Transmission Of Multimedia Data Over Wireless Ad example essay topic

Transmission of Multimedia Data over Wireless Ad-Hoc networ sA. Berk BarutluAbstractAd-how networking has been of increasing interest and therefore recognized as an important research area in recent years. This paper is about transmission of multimedia data over wireless ad-how networks, the problems and the related issues. 1. Introduction 1.1 Ad-Hoc Networks An ad-how network is a collection of wireless mobile nodes that will dynamically form a temporary network without the use of any existing network infrastructure. The technological developments that have enabled ad-how networks are divided into two major groups; the first group is the devices that are small and light enough to carry them around like printers, laptops, PDA's, ... etc., and the second group is wireless network interfaces, like Wireless LAN, Bluetooth, GSM, ... etc., that are available for these types of devices.

Since no pre-installed base stations are required, ad-how networks can be deployed quickly in cases such as conventions, search & rescue, disaster recovery situations and battle field communications. For example, in case of conventions, meetings in which the laptops and the other devices are connected in a wireless network in order to exchange data and share resources, like a printer, ... etc... Another example is the occurrence of natural disaster, like an earthquake, which results in the destruction of existing network facilities. Ad how networks fill the communications void created in such a situation to coordinate the efforts of rescue. Transporting multimedia data over ad how networks is a challenging problem.

At that point, before the investigation of that problem, first we have to mention the multimedia data and it's characteristics. 1.2 Multimedia Data The word multimedia is made up of the two Latin words " Multi" = "numerous" and " Media" = "medium" = "intermediary". In information field, Multimedia means "multiple intermediaries" between the source and sink of information or "multiple means" by which information is stored, transmitted, presented, and perceived. Digital multimedia is the field concerned with the computer controlled integration of text, graphics, still and moving images, animation, sounds, and any other medium where every type of information can be represented, stored, transmitted, and processed digitally. 1.2. 1 Characteristics of Multimedia Data: A multimedia object is usually a composition of several data objects. These data objects can be in different data formats, such as text, image, video, audio, ... etc.

The objects are ordered spatially, by linking various data objects into a single entity with dealing object size, rotation, and placement within the entity, or temporally, creating a multimedia object according to temporal relationship with the requirement of the synchronization of the data objects, to create composite multimedia objects. The synchronization can be continuous or point. Continuous, like the video conferencing, where audio and video signals are created at a remote site, transmitted over the network, and synchronized continuously at the receiver site when presented, it requires constant synchronization of lengthy events. On the other hand, in point synchronization, a single point of a media block coincides with a single point of another media block, such as a slideshow with blocks of audio allotted to each slide.

Multimedia data is often classified according to if it is non-temporal or temporal. Non-temporal data is often called static, such as text, images and graphics, and temporal data is called dynamic, like audio, video and animation. A multimedia object can consist of both static and dynamic data objects. An example of this would be a document describing the weather, with text and a video on the movement of clouds in the area. Dynamic data divides into two subgroups: Non-changing dynamic data, non-real-time audio, video, animation, and changing dynamic data, which includes real-time audio, video, answers to database qu aries and other data changing according to given input or input time includes real-time audio, video. 2.

Literature Survey Common features to all ad-how systems are the use of a shared medium for data transfer and of multi-hop communications to reach a distant destination. These characteristics pose challenging issues, especially related to traffic routing and access control. [Chiasserini] 3. Discussions It is a great challenge to provide multimedia service in ad-how networks. Due to it's real time nature, real time multimedia transport has stringent bandwidth, delay, and loss requirements. Such networks are characterized with frequent link failures, as well as congestion.

In fact, a wireless link usually has higher transmission error rate because of shadowing, fading, path loss, and interference from other transmitting users. An end-to-end path found in ad-how networks has an even higher error rate since it is the concatenation of multiple wireless link. Moreover user mobility makes the network topology constantly change. In addition to this, ad-how networks also reconfigure when users join or leave the network.

An end-to-end route in ad-how networks may only exist for a short period of time. The frequent link failures and route changes cause packet losses and reduce the received video quality. This is different from wire line networks, where packet loss is mainly caused by congestion and buffer overflow. To provide an acceptable received video quality in ad-how networks, there should be effective error control to reduce packet losses to a certain level. Traditional error control techniques, including Forward Error Correction (FEC) and Automatic Repeat Request (ARQ) have been adopted to take link failures into consideration. Even though some packet loss is generally tolerable, the quality of reconstructed video or audio will be impaired and errors will propagate in the following frames because of the dependency introduced among consecutive frames at the encoder.

