PATENT ABSTRACT
In a three tier client-server architecture, an universal application (UAP) server providing a middle or second tier between a third tier of application servers and a first tier of client devices to provide the controlled delivery of computer based application programs running on a set of application servers to a number of users using a wide variety of client devices without requiring the installation of software on, or changes to the application servers or application programs. The UAP server or application broker comprises a status manager engine, a session manager engine, a data store, a data store engine, a web server, and multiple instantiations of protocol engines design for a given application type and multiple instantiations of display engines for downloading to and operating on client devices. The UAP server provides: (1) means to support standard graphics based computer applications connected to clients of varying capability via a network of varying bandwidth and latency by automatically varying the type and number of graphic requests and their networking encoding to provide near optimum performance while maintaining the correct visual representation, (2) automatic construction of user worktops based on user data contained in a datastore, (3) loading balancing of application servers upon application launch and (4) resumable connections to client devices.

PATENT DESCRIPTION
CROSS-REFERENCE TO RELATED INVENTIONS 
     This application claims the benefit of provisional application serial No. 60/080,790, entitled “Application Broker” filed Apr. 6, 1998. Pending this application is a continuation-in-part of the application Ser. No. 09/190,757, now U.S. Pat. No. 6,104,392 entitled “Method of Displaying Applications on a Variety of Client Devices in a Client/Server Network,” filed Nov. 12, 1998. 
    
    
     STATEMENT REGARDING FEDERALLY FUNDED RESEARCH 
     Not Applicable. 
     REFERENCE TO A MICROFICHE INDEX 
     Not Applicable. 
     COPYRIGHT NOTICE 
     Copyright 1999 The Santa Cruz Operation, Inc. A portion of the disclosure of this patent document contains materials that are subject to copyright protection. The owner has no objection to the facsimile reproduction by anyone of the patent document or patent disclosure, as it appears in the Patent and Trademark Office patent file or records, but otherwise reserves all rights, copyright rights whatsoever. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to networked data processing environments using a client/server architecture, and, in particular, to client-server systems where there exist one or more clients of varying capability connected via network connections of varying bandwidth and latentcy to one or more servers providing application program services or database services to the connected clients. 
     2. Background Information 
     Until the 1980s the computer network typically was used as a means of connecting to a large mainframe environment using dedicated hardware terminals and proprietary protocols. Next UNIX servers grew in usage and with it came standardization of the networking protocols, in particular TCP/IP (Transmission Control Protocol/Internet Protocol). Simultaneously, there was a shift in the computing paradigm towards client/server architectures. This allowed the processing power to be distributed over the network and not be limited to servers which could not scale to meet the growing number of users and their increasing demands. This lead to the need for clients to become more intelligent and powerful. Significant desktop clients came into use: Microsoft Windows. Each iteration of this operating system brought about more functionality requiring more powerful desktop clients. More and more software had to be installed on these clients leading to what is termed “fat clients” and each client required individual configuration. People began to find that the amount of time and money required to maintain these powerful clients was increasing. 
     High availability networks together with hardware and software needed to support such networks have become the norm. In these environments there is not a homogeneous structure of one type of server and one type of client, but a variety of such devices. Within a network there is a wide variety or servers and clients. Upgrades and new applications for this diverse mix of clients usually require that each client be individually upgraded. Also each user has specific needs on the desktop client: configuration, security, access control, mobility. The information services department provides this by administering each client separately. If remote offices are involved, costs to do this increase significantly. Performance in this heterogeneous client network must also be maintained. Slow performance takes up time and money. Networks vary in bandwidth, e.g. modem links, ATMS, Frame Relays, etc. 
     The World Wide Web (the “Web”) has come to the forefront in the current era of the Internet/Intranet and networks have become an integral part of day to day work. Modem speeds double every year and 100 Mbit/sec Local Area Networks have arrived. The Web is now a well-accepted medium for publishing information, in the form of text and graphics (including sound and video). Web programming languages such as Java, JavaScript, and CGI have now extended the Web to applications. This is fine for new applications but existing applications also need a route into this world. 
     Existing applications have either had a character-based or windows-based user interface. Now such applications need a web user interface. The web user interface provides a presentation layer to the user of the application. It must provide an input/output method for the user to interact with the application. There are a number of ways to do this including: (1) HTML (HyperText Markup Language) replacement of the current user interface; (2) Non-Java plug-ins; and (3) Java-based emulation. The first solution involves rewriting the application. The second involves installing more software on the clients leading to “fat clients.” The third is preferred. 
     A large number of vendors offer a character or graphical emulation package that runs on desktop clients such as Windows, UNIX, etc. These emulators could be rewritten in Java and such Java emulator will run on just about any client. However, this approach leads to fat Java clients. For performance reasons, users will not want to wait for large Java applets to download. These Java applets will grow in size, as users demand more and more functionality. Storing these Java applets locally solves the performance problem but leads to fat clients. If state information is stored on the client leading each client to have its own particular configuration parameters, the problem of fat clients is further exacerbated and each client is being managed individually rather than from a central place on the server. 
     Web browsers have an API (Application Programmers Interface) enabling software developers to provide helper applications that allow users to run applications or view unsupported document types on their client platform. These are termed “browser plug-ins.” They are both platform-specific and browser-specific. For example, for two platforms (Windows and UNIX) and two browser types (Netscape and Microsoft), four different implementations of the plug-in would be needed. This type of solution is not cross platform and the majority of these plug-ins are proprietary (e.g., Microsoft ActiveX) locking users into vendor specific solutions. 
     Once the web display of an application is possible, the next step is to make it available to all users. A number of methods that could be used include: (1) local installation; (2) push technology; (3) on-demand access. Local installation involves an administrator installing the application or connectivity software on every single client. This is disadvantageous in that it makes the clients more difficult and costly to manage and leads to fat clients. Push technology involves storing all the files and data associated with users and applications on a server and transmitting them out via virtual channels on a network to clients. Where all storage is on the sever, users experience poor performance in waiting for applets and applications to execute, or downloads are cumbersome and in some cases unusable. Local storage of applications and state information is used to improve performanc. This approach starts off well by using a central server but when applications and any associated state are stored on the client, the fat client problem arises. With on-demand access as used in the present invention, user state, applications, connectivity software and the associated configuration data are stored on a server. Applets are downloaded on demand when the clients request an action, such as start up an application. All state information is kept on the server and can then be managed centrally rather than individually on each client. Keeping state information on the server also makes the client resilient. If the client connection is lost or the client itself is replaced, nothing is lost and no replication is needed. 
     Next the applications and data must be made available to selected users in a secure manner. For manageability, this is done centrally on a server and made available by the most common medium to all users, the Web. But this raises more questions: 
     What do web pages on that server have to contain? 
     What editor has to be used? 
     How do you make it available to selected users or groups of users? 
     Are there different web pages for different types of users? 
     Where does the user profile and application configuration reside? 
     Do users authenticate themselves every time they want to run applications? 
     How is the authentication done? 
     What if the user is already authenticated on the server and does not want to do again and again for each application? 
     What if all of this information is already available and duplication is not desired? 
