Remote Printing Application Using Proxy Services

TheRelay,DataTransfer, andCodeExecproxy services can be used to implement the remote printing application. The Relay proxy service is used when the mobile application calls the

Printer Finder service. The Printer Finder service has a list of the addresses of printers in the campus. Upon receiving a request from a mobile application, thePrinter Findersearches for a printer based on the preferences of the user. As described in section 3.3.1.1 receiving the response fromPrinter Finder may takes some time, especially if there is a large number of printers. ThePrinter Finder is a good candidate for being called through the Relayproxy service. The address of thePrinter Finderservice and input parameters are passed to theRelay

proxy service. TheRelayproxy service calls thePrinter Finderservice on behalf of the mobile application. The Relayproxy service saves the returned result in its database and sends the result to the mobile application (figure 3.3).

Figure 3.3: CallPrinter FinderVia Proxy

TheDataTransferproxy service is used to transfer data from the mobile application to the proxy. For the remote printing application, theDataTransferproxy service is used to transfer: (i) the document to be printed; and (ii) thePrinting Service Clientapplication, as an offloaded task, to the proxy. ThePrinting Service Clientis used to communicate with thePrinting Service

and is provided by the university to users. TheCodeExecproxy service is used by the proxy to execute the Printing Service Client application on the proxy. Figure 3.4 illustrates how a mobile application uses the DataTransfer and CodeExec proxy services to call the Printing Service.

3.3.2

Tourist Assistance Application

Examples of desirable augmented reality (AR) applications for mobile devices include e-Health [49], tourist assistance [26, 27, 61], gaming, navigation and industrial maintenance [53]. AR is defined as “a real-time direct or indirect view of the real world environment that has been enhanced/augmented by adding virtual computer generated information to it” [18]. AR appli- cations help users gain better perception of the real world and enables users to interact with it.

Figure 3.4: CallPrinting ServiceVia Proxy

The information about the real environment is gathered using sensors and then provided to the AR application. The AR application processes the input information and augmented it with extra data. The extra data is then rendered to the users.

Huang et al. [33] notes that the AR paradigm has three main properties:

• combines the real world with the virtual world

• provides interactiveness with user in real-time

• provides 3-D objects to be added to the 3-D real environment

This means that AR applications often includes 3-D image processing tasks. Additionally, AR applications are expected to respond in real-time since they are interactive. Consequently, AR applications need computational power typically not found on mobile devices. In addition, the communication latency incurred by the limited bandwidth and the low reliability of wireless links, impacts the interactiveness of AR applications.

An AR application can be partitioned as follows. The mobile application on the mobile device gathers input data e.g., image, video, or voice. The data is transferred to a remote service for processing. This remote service is on a cloud. After processing the input data collected by the mobile application, the result is sent in an appropriate format to the mobile application, which is responsible for rendering the result to the user. It is shown that it is faster to offload the processing to a remote server rather than executing it locally on the mobile device, specially if the Wi-Fi connectivity is available [28].

As the second example application we consider an AR application that is designed for mobile devices and is used to assist tourists visiting historical sites. The application on the tourist’s mobile device is used to capture images or video from the historical site to be sent to a remote service in the form of video or a stream of images. The remote service processes the stream of images or the video frames. The process might involve recognition of the site and extracting information about the site, such as historical information, from databases. The remote service sends the information in the form of text or retrieved images to the mobile application. The mobile application renders the received information in an appropriate format for the user. While the user is moving around in the site, the remote service can provides more detailed information about the view that the camera of the mobile device is pointing to.

3.3.2.1 Using the Proxy-based System

As described earlier, AR applications should have a real-time response. The communication delay when an AR application is installed on a remote location e.g., a public cloud, has negative impact on the responsiveness of these applications. One approach to reducing the impact of communication delay is to move the remote service, or only a part of it, to a location in the vicinity of the mobile device, whenever a mobile application needs the service. In this way the network latency between the mobile application and the service has less impact on the application.

