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Issues in Distributed Multimedia
SystemsJoseph C. (JC) Montminy, III and James MacGlashan
CMSC 621, Advanced Operating SystemsDr. Deepinder Sidhu
October 23, 2007
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What is a distributed multimedia system?
• Networks of personal devices that deliver different types of content (audio, video, web, etc) [1]– Cell phones, MP3 players, PDAs, etc.– Must consider devices beyond
traditional “computers” (Marculescu et al.)
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A Real-World Example:Broadcasting The Price Is Right over TV, the
Internet, and Mobile Phones
TPIR image courtesy http://l.yimg.com/img.tv.yahoo.com/tv/us/img/site/72/33/0000037233_20070118115905.jpgSet image sourtesy http://www.cbs.com/daytime/price/slideshow/new_sets/index.php?id=101_11 VCast image Courtesy http://www.geniusdv.com/weblog/archives/Vcast.PNGComcast image courtesy http://www.wtmy.com/comcast.jpg Innertube image courtesy http://www.cbs.com/innertube/
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Networking Issues
• We have the problems that exist in pervasive networks [4]– Devices may be mobile and their connection
may change during transmission– The environment is dynamic– Heterogeneous devices that may be running
different architectures
• We have streaming data [4]– May need to synchronize multiple feeds to
achieve QoS
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Networking Issues continued
• Minimize Latency [3]– Time delay to send a packet
• Minimize Jitter [3]– Variance in the latency of each packet
• Maximize Bandwidth [3]– Amount of data which can be
sent/received at once
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What are some of the challenges in distributed multimedia?
• Power [3]– Personal devices have a finite power supply,
unlike traditional personal computers– Two processes that consume power
• Computation on the device• Receiving and sending data from device
• QoS [3]– Different data have different needs– Connection quality can change rapidly– Power consumption vs. QoS must be
considered
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What are some other challenges in distributed multimedia?
• Device Architecture [3]– What types of chips are appropriate for
mobile media-playing devices?– Standard computer chips may be
excessive and a power drain• Security/Copyrights [2]
– How do media providers ensure that their content is not abused or misused once it is delivered to clients?
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Challenges continued...
• What is the scale of the network? [3]– Large networks may require distribution of
servers to maintain QoS
• Direction flow of media [3]– Will media always be requested from a known
source, or is every node a potential server of media?
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Real World ExampleiPhone w/ Youtube
• Challenges [1]– Designed for desktops
– Limited power
– Variable network quality
– Flash based multimedia
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Real World ExampleiPhone w/ Youtube
• Solutions [1]– Convert videos to H.264
on Youtube servers (Apple)
– Use hardware H.264 decoder on iPhone
– Buffer data as it arrives, delay start of video stream
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Copyright Enforcement in Distributed
Multimedia [2]
• This paper primarily addresses the issue of
distributing media to clients while also
ensuring this distributed media is only
used in ways agreed to between the client
and the administrator of the media.
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The Pitfalls of Media Distribution
!
COPIES: 0PRICE/COPY: $100EXPECTED REVENUE: $0ACTUAL REVENUE: $0
COPIES: 1PRICE/COPY: $100EXPECTED REVENUE: $100ACTUAL REVENUE: $100
COPIES: 5PRICE/COPY: $100EXPECTED REVENUE: $500ACTUAL REVENUE: $100
Legal Acquisition
Illegal A
cquisi
tion
Illegal Acquisition
Illegal Acquisition
Illegal Acquisition
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An Alternative: Distributed Multimedia with
Enforceable Contracts• Owner and end user agree on contract terms.
– What kinds of operations (read, alter, save) may be applied to the media?
– How many times may be operations be executed?
– What are the costs of the operations?
• Owner sends the end user the media, along with a special tool to use the media.
– The tool enforces the rules agreed to in the contract.
– The media is very difficult for the end user to use without the tool.
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Media
Distributed Media with Enforceable
Contracts in Action
Tool
View
Copy
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Securing Distributed
Multimedia Components [6]• We may have an array of multimedia sources
(input devices) and sinks (output devices) on
multiple nodes within a network.
• There are multiple security concerns:
– We must keep the user’s connection to the system
secure.
– We must keep the communication between devices on
the distributed system secure.
– We must ensure that users can only use and connect the
devices they are authorized to access
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An Example of Using Components in a Distributed
Multimedia System: A Videoconference
This example was also introduced in the original paper; we are illustrating it here.
InternetInternet
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The Need for Authentication: Preventing the Improper
Connection of Components
This example was also introduced in the original paper; we are illustrating it here.
InternetInternetTOP SECRET
TOP SECRET
TOP SECRET
SECRET
Conversations can only be broadcast to the same level
The broadcast should have never
reached this machine!!!
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The Need for Authentication: Preventing Unauthorized
Access to Information
This example was also introduced in the original paper; we are illustrating it here.
InternetInternet
TOP SECRET
UNCLASSIFIED
TOP SECRE
T
SECRET
An unauthorized user should not be able to access secured
components!
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Logistical Concerns
• Securing Communication Between Devices
– Use hardware-implemented encryption algorithms
instead of software for speed
• Authentication Between Devices
– A distributed authentication scheme such as Kerberos
can be used.
