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7/31/2019 Gl 2311161122 http://slidepdf.com/reader/full/gl-2311161122 1/7 Harsharndeep Singh, Meenu Dhiman, Pankaj Kumar Sehgal / International Journal of Engineering Research and Applications (IJERA) ISSN: 2248-9622 www.ijera.com  Vol. 2, Issue 3, May-Jun 2012, pp.1116-1122 1116 | P age A Survey on Video Streaming Schemes over MANETs Harsharndeep Singh * Meenu Dhiman** Pankaj Kumar Sehgal** M.Tech Scholar I.T. Deptt. I.T. Deptt. I.T. Deptt., MMU Mullana MMU, Mullana MMU, Mullana  Abstract  —  Real time video streaming over wireless networks is an increasingly important and attractive service to the mobile users. Video streaming involves a large amount of data to be transmitted in real time, while wireless channel conditions may vary from time to time. It is hard to guarantee a reliable transmission over the wireless network, where the parameters specifying the transmissions are; bandwidth, packet loss, packet delays, and outage times. The quality of the video is affected negatively when network packets are lost, and the mobile users may notice some sudden stop during the video playing; the picture is momentarily frozen, followed by a jump from one scene to a totally different one. In this paper, a survey on different issues and analysis of proposed techniques for video streaming over MANETs is presented. This survey paper analyzes different schemes for video streaming in MANETs i.e. cross-layer design schemes, multiple description coding (MDC) schemes and multipath routing schemes. Keywords:  MANETs, Video Streaming, cross- layer design, MDC, Multipath routing. 1. INTRODUCTION MANETs does not have any fixed infrastructure, so the mobile nodes are free to move within a network which results in dynamic change of network topology. Other MANETs issues are limited bandwidth, lack of centralized monitoring, cooperative algorithms, limited physical security, energy constrained operations, etc. Ad-Hoc networks are categorized into two types of routing protocols, i.e. Table-driven routing protocols and On-demand routing protocols. Table-driven routing protocols are also known as pro-active routing protocols. These protocols attempt to maintain an updated routing table with routes to all known destination nodes in the network. This has the advantage of minimizing the delay during routes lookup and the disadvantage of these protocols is that it consumes a lot of network bandwidth. Whereas On-demand routing protocols only update the routing table in response to a routing request. This has the advantage of minimizing network traffic overhead and disadvantage of these protocols is increased delay.Video streaming in MANETs [1] is one of the most challenging issues. Video streaming in MANETs is mainly affected by these factors like node mobility, dynamic change in topology, multi path shadowing and fading, collusion, interference and many more. The dynamic change in topology causes periodic connectivity which results in large packet loss. Packet loss has the largest impact on the quality of the video. Video streaming in real time requires special techniques that can overcome the losses of packets in the unreliable networks. The paper is organized as follows. Section 1 discusses the introduction to MANETs and video streaming. Section 2 presents video streaming issues for MANETs. Section 3 presents different schemes for video streaming. Section 4 presents the conclusion. 2.  VIDEO STREAMING ISSUES There are several aspects of mobile ad-hoc networks that complicate the issues of video streaming. These aspects are:-  Wireless medium: Operating on a wireless medium, MANETs are susceptible to the traditional problems with wireless communications. Wireless transmissions are susceptible to various transmission errors, caused by interference from other electrical equipment, multi-path fading, or colliding transmissions by other nodes. Recovering from such errors may require retransmission of data. This leads to an increase in delay and jitter, impacting the quality of the multimedia stream. Each node has a limited transmission range. This range is dependent upon many factors, such as the wireless transmission protocol, antennae size, energy use, obstacles and weather conditions. This limited range means that data must be routed through several other nodes to reach the destination. Each hop adds processing delay and increases the possibility of introducing a

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  • 7/31/2019 Gl 2311161122

    1/7

    Harsharndeep Singh, Meenu Dhiman, Pankaj Kumar Sehgal / International Journal ofEngineering Research and Applications (IJERA)

    ISSN: 2248-9622 www.ijera.comVol. 2, Issue 3, May-Jun 2012, pp.1116-1122

    1116 | P a g e

    A Survey on Video Streaming Schemes over MANETs

    Harsharndeep Singh * Meenu Dhiman** Pankaj Kumar Sehgal**M.Tech Scholar I.T. Deptt. I.T. Deptt.

