Remote Desktop Robot Teleoperation Computer Science Essay

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Introduction:

The remote control Teleoperation has gained considerable attraction in recent years; new potential application in Teleoperation system offers challenging remote control development. Today, robot system is not only applied in space exploration and factory automation, but also in surgical operation assistance, home healthcare and rehabilitation. In teleoperation system, remote sensing measurements and control commands, video images are transmitted via various media such as microwave, radio and computer network. The speedy evolution of communication system, related programming languages and software's provides the more and cheap solutions to the teleoperation system [1].

Going with rapid growth of the internet, one of its main applications is internet based teleoperation, where internet used as a bridge between client and robot. Currently there are some problems in remote robot teleoperation, such as random data transmission delay, signal drop out. All these may result in instability task desynchronisation and loss of transparency in teleoperation system. Therefore effective control teleoperation via internet becomes very important. Traditionally there have been a myraid design for teleoperation architecture were delays exists in the control of telemanipulators and observation, where as these attempts in general grouped into three approaches; predictive control [2], bilateral control [2], and teleprogramming [1]. In teleoperation system a type of human machine system, the operator remotely controls the robotic vehicle by sending commands of navigation and motion to robot and robot will execute these commands. In such typical operation procedure sensors of the remote robot will pickup relevant information then artificially send back to the operator through network, which helps operator in making correct and appropriate decisions during teleoperation [1, 2].

Various remote control systems been performed for nuclear control systems been performed for nuclear power plant maintenance, under water manipulation, storage tank inspection, space exploration, satellite repair etc. The control command and remote sensing measurements been transmitted via various mediums like microwave, radio, computer networks etc. Along with there is a growing need for human to visit actual remote displays, such as schools, factories etc, and to share robots for research and teaching. To achieve these demands remote control system has to be developed on convenient communication public media, and which has ability of multimedia transmission [3].

Where few remote access technologies we use in our daily life, like network services, FTP, WWW, Email etc, provides us suitable tools and devices to share remote information, among these services there is tremendous growth on WWW (World Wide Web) which is most famous. The main feature about internet is that which provides all services on network, for example, through internet one can visit laboratory and its documents, videos and transmission photos and also it is possible to read real time news [2, 3].

A number of internet based teleoperation systems are developed, and they all developed using internet, but they all have different site implementations and technical details. Recently, not only teleoperation systems been developed, but also many other remote teleoperation aspects and manipulations are under research. Issues pertaining communication delay, channels, bandwidth and tele presence are all been covered with varying degrees [2]. In particular, big interest been generated by internet as an interactive medium for teleoperation systems. Most of the remote control architectures consists of three three approaches predicatively displays/ control, bilateral control and tele programming [2, 3].

After initiations hypertext transfer protocol (HTTP) in 1992, the first internet robotic system was appeared in 1994 in Mercury project [2], 'MAX' teleoperation and the telerobotic garden. This robot mainly based on the robotic arm, that is been directly controlled by human operators. In contrast, research on second generation autonomous internet based navigation in uncertain environment is recently begun [3].

In this project tried to develop a autonomous telerobot to provide multilevel remote control module for remote operator. Here operator can directly sends commands for wander mode, unguarded mode, teleoperation mode and for command mode with a help of internet. In each mode operators can give different commands to remote robot, where as in wander mode robot will move independently with a help of sonar sensors, here no need of giving any commands this is like independent mode. In unguarded teleoperation mode, this mode usually used …………………………..And teleoperation and commands module are dependent on operator commands, here operator can control totally with help of keyboard or with a help of joystick.

Due to limit of current artificial intelligence, it is impossible to design a completely autonomous robot to deal with complex tasks in remote places, therefore combining human decisions making capacity, to control panel of telerobot, this process of combining needs internet. Internet becoming favoured form the other interactive communication, the internet has an advantage of availability from all over the world, which makes possible to control from all over the world [1, 2].

Chapter 2

Background knowledge:

This chapter proposed to give background information and concepts used in this paper, and also it discusses some previous work carried out in this field.

Internet teleoperation:

In early days most of the internet controlled robots were based on CGI (Common Gateway Interface) to interface between the web browser and physical device being controlled. Common gateway interface (CGI) was launched by the web browser in order to give response to HTTP requests, and the CGI results as a HTTP response sent to it. HTTP is stateless response request protocol, means it is very easy to implement but have some demerits. As HTTP is stateless, state been controlled by CGI process and the browser. This one can be achieved by broadcasting extra identification information with each request, known as cookies []. The request response paradigm means, once after processing client request by server there is no other way to contact client, the client will be always initiator. This will be a problem client concerned about state of non stationary remote process, to receive constant updates from server client has to request server at regular intervals.

