Presented by: Elhadi Adam Elomda ECET 581, IPFW Director: professor Paul I-Hai Lin

1. Proxy-based Adaptation for Mobile ComputingWritten by:Markus Endler, Hana Rubinsztejn, Ricardo C. A. da Rocha, and Vagner SacramentoMay 2005 Presented by: Elhadi Adam Elomda ECET 581, IPFW Director: professor Paul I-Hai Lin

2. Order of Presentation Coverage • Introduction • Proxy Classifications • Characteristics of the Proxy-Based Architecture • Common Proxy Functions • Proxy Frameworks • Conclusion

3. How does the server find the new VLR? The Answer is via a proxy 1) Introduction A proxy (also know by gateway, intermediary or agent)is a computer placed in the path between a server and its clients. Server VLR VLR In most cases, proxies act as protocol translators, caches, and content adapters for clients and are placed on, or close to, the border between the wired and the wireless networks VLR: Visitor Locator Register

4. Mobile Service Proxy • Proxy could move with the client if necessary • Proxy informs servers of location changes Server Proxy/client Proxy/client Proxy/client

5. Why Proxies are used in Mobile Computing and Wireless Communication ? Proxies are mainly designed to: • Bridge the differences between the wired and wireless networks such as throughput, latency, reliability, probability of disconnection, etc. • Support the mobile host: Display size, user input/output, processing capacity, size of RAM and persistent memory, limited energy supply, etc. • Perform application-specific adaptations and requirements such as fast response time, low network latency, reliable communication, mobility or disconnection transparency, cache coherence, etc. • implement specific services in ad hoc mobile networks

6. Besides those canonical functions, proxies can perform: • Handover, session or consistency, management, Personalization, Authentication, Check-Pointing, and service/resource discovery, saving network bandwidth, reducing access latency, and coping with network and device heterogeneity. _______________________________________________________ What are the major advantages of a Proxy? • Allows legacy services to be directly used for mobile access • Avoids an overload at the servers • Detects Mobile Host (MH) disconnections and selection of the required adaptation • Implements, adapts, and customizes the transformations

7. 2) Proxies Classifications There are two types of proxy classifications: • Architecture-based Classification, which emphasizes the general characteristics of the proxy-based (software) architecture • Tasks-based classification, which focuses on functionality assigned to the proxies • Others classifications based on:(1) system architecture distinguishes between centralized and distributed architectures, options for proxy placement, and proxy configurability/programmability; (2) functionality (3) interactions(synchronous or asynchronous communication).

8. i.Architecture-based Classification proxy-based, software,architectures can be classified according to: • Levels, three generic:(a)Communication-level to handle all flavors of (TCP) and Wireless CORBA (b) Middleware-level to handle security, recovery, or any general tasks neither tailored to specific type of application. (c) Application-level to handle specific type of application such as Web-browsing data handling • Placement: Client-side proxy, server-side proxy, and a proxy pair. Also, It can be centralized or decentralized • Single-/Multi-protocol:(a)A single protocol to bridge the wired-wireless gap such as TCP or HTTP protocol (b) a multi-protocol to supports wired-wireless translation such as UDP, SMTP, SMS, WSP protocols. Examples of the latter group are iMobileEE, TACC, and eRACE • Communication and Extensibility:Server and the client communication in Synchronous mode or Asynchronous mode, see table 1 for illustration. Also communication among proxies can be direct or indirect • Extensibility and Programmability:In extensibility, proxies can be easily tailored to the specific needs of an application or middleware at deployment time. Programmability supports the dynamic loading of filters or new modules implementing specific functionality

9. ii.Common Proxy Tasks The most common proxy tasks are: • Protocol Translation and Optimization: Focus on Transport layer and above • Protocols translation: header Trans-coding, data alignment, encoding; and Using (Wireless Application Protocol)WAP Gateway to convert between wire-line session, presentation, and application level protocols and the corresponding WAP protocols stack. • Protocols optimization, mostly HTTP and TCP, include: caching of data, connection multiplexing, header and payload compression, adaptive TCP flow control, and data volume reduction. • Most optimizations method are TCP Split connection Protocols (e.g. MTCP, I-TCP, M-TCP, SRP, etc.) and Wireless-Profiled TCP, adapted in the WAP 2.0 for wireless MAN and WAN , which uses the ratio of inter-packet for rate control vs. packet loss and timeouts • Other optimization techniques related to multimedia transmission and presentation

10. Common Proxy Tasks Continue • Content Adaptation:To transform the payload for optimized transmission and presentation. It is mostly determined by quality of the wireless link and the device’s merits. Its protocols are: • Distillation, highly data compression way, and refinement can be applied orthogonally to each type of data (text, image, video, etc.). Active-Proxies focuses on them. • summarization is partial data compression with possibility of loss information. Example, text and video for mobile and wireless devices • intelligent filtering is a mechanism to drop or delay data delivery by applying filters on a data path according to network or target device conditions. Mobiware is a QoS-aware middleware introduces active Media Filters perform temporal and spatial scaling for multi-resolution and Adaptive FEC (Forward Error Correction) Filters to protect content against physical radio link impairments • trans-coding is a commonly used for the conversion of video formats or for the adjustment of HTML and graphics files. It depends on type of content and on an external annotation describing specific requirements of the device and the adaptations to be performed (Web content transcoding)

11. Common Proxy Tasks Continue • Caching and Consistency Management: To reduce traffic to and from the source server, restrict the user-perceived latency, conserve wireless bandwidth and the mobile device’s battery power, as well as handle client disconnections • Session Management: To maintain an application’s or service’s session state in spite of disconnections and migrations of the user. • Handover Management, (Wireless CORBA and Mobile IP): To update the MH location/address and to transfer its session state from the old to the new network. • Discovery and Auto-configuration: To handle complexity, changes in services or devices availability, and allow to choose the most reliable service by hiding network heterogeneity and dynamicity • Security and Privacy: To handle privacy, authorization, user authentication, or data encryption. • Check-pointing and Recovery: To handle handover and disconnected operation of all MH environment. • Other tasks: Personalization, content Creation, and name resolution

12. 3) Proxy Frameworks Several efforts have been made to develop generic proxy architectures, or proxy frameworks, that can be customized or extended to solve a particular problem. Most proxy frameworks provide general-purpose solutions for the following four main issues: • implementation and composition of adaptation modules, called adapters • Description of the conditions in which the adapters should be applied • Monitoring of the context, such as the mobile device’s profile, the application’s state and the communication bandwidth; • The loading of adapters.

13. Table 1: Comparison table of extensible well-know proxy frameworks WBI: Web Intermediaries,

14. Conclusion The presentation covered the following aspects: • Introduction to a proxy • Classifications of the proxy-based architectures for mobile computing and their responsibilities • common and recurrent set of functions, structures, and architectural patterns in proxy implementations • common proxy frameworks and their main characteristics

15. Thanks! Any questions?