    I.T. Deptt., MMU Mullana MMU, Mullana MMU, Mullana

    AbstractReal time video streaming over wireless networks

    is an increasingly important and attractive service

    to the mobile users. Video streaming involves a

    large amount of data to be transmitted in real

    time, while wireless channel conditions may vary

    from time to time. It is hard to guarantee a

    reliable transmission over the wireless network,

    where the parameters specifying the transmissions

    are; bandwidth, packet loss, packet delays, and

    outage times. The quality of the video is affectednegatively when network packets are lost, and the

    mobile users may notice some sudden stop during

    the video playing; the picture is momentarily

    frozen, followed by a jump from one scene to a

    totally different one. In this paper, a survey on

    different issues and analysis of proposed

    techniques for video streaming over MANETs is

    presented. This survey paper analyzes different

    schemes for video streaming in MANETs i.e.

    cross-layer design schemes, multiple description

    coding (MDC) schemes and multipath routing

    schemes.

    Keywords: MANETs, Video Streaming, cross-layer design, MDC, Multipath routing.

    1. INTRODUCTIONMANETs does not have any fixed infrastructure, so

    the mobile nodes are free to move within a network

    which results in dynamic change of network

    topology. Other MANETs issues are limited

    bandwidth, lack of centralized monitoring,

    cooperative algorithms, limited physical security,

    energy constrained operations, etc. Ad-Hoc networks

    are categorized into two types of routing protocols,

    i.e. Table-driven routing protocols and On-demandrouting protocols. Table-driven routing protocols are

    also known as pro-active routing protocols. These

    protocols attempt to maintain an updated routing

    table with routes to all known destination nodes in

    the network. This has the advantage of minimizing

    the delay during routes lookup and the disadvantage

    of these protocols is that it consumes a lot of network

    bandwidth. Whereas On-demand routing protocols

    only update the routing table in response to a routing

    request. This has the advantage of minimizing

    network traffic overhead and disadvantage of these

    protocols is increased delay.Video streaming in

    MANETs [1] is one of the most challenging issues.

    Video streaming in MANETs is mainly affected by

    these factors like node mobility, dynamic change in

    topology, multi path shadowing and fading,collusion, interference and many more. The dynamic

    change in topology causes periodic connectivity

    which results in large packet loss. Packet loss has the

    largest impact on the quality of the video. Video

    streaming in real time requires special techniques that

    can overcome the losses of packets in the unreliable

    networks. The paper is organized as follows. Section

    1 discusses the introduction to MANETs and video

    streaming. Section 2 presents video streaming issues

    for MANETs. Section 3 presents different schemes

    for video streaming. Section 4 presents the

    conclusion.

    2. VIDEO STREAMING ISSUESThere are several aspects of mobile ad-hoc networks

    that complicate the issues of video streaming. These

    aspects are:-

    Wireless medium: Operating on a wirelessmedium, MANETs are susceptible to the

    traditional problems with wireless

    communications. Wireless transmissions are

    susceptible to various transmission errors, caused

    by interference from other electrical equipment,

    multi-path fading, or colliding transmissions by

    other nodes. Recovering from such errors may

    require retransmission of data. This leads to an

    increase in delay and jitter, impacting the quality ofthe multimedia stream. Each node has a limited

    transmission range. This range is dependent upon

    many factors, such as the wireless transmission

    protocol, antennae size, energy use, obstacles and

    weather conditions. This limited range means that

    data must be routed through several other nodes to

    reach the destination. Each hop adds processing

    delay and increases the possibility of introducing a

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    Harsharndeep Singh, Meenu Dhiman, Pankaj Kumar Sehgal / International Journal ofEngineering Research and Applications (IJERA)

    ISSN: 2248-9622 www.ijera.comVol. 2, Issue 3, May-Jun 2012, pp.1116-1122

    1117 | P a g e

    bottleneck into the network path. For each hop,

    there is also the added possibility of a transmission

    error occurring, which adds delay and increases

    jitter.

