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Wireless Multimedia Networks
Hamid R. RabieeMostafa Salehi, Fatemeh Dabiran, Hoda Ayatollahi
Spring 2011
2
Outlines
²Wireless & Multimedia² Motivations
² Requirements
² Challenges
² Solutions
²Hot topics² Video Streaming over IEEE 802.11
² Video Streaming In Mobile Ad-hoc Networks
² Wireless Multimedia Sensor Networks (WMSN)
² IPTV over WiMAX
Digital Media Lab - Sharif University of Technology
Wireless Networks
² A Wireless revolution is set to transform the world telecommunications
Industry.
² Wireless networks are a class of networks that use infrared or radio
channels as the transmission medium.
² Classification of growth of wireless networks:
² First generation analog voice wireless networks.
² Second generation digital voice/data networks are under development.
² Third generation networks are designed to carry multimedia traffic.
3 Digital Media Lab - Sharif University of Technology
Wireless Classes
² Wide Area Networks (WANs)
² greater mobility, but lower data rates
² Cellular networks
² Local Area Networks (LANs)
² higher bandwidths, but a limited coverage
² Wireless LANs (WLANs) and HiperLANs
² Personal Area Networks (PANs)
² deployed for cable replacement
² Bluetooth and Ultra Wide Bands (UWBs)
4 Digital Media Lab - Sharif University of Technology
Wireless & Multimedia
² Strong trends in using multimedia wireless technologies in
recent years² Wide-spread use of wireless technologies
² Multimedia applications become popular
² new hardware opportunities allow for more efficient use of
energy in mobile devices
5 Digital Media Lab - Sharif University of Technology
Motivations
² Why should we study/research multimedia topics?
² Huge interest and opportunities
² High speed Networks
² Powerful (cheap) computers (Laptops … cell phones)
² Abundance of multimedia capturing devices (cameras, speakers, …)
² Tremendous demand from users (mm content makes life easier, more
productive, and more fun)
² Here are some statistics …
6 Digital Media Lab - Sharif University of Technology
Motivations
² YouTube: fastest growing Internet server in history
² Serves about 300—400 million downloads per day
² Has 40 million videos, most of them (87%) less than 5 min
² Adds 120,000 new videos (uploads) per day
² CBS streamed the NCAA March Madness basketball games in 2007 online
² Had more than 200,000 concurrent clients
² And at peak time there were 150,000 Waiting
² Plus …
² Pretty much all major web sites have multimedia
clips/demos/news/broadcasts/…
7 Digital Media Lab - Sharif University of Technology
Multimedia Requirements
² As mentioned before:²² SynchronizationSynchronization :video and audio should be synchronized to within 20
msec.
² Throughput:Throughput: the minimum video bit-rate to be supported is 32 kbps. Video
rates of 128 kbps, 384 kbps and above should be supported as well.
² DelayDelay: the maximum end-to-end transmission delay is defined to be 400
msec.
² JitterJitter: the maximum delay jitter (maximum difference between the average
delay and the 95th percentile of the delay distribution) is 200 msec.
²² Error RateError Rate: the video conferencing system should be able to tolerate a
frame error rate of 10−2 or bit error rate of 10−3 for circuit switched
transmission.
8 Digital Media Lab - Sharif University of Technology
Multimedia Service Requirements
² Resource sharing
²Multimedia data integration
² Local intelligence and autonomy
² Graphical interfaces
² Vendor independence
9 Digital Media Lab - Sharif University of Technology
Wireless Multimedia Transmission Requirements
² To achieve a high level of acceptability, several key
requirements need to be satisfied by multimedia streaming
solutions
²² easy adaptability easy adaptability to wireless bandwidth fluctuations
²² robustnessrobustness to partial data losses and high packet error rates
²² support for heterogeneous support for heterogeneous wireless clients with regard to
their access bandwidths, computing capabilities, buffer
availabilities, display resolutions, and power limitations.
