more client processes 13m to 13m and 13q to 13p, respectively.
 Continuing the above-mentioned example, suppose a user of composite service provider 10a places a query for a World Wide Web search. This query invokes client process 13m causing a request to be sent to service implementations 19/ and 19A: for searching the World Wide Web using respective search engines associated with these services. Results from such searches may then be provided from service implementations 19/ and 19A: to client process 13m. Hence, in this example, a user executes separate searches on separate search engines of separate service providers from a single query on another separate service provider. In other words, a composite service provider executes a business process which in turn causes component service providers to execute respective business processes.
 Accordingly, it should be understood that a component service provider may have several services to offer its clients. Thus, component service providers may have a platform of services available to subscribers or clients. Such
services may be invoked through various invocation infrastructures such as Common Object Request Broker Architecture ("CORBA"), Java Remote Method Invocation ("Java RMI"), Hypertext Transport Protocol ("HTTP"), among others. Moreover, this invocation may be manual; for example, a phone call from a composite service provider representative to a component service provider representative.
 In the telecommunications field, Competitive Local Exchange Carriers (CLECs) resell local telephone service of Incumbent Local Exchange Carriers (ILECs). Thus, a CLEC may offer services of several ILECs of which it is a client and vise versa. In a CLEC business model, there is interaction between ILEC and CLEC business processes. By way of example and not limitation, a CLEC customer service representative may interact with provisioning ILEC processes to place an order, inquire about an order, or to cancel an order.
 Accordingly, with respect to the above-mentioned Internet example and telecommunications example, in order to offer their selection of services, a composite service provider relies on services of its component service providers. Therefore, it is incumbent upon composite service providers as clients of component service providers to enter into agreements to guarantee that service needs are met. Examples of such guaranteed service needs may include maximum response time and minimum throughput. These agreements are referred to hereinafter as Service Level Agreements (SLAs). SLAs also assist component service providers in managing their resources to meet their client's needs. Without such SLAs, a component service provider may be overwhelmed by requests from one client organization, which can affect service level to other clients.
 SLAs pertain to services at an application level, as distinguished from end-to-end quality of service (QoS). QoS conventionally pertains to quality parameters of a system infrastructure, or more particularly network performance. A taxonomy of QoS may be found in "Taxonomy of QoS Specifications," by Bikash Sabata, et al., Proceedings of WORDS '97, February 1997.
 Quality objects, which are described in more detail in "Specifying and Measuring Quality of Service in Distributed Object Systems," by Joseph P. Loyall, et al., Proceedings oflSORC '98, April 1998, facilitate specification monitoring of QoS contracts between clients and service providers. However, this specification monitoring is directed at service implementation details and not invoked functionality. Moreover, in QoS contracts, a client is required to specify resource requirements. However, a client may have limited knowledge of resource usage of an invoked service.
 A QoS web server is described in "Supporting Quality of Service in HTTP Serveis,"Proceedings of the Seventeenth Annual SIGACT-SIGOPS Symposium on Principles of Distributed Computing, June 1998. This QoS web server allows allocation of server resources to specific web page requests. System capacity is represented by an estimate of bytes per second served by the server. Thus, issues of guarantees to clients are not addressed.
 A product called "SilkMeter" from Segue Software, Inc. of Lexington, Massachusetts, is a software system for supporting usage control in CORBA environments.
SilkMeter supposedly controls object usage and access based upon customer-defined usage policies, and provides metering capabilities allowing software owners to monitor usage activity and to bill users accordingly. However, SilkMeter does not support implementation of SLAs.
 Hewlett-Packard Company of Palo Alto, Calif., has announced a web QoS strategy. In this announced strategy, website operators may create classes of users with priorities assigned to each class, and more particularly operators may create service classes and allocate capacity to each of them. However, this strategy falls short of providing mechanisms that allow organizations to enter into SLAs. For example, in this strategy, if two organizations are at the same priority level, then it is possible that requests from only one of them will be serviced.
 Accordingly, it would be desirable to provide specification and fulfillment thereof for SLAs between organizations. Advantageously, it would be desirable for such SLA specification and fulfillment to be applicable to a variety of services and implementations and to facilitate deployment over existing distributed system infrastructures.