However, the current best-effort network architecture does not offer any Quality of Service (QoS) guarantees for video transport. The Transmission Control Protocol (TCP) is mainly designed for reliable data traffic. It is not suitable for real time multimedia data because the delay and jitter caused by TCP retransmissions may be intolerable, TCP does not support multi cast, it's slow-start and congestion avoidance are not suitable for real time multimedia transport. The User Datagram Protocol (UDP) typically used in almost all real time multimedia applications, only extends the best-effort, host-to-host IP service to the process-to-process level. When congestion occurs, an unlimited amount of UDP data grams may be dropped since UDP is non-adaptive. Real time multimedia applications must implement additional rate control and error control mechanisms in order to cope with network congestion.

The mesh topology of ad-how networks implies the existence of multiple paths between two nodes. Path diversity provides an effective means of combating transmission errors and topology changes that are typical in ad-how networks. Path diversity provides a new dimension for video coding and transport design. Using multiple paths can provide higher aggregate bandwidth, better error resilience, and load balancing for a multimedia session. Similar observations were made in wire line networks for audio and video streaming by using multiple servers. However, research's on this area shows that multi path transport has more potential in ad-how networks, where link band with may fluctuate and paths are unreliable.

Also multi path routing is easier since many ad-how routing protocols can return multiple paths for a route query at only limited additional cost. Moreover, data partitioning techniques, like stripping and thinning, have been demonstrated to improve queue ing performance of real time data. Using multiple paths for real time transport provides a novel means of traffic partitioning and shaping. It has been shown that traffic partitioning can reduce short term correlation in real time traffic, thus improving the queue ing performance of the underlying network. Realtime Transport Protocol (RTP), is a multi cast oriented protocol for Internet real time applications. It does not support the use of multiple flows.

Usually, uses a multi cast tree and a whole audio or video stream is sent on each edge of the tree. RTP also focuses on multi cast applications where feedback is suppressed to avoid feedback explosion. Stream Control Transport Protocol (SCTP) is a message-based transport layer protocol initially designed for reliable signaling in the Internet. One attractive feature of SCTP is that it supports multi-homing and multi-streaming, where multiple network interfaces or streams can be used for a single SCTP session. With SCTP, generally one primary path is used and other paths are used as backups or retransmission channels. Multi flow Realtime Transport Protocol (MRTP) is for real time transport over ad-how networks by using multiple paths.

Multiple paths maintained by an underlying multi path routing protocol, MRTP, and its companion control protocol, Multi-flow Realtime Transport Control Protocol (MRTP), provide essential support for multiple path real time transport, including session and flow management, data partitioning, traffic dispersion, time stamping, sequence numbering and Quality of Service (QoS). Compared with RTP, MRTP provides more flexible data partitioning support and uses multiple paths for better queue ing performance and better error resilience. With MRTP, since only a few routes are in use, it is possible to provide much timely feedback, enabling the source encoder and traffic allocator too quickly adopt to the path changes. MRTP is like a natural extension of RTP exploring path diversity in ad-how networks. SCTP can not be applied directly for multimedia data because there is no time stamping and QoS feedback services.

But MRTP, the design is focused on supporting real time applications, with time stamping and QoS feedback as its essential modules. MRTP is also complementary to SCTP providing the essential functionalities and the flexibility in supporting multimedia services. 4. Conclusion This paper reviews the ad-how networks and their applications, multimedia data and it's characteristics, and the problems with possible solutions about transmission of multimedia data over wireless ad-how networks. In addition, the transport layer protocols for multi path transport of multimedia data, multimedia traffic partitioning, and a brief information about Multi-flow Realtime Transport Protocol (MRTP). 5.

Bibliography

[1] Carla-Fabian a Chiasserini. Wireless Ad-how Networks, Politecnico di Torino [2] Shiwen Mao, Dennis Bush mitch, Sathya Nara mayan, Shivendra S. Panwar. MRTP, Polytechnic university. [3] Thomas Plage mann, Jon Evil Andersson, Vera Goebel, Carsten Griwodz, Pal Halvorson. Ad-how Info Ware: Middleware Services for Information Sharing in Ad-how Networks, University of Oslo. [4] Yi han L'Y, Shiwen Mao, Shivendra S. Panwar. The case for multi path multimedia transport over wireless ad-how networks. [5] L. E: Doyle, A.C. Ko karam, . O. Mahony Trinity college.