The first online robot was introduced in 1994, since from this time WWW has undergone in major changes. The introduction of Java was the major development in internet teleoperation, as it allows code to be executed on client side, where as previously all code has be in CGI process. This CGI process was used by number of internet teleoperation projects including PUMA paint robot [] and the NASA path finder interface []. Using Java applets, both client machine can provide more sophisticated interface and also can provide its own protocol to communicate with the server. The use of different protocols can helps to overcome above mentioned HTTP limitations. With constant connection between server and client machine, both sides can communicate when fresh information needs to be transmitted. With client running Java applet to communicate with the server machine, this system is called as distributed.

Server machine: Machine which is connected to the robot, and directly communicates with the robot. This machine also intern connected to the internet in order to receive signals from remote operator.

Client machine: Is also called as remote operator machine, is a remote machine used to send control commands and signals to the remote robot. Which intern sends commands and signals to the server machine, the server and client machines were connected with a help of network media.

Network protocols:

The internet reference model or TCP/IP describes the communication between two or more computers; this model consists of four layers, hand shaking signals and communication signals controlled by this four layers.

Network access layer: This layer describes about all electrical and physical characteristics of network devices, it provides specification to each data entries which is about to transfer, and also it provides correct possible errors at physical level [].

Transport layer: Which provides transparent data transfer between end users, through segmentation/ desegmentation, flow control, error control and also it cares about TCP and UDP.

Internetworking or Internet layer: Which provides procedural and functional means for transferring different variable length data sequences from source to destination, and also it take care about quality of service.

Application layer: In this layer high level protocols operate and live.

For client and server data exchanges application and transport layer are very important.

State of art:

There have been many internet based teleoperation experiments, some of which briefly discussed in below section before start with the actual investigation of project.

Fiorini and Oboe [] has investigated behaviour of the internet with continuous control of robot using force feedback, results of network performance between the nodes over internet suggests the delay characteristic of link can be modelled using variance and mean of round trip delay. They also identifies the second problem with tele robotics that of loss of packets. Protocol which identifies the both problem and gives correct performance is determined as Real time network protocol (RTN); this protocol is designed to connect the client machine with specific performance requirements. They also discuss about two approaches for providing RTN services, either to use current standards at cost of compatibility. The real time protocol with the real time control protocol is an example for first type protocol, and used for multimedia streaming over the internet. Tenet is example for second type and it was designed on the basis of RTN, can be built over data link which does not guarantee for maximum delivery time, Tenet therefore works on architecture that provides guarantee FDD1 and ATM2. Finally they recommend the base development of RTP for real time control [].

Filippo presented report on remote robot teleoperation through TCP/IP protocol using remote desktop control software, but here Filippo has given

Lasso Andras Honlapja [] has developed and implemented a modern internet based telerobot architecture. They used a RTP protocol to transmit the video and command signals between server and client. Video data making use of Java frame work to transfer the images with JPEG coding, commands transmitted with a help of TCP/IP and other administrative and time sensitive data uses the some media []. According Honlapja experiments and results, he conclude that current web technology and internet enables the teleoperation trough WWW (World Wide Web), and low quality internet may need special real time protocols and compression.

The paper [] presents the investigation about the Rob web link robot teleoperation, this system implemented based on server/ Client architecture using Linux as platform with HTTP server, which gives the WWW (World Wide Web) service. The client access the server machine with help of WWW link invitation received from server machine. The application protocol which allows for server and client machine to stream videos, and in sending parameters through TCP/IP. In this investigation good results are obtained and implemented through TCP/IP protocol, but for real time operation author suggested RTP protocol.

Book et al has used the internet as a supervisory controller, the client operator has a actual simulated work environment provided with a help of internet. The graphical images provided to the remote operator with help of internet [].

Rovetta et al have used the electric mix of communication media for performing telesurgery, the idea be hand this is to use local surgeon's for general aspects of the surgery. Where remote surgery specialist take place for more specific parts of surgery. The communication media includes satellite channel for exchanging robot commands and video images, and internet for written documents [].

Anderson, uses the internet as a medium for sequential modular architecture for robotic and telerobotic architecture. Here commands and signals are transmitted to the robot via internet, this modular controller based on the earlier work assuring the passivity of the architecture for given delay [].