10 Digital Media Lab - Sharif University of Technology
Challenges in Wireless Multimedia
² Network Challenges² Heterogeneous Networks
² bandwidth, reliability, and receiver device characteristics
² Delay
² queuing, propagation, transmission, and processing delays
² Lost or discarded Packets
² complexity/power limitations or display capabilities of the receiver
² Packet loss up to 10% or more
² Variations in Channel Condition
² different access technologies, multipath fading, , cochannel interference,
noise, mobility, handoff, competing traffic from other wireless users
² Finite BW resources
11 Digital Media Lab - Sharif University of Technology
Challenges in Wireless Multimedia
²Device Challenges²Mobility
² Hand off
² Adaptive Decoding² Optimizing rich digital media for mobile information devices with
limited processing power, limited battery life and varying display
sizes
12 Digital Media Lab - Sharif University of Technology
Solution for the improvement of multimedia communication over wireless Networks
² High performance local and metropolitan area networks
has to be designed including control schemes which
provide high throughput while simultaneously supporting
real time services.
² The topic of multimedia QoS is very broad and there is an
extensive pool of solutions in the literature.
² In this present, we only mention some of these solutions.
13 Digital Media Lab - Sharif University of Technology
QoS on Wireless Networks
² A multitude of protection and adaptation strategies exists
in the different layers of the Open Systems Interconnection
(OSI) stack² Data Link-Layer QoS
² Network-layer QoS
² Application-layer QoS
² End-user QoS
14 Digital Media Lab - Sharif University of Technology
QoS on Different Layers
² Data Link Layer QoS² Concerned with
² Network Layer QoS² Concerned with reliable and fast delivery of multimedia data over the wireless
technologies
² Application Layer QoS² Concerned with the quality of the multimedia encoding, delivery, adaptation, decoding
and play out on the client device
² End-user QoS ² Concerned with the end-user experience in terms of audio and visual quality
² Cross-layer solutions² QoS schemes implemented at each of these layers have an effect on each other
15 Digital Media Lab - Sharif University of Technology
16
QoS Support required at every layer
² Physical Layer
² Robust modulation
² Link adaptation
² MAC Layer
² Offer priorities
² Offer guarantees (bandwidth, delay)
² Network Layer
² Select “good” routes
² Offer priorities
² Reserve resources (for guarantees)
² Transport Layer
² Attempt end-to-end recovery
when possible
² Application Layer
² Negotiate end-to-end and with
lower layers
² Adapt to changes in QoS
Digital Media Lab - Sharif University of Technology
17
QoS Flavors
²Similar to RSVP in the Internet
²Has to implement connection admission control
²Difficult in WMNs due to:²Shared medium (see
provisioning section)²Fading and noise
²Similar to diffserv in the Internet
²Offers classes of services²Generalization of
fairness²A possible
implementation on next slide
Guarantees Priorities
Digital Media Lab - Sharif University of Technology
Application Layer Solutions
² There are several aspects to application-layer QoS that deal with all stages of
the applications lifecycle:
² Encoding
² The choice of right encoding settings
² Delivery
² Adaptation
² Adaption Capabilities are used to minimize the effects of poor network conditions
² Decoding
² Error Correction & Concealment
² On the client device
² interpolate the missing multimedia data from the received data in order and mask these
errors to improve the end-user perceived quality
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End User QoS
² End-user QoS is the primary goal of application-layer QoS schemes and a
somewhat secondary goal of network-layer QoS schemes
² methods for assessing end-user QoS:
² subjective assessment and testing
² objective assessment and testing
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HOT TOPICS
Video Streaming over IEEE 802.11
Video Streaming In Mobile Ad-hoc Networks
Wireless Multimedia Sensor Networks (WMSN)
IPTV over WiMAX
20 Digital Media Lab - Sharif University of Technology
Hot Topics
²In this section, we cover some hot topics!² Video streaming over 802.11
² Video Streaming In Mobile Ad-hoc Networks
²Wireless Multimedia Sensor Networks (WMSN)
² IPTV over WiMAX
21 Digital Media Lab - Sharif University of Technology
VIDEO OVER 802.11
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Motivation for video over 802.11
² The number of homes with TV is greater than the number
of homes with Internet
² The average US home has 3 TVs
² 802.11 must work when every home is simultaneously
using their network
² People are used to high-quality video
² The potential market is huge
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Use Cases
• Many applications including … – Delivering multiple HD streams to several receivers– Displaying stored digital contents from media servers to display devices– Browsing contents in distributed devices through big screen TVs
Home PC
STB (Cable TV access)
DTV
Wireless AP(Internet gateway)
Digital cameraCamcorder
PMP
DVD player
Projector
Home theater(AV receiver)
24Digital Media Lab - Sharif University of Technology
Transport Stream
I Frame P Frame B Frame
P Frame PayloadPES Header
SPH TS Header TS Payload ...