     As the above list shows, providing a display mechanism via Java emulation is only a partial solution to web-based delivery of applications. 
     To achieve optimal performance on all networks is difficult. Protocols are designed with specific functions in mind, e.g., inter-process communication, graphics rendering, etc. Protocols are rarely designed with the goal of providing uniform performance over complex network routes that have different permutations of bandwidths. To choose the right protocol a number of assumptions could be made. For a high bandwidth network, such as a fast LAN with low latency, the X protocol works well but is unusable over a slow modem link. For a low bandwidth network, such as a slow WAN or modem connection, compression can be used to optimize performance. The ICA protocol of Citrix Systems, Inc. works well over a slow modem connection but is inefficient on a fast LAN connection. 
     It would be advantageous to be able to deliver upgrades to existing applications or roll out new applications to diverse clients; to be able to centralize the administration of clients and their applications; to be able to balance loads in a heterogeneous client server network and to provide high security and manage sessions across heterogeneous servers and services. 
     SUMMARY OF THE INVENTION 
     The inventive universal application server, also termed an application broker, is added in a nondisruptive manner to an existing computer network environment forming a second server tier intermediate the application servers tier on a third tier and the client devices on a first tier. The system provides the following elements: 
     a shared database that is used to describe the location of the application programs, the application servers, the users of the system and a description of which users are provided with access to which application programs; 
     a set of protocol engines processes which support industry standard display protocols (X11, telnet, VT220, etc.) which form the protocols as used by the application programs; 
     a set of display engines processes which are designed to operate within the various client device environments and which communicate with the PE to provide presentation and user interaction services with the users of the client devices; 
     a set of delivery servers which can be used to deliver the display engines to the client devices on demand; and 
     a set of management engines—a data store engine, a status engine, a session manager engine, an administrative engine that allow manipulation of the shared database and control of the operation of the system. 
     Once the application broker has been installed into the existing client server environment it operates in the following manner. Management processes define and maintain the shared database. This consists of making entries for each user of the system for each application server and for each application program. Users connect to the application broker from their client devices and are authenticated against the database. Display engine components are automatically downloaded to the client device, and are used to present the user with a webtop (visual menu) of applications that are available for execution. The contents of the webtop are specific to the user and are constructed dynamically from the database. The user chooses which applications to run. This information is passed from the display engine running on the client device to the universal application server The universal application server, using information stored in the database determines the location of the application program and communicates using industry standard protocols with the appropriate application server. This communication causes the launch of an instance of the application program to take place. The application program launches and is instructed to perform user interaction over a standard protocol by the universal application server. 
     The application broker also arranges to create an instance of the appropriate protocol engine to handle the specific protocol used for a number of applications, such as X-windows applications. It also downloads a suitable display engine to the client device to interact with the user. The protocol engine takes output requests from the application program and converts them into a form that is suitable for use by the downloaded display engine. This information is then forwarded to the display engine where it then converts the information into a form suitable for display within the client device environment. The user interactions with the display engine and the result of these actions (typing, mouse manipulation etc.) are transmitted to the protocol engine. The protocol engine converts these user inputs into the standard protocol used and passes them to the application program. 
     As set forth in the copending application referenced above the protocol engines and display engine processes transmit to and display on the display device of the client device, display requests of the requested application service which are not supported by the client device. The protocol engine is initialized with parameters of the client device comprising display operations supported by the client device, the relative cost of each supported operation and a local performance factor and parameters of the connection from the server to the display engine comprising bandwidth and latency. The protocol engine maintains a first queue for retaining pending display requests and a second queue for retaining transmitted display requests of the requested application service for display on the client device. Each request has a corresponding relative cost and request time determined by the relative cost and the local performance factor. The protocol engine also maintains a total request time for all requests in both queues and maintains a total network time for all requests in the second queue. 
     While the total request time is less than a predetermined first value, the protocol engine accepts new pending requests from the application service that are to be displayed on the client device. The protocol engine executes the new pending display request to create an image to be displayed on the client device, saves the resulting image to memory and determines for the image its relative cost and its corresponding request time based the local performance factor received from the display engine. The protocol engine also converts the new pending display request from the application service into a sequence of converted requests that are supported by the client device, places the sequence of converted requests in the first queue, determines for each converted display request in the sequence its relative cost and its corresponding request time based on the local performance factor, and increments the total request time by the request time of each added request. Further while the total network time is less than a predetermined second value optimizing the first queue using a merge optimization occurs when the request times of the pending requests in the first queue exceed a predetermined third value. The total request time is updated based on the results of the merge optimization. Next a pending request is read from the first queue and labeled with a first sequence identifier. Each read request is then encoded for transmission to the display engine over a network connection. A copy of the optimized request is placed into the second queue and the total network time is incremented by the request time for the newly added request. The encoded display request is transmitted to the display engine. The display engine unencodes the received converted display request and displays it on the client device. Next it generates a second sequence identifier corresponding to first sequence identifier of the displayed request; and periodically transmits to the protocol engine the second sequence identifier of the last received display request displayed on the client device. 
     Upon receipt of the second sequence identifier, the protocol engine further comprises the steps of: 
     deleting from the second queue the display request whose first sequence identifier is the same as the second sequence identifier and all pending displayed requests in the second queue having first sequence identifiers that are prior to such second sequence identifier; and 
     decrementing from the total request time and from the total network time the request time values of each of the deleted display requests. 
     The application broker using the information contained in the data store regarding the application programs and the application servers used to run them is able to keep track of which third tier server is actually running the application program. The number of all applications running on each application server is tracked. At launch time of the application program, the application broker chooses the application server from the list associated with the application that currently has the lowest number of applications running on it. This selection process provides a load balancing mechanism for the application servers. 
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
     For a better understanding of the invention reference may be made to the preferred embodiments of the invention shown in the accompanying drawings where: 
     FIG. 1 illustrates a Universal Application server (the “UAP”) system comprised of a client/server network showing the interconnection of the UAP server to other applications and database servers and to a diverse set of clients. 
     FIG. 2 is an illustration of the Adaptive Internet Protocol (AIP) Link as implemented in the UAP system. 
     FIG. 3 shows the processes operating in the display engine and protocol engine components of the present invention. 
     FIG. 4 is a more detailed data flow diagram of the AIP link of the present invention; 
     FIG. 5 is a table of sample of AIP requests. 
     FIG. 6 presents a table of AIP request translations and a table of relative costs for performing an AIP request. 
     FIGS. 7A and 7B illustrate a flow diagram of the startup process of the application broker system. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Overview of a Universal Application Server System 
     As used in this application the term “engine” is used to refer to a process, method or series of related processes or methods for performing certain actions. For example the session engine is a process that is used to control a current session between the server and a client device. Also the terms “universal application server,” “UAP server,” and “application broker” are used interchangeably. Also the same or similar item occurring in more than one figure carry the same or similar numeric designation. 