SUMMARY OF THE INVENTION
 An aspect of the present invention is a service level agreement manager. Such a service level agreement manager is disposed between one or more client process run on one or more computer systems and a service implementation run on one or more other computer systems. Moreover, a client process may be a service implementation. Such a service level agreement manager comprises an admission controller, a performance measurement module and a specification module.
 Another aspect of the present invention is a method for service level formation. More specifically, a specification module of a service level agreement manager is invoked. Performance information is obtained from a performance measurement module. A client provides anticipated usage information for a target service. The performance information and usage information is compared to determine if a basis for forming a service level agreement exists.
 Another aspect of the present invention is a method for managing system performance. More specifically, a service level agreement manager determines whether a client's request is within the scope of a service level agreement. For example, it may be determined whether a request is within the scope of a service level agreement in effect between a requesting client and a service provider of a service implementation for which this client's request is targeted. If the request is within the scope of the service level agreement, the service level agreement is provided to a performance measurement module and to a service organization's service implementation. Results are then obtained from this service implementation in response to this request. Performance parameters associated with sending a request from and receiving a response to a service level agreement manager may be measured. These performance parameters may then be check against performance parameters agreed to in the service level agreement.
 Advantageously, a service level agreement manager in accordance with the present invention may be independent of service implementation with respect to com
patibility issues. Such a service level agreement manager need not directly monitor or measure resource usage of a service provider, rather it can measure response performance therefrom. Moreover, any of several well-known optimization technique can be used within such a service level agreement manager. Furthermore, such a service level agreement manager may be used with any of a variety of invocation infrastructures.
 These and other features, advantages, objects and embodiments of the present invention will become more apparent from reading the following Detailed Description of the Preferred Embodiments or by practicing the present invention.
DESCRIPTION OF THE DRAWINGS
 The features of the present invention, as well as objects and advantages, will best be understood from reading the appended claims, detailed description and accompanying drawings where:
 FIG. 1 is a block diagram of a group of component service providers of the prior art.
 FIGS. 2, 2A and 2B are block diagrams of exemplary embodiments of networks in accordance with the present invention.
 FIG. 3 is a flow diagram of an exemplary embodiment of SLA formation in accordance with the present invention.
 FIG. 4 is a flow diagram of an exemplary embodiment of SLA usage in accordance with the present invention.
 In the drawings, same reference numbers refer to like components throughout the several figures.
DETAILED DESCRIPTION OF THE
 In the following detailed description, reference is made to the accompanying drawings which form a part of this detailed description, and in which, shown by way of illustrative example, specific embodiments are described. These embodiments are described in sufficient detail to enable those of skill in the art to practice the present invention. However, it is to be understood that other embodiments of the present invention not described herein in detail may be utilized. Therefore, the following detailed description is not to be taken in a limiting sense.
 Referring to FIG. 2, there is shown a block diagram of an exemplary embodiment of a system 200 in accordance with the present invention. SLA manager 110 may be put into or is in communication with one or more client computer systems ("clients") 100. As illustratively shown, SLA manager is in communication with clients 100a and lOOfc. Clients 100 may comprise one or more composite service providers, as described elsewhere herein and may comprise one or more computer systems for running one or more client processes. By communication, it is meant electrical, optical, transverse electromagnetic wave, among other forms of communication.
 SLA manager 110 may be put into or is in communication with a service provider 120. A service provider 120 provides service implementation 119. Service provider
120 is a component service provider, as described elsewhere herein, and may comprise one or more computer systems for running service implementation 119.
 Accordingly, it should be appreciated that SLA manager may contemporaneously manage more than one client 100.
 SLA manager 110 provides a front-end for service implementation 119. SLAmanager 110 comprises admission controller 113, performance measurement module 111, and specification module 112.