Wakita et al, suggest that combination of visual monitoring and intelligent and basic set of high level commands are the intelligent monitoring for remote telerobots. In 1995 they conducted test based on internet from Jet propulsion laboratory in Los Angeles to ETL lab at Tsukuba, Japan, during this experiment they found that less command abstraction will help for easy intervention of the teleoperation into the telerobotic work [].

Oboe and Fiorini also suggest the bilateral architecture for remote teleoperation, they concentrated more on time varying nature of the internet and non linear dynamics of the telerobot, and this experiment consists of hardware based master and virtual slave software's.

Bejczy et al, suggested "Phantom robot" for remote teleoperation here idea is to prediction of robot model over live video images feed from remote system. Human intelligence is used to cover gaps in model discrepancies.

Conway et al presented method for teleoperation. Their idea is to project intelligence over distance, mixing autonomy with human intelligence and various tele automation tools are introduced, in that most important one is time clutch. This time clutch gives the ability to lock and unlock the remote manipulator temporally, and which gives greater flexibility and efficiency in computing some difficult tasks.

Another important remote teleoperation project by German Aerospace Research Establishment - ROTEX []. This is arm of a space shuttle flew in 1993, and which is tested and controlled from ground based supervision for space based tasks. ROTEX was an electric approach for remote teleoperation, it used the n-step discrete kalman liter for prediction, and active compliance was used to give quick dynamic responses. Telesensor programmings were used to provide human interaction with the arm. The bandwidth limitation and time varying delays are described, and using these description a state of space controlling model was presented, and in this project includes mere sections, each sections explains about each stage. Section2 explains about time varying delays and bandwidth limitation. Section 3 explains about building of architecture around the space model of section2, this architecture depends on trajectory supplied by teleoperator, robot will executes this trajectory autonomously. The tele operator only steps in unexpected situations. Section 4 presents experimental results. Section 5 provides remark and directions for further research.

From Filippo report [] , Accuracy and reactivity of a teleoperator is very important and is improved by enhancing the situation awareness. The term situation awareness means which indicates and helps to know where robot is working. It is very important maintain and acquire high awareness, since unawareness may lead to serious and dangerous errors. So according to filippo the user interface is arguably central element for teleportation, as all information exchanged between user and robot pass through it, therefore poor interface system will be main bottle neck problem for whole system.

As it is known that in teleportation main attention is given to visualization it plays very important role and it provides considerable amount of highly constrated information in a way which is easy for user to ingest. Here filippo thinks cameras are not best tool to get information about surroundings monocular view may cause strong abjection of perception, and also it is difficult to estimate the distance. To overcome this problem filippo uses stereoscopy, immersive and multiple cameras, but also filippo thinks this system has some limits. Stereoscopy helps in distance estimation but it doesn't increases the angular range of sensing; beside, its benefits disappear as operators become used to their interface and task. Multiple cameras are problem in term of mounting, cost, and space wise.

Along with all these sensors filippo uses range sensors in his project, filippo thinks range sensors are most efficient kind of sensor in acquiring data about surroundings. And also filippo uses sonar sensors instead of laser sensor because of cost, where laser sensors can cover more angular range with high resolution and accuracy but sonar sensor have poor angular resolution, filippo thinks this can be compensated with being cheap and installed in large numbers.

Main characteristics:

From filippo report it is clear that main importance was given to sonar data and video images. As main aim of filippo was to combine sonar data and video images taken from Microsoft webcams, he used two cameras back camera and front camera for effective operation of a telerobot. And effective programming tools like open GL, and open CV is used to combine sonar data and video images data.

Filippo used radio serial modem to read the sonar data.

Ad-hoc 802.11 network connection used to control the robot.

Disadvantages:

Here not much importance is given to different types of teleportation.

In this project to read sonar values, it is necessary to radio serial modem. This is again different application. So it is difficult to read sonar values at particular position of a telerobot.

Ad-hoc 802.11 network connection has limited connectivity, it is not possible to control robot from another place.

System overview:

In order to interface this service to the internet two separate software tools were used. The client machine is a remote operator machine. The server machine will be resided on robot in remote place. The both machines is an online machines installed with Windows 7 operating system. In all fundamental cycle, server machine feeds video information to the client, and client issues control commands to the server.

Figure: Shows the system architecture.

Control of enforced through sending commands to the robot attached to the online server machine by serial to USB connection. First; server machine installed with ÁRIA', which is C++ library. ÁRIA' provides on interface and frame work for receiving and controlling data from robot, and ARIA includes useful utilities for writing robot control as well writing cross platform code.