     As shown in FIG. 1, the network  10  comprises three tiers used to illustrate the connections of the various inventive processes and routing of data information among the various processes and components comprising the network. First tier  12  contains a variety of diverse client devices, generally indicated at  14 , having different interfaces, such as PC  14 A, UNIX computer  14 B, network computer  14 C, all illustrated as having a Java Virtual machine interface  16  to second tier  40 , or a thin client  14 D shown having a browser interface  18 . The inventive processes are also useable in a standard Microsoft Windows environment that uses interfaces such as Win16 and Win32. In addition, administration computer  20 , illustrated as a network computer, is also grouped in first tier  12  and is in communication with processes running on second tier  40 . 
     Second tier  40  comprises UAP server  50  having various engines or processes executing thereon together with various interfaces to first tier  12  and to third tier  80 . The interfaces to first tier  12  include X windows interface  52 , character based interface  54 , Java interface  56 , and HTML interface  58 . The interfaces to third tier  80  include an X Windows interface  60 , terminal emulators  62 , web server  64 , and lightweight directory access protocol (LDAP) interface  66 . The third tier  80  includes the various application servers, generally indicated at  82 , including UNIX X Windows server  82 A, Windows NT server  82 B, UNIX and IBM character-based application servers  82 C, directory services servers  82 D, the Internet  82 E and various data base servers  82 F. UNIX X window server  82 A and the Windows NT server  82 B interface to second tier  40  via X Windows interface  60 . UNIX and IBM character-based application servers  82 C interface via appropriate terminal emulators  62 . Web server  64  provides the interface to the Internet  82 E while the directory services server  82 D uses the LDAP interface  66 . Although all of the application servers are shown in FIG. 1 as being in a single tier, it should be realized that the application servers can also unction as clients to other servers not shown and that the requested application may reside in a server located elsewhere in the network. Also shown are session manager engine  70  that controls active sessions between client devices  14  and application servers  82  and the administrative engine  72  which controls the operation and administration of UAP server  50  and which is in communication with the administrative computer  20  operated by a system administrator. 
     Client connections and requests,  30 , are routed to the appropriate interfaces on UAP server  50  which in turn processes them using one of more of the UAP engines described below and obtains the requested service or data from the appropriate application server  82 . UAP server  50  then returns to the client devices  14  display requests from the requested application and other data. UAP server  50  resides on a host or server on the network that has a web server running on it. It can be viewed as a black box sitting somewhere on the network that enables any client to access any service by providing the intelligence needed to do this. 
     A variety of naming standards and methods are used to access resources on the network. Computers on the Internet use conventions such as Domain Name Service (DNS) or Windows Internet Naming Service (WINS). File naming conventions are tied to operating systems of which there are many. For example, Microsoft operating systems use the Universal Naming Convention (UNC). These resources are disparate and different entry points and methods are needed to access them. The UAP server provides an integration point for a wide variety of naming standards by federating the name spaces. It provides a single point of entry to access any network resource. The X/Open Federated Naming (XFN) based scheme is the preferred naming standard to permit such integration amongst these variety of naming services and standards. 
     Large and complex information about network resources is usually kept by directory servers, for example, Novell® NDS™, Microsoft Active Directory, Netscape Directory Server™. UAP server  50  does not provide a complete replacement or duplication of these services. UAP server  50  provides a thin layer that interfaces into these services using LDAP (Lightweight Directory Access Protocol). LDAP is a current defacto industry standard interface to directory services. By doing this UAP server  50  avoids duplication of information and functionality which may already be present on the network. It would be unnecessary and time-consuming process to replicate this information. For example, if a thousand users are already set up, the use of the LDAP layer allows use of this information by UAP server  50  and administrative engine  72 , rather than making administrators recreate it and double the maintenance load. 
     As illustrated in FIG. 2, UAP server  250  contains the following processes: administrative engine  272 ; status manager engine  274 , protocol engines,  276 A- 276 C, display engines  278 A- 278 C; web server  264  and webtop storage  268  for the storage of user webtops; data store  273  containing various user and system data such as the LDAP protocol, user passwords, user application objects, startup engine, and other data related to the operation of UAP server  50 , data store engine  271  and one or more session managers  270 , which can be configured to permit suspendable and resumable sessions. Login port  251 , reconnect port  253 , a plurality of session ports  255  are provided for communication with client devices. Display engines, generally designated  278 , are stored on UAP server  250  and are downloaded to client device  214  when needed. Client device  214  is a computer system that has a display and input devices such as a keyboard, mouse, touchpad, etc., as is known in the art. Shown in the third tier  280  are three application servers, generally designated  282 , X Windows server  282 A, Windows NT server  282 B, and character-based server  282 C. 
     UAP server  250  provides administrative engine  272 . Only authorized administrative users have the ability to run this process. The main functions of the administrative engine  272  are: 
     Publishing applications and documents to users 
     Organizing user profiles (what each user is allowed to access) 
     Viewing and changing the contents of the organizational hierarchy 
     Monitoring and controlling sessions, including viewing which users are logged on and what applications are running, and stopping applications 
     Configuring the UAP server settings such as logging and diagnostic specification, authentication mechanisms and file locations 
     Sitting at the heart of UAP server  250  is a suite of server engines or processes that coordinate all functions. These are status manager engine  274 , data store engine  271 , session manager engine  270 , protocol engines, generally designated  276 , and the display engines  278 . These engines cooperate to provide the central point of access to the client devices and handle the following: 
     Security management 
     Retrieval and storage of state associated with users and applications 
     Invocation of applications and their supporting display mechanisms 
     Session management 
     Status manager engine  274  provides initialization and control over all the other server engines. It is the first process that is launched when UAP server  250  starts up. It is designed to manage all other processes and act as a central point of brokering requests and actions. 
     Data store engine  271  provides the initial interface to a connecting client device. It controls the contents of data store  273 , which holds information about services, network devices, as well as users and their associated applications and data. UAP server  250  uses a bootstrap applet  221  that downloads itself to the client device  214  on demand from a user. This applet then connects to data store engine  271 , which provides an authentication service, after which requests can be issued to the data store engine  271  to: generate webtops; configure the webtop; invoke applications; retrieve documents; and, if requested by the system administrator, view and modify the contents of the data store itself for system administration. For each application, data store  273  contains a list of the application servers that are able to run this particular application. 
     The data store is a hierarchy based upon the X 500  standard. The major items contained with the database are: 
     People. These represent the users of the system. The location of the person within the hierarchy can be used to reflect the organization of the company. In particular, it is possible to group people to provide for easy administration of people that have access to similar application programs. Information stored for a person includes authentication information such as application passwords and login password, a list of groups to which that person belongs and a list of applications that should be presented to that user. 
     Applications. These items represent the application programs that are deliverable by the system. The location of an application program within the hierarchy is used to determine which users will be presented with that application. Information present for an application includes, protocols used by the application (X11, Telnet, etc.), location of the application (application server name, location within the file system on that application server) and configuration information required to launch the application (environment settings for the application server, command line arguments, display size information etc.). 
     Groups. These items are used to form convenient administration objects. They can be used to simplify the delivery of applications to sub-sets of users or to provide access of sets of applications. 
     The actual database itself is federated and can access data from several sources. These include directory services (via LDAP protocols), local system authentication information (passwords etc.), and dynamic state information (running applications etc.). 