Variable length
Fixed lengthSPH TS
HeaderTS
Payload
MAC header
IP header
UDP header PayloadRTP
header
25 Digital Media Lab - Sharif University of Technology
One TS contains audio, video, data
TS Header (4 bytes) has an adaptation field control. This is used among other things to identify the presence of PCR (Program Clock Reference) following the header.
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From video frames to 802.11 packets
²Video frames typically span multiple 802.11
packets
²TS header may contain PCR – critical for keeping
audio/video in sync² if lost, quality suffers dramatically
²The effect of 802.11 packet loss is different
depending upon its contents
27 Digital Media Lab - Sharif University of Technology
Video over Wireless Challenges
² Hey, it is wireless
² Interference, path loss
² Limited number of channels in unlicensed bands
² Channel characteristics constantly change (dynamic)
² Medium access non-deterministic (802.11 is originally designed for data)
² STA physically moves in the same BSS
² Inter-stream synchronization
² Between audio rendered at remote speakers and video
² Between one video stream and multiple audio streams
28Digital Media Lab - Sharif University of Technology
Current 802.11 Mechanisms
² Distributed medium access (EDCA)
² prioritization
² Centralized medium access (HCCA)
² admission control and bandwidth reservation
² Direct Link
² Dynamic channel selection (802.11h)
² RRM/Management (802.11k/v)
² HT (802.11n)
² PHY techniques for improved robustness
29Digital Media Lab - Sharif University of Technology
802.11k&v Features for Video
² 11k: Frame Request/Report identifies STAs/APs (channel survey).
² 11k: Location (LCI) Request/Report may provide location information
to sort STAs into in-home or external.
² 11k: Noise Histogram and Channel Load
² 11v: Extended Channel Switch permits relocating BSS to selected
channel (selection based on channel survey).
² 11k: Link Measurement and Beacon Request/Report characterize
initial link quality in terms of signal level (RCPI) and SNR (RSNI) for
video stream at setup time.
30 Digital Media Lab - Sharif University of Technology
802.11k features to monitor quality
² 11k: Transmit Stream Measurement Request/Report for direct video stream monitoring using triggered reports (alerts) on transmit stream MSDU retries, discards, failures or long delay.
² 11k: Link Measurement Request/Report to track ongoing video link quality in terms of signal level (RCPI) and SNR (RSNI) for STA to STA streams.
² 11k: Beacon Request/Report to track ongoing video link quality in terms of signal level (RCPI) and SNR (RSNI) for AP to STA streams with conditional reporting (alerts).
² 11v: Presence Request/Report may detect onset of motion of transmitting or receiving STA to indicate changing link conditions.
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Limitations in current 802.11 mechanisms
² Limited prioritization
² Lack of inter-layer communication
² Limited set of QoS parameters
² Limited capability to dynamically tweak QoS parameters
² Lack of content-specific methods
32Digital Media Lab - Sharif University of Technology
Possible areas of work
² MAC-level techniques
² Selective Repetition to mitigate packet loss
² Smart packet drop
² Finer prioritization among streams and within one stream
² Content-specific methods
² QoS policy (establishing, monitoring, adaptation)
² Inter-Layer communication (Vertical interaction)
² PHY-MAC
² MAC-higher layers
33Digital Media Lab - Sharif University of Technology
Possible solutions: Illustration
MPEG2 Packetized Video Elementary Stream
MPEG2 Packetized Audio Elementary Stream
Other data
MPEG2 Packetized Transport Stream
…
•
• Dynamic QoS• Finer granularity priority levels• Content aware protection, transmission, retransmission, etc.
PHY frame
• Content-aware PHY adaptation• Beamforming / STBC• Coding / Modulation, etc.
MAC frame
… PHY frame
MAC frame
34 Digital Media Lab - Sharif University of Technology
Multiple Priority Levels
² Inter-stream and Intra-Stream priorities
² Real-time video has different QoS requirements compared to stored
media.