    Resource constraints: The devices participating ina MANET will predominantly be small devices,which imply limited processing power, memory

    and storage capacity. Being small mobile devices,

    they will normally be battery powered, which

    means energy consumption must be kept at a

    minimum. Wireless communication will often

    mean limited bandwidth, and as mentioned, the

    nature of wireless communications means that this

    bandwidth is shared by all devices in the

    surrounding area. Additionally, an increase in

    network traffic places additional load on the nodes

    in the network, which in turn increases energy

    consumption. It is therefore important to keep

    network traffic overhead at a minimum. Heterogeneity: While most or all of the nodes in a

    MANET will have some resource constraints

    imposed on them, the capabilities and resources of

    each node can be very varying. A laptop computer,

    for example, has several times the processing

    power and storage capacity of e.g. a cellular phone,

    while a cellular phone has communication

    capabilities usually not available to a computer.

    Link bandwidth may also vary dramatically

    depending on the type of wireless interface used

    for communication.

    Lack of fixed infrastructure: The lack of a fixedinfrastructure requires that nodes function as

    routers in the network. This can introduce large

    bottlenecks, if a lot of responsibility is assigned to

    a node with very limited resources.

    Topology changes: The node mobility leads tocontinuous changes in topology, which means that

    routes may be formed and broken rapidly. When a

    route breaks, the discovery of a new route will

    most likely introduce delays, which will affect the

    quality of an ongoing media stream. In addition,

    the topology change may introduce new bottleneck

    links in the network path, leading to a reduction in

    bandwidth. In the worst case, parts of the network

    may even separate in such a way that there is no

    route from one part of the network to another. Thisis known as partitioning. If source and destination

    nodes wind up in separate partitions, the media

    stream will be broken.

    Malicious nodes: There is also a real concern thatmalicious nodes may delay or disrupt network

    traffic, by providing false routing information to

    neighboring nodes. One type of malicious nodes

    are so-called lack holes, that masquerade as a

    bogus destination. Models show that using the

    AODV routing protocol, if only 0.8% of nodes are

    black holes, the resulting packet loss is close to

    50%. If the fraction of lack holes increases to

    4.0%, the resulting packet loss is close to 80%.

    Such high packet losses would adversely affect amultimedia stream.

    3. DIFFERENT SCHEMES FOR VIDEO

    STREAMINGThis section consist different techniques for real-

    time video streaming over MANETs.

    3.1 CROSS LAYER DESIGN SCHEMESIn cross layer design knowledge has been shared

    between all layers to obtain the highest possible

    adaptivity. Yang Xiao et al. [2, 3] propose a two-

    level protection and guarantee mechanism for voice

    and video traffic. This mechanism is basicallydesigned to control the number of collisions

    independent of the number of active stations for data

    transmission. This mechanism dynamically control

    data traffic parameters based on data traffic load.

    Number of rules are defined such as fast-back off,

    dynamically adjusting parameters when fail,

    dynamically adjusting parameters when consecutive

    successful. In Fast-backoff: The proposed backoff

    method achieves a larger window size much quicker,

    and becomes faster when the backoff stage is large,

    when compared to the original binary exponential

    backoff. Dynamically adjusting parameters when fail

    rule: when a frame reaches the retry limit and is

    dropped, some adjustments in parameters are made.

    Dynamically adjusting parameters when consecutive

    successful rule: when a station successfully transmits

    m consecutive frames, the parameter adjustment are

    made until the original low limit is reached. S.