     At any given time while UAP  250  server is active, session manager engine  270  contains dynamic information about which users are connected and the applications they are running. In addition, session manager engine  270  is responsible for invoking applications after the client device request has been processed by data store engine  271 . Session manager engine  270  can be viewed as the keeper of all live information in the UAP server  250 . Session manager engine  270  tracks which applications are running on which application servers. At launch time of a given application, session manager  270  obtains the list of application servers capable of running this application and chooses the application server that can run the requested application and that currently has the lowest total number of applications running. This selection process provides a load balancing mechanism. More complex load balancing schemes can be used but we have found that this process produces a reasonably even sharing of the processing load amongst the application servers. 
     Protocol engines  276 A- 276 C and display engines  278 A- 278 C provide the emulation necessary for the user to view and interact with applications. Preferably, UAP server  250  via session manager  270  associates one protocol engine and one display engine for each corresponding application type. They are invoked and the display engine is downloaded on-demand to the requesting client device. Protocol engines  276 A- 276 C run on UAP server  250  and perform the bulk of the emulation by acting as a client of its associated application type running on the network. The protocol engine understands the standard protocols the application types currently use. X-windows type applications would use a protocol engine that is different than the protocol engine used for Microsoft Windows type applications. The appropriate protocol engine translates the standard protocol requests into an adaptive Internet protocol that the display engine on the client device can display. Using this method existing applications continue to run on servers they are currently installed on, untouched and without any re-engineering or re-writes needed in order to function with the client device. Preferably, the protocol engines are implemented as native binaries to ensure optimal performance on UAP server  250 . 
     Display engines  278 A- 278 C are preferably Java applets that are downloaded on demand by the client device. The display engines are small in size—around 200 Kilobytes—and render the application on the client device display and allow input/output to the user. As a result the display engines are quick to download, even over low-bandwidth networks. The display engines know nothing about the state of the application that is being run. There is a display model mismatch between the existing application environments and the display model used on the display engine. Operations that are not supported on the display engine (e.g., plane-masking, logical operators etc.) are carried out on the protocol engine and sent down as supportable operations (e.g., bitmap copy from memory) to the display engine. 
     The most common mode of access to the UAP server is from web browsers. Users of UAP server  250  interact with applications and documents on the network using the web equivalent of a desktop—the webtop. UAP server  250  gathers all objects (applications, documents, etc) associated with a user and dynamically creates a web page to represent this information. This web page contains smart applets, preferably written in the Java programming language, represented as graphical icons (see  225 A- 225 C). When the user clicks on these smart icons, requests are issued to invoke services or applications or view documents. The navigation model that is used in browsers involves going back and forward between pages. From time to time pages with applications running inside them may be out of view on the display screen of the client device. Browsers temporarily cache Java applets such as the display engine inside these pages that are out of view. After a certain amount of time these applets are cached out by the browser. UAP server  250  works around this problem by providing an automatic reconnect of the display engine without shutting down the application (as indicated at path P 10  between display engines  278 A-C and reconnect port  253 ). 
     UAP server  250  uses session manger engine  270  and sessions to provide and control the access and interaction of the user with the desired network application or database. A session is associated with each application or database the user may be running. An application session can be configured by administrators to be resumable. With a resumable session users can disconnect themselves from UAP server  250  but the resumable applications remain running. When the user reconnects to the session, the application is presented in the same state as it was when left. This reduces start up time for applications and allows client resilience. For example, some applications take a long time to start up. At other times, after starting the application, the user goes through a laborious route to a particular point, for example, a character-based data entry application with a large number of menu options or a processor intensive query or calculation. In a network-centric environment, the connection from client to server is critical. If the connection drops for any particular reason, for example, if a modem connection is interrupted, the server must be able to recreate the state associated with the client device when it reconnects. The suspend/resume facility of session manager  270  allows this to occur. During the configuration process, administrators can choose to disallow the resume facility, on a per application basis, to save server resources. For example, a simple calculator application is unlikely to need resuming. Administrators also have the ability to terminate application sessions while they are running. 
     Operation of the UAP Server 
     The process used by the UAP server to allow client device  214  to connect, deliver the client&#39;s webtop and run applications or view documents is illustrated in FIG.  2 . Client device  214  connects to web server  264  as shown at path P 1 . Here the user is shown connecting to web server  264  via a Java enabled web browser  218  but the user can also connect by other means including using a Java virtual machine running on the client device or use of a native binary application. 
     Web server  264  retrieves from data store  268  a web page containing UAP bootstrap applet  221  and returns it to web browser  218 . Bootstrap applet  221  is executed on client device  214 . This applet connects with data store engine  271  via the login port  251  as shown in path P 2 . Data store engine  271  then provides client device  214  with login applet  223  via path P 2 . Login applet  223  is executed on client device  214  and the user is authenticated to UAP server  250  using this applet. If the correct user-name and password are supplied, applet  223  issues a request to data store engine  271  to search and find the webtop for that user. A webtop  225  is created dynamically using the objects associated with the user stored in data store  273  and is loaded into browser  218  running on client device  214 . For a new user, the system administrator provides the initial objects to be used in the construction of the web page together with the level of user privileges available to the user. 
     Session manager  270  begins a bottom up traversal of the data store hierarchy starting from the user and expanding any groups. During this traversal a list of applications specific to the user is created. When the traversal is complete, the list of applications forms the set of applications to be made available to this user. Session manager  270  transmits presentation data for the application set to the login applet  223  (this includes textual and graphical representations, i.e., a web page or webtop) that, in turn, presents the application set in a manner appropriate to client device  214 . The user chooses an application to launch (via some sort of input device supported by client device  214 . 
     When the user clicks one of the icons ( 225 A- 225 C and preferably a smart Java icon) webtop  225 , the web page associated with that object is downloaded from web page store  268  and web server  264 . If the object is an application, then the appropriate display engine for the client device is downloaded. In FIG. 2, three display engines  278 A,  278 B, and  278 C are shown on web browser  218  indicating that this user is using three applications. 
     Each display engine  278  performs an initialization routine with client device  214  to determine supported display operations and display performance factors. Preferably, each display engine  278  contains a table  279  of display operations that are expected to be supported by the client device in its operating environment. The display engine performs a test of the client device to determine which of the display operations in the table can actually be performed on the client device and modifies table  279  to indicate which operations are supported on the client device  214 . The modified table  279  is stored in the display engine and is also sent to UAP server  250  for further use. 
     The display engine also calculates a local performance factor or scaling factor for the client device to determine the relative cost of performing the supported display operations. Preferably, two bitmap copy operation tests are performed, i.e., data in memory is written to the display. In the first test, a small number of pixels, one or two, are written to from memory and the time to perform this operation is noted. This step is repeated an arbitrary number of times and an average time T small  is determined. This time, in microseconds, represents the overhead to work with a pixel. In the second test a larger image involving a larger number of pixels is copied from memory to the screen and the time to perform this T large  is noted. Next the Per Pixel Cost, PPC, is determined as follows: 
       PPC=[T   large   −T   small ]/[Number of pixels written in second test] 
     This local performance factor, PPC, is communicated to UAP server  250  for use by the protocol engine in determining request times for the requests found in the two queues. 
