Transcript Slide - SmartLab

The long, interesting tail of Indie TV
Daniel Cutting, Aaron Quigley, Björn Landfeldt
CTSB Workshop, Pervasive 2006, 7th May 2006
Indie TV
• Producing video content is now easy and cheap
• More publishers and more niche content
• Already specialised TV channels on the web appealing to
niche audiences
• Sail.tv, Democracy TV, YUKS TV
• Logical conclusion is a tailored channel for each viewer
based specifically on their interests
Implicit group messaging
April 28, 2006 Slide 2
Indie TV
• Indie TV has 3 components, Creators, the Disseminator,
and Blenders
• Content is produced by creators who describe its
audience in terms of interests
• E.g. a dramatic thriller is destined for an audience
interested in “drama” and “thrillers”
• The Disseminator delivers the content to this audience
• The Blenders combine content as it arrives for playback
• We focused on the dissemination aspect only
Implicit group messaging
April 28, 2006 Slide 3
Indie TV
Implicit group messaging
April 28, 2006 Slide 4
Dissemination via “implicit groups”.
• Explicit groups
• Viewers named
• Pre-defined by creator
or viewers need to join
• Kim, Julie
Implicit group messaging
April 28, 2006 Slide 5
• Implicit groups
• Viewers described
• Creator defines “on the
fly”, viewers don’t need
to join
• Drama & Thriller
Implicit group messaging.
• Multicast messages from any source to any
implicit group at any time in a P2P network
• Each peer described by interests, e.g. “Drama”, “Sci-Fi”
• Implicit groups are specified as logical expressions of
attributes, e.g. “Drama AND Thriller”
• System delivers messages from creators to all viewers
matching target expressions
• Iterative design process
• Theoretical, implementation, simulation, theoretical…
Implicit group messaging
April 28, 2006 Slide 6
Initial theoretical model.
• A fully distributed, structured overlay network
• Peers maintain a logical Cartesian surface (like CAN)
• Each peer owns part of the surface and knows neighbours
• Peers geometrically ROUTE to locations by passing from
neighbour to neighbour
Implicit group messaging
April 28, 2006 Slide 7
Initial theoretical model.
• Peers’ locations on the
surface determined by
their attributes
Benoit {Action, Thriller}
Kim {Drama, Sci-Fi, Thriller}
Julie {Drama, Thriller, Romance, Action}
Implicit group messaging
April 28, 2006 Slide 8
Initial theoretical model.
• Can calculate all regions
on the surface where the
matching viewers must
exist
• Multicast content from
creators to the regions
matching the audience
description
Implicit group messaging
April 28, 2006 Slide 9
Initial implementation.
• OMNeT++/INET simulation of a real network
• The simulation raised some concerns we had not
considered in the initial design
• The overlay hop between peers on the surface resulted in
many IP hops at the network layer which led to extremely
long end-to-end delays
• The design was adequate for large/medium implicit groups
but required too much overhead for small groups
Implicit group messaging
April 28, 2006 Slide 10
Revised theoretical model.
• The simulation led us to revise the model taking these
problems into account
• To counter the latency problem, we stored pointers to
the peers on the surface, rather than locate the peers
there themselves
• This allowed us to have peers that were physically close to
be close on the surface, regardless of their attributes
• To counter the group size problem, we introduced a
hybrid approach
• Smaller groups used a distributed index to find members
• Initial model retained for large groups
Implicit group messaging
April 28, 2006 Slide 11
Distributed index.
• Every peer registers
at a rendezvous point
(RP) for each of its
attributes
• Every registration
includes IP address
and all attributes
Implicit group messaging
April 28, 2006 Slide 12
Distributed index.
• To CAST, select one
term from target
• Route CAST to its RP
• RP finds all matches
and unicasts to each
Implicit group messaging
April 28, 2006 Slide 13
Evaluation.
• New implementation’s
performance was vastly better
• Delay was greatly reduced and within required limits
• Overall network peer and link stress was also reduced,
especially when delivering content to small or empty
groups (load was now proportional to group size)
Implicit group messaging
April 28, 2006 Slide 14
Conclusion.
• We had an elegant theoretical model to begin with
• But, abstracted details of the system too much
• A structured overlay network has to be based upon
physical computer network with peers, routers, fast and
slow network links
• The possibility of highly variable group sizes had been
similarly neglected
• Implementing the simulation brought these problems to
the fore and allowed a quick revision of the theoretical
model
Implicit group messaging
April 28, 2006 Slide 15
Questions?
Implicit group messaging
April 28, 2006 Slide 16