Characteristics of ARIA:

ARIA provided with full source code with GNU (General public licence).

ARIA is portable C++, and can be re compiled for different platforms and compilers [].

ARIA includes JAVA interface [].

ARIA also included with python interface.

In ARIA several predefined actions and components are provided with obstacle avoidance [].

ARIA provides locking function for thread safe access [].

The second group of software controls interface from ARIA to the internet, where as these programs are programmed using java and C++. Because of universal feature, it allows to abstract from each single system architecture while implementing with any general purpose computer with internet connection and WWW browser.

Interface:

When the remote operator uses a java enabled internet browser to retrieve the robot's control web page, operator will be presented with a java application on applet (Which is used to provide interactive feature). This applet run in the client operator side, interfacing with it contact the operator side. Interfacing with it contact the operator will have with the same system, this applet handles client operator system interface by receiving the all control commands and displaying all necessary information needed by the operator.

The custom CGI script will handle the request to any execution. Initially, the script will be passed with a unique identifying internal number matches to the specific command. Using information of in call, port connection will be opened to the robot control ARIA. This ARIA program check the validation of command format and parameter range first, once the port connection is established and check is passed, request is sent to move the robot to desired destination and capture an image. When the result of request is received, the CGI script displays the HTML page. First, it extracts the information from the data packet sent by server. This will provides the name of HTML field to place at the head of internet browser page. Next, it will in line and adjust the captured and converted GIF image, and place it within image amp with unique identification number. Additional navigation icons are provided in this page, these icons allow user to comment about execution quality, move to previous or next command page. Finally, the CGI script writes out the unique internal user file, which contains the current state information concerning the page and coming with image just delivered such as position of the robot image captured etc. This allows for sequential request by user to result in exact robot motions relative to the operator current image.

Communication:

In the teleoperation system, robot and human operator interact with each other to carry out needed tasks cooperatively. In order to control the robot, it is necessary to obtain current information about the robot, and to give commands to the robot through communication. Internet offers the base for two directional information flows to alter this type of interactive operation. In the whole system server machine is connected to the internet to admit incoming HTTP request for network connections, it also act as a control centre, so that it can send signals or commands to the controller port of robot after receiving requests from the operator.

Vision system:

The fundamental visual information originates from cameras. The camera used to collect the information about robot current environment. The challenges here is to focus at the issue acquiring and converting correct stereovision information and connecting all these activity in order to provide a good visual environment for operator, in this system, cameras are attached an server side. Image capturing capture request received from client, camera digitizes on image convert that image into a GIF. The file will be output into an temporary space in server and assigned with unique number. This number is passed back into the requesting process in order to display a correct image in the HTML document passed back into the suitable user.

In order to control the robot effectively, operator must need a continuous stream of image feedback from the server. Therefore images are automatically transferred from server to client automatically, which is achieved by special java program in order to avoid manually reloading of images, where as transfer speed and uploading speed on client is depends on the speed of internet using.

Control command:

When all connection is made, the robot control panel checks for authentication using a known encoding. This step prevents the unauthorized check of robot hardware to avoid or limit the prospective, end operators within scope of safe group. This is very importance as we move towards devices with the content of physical expressions of energy in remote environment. Measures to prevent at least most of the attacks of navie should be included in such systems. Authorized connections to the robot from ARIA include a request type descriptor. The request converts type position will be query, internal status instruction or motion commands. The robot can be commanded using either direct commands to the joints of robot motors or by giving a Cartesian pose from which inverse kinematics are evaluated for respective robot joint values. It's very important to note the ARIA keeps track of the robot's state so that no additional communication is necessity to the robot to fulfil any robot position quarries. In addition, the request mask determines which joint values ought to be moved, and this result displayed on ARIA window. This allows for desired single degree of freedom movement.

Motion requests are translated by the ARIA into local native commands and sent on the internal communication port to the robot hardware. The ARIA will check for position checking, when all control quarries of the robot motions are stopped. To communicate over the internet a server machine should be installed with java enabled program, which establishes connection between server and client. This program binds a socket to its end of the connection. To communicate server and client writes and reads to the socket they bound to connection, client and server must have some protocols by which they communicate each other. The protocols which server and client used are totally dependent on the type of communication required.