     Each protocol engine uses database engine  271  and session manger  270  to determine which application server to contact and the protocol to use to launch the application. Each protocol engine connects with the application server identified by session manager  270  and starts the application, passing identification data to ensure that the launched application transmits user interaction and display requests to the correct instance of protocol engine. For each application the data store  273  holds a list of application servers that are able to run the application that is being requested by a particular instance of a protocol engine. This list is used by the launch process to determine which application server in the third tier is used to actually run the third tier application program. Session manager  270  keeps track of the total number of applications running on each application server. At launch time, session manager  270  selects the application server for the list associated with the application that currently has the lowest number of applications running on it. This selection process provides a load balancing mechanism for the application servers in the list so as to reasonably even the load among the application servers. 
     Display engine  278 A issues a request to data store engine  271  to find the application, in this case, the X Windows application  282 A. This request is passed onto session manager engine  270  which checks to see if the requested application is running and needs to be resumed to the user. If an appropriate protocol engine is not already running on behalf of this user one is started by the session manager. Protocol engines are able to handle multiple applications that use the same protocols and so only one of each application type is required per user. An X Windows protocol engine can be used by multiple X Windows applications but not by a Windows application. 
     Session manager engine  270  starts the requested application on the network using a password stored in an encrypted cache (not shown) in data store  273  if it has already been supplied. If the password has not been supplied, session manager engine  270  prompts the user via display engine  278 A for a password that is then stored in the encrypted cache. Session manager engine  270  then invokes the correct protocol engine for the requested application type, in this case protocol engine  276 A. Protocol engine  276 A establishes a new connection, as shown at path P 3 , to the requested application  282 A that had been previously started by session manager engine  270 . Session manager engine  270  stores the information about the protocol engine  276 A used with application object  282 A in data store  273 . As part of this sequence, if the application is one in which the application needs to connect to the protocol engine (which is the process used for X Windows applications) then information that is required by this mechanism is placed in the application&#39;s environment to allow it to connect to the appropriate protocol engine. Next because application object  282 A is an X Windows application type, application  282 A connects to protocol engine  276 A. Application  282 A is then in a suspended state. Information is passed back to the display engine  278 A in order to enable it to connect back to protocol engine  276 A. If the application is already running then it will be already connected to an active protocol engine and will be in a suspended state thus the startup steps to establish a connection to the application are not required. 
     Similar actions are performed by display engines  278 B and  278 C to request use of Windows application  282 B and character-based application  282 C, respectively. Instances of protocol engines  276 B and  276 C are established by session manager  270 , and protocol engines  276 B and  276 C establish connections to applications  282 B and  282 C, respectively, along paths P 4  and P 5  respectively. For the character-based application types, the open connection to the application is passed to the protocol engine. 
     Display engines  278 A- 278 C on client device  214  connect to ports  255 A- 255 C on the UAP server and authenticate themselves. Display engines connect back using the information sent back from the appropriate protocol engine (this includes port number and temporary authentication information). This mechanism ensures that a separate connection is used for each display engine and avoids the need to multiplex data over a single connection. Status manager engine  274  receives these requests from the ports  255  via path P 6  and passes it onto session manager engine  270 . Session manager engine  270  then connects up the requesting display engine to the appropriate protocol engine. In this case display engines  278 A,  278 B, and  278 C are connected by session manager engine  270  to protocol engines  276 A,  276 B and  276 C, respectively via paths P 7 , P 8  and P 9 , respectively, and ports  255 A,  255 B and  255 C, respectively. Login port  251  remains open and is used for later launch requests and updates to the webtop. 
     The launch process described above is illustrated in the flow diagram presented in FIGS. 7A and 7B. There the launch process  700  starts at step  702 . The process proceeds to step  706  where status manager engine  274  is started. Next at step  710 , all other engines are initialized. The process proceeds to step  714  where the application broker or UAP server is waiting for a request from a client. If no request is received the process proceeds to step  718  to wait for a client request and then back to step  714  to see if a client request has been received. If a step  714  a client request has been received, the process proceeds to step  722  where web server  264  retrieves bootstrap applet  221  from web pages store  268  and download it to client device  214 . At step  726  the user presents login information such as user name and passwords using bootstrap applet  221 . At step  730  the user information is checked and if it is not approved, the process proceeds to step  734  where the login is rejected. Here the process loops back to step  726  to receive user information. In the event of a rejected login various known mechanisms such as allowing multiple retries or sending the login information to the system administration and management engine  72  for use by the systems administrator. 
     If at step  730 , the login information is correct, the process proceeds to step  738  where the session manager downloads to client device  214  a webtop that is built up using the bottom up traversal of the data store  273  containing icons representing the application programs available to the user. The system at step  742  waits to receive a request from a client for an application. If none is requested the process proceeds to step  746  to wait for a client application request and then loops back to step  742 . If an application request is received at step  742  the process proceeds to step  750  where a check of the data store for the user&#39;s password is performed. If no password is found the process proceeds to step  754  where a password request screen is downloaded to client device  214  asking the user to create a password. At step  758  it is determined if the user has submitted a password. If not, the process goes to step  762  where the session is ended. If at step  758  if a password is given the process, at step  766 , encrypts it and places it in data store  273  to be used for future logins. The process proceeds to step  770 . At step  750  if the password has been found in the data store, the process proceeds to step  770 . 
     At step  770 , a determination is made if an existing session is in place for this user and the requested application. If it is, at step  774 , the user is connected to the existing session, If not, a new session is started at step  782  and the session manager performs the load balancing previously described. Proceeding from either step  774  or  782  the session manager, at step  778 , instantiates the appropriate protocol engine if one is not already running for the requested application type, instantiates display engine for the client device type, and downloads the display engine to the client device. Also here the instantiated protocol engine establishes a connection to the application server and the requested application. The user then interacts with the requested application. A determination is made at step  790  whether or not the application is resumable in the event that the connection to the client is ended. This information is either retrieved from data store  273  and can be determined from user input gotten when the application is started. Disconnection&#39;s can be voluntary by the user or accidental due to network problems. If the application is not to be resumable, the process goes to step  794  to disconnect the application upon the user exiting. If the application is resumable, the process at step  798  will keep the connection to the application server and suspend the instance of the application that was running until the client device and user reconnect. 
     The application program that is instantiated on the application server residing on the third tier can be a program such as, for example, a drawing program, a spreadsheet program, a database program. The nature of the application program is not critical to the operation of the universal application server. Also the connection between the protocol engine and the third application server can be extended to other servers as is known in the art to order to access the desired application program. This routing information would be stored in the datastore. 
     The connection between the requesting display engine and the protocol engine forms an adaptive Internet protocol link. The first phase in this link is to pass parameters identifying the characteristics of the client device and network connection to the protocol engine. These include the local performance factors and the supported display operations table, and the bandwidth of the connection. The adaptive Internet protocol link then tunes itself for optimal performance for the given connection and client device. Finally, the display screens of the application are displayed on the client using display operations supported by the client device. The adaptive Internet protocol link and, in particular, the protocol engine, monitors any changes in the network connection between the protocol engine and the display engine. 