² Current standard has provision for video access category and provides
one service to all kinds of video including real-time video, stored media
etc
² Possible scope for improvement
² Use different set of channel access parameters to differentiate premium
content, real-time, stored media content
² For example, more granular control of AIFSN can be used to differentiate
video streams
3535 Digital Media Lab - Sharif University of Technology
Content Aware Techniques
² Some video frames are more important than others (I > P > B frames)
² Current MAC/PHY layers don’t differentiate among different frames
² Possible content-specific methods
² MAC Layer
² Frame based retry limits, fragmentation size, QoS parameters
² As a result of PHY/MAC communication:
² Frame based FEC coding, modulation scheme, 802.11n specific features
such as STBC, Beamforming etc.
3636 Digital Media Lab - Sharif University of Technology
Summery
² Video is different from data; existing 802.11 mechanisms are not sufficient
² The home networking industry at present is not planning to use 802.11 for
video distribution!
² Instead, cable or powerline are being used
² 802.11 will be the medium of choice only if more is done in a timely
fashion.
The industry is ready for 802.11 based Video Streaming NOW.
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VIDEO STREAMING IN MOBILE AD-HOC NETWORKS
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Introduction
² Many challenges, and many techniques..
² .. attack different challenges with different techniques
² > 100 papers
² Wireless networks → wireless mesh networks →MANETs → Wireless
Sensor Networks (WSN)
² Download and play → Streaming on demand → Live conversations
² Attack different layers to solve the problem
² A brief overview → work in progress
39 Digital Media Lab - Sharif University of Technology
Figure: Example streaming scenario over a MANET
40 Digital Media Lab - Sharif University of Technology
Traditional Challenges
² Stringent requirements (QoS)
² Bandwidth, limited packet-loss, delay and jitter
² Buffering and re-transmission increase delay
² Download and play vs. Streaming on demand vs. Live conversations
² Network congestion impacts QoS severely
² Streams have steady bit-rates; map to end-to-end network capacity
² Reduce bandwidth with video coding
² Compression, redundancy, reducing resolution
41 Digital Media Lab - Sharif University of Technology
Wireless Channel Challenges
² Wired links: static and reliable (guided and shielded)
² Wireless links: dynamic and unreliable (open medium)
² Shadowing, multi-path fading and hidden node problem
² High chance of packet collisions
² Random packet losses →Not only caused by congestion
² Bandwidth constrained
² High density: Bandwidth !
² Time varying links and capacity regions
² Long-lasting QoS-guarantees are challenging
42 Digital Media Lab - Sharif University of Technology
Multi-hop Induced Challenges
² Increased delay
² Delay increase almost linearly per hop
² Particularly challenging for live streaming
² Increased packet-error rates
² Both intra- and inter-path interference
² Routing (Need to satisfy QoS)
² Routes that give the subjective best video quality
² Requires multi-metric routing
² Hard to obtain a global view
43 Digital Media Lab - Sharif University of Technology
Mobility-Induced Challenges
² Adds dynamicity
² Further complicates getting a global, consistent view of the network
² Partitioning → Delay Tolerant Networking (DTN)
² Re-routing (links break)
² Disruptions in ongoing streams
² Burst of packet loss
² Out-of-order delivery
² Possible oscillating effect
44 Digital Media Lab - Sharif University of Technology
Resource Constrained Devices Challenges
² Heterogeneous devices (PDA’s, Laptops, etc.)
² Computational constraints
² Limits encoding, decoding and transcoding
² Intermediate nodes become bottlenecks
² Battery constraints
² Computation and transmission drain battery
² Empty battery: nodes disappear, causing disruptions and possible partitions
² Memory and storage constraints
² Limits buffering
² For DTN: high requirements on storage space
² Presentational constraints
² Screen resolution
45 Digital Media Lab - Sharif University of Technology
Handling Disconnections Challenges
² High mobility and/or low density² Other causes: obstacles, dying/failing nodes, node/link saturation
² Long lasting: requires delay tolerance
² How to predict partitioning / link disruptions?
²Where to buffer/replicate content?