 Referring to FIG. 2A, there is shown a block diagram of an exemplary embodiment of a system 210 in accordance with the present invention. System 210 comprises clients 100a through lOOrf, SLA managers 110a and llOfc, and service providers 120a and 120fc. Service providers 120a and 120fc comprise respective service implementations 119a and 119fc. One or more invocation infrastructure 211 may be used for connectivity between clients 100a through lOOrf and SLA manager 110a and llOfc. Accordingly, it should be appreciated that SLA managers 110a and HOfc may be used with any invocation infrastructure 211. Moreover, it should be appreciated that a client 100a may be able to access more than one service implementation, such as service implementations 119a and 119fc, by using respective SLA managers, such as SLA managers 110a and llOfc. Moreover, it should be appreciated that service providers 120a and 120fc may be a same provider.
 Referring to FIG. 2B, there is shown a block diagram of an exemplary embodiment of a system 220 in accordance with the present invention. Client 100a may access one or more of service implementations 119c through 119e via respective SLA managers 110c through llOe. As illustratively shown, a service implementation may be coupled to a SLA manager downstream from a client and may be coupled to one or more SLA managers farther downstream from the client. For example, service implementation 119 is couple to SLA manager 110a which is downstream from client 100a, and it is coupled to SLA managers 110c and llOrf which are further downstream from client 100a than SLA manager 110a.
 With continuing reference to FIG. 2, and additional reference to FIG. 3 where there is shown a flow diagram of an exemplary embodiment of SLA formation in accordance with the present invention, SLA formation is described.
 At 301, a client 100a is put in communication with SLA manager 110. This communication may be off-line or on-line. By off-line, it is meant a representative of a client is in contact with a representative of a SLA manager, for example by calling a toll free number to place an order. By on-line, it is meant that a client has contacted a SLAmanager using an invocation infrastructure, for example by accessing a web page for this SLA manager and inputting requested information.
 At 303 SLA specification module 112 is invoked. At 305, SLA specification module 112 accesses performance information from performance measurement module 111. At 304, a service provider 120 presents a list of offered services or functions to a client 100a, and client 100a specifies its usage parameters for each offered service it selects. Examples of usage parameters include but are not limited to
total number of concurrent users, selected services or functions, among others. For services selected, a client may specify peak invocation rate and average invocation rate. By invocation rate, it is meant the number of invocations of a service per unit of time.
 At 306, performance information obtained at 305 is compared with service(s) selected and associate usage information obtained at 304 to determine if a basis for a SLA exists. In this context, a basis for such a SLA is availability of resources to satisfy a specified request.
 If at 306 a basis for a SLA agreement exists, at 307 client 100a and one or more service providers 120 may enter into a SLA agreement. SLA specification information associated with a resulting SLA agreement is provided to admission controller 113 at 308.
 If at 306 there is no basis for agreement, then a reply is sent to client 100a that client provided usage parameters for identified selected services are in excess of service provider's capacity.
 With continuing reference to FIG. 2 and additional reference to FIG. 4, where there is shown a flow diagram of an exemplary embodiment of SLA use in accordance with the present invention, processing a service request using a SLA is described.
 At 402, admission controller 113 determines if a request from client 100a, for example, is received. If a request is received, then using an existing SLA associated with this received request, admission controller 113 determines whether to accept or reject such request at 403. Admission controller 113 may be configured to maximize a customizable benefit function to one or more service providers 120. By way of example and not limitation, this may entail allocation of resources to clients in accordance with SLAs between clients and service providers. Accordingly, this decision by admission controller 113 may include factors such as impact on SLAs with other clients, potential benefits of servicing a request, potential penalty in rejecting a request, among others.
 In an embodiment, a measurement and learning based implementation is used. SLA manager 110 makes an initial estimate of system capacity by measuring system performance under a simulated load. Thereafter, SLA manager 110, through use of performance measurement module 111, continues to measure actual performance of one or more service implementations to refine this initial estimate of the fraction of capacity used by each function. Examples of performance measurements that may be used include requests served per unit of time, bytes served per unit of time, and response time.
 By way of example and not limitation, suppose response time is used as a performance indicator. Each function fi in the interface of a service implementation is associated with a range of time. This range of time denotes minimum and maximum response time for this function. An initial estimate of system capacity may be generated by determining a maximum number of concurrent instances of fi that can be executed within an acceptable response time. These measurements may further be used to determine the fraction of total capacity consumed by each invocation of ,f;.
 Accordingly, SLA manager 110 has opportunity to learn access patterns of its clients, so an estimate, improved