     Adaptive Internet Protocol (AIP) Link Operation 
     The AIP link will be described in detail in relation to protocol engine  276 A and display engine  278 A. To deliver access to multiple types of client devices over a variety of network connections, the AIP link has to adapt to the characteristics of the client device and the network it is on. The AIP link does this by providing heuristic mechanisms that optimize the responsiveness of applications by monitoring, measuring and adapting the ways in which data is transferred between applications and the client devices including: 
     Round-trip measurement, latency and bandwidth 
     “Just fall” transmission window management 
     Use of machine independent drawing capabilities (e.g., Java) for specific graphics functions 
     Color management 
     Data compression 
     Server-managed client caching 
     Queue management for graphics operations 
     Metering adjustment for “busy” networks 
     Suspendable/resumable sessions 
     The goal of the AIP link is to maximize use of the connection to the client device by trying to limit the number of transmitted requests while not overloading the connection and to optimize the requests to the fullest extent possible while not underutilizing the connection. 
     FIG. 3 shows the major process structure of the AIP link  300 . The AIP link  300  comprises two major processes working cooperatively: Protocol Engine (PE)  276 A and Display Engine (DE)  278 A. The initial conditions are for PE  276 A to be running on UAP server  250  waiting for DE  278 A to contact it. The two processes are connected via a network connection using a standard network transmission protocol such as TCP/IP (path P 7 ). Following this connection, the two exchange a series of requests to establish the characteristics of the client device, e.g. type of device, operating system, and the network connection, e.g. bandwidth and latentcy. DE  278 A sends to PE  276 A modified table  279  that describes the display operations or graphics primitives supported by client device  214  and the relative cost of executing each of these operations or primitives. 
     In the following description of the various processes the numbering of the steps is for convenience and to ease understanding of the processes. It will be apparent to those of skill in the art that the sequence of various steps may be changed without affecting the overall operation of the process. 
     As show in FIG. 4, in PE  276 A, process  310 , at step  1  waits for the Total Request Time (TRT) for the selected application to be less than a first pre-set limit and if it is it accepts from the selected application a received display request  312  formatted in a standard network display protocol, such as the X11 Windows protocol. The TRT represents the time costs for all of the requests currently found in PE  276 A, specifically those in the Pending Request Queue (the first queue) and the Transmitted Request Queue (the second queue) described below. 
     At step  2 , process  310  executes received application display request  312  and writes the resulting image to memory. At step  3 , using modified table  279  of supported display operations previously sent from DE  278 A, process  310  performs various transformations as is known in the art on request  312  converting it to a series of AIP requests which are simpler operations that are supported by client device  214 . FIG. 5 presents a table listing some of the AIP requests that are available for use in the conversion process. This table is not meant to be an exclusive listing of all available AIP operations and other operations can be used as will be appreciated by those of skill in the art. Steps  2  and  3  can be performed in any order. 
     At step  4  costing is determined for the image and for each of the converted requests created in steps  2  and  3 , respectively. Process  310  utilizes the performance factor, i.e., the PPC factor, received from DE  278 A and determines the estimated time costs for sending and displaying the converted requests or the image at DE  278 A. The request times for the converted requests are added to the TRT value. Sample translations of X11 Windows display requests are shown in Table  1  of FIG. 5 along with a brief description of the operation. Given in Table  2  of FIG. 5 in columns  2  and  3 , are representative, empirically determined relative costs and estimated time costs (request times), respectively, for performing the operations in the converted request. 
     At step  5  the converted display requests are placed at the head of Pending Request Queue (PRQ)  320  and process  310  repeats again from step  1 . 
     At step  6  process  330  waits for the Total Network Time (TNT) for the selected us application to be less than a predetermined second value and for the total of the request times for the pending requests in PRQ  320  to exceed than a predetermined third value. If both conditions are met all pending requests in PRQ  320  are, at step  7 , optimized and written back into PRQ  320  and the TRT value and the TNT are adjusted based on the results of the optimization. The TNT represents the request times for all of the requests currently found in TRQ  340 . 
     The optimization process of step  7  consists of step  7 A, prune optimization of the converted requests with those in PRQ  320 ; step  7 B merge optimization of the image with those requests in PRQ that effect the same screen area on DE  278 A; step  7 C, schedule optimization (attribute scheduling); and step  7 D, update optimization (update scheduling). The optimization process is further discussed below in the subsection entitled Queue Optimization. 
     At step  8  the request at the tail of PRQ  320  is removed to be sent and a first sequence identifier, the send sequence number (SSN), is incremented and saved with the removed request to identify that request. At step  9  the removed request and its SSN are added to the head of Transmitted Request Queue (TRQ)  340  and the TNT is incremented by the request time of the newly added request (this also increments the TRT value). At step  10  the removed request is encoded into a form suitable for transmission over network connection P 7  and sent to DE  278 A. Preferably, to reduce the amount of data to be sent, the SSN identifier is not sent as part of the request. Requests are labeled or tagged with the SSN in the TRQ but the actual SSN identifier is not sent as part of the transmitted request. Corresponding identifiers are maintained by both the protocol engine and the display engine as each sends and receives requests. These identifiers are used as a reference point between the display engine and protocol engine. Again the order of steps  9  and  10  is not critical and the two operations can be performed in either order or simultaneously. The encoding process step  10  consisting of: step  10 A, coordinate compression; step  10 B, Run Length Encoding (RLE); step  10 C, serialization, step  10 D, delta compression; and step  10 E, Zlib compression. Encoding is further discussed in the subsection Encoding and Performance Monitoring set forth below. At step  11  the encoded request is written to the connection and sent via path P 7  to DE  278 A and process  330  repeats from step  6 . 
     In DE  278 A, process  360  at step  12  is waiting for receipt of an encoded request. Upon receipt of an encoded request, at step  13  the request is unencoded consisting of one or more of the following depending on the compression techniques that were used in the request: step  13 A, Zlib expansion; step  13 B delta expansion; step  13 C, RLE expansion; and step  13 D, coordinate expansion. At step  14  the request is queued for execution and is displayed  372  on screen  370  of client device  214 . At step  15  a second sequence identifier, the Return Sequence Number (RSN), is generated by adding one to the current RSN and this will match the SSN identifier associated with the just executed request. At step  16 , if more than one second has past since the last time an RSN was sent or if there is no data now available from the network the current value of the RSN is sent to PE  276 A for use by process  350 . Process  360  then repeats beginning at step  12 . As is known, the protocol engine and display engine rely on the transport mechanism of the network connection P 7  to maintain the proper ordering or sequencing of the transmitted requests. This keeps the RSN identifier in synch with the SSN identifier and removes the need to send the SSN identifier with the transmitted request. 
     At PE  276 A, process  350  at step  17  performs the RSN processing where the RSN identifier received from DE  278 A via connection P 7  is read and TRQ  340  is updated by removing each request from the tail of TRQ  340  until the SSN identifier for the request at the tail of TRQ  340  is greater than the RSN identifier and the TNT and TRT values are updated by subtracting the request time of each request as it is removed from TRQ  340 . These changes may result in the new total times falling below the predetermined first, second and third values mentioned above, in which case, more requests may be read and transmitted. At step  18 , process  350  performs periodic monitoring of the connection P 7  and adjusts encoding process  330 , as discussed below, in response to conditions (bandwidth available) found on the connection P 7 . Process  350  repeats starting at step  17 . 