² Routing through time (not only space) ! Delay tolerant
routing / Space-time routing
² Affect signaling (how to play, pause, start, stop replicas)
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Techniques Tree Structure
47 Digital Media Lab - Sharif University of Technology
Video Coding Techniques
² Main goal: Adapt video frames to
optimal bit-rate stream(s)
² Multi-stream Coding
² Combine with multi-path routing
² Layered Coding² Primary path: base layer
² Others: enhancement layers
² Multiple Description Coding (MDC)² All descriptions equally important
² Primary path can break :)
² Handling Transmission Errors
² Traditional channel coding techniques
FEC, Rapture codes
48 Digital Media Lab - Sharif University of Technology
Middleware
² Main goal: Provide interface to application, and allow adaptation of
underlying protocols
² A middleware alone cannot solve challenges
² Few efforts among identified articles
² Could be possible if layers exist as changeable components
² Then, adapt and change layer components dynamically during runtime
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Caching and Replication
² Main goal: Provide replicas that are closer in
distance or time (or both)
² Link prediction² Location awareness (e.g., GPS)
² Clustering
² Caching: improve efficiency
² Service Replication: partitioning → delay tolerance,
e.g., NonStop
² Peer-to-Peer Approaches: levitate the best from the
P2P paradigm
² Store-carry-forward: message ferries, exploit
mobility, e.g.,V3 and MOMENTUM
50 Digital Media Lab - Sharif University of Technology
End-to-end Transport Techniques
² Main goal: Signaling and flow-control →avoid congestion
² Rate-control closely related to video coding, since content should not be postponed
² TCP:
² Does not match video transmission (e.g., retransmissions)
² Mistakes packet error as congestion
² Timeout - what happens during partitions?
² UDP: Basically no control!
² How to issue fairness between streams: FairCast
² TRFC (TCP Friendly Rate Control): not intended for MANETs
² Stream Control Transmission Protocol (STCP): does not fully levitate multi-path
routing
² Provide interface to multi-path routing
51 Digital Media Lab - Sharif University of Technology
Routing Techniques
² Main goal: Keep route(s) from source to destination² Cross-layer design, multiple metrics² Single-path routing
² OSLR,AODV: hop-count →no QoS guarantees² QoS Routing ² Hierarchical routing
² Multi-path routing² Multi-path versions of OLSR and AODV² Coding Aware Routing
² Route selection with coding parameters in mind. ² Coding Intrusive Routing
² Coding affected by paths and resources.
² Multi-cast routing² Multiple multi-cast trees
² Energy Aware Routing (WSN)
52 Digital Media Lab - Sharif University of Technology
Lower Level Adaptation
² Main goal: Adapt lower layers
² Increase bandwidth with added multiple-input multiple-output
(MIMO) support , e.g., upcoming 802.11n
² Add QoS support, e.g., 802.11e
² Dynamic re-transmission scheme
² Adapting transmission range (WSN)
53 Digital Media Lab - Sharif University of Technology
Cross-Layer Design
² Main goal: Optimization at all layers
² Examples: Coding aware routing, packet error rate aware coding..
² Most efforts surveyed are in fact of cross-layer design!
² Pro:² Allow optimization based upon conditions (network and application requirements)
² Con:² Design complexity: like code
² Oscillating optimization effect
² Backward compatibility
² Compromise: Do not allow direct interaction, but enable a component for
delegating this
² Holistic approaches
54 Digital Media Lab - Sharif University of Technology
Summary
² Cross-layer approach with upper layers adaptation widely recognized
² Adaptable video coder: rate adaptation with multi-stream coding and
error correction
² Multi-path routing: routes matches video descriptions
² Formulate as an cross-layer optimization problem → Huge solution space
→Considered NP-Hard
² Centralized solution algorithms → distributed algorithm
² Still need adequate signaling → Delay tolerant overlay (cache / proxying)
² More emphasis on resource awareness and mobility
55 Digital Media Lab - Sharif University of Technology
WIRELESS MULTIMEDIA SENSOR NETWORKS (WMSN)
56 Digital Media Lab - Sharif University of Technology
Wireless Sensor Networks
² Wireless Sensor Networks are networks that consists of sensors which
are distributed in an ad hoc manner.
² These sensors work with each other to sense some physical
phenomenon and then the information gathered is processed to get
relevant results.
² Wireless sensor networks consists of protocols and algorithms with
self-organizing capabilities.