• Authentication Between the Server and the Client
– Can use established authentication algorithms.
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The Switchboard Matrix• Each node maintains an access control matrix for its components
– Components can be both physical (cameras, microphones) and software (duplication, compression algorithms, etc)
• The matrix entry for a particular component has two portions
– Attributes – What features of a component is a client allowed to access?
– Operations – What actions is a client allowed to take with a given component?
• Connection beyond the server hosting the component is considered an “operation”
– Allows easy access checking for information export.
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Example of a Switchboard Entry
This example is adapted from the original paper.
User1
…
Userk
Professor
…
Usern
Device1 … Devicej … Devicem
LCD Projector
AttributesTV In
DVD InComputer In
OperationsPower ONPower OFF
FocusShift Image
Enlarge Image
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Example of a Switchboard Entry
This example is adapted from the original paper.
User1
…
Userk
Technician
…
Usern
Device1 … Devicej … Devicem
LCD Projector
AttributesTV In
DVD InComputer In
OperationsPower ONPower OFF
FocusShift Image
Enlarge Image
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Multimedia Based Content Distribution Networks [6]
• Distributed network with servers spread out geographically
• Network is established to store and send content to clients
• When a client requests content, the 'best' server in the network with the content must be chosen for handling the request
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Issues with a Multimedia CDN
• A higher QoS demand than CDNs for static
files (i.e. images, documents)
• A server does not only need to be able to
host content, but must also be able to
provide content in a format usable by the
client
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Solutions to issues
• Chosen server must satisfy a clients QoS
requirement
• Store multiple copies of the content in different
formats
• Support format transcoding on the fly
• Grid based CDN may be utilized to manage
requirements
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Grid Architecture
• A grid network is a network composed of grid
‘nodes’
• A node contains a number of different elements
which can be composed of numerous servers
• Common elements include: Server Element,
Computing Element, Worker Element
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Grid Architecture cont…
• Server Element generally hosts data
• Worker Element handles execution of processes
• Computing Element manages Workers
• Client initiates communication with network via a
resource broker which selects a grid node to
service the client
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Grid Architecture for a Multimedia
CDN• SEs host media content, usually in multiple formats
• WEs can handle transcoding of the content into different
file formats to provide to the client and then store result
on the SE for later requests
• Select Grid node based on content availability, speed to
client, and ability to provide file in correct format (via
stored data or real time transcoding)
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Further Complications
• The closest grid node with the content may not
be best to transcode the content
• Allow for one node to act as a content server and
a different node to handle transcoding
• In addition to content availability and speed to
client, workload and intranode speed must be
considered
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Node Selection Architecture
• Incorporate multiple monitors to facilitate selection process
• Transcoder Hub stores latency distances between node elements
and node elements to UI
• Content Tracer finds SE with desired content
• Transcode Monitor finds free available transcoders
• Computing Element Tracer monitors load of active transcoders
• Transcode Selector chooses best pair of SE and CE for transcoding
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Sequence of Events for Request
which Requires Transcoding
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1. Request is made from a Client’s Grid Interface
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2. Transcode Selector queries Content Tracer for content servers with desired content
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3. Transcode Selector queries Transcode Monitor for available transcoders
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4. Transcode Selector queries Transcode Hub for distances between available nodes and between client interface
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5. Transcode Selector queries CE Tracer for the loads of all transcoders including ones too busy to respond to the transcode monitor (useful if all transcoders were busy).
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6. Transcode Selector chooses best pair of SEs and CEs for request and has CE Tracer allocate the task to the chosen CE and update its load status
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7. Chosen CE will inform Transcode Hub if it is now too busy for additional requests
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8. Chosen CE will retrieve content from the chosen SE, initiate processing of it and return the result to the client interface and store the new format for later requests
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Sources
• [1] Apple (http://www.apple.com/pr/library/2007/06/20youtube.html)
• [2] Evans, David. An Architecture for Enforcement of Usage Contracts in Distributed Multimedia Systems. Proceedings of the 1996 conference of the Centre for Advanced Studies on Collaborative research, November 1996.
• [3] Marculescu, Radu et al. Distributed Multimedia Design: A Holistic Perspective. Proceedings of the conference on Design, automation and test in Europe - Volume 2, 2004.
• [4] Tanenbaum, Andrew S. and Maarten van Steen. Distributed Systems: Paradigms and Principles, 2nd ed. Upper Saddle River: Pearson Prentice Hall, 2007.
• [5] Novelli, G., Pappalardo, G., Santoro, C., and Tramontana, E. 2007. A grid-based infrastructure to support multimedia content distribution. In Proceedings of the Second Workshop on Use of P2p, GRID and Agents For the Development of Content Networks (Monterey, California, USA, June 25 - 25, 2007). UPGRADE '07. ACM, New York, NY, 57-64. DOI= http://doi.acm.org/10.1145/1272980.1272983
• [6] Zimmerman, Chris. Making Multimedia Systems Secure: The Switchboard Approach. ACM SIGOPS Operating Systems Review, Vol. 28, Issue 1, January 1994.
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Questions?
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Issues in Distributed Multimedia
SystemsJoseph C. (JC) Montminy, III and James MacGlashan
CMSC 621, Advanced Operating SystemsDr. Deepinder Sidhu
October 23, 2007