     Relative Cost and Request Times 
     The cost of executing a display request on the client device consists of the following items: 
     1. Overhead of executing a single request irrespective of other factors. 
     2. Time cost based upon the number of pixels touched by the request. 
     3. An indication of the situations in which the request can be executed directly to the display hardware. If the request is not executable directly to the display then the display engine will simulate the request by drawing into memory and then copying this to the screen, thus incurring additional costs for the copying. 
     The costs for 1 and 2 are a relative factor that is to be scaled by an overall performance figure calculated for the client device to provide a request time (see Estimated Request Time column in Table  2  of FIG.  5 ). As explained previously, the display engine executes a series of graphic requests both to the screen and in memory to compute this overall factor. This factor is also transmitted to PE  276 . Table  2  of FIG. 5 provides some samples of relative costs along with estimated request times for a specific client device. 
     Table  2  of FIG. 5 provides relative costs—basic and per pixel—of the various graphics operations. Table  2  does not provide costs for all of the AIP request display operations. In actual operation, costs for all AIP requests supported by DE  278  are provided in a table in PE  276 . It contains a per pixel relative cost and a basic relative cost for each operation. The basic cost is empirically determined by testing execution of a given AIP request or display operation on a given class of client device in a given operating environment and is provided as part of the cost table that is found in each protocol engine. These basic costs can be thought of as being fixed. The performance factor—the per pixel cost, PPC—is determined as discussed previously and can be thought of as a dynamic or localized cost for the particular client device. The cost numbers are used by the cost calculation in the following way. The cost per pixel value is multiplied by an estimate of the number of pixels touched by the operation. The basic cost per display operation is multiplied by the number of basic operations that make up the request. For example, the operation AIP_POLYLINE is one where multiple line segments are being drawn so the basic relative cost for a 10 segment polyline operation would be 745 (10×74.50). Finally, the sum of these two values is multiplied by the performance factor (the PPC) that has been calculated for DE  276  on the client device to produce an approximation of the time taken by DE  276  to execute the request. 
     The actual numbers in Table  2  of FIG. 5 are calculated from the following two equations: 
     
       
         pixelCost=( m   2   −m   1 )( L   2   /b+L   1   /b )/ (n   2   −n   1 ) 
       
     
     
       
         itemCost= m   1 −( L   1   /b )− n   1 *(sizeCost) 
       
     
     These form the solution to the equations 
     
       
           m   1   =L   1   /b+n   1 *pixelCost+itemCost 
       
     
     
       
           m   2   =L   2   /b+n   2 *pixelCost+itemCost 
       
     
     where 
     m 1  and m 2 =single request time (s) for samples 1 and 2 
     L 1  and L 2 =single request length (bytes) for samples 1 and 2 
     b=client device bandwidth (bytes/s) 
     N 1  and n 2 =number of pixels for samples 1 and 2 
     The results are computed using two samples per request tropically a 10 pixel test and a 500 pixel test. The results of the above calculations should then be multiplied by the current display rate of the test client device to produce the relative basic cost value shown in Table  2  of FIG.  5 . The estimated request times given in Table  2  of FIG. 5 are calculated for a client device that reports a performance figure of 9.15 megapixels per second. 
     Bandwidth and Latency 
     PE  276 A and DE  278 A cooperate to establish the bandwidth of connection P 7  and the latency. The latency is established as half of the average time that it takes to send a very small data packet from PE  276 A to the DE  278 A and back. The bandwidth is estimated by sending a series of large data packets and timing the difference between the arrival of the first packet and the last. The bandwidth is then defined as the total number of bytes transmitted divided by the total time difference. The bandwidth and latency are periodically measured. The size of the small request is about 3 bytes in length and the size of the large request is about 1024 bytes. The actual number of packets used is increased up to the point that more than 250 ms are needed to perform for the overall test. So the test is run starting using one packet, then if 250 ms have not been used, a series of 2 packets is then sent and again if 250 ms have not be used the test is repeated with a series of 3 packets. The number of packets is increased until about 250 ms are used for the test. The series is normally 5 packets but on lower bandwidth connections a smaller number is used to limit overall time taken. 
     This request time for a display operation which is added to the TRT value is based upon the following: 
     1. The size of the request in bytes as it will be transmitted via the network connection. 
     2. The time cost for executing one of these requests on the DE. 
     3. The time cost for this request based upon the number pixels it will change. 
     4. The time cost for copying the results to the actual display if this request can not be executed directly to the client display. 
     The size of the request is estimated by taking the size of the actual data points to be transmitted and multiplying these by the current compression ratio that is being achieved by the network encoding layer. This, in turn, is divided by the current network bandwidth to give an estimate of the total time required to transmit this request. The costs for 2, 3 and 4 are calculated by reference to table  279  obtained from DE  278  at startup. The total of these three values is then multiplied by the current overall performance factor of the DE to give an estimate of the time taken to execute the request by the DE. This is then combined with the estimated transmission time to give an overall request time for that request. The Total Request Time (TRT) is calculated for all queued requests (both those in the PRQ and those in the TRQ) for each application. New display requests from the application are not accepted by the protocol engine when the TRT exceeds the first preset value, typically 5 seconds. The PE  276  will not accept further display requests from the application when the request times of the requests in the PRQ and TRQ exceed this value so that the connection to the DE will not be overloaded. 
     The Total Network Time (TNT) is comprised of the request times of the requests in TRQ  340  plus the latency time associated with the network connection. The PE maintains a TNT required to send all of the requests currently in TRQ  340 . The PE monitors the time associated with requests in the TRQ and will not transmit any further requests once this value reaches a pre-set value. This preset value is normally set at 2 seconds. This mechanism is used to ensure that a large backlog of requests does not build up for slowly executing client devices while ensuring that the full bandwidth of the network is used when this is the limiting factor. 
     Queue Optimization 
     Request optimization (FIG. 4, step  7 ) will take place if a reasonable number of requests are in the PRQ which is the case in normal operation. This process operates on an estimate of what will happen in the future in terms of request execution time not on what has happened in the past. This is important when dealing with requests for which the execution time varies greatly. 
     When there is space to send new requests to the DE a process of optimizing the PRQ is performed. Basically this portion of the PE process looks through the requests in the PRQ. It attempts to remove requests that are redundant, converts sequences of requests that operate on the same screen area to a single less expensive request, re-orders the queue to reduce overhead in the DE and adds hints to the queue to make the performance of the DE more efficient. Because this process can be expensive in terms of time, the optimization is only performed when the total execution time of the requests in the PRQ exceeds a preset threshold that is proportional to the predetermined first value (typically 5 seconds). The typical value used for the predetermined third value is {fraction (1/20)} of the first value. These figures are all arbitrary and are based upon an acceptable level of application latency. Advantageously, for slow clients or networks more optimization is performed (since the cost of requests is higher) and that for faster networks and clients the optimization is only performed when there is a large amount of output. 