The communication socket connection also provides mutual exclusion for correct functionality even during handling multiple requests. Since this projects interface design is internet based and requests are even driven the robot is left idle, after operator has completed his command, until operator makes another request. Instead of allowing this exclusive access to the robot, leaving robot ideal until operator contemplates next action, it services the additional requests from another users. By multitasking, it provides increases access to robot as well as more effective use of system resources. However, it is necessary to provide method to guarantee that few atomic operations are exclusive, for example an request to move forward and stop must be exclusive. This insures that no other motions happen between this forward and stop action. If we failed to implement this, it is not guarantee that pose parameters derived back to the user were actually accepted from the location that they are requested.

Control:

The critical issue of internet based teleoperation is random time delay. Previous work on teleoperation with random time delay has focused on content delay system. However, they are not applicable to the internet based teleoperation, since the internet delays are modelled as random variables. Maximum worst design controller can be considered as solution to the random time delay. However, even control algorithm cannot stabilize system when delay varies from maximum to zero; few qualitative experiments have been taken in order to gain some insight into the problems of internet based telerobotic systems. The experiments spot out the characteristic of internet and the effects of performance on teleoperation. However, design of suitable control flow still requires some specific techniques for handling problems of random time delay.

Chapter 4

Internet based teleoperation has been a hot research topic in automation field and robotics. My topic of investigation is to study about remote robot Teleoperation using internet, which includes different types of remote desktop application software's.

In this paper testing with two types of internet based application

Server based software

Remote desktop software's

Server based software:

Sever based software's are the one which dependent on IP address of server machine, in this investigation 'Mobile eye' is been used as sever based software. Mobile eye is graphical application for remotely controlling a robot via internet; this application client software was developed by adept mobile robots researchers. It uses the ArNetworking protocol to connect to server machine placed on the robot's onboard, ArNetworking networking is library in Aria. Aria is C++ application software. Here client and the server exchanges the information with a help of RTP protocol. It developed using the C++ frame work and which implements all protocol. Client and server needs to establish the RTP session before communicating each other, this session will contains the server and client machine []. Due to RTP protocol the server session has to be configured, and server IP address added as a transmission destination.

Comments:

Main disadvantage about this server based software 'Mobile eye' is that it needs a server IP address in order to establish connection between server and client machine. In our investigation main idea is to control the robot remotely with a help of client machine, here operator will be at remote place and it is difficult to know the IP address of server machine.

As with this server based software's it is not been possible to control from far place, it got some limitation like server machine has to be in certain distance and operator should control from certain distance.

Our another main idea is to provide video images to the remote operator for successful navigation of remote robot, but with these software's it is not been possible to transfer video, mpeg, jpeg images to the operator.

As server based software works on RTP protocol it is been found that compare remote desktop application software's, server based application software's have the less time delay, delay in communicating with server machine is less.

In server based application software it is possible to secure the connection between server and client with help of username and password.

It is possible to check graphical representation sonar values.

For this server based application software's no need of any invitation from server machine, without any invitation it is possible to connect to server.

Remote desktop connection:

Remote desktop controller is a client/server software package allowing remote network access to graphical desktop. This software basically helps to get a view of remote server desktop machine and thus control it with local mouse and keyboard, it can also be used to control and perform administration tasks in Windows, UNIX and other network environment. This software basically requires a TCP/IP connection between server and client, each computer will be having unique IP address and also name in DNS []. It is necessary to know name of the server or IP address to comet server and client laptops. The initial handshaking will consists of server and client initialization messages when server and client connection establishes, where as server begins by requesting authentication from the client using a challenge response method, which is usually request for password at client end. The server and client then exchanges messages to desktop pixel and size format to use.

Desktop sharing has many applications

Remote login allows user to access their remote computers from any internet enabled device, including laptops, desktops and even PDA's.

Desktop sharing allows for interactive collaboration between different users in real time.

Application sharing lets allows testing software's without installing or downloading anything.

How it works:

Desktop sharing software works by sending packets of information from remote computer to host computer screen at any time given time,

Remote control software:

Remote control software provides ability to access and login computers remotely. Employing remote control software allows personnel to transfer folders and files quickly and easily. Remote control software allows user to control computer remotely over any TCP/IP connection. Most of the remote control software's emulates the client computer to make it look as if they are in front of it, with remote control software it introduces many features, such as video and file transfer, keyboard and mouse emulation with ability to manage the computer remotely.

Some of the benefits of remote control software's are

Provides the very quick response to remote issues.

Which help in reducing overall cost.

Stream lines and centralizing computer support.

Reduces the involvement of the end users.