    Kompella et al. [4] proposed a Branch- and- Bound

    method for solving optimization problems, especially

    in discrete and combinatorial optimization. This

    method use RLT to reformulate and linearize OPT-

    MR into an LP relaxation L-MR. The optimal

    solution to this LP relaxation provides a lower bound

    LB for the original problem [5]. Since such an LP

    relaxation usually yields an infeasible solution to the

    original problem, a local search algorithm should beemployed to obtain a feasible solution to the original

    problem. The resulting feasible solution then

    provides an upper bound UB for the original

    problem. Under branch-and-bound framework, the

    original problem OPT-MR is partitioned into sub-

    problems, each having a smaller feasible solution

    space, based on the solution provided by the LP

    relaxation. New sub-problem are organized as a

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    ISSN: 2248-9622 www.ijera.comVol. 2, Issue 3, May-Jun 2012, pp.1116-1122

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    branch-and-bound tree, while this partitioning or

    branching process is carried out recursively to obtain

    two new sub-problems at each node of the tree. In

    this manner, the branch-and-bound process can

    fathom certain nodes of the tree, eliminating them

    from further exploration. The effectiveness of thebranch-and-bound procedure depends strongly on

    that of the employed fathoming strategy. H. Wang et

    al. [6] proposed a cross-layer optimized framework

    which jointly considers the video coding and

    transmission in wireless mesh networks. This

    solution makes use of dynamic programming to solve

    the minimum distortion problem and provide the

    optimal solution by using bisection method. The

    Optimal Solution [7] for the Minimum Distortion

    Problem:the minimum distortion problem, which is a

    constrained optimization problem, can be

    transformed into an unconstrained optimization

    problem using the redefinition of the single-packetdelay. To solve the optimization problem, we define

    a cost function Gk(vka, . . . , vk) which represents

    the minimum average distortion up to and including

    the packet k , given that vka, . . . , vk are the

    decision vectors for the packets (k a), . . . , k. Let O

    be the total packet number of the video clip, and we

    have O = N I. Therefore, GO(vOa, . . . , vO)

    represents the minimum total distortion of the whole

    video clip. The Optimal Solution for the Minimum

    Delay Problem:for every given Tp max, we can find

    the parameter vector which results in D(Tp max),

    the minimum average distortion of the whole video

    clip, where each packet delay has to be below the

    maximum delay Tp max. we can use bisection to find

    the optimal Tp max such that D(Tp max) = Ds

    max, which solves the minimum delay problem .

    Simulation results indicate that the proposed

    framework has significant performance enhancement

    over other systems where some system parameters

    take fixed values. The performance gain is

    significant, especially when the delay requirement is

    stringent. Y. Mao et al. [8] propose a multimedia

    network architecture that use slice priority of NAL

    and partial checksum technique named ASIC. In

    order to maintain better video quality for user, this

    technique defines transmission priority so that the

    video with higher priority data can be delivered first.To improve the throughput, partial checksum for

    insensitive video data is calculated. The system

    encapsulates sliced data into NAL-unit and partial

    checksum is calculated for these sliced data by the

    information stored in NAL header. The slice data

    which is generated by VCL is the input of ASIC. The

    advantage of this scheme is that when there is limited

    bandwidth the transmission order is dependent on the

    priority of slice. If every packet has same

    transmission priority, then packet loss and delay time

    causes video fragmentation [9]. In high bit error ratio

    environment, the partial checksum can reduce error

    video packet loss so that the throughput can be

    improved. The multimedia network ASIC is designedin Verilog hardware description language and

    synthesized by Synopsis using CCU 0.09 um CMOS

    single-poly eight-metal standard cell library. The

    proposed multimedia network ASIC operates faster

    when compared to other networks. The system

    achieves 14.58Gbps (455.8 MHz * 32bits) so that can

    deal with 10Gbps fast Ethernet traffic. Besides, ASIC

    supports NAL so that it is more suitable for

    H.264/AVC streaming video delivery.

    3.2 MULTIPLE DESCRIPTIONS CODING

    SCHEMES

    Multiple descriptions coding (MDC) is a sourcecoding technique that generates multiple correlated

    bit streams, each of which can be independently

    encoded and decoded. Each bit stream, called a

    description, is transmitted through the networks and

    is expected to follow a different path to reach the

    destination. The errors that could occur among

    descriptions are independent and, hence, the

    performance of MDC is maximal. Therefore, MDC is

    considered as a promising technique to enhance the

    error flexibility of a video transport system by

    transmitting the video over multiple independent

    channels like MIMO. The different techniques for

    MDC are presented below in a chronological order.