57 Digital Media Lab - Sharif University of Technology
Applications of Wireless Sensor networks
The applications can be divided in three categories:
1. Monitoring of objects.
² Structural Monitoring, Eco-physiology, Condition-based Maintenance, Medical
Diagnostics, Urban terrain mapping
2. Monitoring of an area.
² Environmental and Habitat Monitoring, Precision Agriculture, Indoor Climate
Control, Military Surveillance, Treaty Verification, Intelligent Alarms
3. Monitoring of both area and objects.
² Wildlife Habitats, Disaster Management, Emergency Response, Ubiquitous
Computing, Asset Tracking, Health Care, Manufacturing Process Flows
* Classification due to Culler, Estrin, Srivastava
58 Digital Media Lab - Sharif University of Technology
Wireless Multimedia Sensor Networks (WMSN)
² The integration of low-power wireless networking technologies with
inexpensive hardware such as cameras and microphones is now enabling
the development of distributed, networked systems that we refer to as
wireless multimedia sensor networks (WMSNs),
² WMSN: networks of wireless, interconnected smart devices that enable
retrieving video and audio streams, still images, and scalar sensor data.
59 Digital Media Lab - Sharif University of Technology
² Cheap CMOS cameras: Cyclops imaging module is a light-weight imaging
module which can be adapted to MICA2 or MICAz sensor nodes
60 Digital Media Lab - Sharif University of Technology
WMSN Applications
² Boost the existing application of WSNs
² Create new applications²² Home automationHome automation
²² Environment monitoringEnvironment monitoring: Arrays of video sensors already are used
by oceanographers to determine the evolution of sandbars using
image processing techniques.
²² multimedia surveillance sensor networksmultimedia surveillance sensor networks: will be composed by
miniature video cameras and will be able to communicate, to
process and store data relevant to crimes and terrorist attacks
61 Digital Media Lab - Sharif University of Technology
WMSN Applications
²² industrial process controlindustrial process control: will be realized by WMSNs that
will offer time-critical information related to imaging,
temperature, pressure, etc.
²² Advanced health care deliveryAdvanced health care delivery: Telemedicine sensor
networks can be integrated with third and fourth generation
(3G/4G) cellular networks to provide ubiquitous health care
services.
²² traffic avoidance and control systemstraffic avoidance and control systems: will monitor car
traffic and offer routing advices to prevent congestion
62 Digital Media Lab - Sharif University of Technology
What’s so special about WMSNs ?
² [Ian Akyildiz: Dec’06] We have to rethink the computation-
communication paradigm of traditional WSNs
² which focused only on reducing energy consumption
² WMSNs applications have a second goal, as important as the energy
consumption
² delivery of application-level quality of service (QoS)
² mapping of this requirement to network layer metrics, like latency
² This goal has (almost) been ignored in mainstream research efforts on
traditional WSNs
63 Digital Media Lab - Sharif University of Technology
What’s so special about WMSNs ?
² Resource constraints
² sensor nodes are battery-, memory- and processing-starving
devices
² Variable channel capacity
² multi-hop nature of WMSNs implies that wireless link capacity
depends on the interference level among nodes
² Multimedia in-network processing
² sensor nodes store rich media (image, video), and must retrieve
such media from remote sensor nodes with short latency
Digital Media Lab - Sharif University of Technology64
What’s so special about WMSNs ?
² High Bandwidth Demand
² Multimedia contents need high BW. So, high data rate and low power,
consumption-transmission techniques must be leveraged
² Multimedia Source Coding Techniques
² Because predictive encoding requires complex encoders, powerful
processing algorithms, and also entails high energy consumption, it may
not be suited for low-cost multimedia sensors
² Cross-layer Coupling of Functionality
² Because of the shared nature of the wireless communication channel, in
multi hop wireless networks, there is a strict interdependence among
functions handled at all layers of the communication stack.
Digital Media Lab - Sharif University of Technology65
WMSN Architecture
66 Digital Media Lab - Sharif University of Technology
WMSN Layers
² Research challenges at different layers of the protocol stack
67 Digital Media Lab - Sharif University of Technology
Physical Layer
² Among other promising technologies, the UWB technology [5] has the
potential to enable low power consumption, high, data-rate
communication within tens of meters → Time-hopping impulse radio
UWB (TH-IR-UWB)
² Although the UWB transmission technology is advancing rapidly, many
challenges must be solved to enable multi hop networks of UWB devices
² The way to share the medium in UWB
Digital Media Lab - Sharif University of Technology68
MAC Layer
²MAC layer functions²arbitration of the channel
² providing error control and recovery schemes
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MAC Layer-Channel Access Policies
² Based on the nature of channel access, some MAC
protocols are geared to provide high link level throughput,
reduce delays, or guarantee QoS for a given packet type.² Contention-Based Protocols
² Contention-free Single Channel Protocols
Digital Media Lab - Sharif University of Technology70
Contention-Based Protocols
² Existing schemes are variants of the Carrier Sense
Multiple Access with Collision Avoidance (CSMA/CA)
MAC protocol
² Constraints² Their goal is limiting power consumption, not delay!