     Preferably in step  7  of FIG. 4, the following four types of optimization are performed. These are pruning, merging, update scheduling (update optimization) and attribute scheduling (schedule optimization). The preferred method uses the following order of optimization—pruning, merging, following by, in either order, attribute scheduling and update scheduling. Pruning need not be done prior to merging but it is more efficient to do so. Update scheduling and attribute scheduling can be done in either order. Of the four types of optimization, merging is the most important in order to achieve good performance with the application and the connection. 
     1. In pruning (FIG. 4, step  7 A), converted requests that will be completely overwritten by a request later in the queue are removed. This optimization is equivalent to executing the series of graphics requests very quickly such that the effects of the earlier requests are not visible. Preferably, this is done prior to merging. 
     2. In merging (FIG. 4, step  7 B) if the cost of a group of converted requests that update a particular screen area is greater than the cost of transmitting an image of that portion of the screen then all of the requests are removed from the PRQ and an image request with its associated request time is inserted. The TRT is adjusted to reflect these removals and additions. 
     3. For update scheduling (FIG. 4, step  7 D), requests that can not be executed directly to the screen are grouped together. Hints are inserted into the request stream so that the DE can execute all of the requests in off-screen memory and then copy the results on screen in a single operation rather than requiring one copy operation per request. 
     4. For attribute scheduling (FIG. 4, step  7 C), requests which require the same color, and drawing modes are grouped together to avoid the need for the DE to switch back and forth for each request. This operation is equivalent to re-ordering the PRQ to make requests that share attributes adjacent within the PRQ. When performing this process it is necessary to ensure that the execution of overlapping requests is not changed. 
     Encoding and Performance Monitoring 
     The encoding process transforms a graphics request into a format suitable for transmission via the network connection to the DE. The DE inverts this process when the request is read from the network connection. The packet format used on the network connection takes the form of a header which has a byte indicating the type of the request, a two byte field which indicates the length of the packet and then a series of bytes which represent the actual request. The data for a particular request varies, but is, typically, either a series of coordinates for requests that involve some form of line drawing or a series of bytes for text and image requests. The encoding process is designed to enable the number of bytes required to represent the request to be minimized thus reducing the time required to transmit the data on a slow network connection. However, the processing time required to actually encode the data can be large. Thus, on higher bandwidth connections the AIP reduces the amount of encoding applied. This reduces the overhead but increases the number of bytes transmitted. 
     The process of encoding uses the following steps 
     1. For coordinate compression, if the request contains a series of coordinates, all of these coordinates are converted to be relative to the first set in the request (FIG. 4, step  10 A). 
     2. If the request contains either text or an image it is compressed, preferably using the well know technique of Run Length Encoding (RLE) (FIG. 4, step  10 B). 
     3. The request is then serialized, i.e., converted into a simple series of bytes with a fixed byte ordering (FIG. 4, step  10 C). During this serialization process any small integer values in the range −64 to +128 are encoded into a single byte. 
     4. Requests that when encoded are less than 32 bytes in length are compared against a cache of previous requests. If the number of differences between the current request and a previous request is less than 8 bytes then the request is re-encoded as a reference to the previous request plus a series of two byte pairs describing the offset of the byte and the replacement value. This compression technique is known as delta compression (FIG. 4, step  10 D). If the encoded request is less than 32 bytes in length, it is entered into a delta compression cache (not shown) and the oldest item in the cache is discarded. Typically, the cache contains the last 32 requests although a lower or higher number of items can be chosen. 
     5. The encoded form of the request is compressed preferably using the well know Z-Lib compression algorithm (FIG. 4, step  10 E). 
     6. The encoded form of the request is sent over the connection to the DE (FIG. 4, step  11 ). 
     At step  18  of FIG. 4, the AIP changes the encoding level based upon the bandwidth connection parameter of the connection as follows: 
     1. If the bandwidth is &gt;300 Kbytes per second steps  3  and  4  are omitted. 
     2. If the bandwidth is &lt;300 Kbytes per second steps  3  and  4  are applied. 
     3. If the bandwidth is &gt;300 Kbytes per second the Z-Lib compressor is disabled. 
     4. If the bandwidth is between 100K and 300 Kbytes per second the Z-Lib compressor is set to use compression level 1 (the lowest and quickest to achieve compression level). 
     5. If the bandwidth is between 3 Kbytes and 100 Kbytes per second the Z-Lib compression level is set to level 5 (a mid range compression level). 
     6. If the bandwidth is less than 3 Kbytes per second the Z-Lib compression level is set to 9 (the highest compression level). 
     Because the performance of the overall system can change over time AIP allows for both the available bandwidth of the network connection and the display speed of the DE to change. The PE uses two processes to track such changes. In the first performance updating process, the PE periodically re-checks the network bandwidth and latency. Typically, this is done about every five minutes. The PE also sends a request to the DE asking it to update the overall performance factor and send this new value back to the PE. These updated values are used in calculating the request times for newly added requests to PRQ  320 . Alternatively, if desired, the request times of requests already in PRQ  320  and TRQ  340  get updated. The details in how these values are obtained were discussed above in the description of the UAP system startup. 
     In the second process, the PE when it moves a request from PRQ  320  to TRQ  340  adds to the request an estimate of the time the request should be removed from TRQ  340 . When the PE removes the request from TRQ  340  it maintains a running average and variance for the percentage error associated with this estimate. If the total of the average error minus half of the variance exceeds a pre-set limit (typically 200%) and the time since the last reevaluation is more than 1 minute then the performance updating process is invoked immediately. 
     The overall effect of these processes is to provide a flow control mechanism that controls the rate that requests are read from the application and at which they are transmitted over the network to the client device. The goal of the AIP system is to ensure that DE  278  never stalls due to lack of available requests, that a large backlog of requests is not allowed to build up and that a reasonable number of requests are made visible to the UAP system within PRQ  320  since it is these requests that are available for optimization by the PE. It will be appreciated that for slower connections, requests will remain in the PRQ for a longer period of time so as to not slow down or overload the connection but advantageously giving the PE greater opportunity for optimization of the requests in the PRQ and conversely, when a more robust connection is available more requests can be sent utilizing the bandwidth of the connection while reducing the time spent in the PRQ increasing performance at the client device thus making the best possible use of the capabilities of the client device and the network connection for maintaining and enhancing performance. 
     The implementation languages that are used are such that the protocol engines are typically created as a native binary for performance reasons. However, they could also be implemented in the Java programming language. The display engines are implemented in several languages to provide a broad coverage of client devices. The Java programming language is used to give support for platforms supporting either Java runtimes or Java supported in a web browser. However for systems that do not support a suitable Java environment native binary versions of the display engine components are used. Further, not all engines need to be in operation at all times, For example, if no client devices are requesting any application services, no protocol engines or display engines will be operating. 
     Other embodiments of the invention will be apparent to those skilled in the art from a consideration of the specification or from practice of the invention disclosed herein. It is intended that the specification be considered as exemplary only with the scope and spirit of the present invention being indicated by the following claims.