    Apostolopoulos [10] suggest to use two different

    channels to transmit even and odd frames that will be

    encoded by using Multiple Description Coding

    (MDC)[11], he suggests that it can be beneficial to

    transmit different amounts of traffic on different

    channels. It may consist of two separate encoders and

    decoders that alternate previous decoded frame it

    uses to perform the prediction. If there are no errors

    or frame losses and both even and odd streams are

    received correctly, then both streams are decoded to

    produce the full frames sequence for final display. If

    one stream has an error or frame losses then the state

    for that stream is incorrect and there will be error

    propagation for that stream. However, the otherindependently stream can still be accurately and

    straightforwardly decoded to produce usable video.

    Shiwen Mao et al. [12], proposed three MCP-based

    video transport techniques for mobile ad hoc

    networks. These schemes take advantage of path

    diversity to get better performance. These three

    schemes are based on the block-based hybrid coding

    framework using MCP and discrete cosine transform

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    (DCT), which is selected by all existing video coding

    standards. The three techniques are (1) Feedback

    Based Reference Picture Selection (2) Layered

    Coding with Selective ARQ. In Feedback Based

    Reference Picture Selection, the reference frames are

    selected based on feedback and predicted path status,the last frame that is selected to be correctly received

    as the reference frame. In this technique the coded

    frames are sent through the separate paths. The

    mapping of frames depends on the bandwidth

    available on each path. Decoder is assumed to send a

    feedback message. If any packet in a frame is lost,

    the decoder sends a negative feedback (NACK).

    Otherwise, it sends a positive feedback (ACK). An

    encoder receives the feedback message for frame n-

    RTT when it is coding frame n, where round-trip

    time (RTT) is measured in frame intervals. Once a

    NACK is received form one path for a delivered

    frame, the path is assumed to be bad until an ACKis received. Similarly, we assume that the path is in

    good status until NACK is received. While

    encoding a new frame, the encoder assume the last

    accurately decoded frame, depend on the feedback

    messages received till this time, and uses that frame

    as the reference frame. In Layered Coding with

    Selective ARQ This scheme makes the use of layered

    video coding. In this scheme, a raw video stream is

    coded into two layers, a BL and an EL. A BL frame

    is encoded using the standard predictive video coding

    technique. Thats why BL has a lower coding

    efficiency than a standard single layer coder. This

    loss in coding efficiency is, however, justified by

    increased error resilience: a lost EL packet will notaffect the BL pictures. Good quality is guaranteed if

    the BL packets are delivered error-free or at a very

    low loss rate. Although this approach is optimal in

    terms of coding efficiency for the enhancement layer,

    error propagation can still occur in the EL pictures.

    Tesanovic et al. [13], proposed a new scheme for

    video transmission for efficient and robust video

    streaming video over wireless channels, through a

    combination of MIMO and MDC technology. Two

    complementary MIMO techniques are used: space

    time block coding[14] and spatial multiplexing. The

    quality of the reconstructed video, already enhanced

    by the inherent MIMO systems properties, is furtherimproved through the use of MDC. MDC has

    evolved and has been adapted to lossy packet

    networks. With correct design, MDC can exploit the

    interactions between descriptions when losses occur

    in multichannels wireless communications to reliably

    recover to the video [15]. Lin et al. [16], investigate

    the influence of two important characteristics on the

    performance of the diversity level of the space time

    code and the error resilient ability of the video coder.

    For MIMO video system, the selection of diversity

    levels and the selection of an error-resilient video

    coder with appropriate redundancy are not

    independent of each other. Where the video data need

    to be lossy coded before transmission over threetransmitting and receiving antennas. The distortion

    caused by the lossy source encoder directly depends

    on the availability of the bit rates. Although a pace

    time coder with full diversity can provide strongest

    error protection of the source data, it usually supports

    a lower bit rate, which means that the video encoder

    can only output low-quality pictures. On the other

    hand, a space time coder with maximum rate

    (minimum diversity) allows the highest bit rate for

    video coding, but its weak error correction ability

    may cause devastating effects in the received video

    quality. The results show that the appropriate source

    coding and channel coding schemes depends on thechannel environment. Hence, to obtain the best