² Sleep cycle and Listen cycle synchronization → more delay
Digital Media Lab - Sharif University of Technology71
Contention-free Single Channel Protocols
² Time-division multiple access (TDMA)
² The frame is organized with a small reservation period (RP)
that is generally contention-based, followed by a
contention-free period that spans the rest of the frame
² Constraints² limited scalability
² complex network-wide scheduling
² Clock drift and synchronization issues
Digital Media Lab - Sharif University of Technology72
MAC Layer-MIMO
²Multiple input multiple output (MIMO) antenna systems² interference cancellation techniques
² Each sensor may function as a single antenna element, sharing
information and thus simulating the operation of a multiple
antenna array
² Constraints² Complexity
Digital Media Lab - Sharif University of Technology73
MAC Layer-LINK LAYER ERROR CONTROL
² 2 error control mechanisms
² Automatic Repeat Request (ARQ) ² use bandwidth efficiently at the cost of additional latency involved
with the re-transmission process
² Forward Error Correction (FEC)² Applying different degrees of FEC to different parts of the video
stream, depending on their relative importance (unequal
protection) allows a varying overhead on the transmitted packets
Digital Media Lab - Sharif University of Technology74
Network Layer
² Several design considerations of traditional WSN routing
are applicable for WMSNs
² network layer functionality of multimedia routing
² Architectural and spatial attributes :because of different types of
sensors with varying capabilities, we need different routing
algorithms
² Real time support: Meeting strict time deadlines
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REAL TIME ROUTING PROTOCOLS
Ø SPEED: A Real-Time Routing Protocol for Sensor Networks
Ø MMSPEED: Multipath Multi-SPEED Protocol for QoS guarantee of
reliability and timeliness in wireless sensor networks
Digital Media Lab - Sharif University of Technology76
Network Layer Routing Protocols
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Transport Layer
²WMSN transport layer is more important than WSN one² High data rates
² Sensitivity of multimedia to congestion
² More than one path between source and sink
²Main transport layer function² providing end-to-end congestion control
Digital Media Lab - Sharif University of Technology78
Transport Layer Protocols
² UDP BASED PROTOCOLS² Usually preferred over TCP
² RTP and RTCP can run over UDP
² TCP AND TCP FRIENDLY SCHEMES FOR WMSNS² Some data such as I-frames are sensitive to loss
² some form of selective reliability, such as that provided by TCP,
must be introduced for these packets in a WMSN.
Digital Media Lab - Sharif University of Technology79
Transport Layer Protocols
80 Digital Media Lab - Sharif University of Technology
Application Layer
² MULTIMEDIA ENCODING TECHNIQUES AT APPLICATION
LAYER
² The main design objectives of a coder for WMSNs are:
² High compression efficiency
² Low complexity
² Error resiliency
² Existing standards (MPEG or H.263 and H.264) require complex
encoders, powerful processing algorithms, and entail high energy
consumption; whereas, decoders are simpler and loaded with a lower
processing burden
Digital Media Lab - Sharif University of Technology81
Application Layer
² But, efficient compression can be achieved by leveraging
knowledge of the source statistics at the decoder only →
distributed source coding² the compression of multiple-correlated sensor outputs that do not
communicate with each other
² Joint decoding is performed by a central entity that
receives data independently compressed by different
sensors
² However, practical solutions have not been developed until
recently. Digital Media Lab - Sharif University of Technology82
Application Layer- application specific querying and processing
²application specific querying and processing² Given a source of data (e.g., a video stream), different
applications may require diverse information (e.g., raw
video stream vs. simple scalar or binary information inferred
by processing the video stream)
² it is necessary to develop expressive and efficient querying
languages and distributed filtering and in-network
processing architectures, to enable real-time retrieval of
useful information.
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Summery
²WMSNs have different characteristics and requirements
in comparison with WSNs.