RADMIN:

Radmin also called as "Remote administrator", which is a product of Famatech International Corporation. Radmin allows user to remotely work or monitor one or more network computers from their work station, it is a completely remote control solution with features of NT security, file transfer, telnet and Multilanguage support built in. Operator can see the remote computer's screen either on their monitor or in full screen window, all keyboard and mouse signals are transferred directly to the remote computer. With Radmin operator or user can work with any remote computer until it is connected to the network or LAN, on LAN real time speed of 200-500 screen updates per second, Radmin speed can be adjusted down or up to save bandwidth. Radmin is very easy to learn and use. This is extremely secured with employing 128bit encryption for all data streams. Radmin utilizes the TCP/IP protocol and most spread protocol is used in the LAN's and WAN and the internet, which means we can control virtually any computer from any part of the world. When in "full control mode "we can have a complete and ultimate control over the remote computer so that it is possible to launch applications, file transfer, even shut it down.

Principle of operation:

Radmin consists of the two separate modules;

Server module: Which needs to install on computer we want access remotely.

The client module: which is needs to install on the computer we want to access remote computer. However, content of folder installed client module can be placed on any other folders of computer and these computers must have client module installed.

All keyboard and mouse signals are transferred directly from local computer to remote computer over network, relaying on the graphical screen updates back in other direction, Radmin server uses the mirror drive (Which is video driver hook) to read remote screen bypassing VDCC video display controllers. Mirror drive which only allows for changing parts of the screen. The newer versions of Radmin consists of direct screen transfer technology, according to the developers of Radmin software claims that the adaptation of new video drivers allow dramatically to increase the rate of screen updates with the minimum utilization of CPU.

Special features:

Connection modules;

Full control: Shows the desktop of remote computer and allows to control with local mouse and keyboard.

View only: This is also same as 'full control' mode but only allows to view the remote computer screen.

Telnet: This is text mode connection to the remote computer to use the system commands and launches the text mode application without graphical interface.

File transfer: This mode allows manipulating remote computer files and folders, allowing the two ways file transfer with auto resume feature.

Shutdown: This is special connection to the shut down the remote computer.

Text and voice chat: It's allows the all users to communicate via text and voice using microphone.

Send message: It is possible to send text messages, which pops on the remote computer.

Real VNC:

Real VNC software makes it possible to look and fully interact with one computer from any other computer or PDA's devices anywhere on the internet. RealVNC is a cross platform, allows remote control between different types of computer, and this software consists of java viewer so that any desktop can be controlled remotely with a help of browser without installing software.

The RealVNC software having simple protocol for remote access to graphical user interfaces, this is based on the concept of remote 'frame buffer', this protocol simply allows server to update 'frame buffer' displayed on a operator, because it operates on frame buffer so it is applicable to all operating systems, this includes UNIX, Windows and Macintosh and also includes PDA's, and protocol operate over any reliable transport such as TCP/IP. This is a 'Thin client protocol'; this is designed to make very few requirements of the viewers. In this way, operator can implement widest range of hardware, and tasks of multiprogramming. Client is simple as possible, 'P he' is a display side protocol and is based on single graphics primitive will put rectangle pixel data at a given X,Y position. But because as we have lot of different encoding schemes for the pixel data, it is possible to select the appropriate scheme for each rectangle we send, and will make the most of client drawing speed the server processing speed.

The lowest encoding denominator is called raw encoding, where rectangle is only data sent in right to left scan line order, all client must support to this encoding. However, encoding can used on any given RealVNC connection also can negotiated according to the abilities of server, client and connection between two. The copy rectangle encoding, for example is mere and efficient can be used when client also have same pixel data elsewhere in its 'Frame buffer'. The server simply sends X, Y co-ordinates by giving position from client can copy the rectangle pixel data. This means operations, such as scrolling a window or dragging which involves the substantial alters to the screen, may only requires a few bytes. Most clients support to this encoding, since it is simple to implement and to save bandwidth. A typical workstation desktop has large areas of colour texts and solid colours; same of most effective encodings will take the advantage of this by efficiently drawing rectangles consisting of one majority colour and sub rectangles of different colours. There are other numerous possible schemes; we can use a MPEG for efficient transmission or JPEG for still images. An encoding will uses same kind of caching of pixel would be better for rendering text, where some character is drawn in some front multiple times sub sequent occurrences of some character will be encoded by reference to the first occurrence.

A rectangle sequence frame buffer makes update, an update buffer will represents the valid frame buffer state from one to another, and in some ways is similar to the video frame, but it is only a small area of buffer so will be affected by given update. Each rectangle thing may be encoded using different schemes. The server can choose good encoding for the particular screen content being transmitted and network bandwidth available.

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