    overall system performance, the source coding and

    channel coding parameters need to be chosen jointly

    and with regard to the channel quality. Joohee Kim et

    al. [17], proposed a multipath video streaming [19]

    framework using channel-adaptive MDC for efficient

    video transmission. in this technique the sender sends

    packets or information through different paths to the

    receiver. Now the receiver will measure average

    packet loss and the available bandwidth for those

    different paths and sends the information back to the

    sender. The proposed channel adaptive multiple

    description coding algorithm generates two correlated

    descriptions by adjusting its source coding bit ratesand the amount of MD coding redundancy according

    to time-varying network conditions[18].

    3.3 MULTIPATH ROUTING SCHEMES

    Routing is responsible to establish and maintain

    possible end-to-end paths from source to

    destination. The main challenge in video streams is

    to classify the routes that ensure the video delivery

    with a satisfying quality. In general, Multipath

    routing can improve QoS by providing: - (i)

    Accumulation of bandwidth and delay: breaking the

    capacity of more than one route. (ii) Route load

    balancing: balance the traffic load in highernumber of nodes.(iii) Fault tolerance: by adding

    redundancy, to reduce the effect of network failures

    onto affected video quality, it is important that the

    paths are disjoint. In case the Multipath routing

    protocol offers multiple paths with sufficient path

    diversity, it is less probable that a link failure

    affecting one of the paths simultaneously affects one

    of the other paths. This is especially beneficial in

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    real-time streaming, where the playback buffer is

    limited and the video coder no longer can rely

    only on time diversity. Johannes karlsson et al. [20,

    21] proposed an error control method for real time

    video streaming. In this technique, the reference

    frame is considered as the last possibly correctdecoded frame. GloMoSim network simulator is

    used for integrating the video codec because there is

    a possibility of video frames loss. Which will

    gradually effect the size of following video frames.

    A new application layer is added as an interface to

    the modified XviD video codec in the simulator.

    They are connected using local sockets in Linux.

    The simulator is event driven and will periodically

    request a new video frame from the video codec. If a

    packet is lost the simulator will also inform the

    video codec about this. The modified XviD codec

    stores some extra bits in the bit stream and is not

    standard compliant. We send videos over a networksimulator where we drop the packets randomly.

    Different packet loss rates are tested, from 0% to

    15% loss. This is tested for two different intra frame

    intervals and for dynamic reference picture

    selection. For the dynamic reference picture

    selection there is no delay in the feedback. This

    means that the encoder will know about a loss

    before it encodes the next frame. If the feedback

    delay is increased the performance of dynamic

    reference picture selection will decrease [22].Toby

    Xu el at. [23] Proposed a proactive link protection

    and receiver-oriented adaptation technique. Initially,

    the source node discovers a route to its destination

    node. After path discovery process source nodestarts to send data to the destination node. Initially

    source node may need to set hop_cnt = 0 of a packet

    and incremented each time when the packet is

    retransmitted. And dest_pos field is used for

    piggybacking the location of the destination node.

    Whenever the destination node receives a packet, it

    includes its current location in its ACK packet. This

    location information is piggybacked to the source

    node. Mobility of nodes may cause path burst which

    results into streaming interruption. This problem is

    undertaken by two new techniques [24].

    Proactive Link Protection: - it is aimed atreplacing a link that is about to break byproactively looking for an alternative one.

    Receiver-Oriented Adaptation: - The idea behindthis technique is making a straight path from

    source to destination with minimum no. of hops.

    In ideal case hop_cnt can be calculated using this

    equation [L/R], where L is the length of the

    connection line, and R is the transmission range.