² Unique features of WMSNs call for protocol designs that
provide QoS at different layers
²We discussed existing solutions and open research issues
at the physical, link, network, transport, and application
layers of the communication stack.
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IPTV OVER WIMAX
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What is IPTV
² IPTV is a system where a digital television service is delivered using the IP
protocol over a network infrastructure. It covers both live TV
(broadcasting) as well as stored video (Video on Demand).
² The playback of IPTV requires either a personal computer or a "set-top box"
connected to a TV
² Video content is typically compressed using either a MPEG-2 or a MPEG-4
codec and then sent in an MPEG transport stream delivered via IP Multicast
in case of live TV or via IP Unicast in case of Video on Demand
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IPTV Architecture
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IPTV Architecture[Uilecan07]
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4 Major Elements
² Video Head-End
² video is captured and processed before being sent over the IP network
² Service Provider Core/Edge IP Network
² the core network of the service provider and includes hardware from many
vendors to construct this network.
² Access Network
² connects the Service Provider to the Subscriber’s home
² WiMAX is an access network
² Home Network
² distributes the IPTV services throughout the home
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IPTV over WiMAX
²Why IPTV over WiMAX?² Maximize the number of subscribers
² In comparison with wired MAN technologies
² Converged wireless broadband access network²more services and better service availability under a common infrastructure
² Supporting the future trends (such as HDTV)² reservation-based bandwidth allocation, cost-effective and infrastructure-free
deployment, and stringent QoS support for the four types of service
² Multicast capability² The multicast technology allows a base station (BS) to send video packets to a
subset number of stations
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IPTV over WiMAX
² Why IPTV over WiMAX?
² Mobility
² IPTV is expected to provide ubiquitous access with mobility support.
² advantage of WiMAX is the support for data communications at vehicular
speeds, feature which was impossible until now in regular cable TV systems.
² Overhead
²WiMAX is decapsulating the frames up to the MAC layer, therefore
it can use payload header suppression and compression techniques
in order to reduce the amount of overhead at Physical and MAC
layers.
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Constraint/Challenges
² Fading conditions to a subset of all subscriber are diverse. Hence
single-user communication scheme for optimizing data throughput
doesn’t work well
² Lack of standardization
² Instant Channel Change
² There is a delay when the viewer wants to change the channel
² a delay between the time the router stops sending over the old channel and
when it starts sending over the new requested channel
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Delivering IPTV Services to both Fixed and Mobile Subscribers [Uilecan07]
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Layered Video
² Each video stream (or program) is encoded into several sub-streams (i.e.,
layers).
² The first layer is called the base layer, and the others are called the
enhancement layers.
² The more layers a subscriber has received, the better the video quality
² different receivers may receive different numbers of layers according
to their channel quality
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² Thus, given this approach of using layered encoded video for video
dissemination, the WiMAX MAC is faced with the following problem
within any scheduling frame:
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for any time slot within the scheduling frame, which layer of which multicast group should be transmitted at what modulation coding level?
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References
1. “Fundamentals of Multimedia”, Chapter 17, Li & Drew cPrentice Hall 2003.
2. Ganesh Venkatesan (Intel), Alex Ashley (NDS), Ed Reuss (Plantronics), Todor
Cooklev (Hitachi),” IEEE 802 Tutorial: Video over 802.11”, March 2007.
3. M. Lindeberg, S. Kristiansen, T. Plagemann and V. Goebel, “Video Streaming
In Mobile Ad-hoc Networks Challenges and Techniques”, Department of
Informatics, University of Oslo, in Workshop: Multimedia in Wireless and
Mobile Networks, 15. June 2009.
4. Uilecan, I.V., C. Zhou, and G.E. Atkin, Framework for Delivering IPTV
Services over WiMAX Wireless Networks. IEEE EIT 2007 Proceedings, 2007: p.
470-475.
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References
5. James She, F.H., Pin-Han Ho, and Liang-Liang Xie, IPTV over WiMAX:
Key Success Factors, Challenges, and Solutions. IEEE Communications
Magazine, 2007. 45(8): p. 87-93.
6. IAN F. AKYILDIZ, TOMMASO MELODIA, KAUSHIK R.
CHOWDURY, “WIRELESS MULTIMEDIA SENSOR NETWORKS: A
SURVEY”, IEEE Wireless Communications ,December 2007
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Any Question
Thank you!Winter 2011
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