The other difficulty of having this application on a mobile device is similar to the second problem introduced for the first example application: transferring data over wireless links from a mobile device to a remote server. The difference is that the tourist assistance application should transfer a stream of small files, as opposed to one large file, which are images, to the remote service. Although, the interruption in transferring a stream of files to the remote service would lead to the establishment of new connections to the remote service that might increase the response time of the service, since the service needs to repeat the view recognition process, which is time consuming. As a result, it is necessary to provide some mechanism that preserves the connection between the mobile application and the remote service, even in the presence of interruptions.

The issues mentioned above are not specific to this application and might affect other mo- bile applications with similar functionalities. The proxy services that can be used in this ap- plication to cope with these issues are introduced in section 3.3.2.2. Section 3.3.2.3 describes how the proxy-based system and introduced proxy services can be used to implement a mobile application for this example AR application that provides better service for the user.

3.3.2.2 Proxy Services Used for the Tourist Assistance Application

TheCodeExecproxy service, as introduced in section 3.3.1.2, can be used to reduce the com- munication latency by downloading and installing the AR application, from a remote server, to the proxy and executing it. The URL of the downloaded service is provided for the mobile application and the mobile application can call the service on the proxy. Since the proxy is in the vicinity of the mobile application, the communication latency will be smaller.

FileStreamerProxy Service. TheFileStreamer proxy service is used to transfer a stream of

files, such as images, from the mobile device to the proxy. The FileStreamer proxy service handles disconnections, i.e. the FileStreamer proxy service is aware of the possible discon- nections and is able to keep the connection to the remote service alive if mobile application is disconnected.

The FileStreamer proxy service is different from theDataTransfer proxy service in three ways: i) the FileStreamer proxy service is able to maintain the connectivity to the mobile application for transferring multiple files, while the DateTransfer proxy service is designed to transfer only one file, ii) Unlike the DataTransfer proxy service, the FileStreamer proxy service can begin delivering data, received from the mobile application, to the remote service, before finishing the data transmission from the mobile application. In this way, the output of the remote service can be presented to the mobile application at the same time that the mobile application is transferring the input data to theFileStreamerproxy service, iii) The integrity of transferred files are not guaranteed by theFileStreamerproxy service (unlike theDataTransfer

proxy service) since it is assumed that theFileStreamer proxy service is used for applications that are time sensitive and a small number of corrupted files in the stream does not affect the performance of the remote service.

Similar to theDataTransfer proxy service, the functionality of theFileStreamerproxy ser- vice can be combined with the functionality of theCodeExecproxy service. The combination of these two proxy services, theCodeExecand theFileStreamer, enables software developers to develop mobile applications that gathers online data and feeds it to a remote service that process the data and provides the mobile application with the result of processing the data.

3.3.2.3 Implementing Tourist Assistance Application via Help of Proxy Services

When the mobile application on the mobile device, such as the tourist assistance application needs to transfer a large amount of data e.g., video or a stream of images, to the remote ser- vice, the network latency plays an important role in the performance of the application. The larger size of the data transferred between mobile application and the service exacerbates the

impact of network latency and may cause more number of disconnections. This condition has a negative impact on the application performance.

Figure 3.5: Run Tourist Assistance Application Via Proxy

Using our proxy-based infrastructure, the tourist assistance application can connect to a nearby proxy and ask the proxy to download and install the remote service. Afterwards, the mobile application can call the service on the proxy machine which is located in a nearby place and, as a result, the network latency will be kept lower. The tourist assistance application uses theCodeExecto download the required service from a remote host to the nearby proxy and run it and subsequently reducing the latency. The FileStreamer proxy service is used to transfer the stream of image files from the mobile application to the proxy. The FileSteamer proxy service provides the disconnection handling, i.e. the FileStreamer proxy service is aware of the possible disconnections and is able to re-connect and continue the communication between the mobile application and the service without the intervention of the mobile application or the service.

The combination of these two proxy services, theCodeExecand theFileStreamer, enables programmers to create mobile applications for other AR services that need the transmission of an extensive amount of input data in the form of stream of images (or other formats) from the mobile application and also requires extensive amount of processing on the input data.