    Hamid Gharavi [25] proposed two multichannels

    routing protocols. The first multichannels routing

    protocol is based on single-path routing. This routing

    protocol suppresses the intrapath interference in a

    collision avoidance network or carrier sense multiple

    access network [27]. The above routing protocol isdeveloped by using link-partitioning scheme where

    the neighbor nodes operate at different non

    overlapping frequency bands. A technique, named

    systematic channel assignment, for this approach

    shows that the partitioning scheme can substantially

    amplifies the throughput performance of a multihop

    link. The second multichannels routing protocol is

    invented for transmission of real-time traffic over

    multiple-path routes. In mobile ad hoc networks,

    especially for real-time traffic, this approach can be

    affected unfortunately from co-channel interference

    due to the concurrent transmission of packets via

    multiple routes. So a dual-path routing protocol isdeveloped, which guarantees a different frequency

    band for each path, thus eliminating interpath

    interference. This protocol reduces the possibility of

    losing all the routes at the same time. Both, dual-

    description video coding [26] and the above

    described routing protocols can enhance the

    performance of real time video transmission over ad-

    hoc networks. Monica et al. [28] proposed a

    multipath [29] multimedia dynamic source routing

    (MMDSR) technique. Initially the source sends a

    Probe Message (PM) packet to destination through

    each one of the paths discovered by DSR. A time-out

    is triggered upon the arrival of the first PM packet at

    destination. The PM packets received after timeoutare discarded, because these packets arrived through

    a path having too much delay. After time-out, a Probe

    Message Reply (PMR) packet generated by

    destination node contains a set of sampled values of

    the QoS parameters collected from all the PM

    packets that arrived in time. The PMR message is

    sent back to the source through each one of the paths

    through which a PM arrived. This information will be

    analyzed at the source, where paths as categorized as

    best_path, medium_path, wrost_path. Then, the

    packets are sent according to their priorities as

    highest priority packets through best_path, medium

    priority through medium_path and lower prioritythrough wrost_path.

    4. CONCLUSION AND FUTURE WORKThis paper provides a classification and specification

    of the challenges involved in video streaming over

    MANETs and the techniques proposed to address

    them. Since most solutions are based on cross layer

    design, this paper gives an overview and analysis of

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    the combination of layers and the exchanged

    parameters that are the most commonly used. This

    survey shows that in general, currently existing

    techniques tackle dynamicity and strict resource

    constraints by jointly optimizing transmission

    parameters at various layers of the protocol stack.Frequent path and transmission errors are handled by

    adding redundancy, typically either by caching or

    replication in an overlay, or by utilizing redundant

    network routes. In order to select optimal

    transmission parameters, it seems widely accepted

    that cross-layer parameter exchanges are needed. Our

    analysis unveils that 65% of the surveyed solutions

    employ cross layering of some sort. Typically, the

    application layer adapts the video stream bit rate

    according to path characteristics obtained at the

    network layer. Conversely, the network layer

    discovers routes with end-to-end characteristics that

    best suit the requirements of the video stream. It isbeneficial to combine multi stream coding techniques

    (layered coding or MDC) with multiple routes.

    Congestion is no longer handled entirely at the

    transport layer, primarily because rate adaptation

    should be handled by a flexible video codec.

    Additionally, the aggregation of network resources

    through the use of multiple routes, which in addition

    adds path redundancy, calls for a transport protocol

    that provides an adequate multipath interface to the

    application. In terms of cross-layer optimization,

    some works increase efficiency by including lower

    link and physical layers in a more holistic cross-

    layering approach. It is hence questionable whether

    such complex systems will behave similarly whendeployed in real networks. This survey concludes that

    few papers include enough information for the

    experiments to be repeatable. Experimental results

    are often difficult or impossible to compare, due to

    the high variability of experiment parameter values.

    There are still certain problems, which are yet to be

    properly addressed. In MANETs, however, the

    probability of the existence of such a path may be

    low at any given point in time. Furthermore, mobility

    can cause this connectivity to disappear and appear

    frequently and unpredictably. Thus, serverclient

    connectivity throughout complete multimedia

    sessions can be very improbable. If these sessionswere terminated whenever a partition occurs,

    streaming across such networks would appear highly

    impractical, no matter how well the system performs

    end to end. More research is required to provide

    delay-tolerant streaming solutions for MANETs

    incorporating the above-mentioned mechanisms.

    Altogether, realizing video streaming over MANETs,

    there already exist many different types of techniques

    to handle the challenges. Yet, there are many

    unresolved issues to be addressed by future research.

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