SPINDLE / DTN

1
Mobility and InteroperabilityAchieving Critical
Mass in Open DTN Technology
Rajesh Krishnan krash_at_bbn.com with inputs from
Michael Demmer, Kevin Fall, Lillian Dai, Tim
Brown, and Abraham Matta
NSF FIND-Mobility Workshop at BBN, Cambridge,
MA September 27, 2007
2
Agenda

• DTN what is fundamentally new about it
• DTN/BP as a unifying protocol framework
• Achieving critical mass for DTN/BP
• New agenda for mobile networking
• Other issues
• Note Thanks to everyone who provided inputs. I
  request participation from all present. Thanks to
  the scribe our goal should be to keep him busy.
  )

3
DTN What is Fundamentally New?Question/Propositi
on

• DTN can be viewed variously as
• algorithms and protocols to deal with
  special-case disrupted networks in which a
  contemporaneous end-to-end path is not available
• extending the scope of existing networking
  algorithms to include disrupted networks as well
  as stable networks adapting across heterogeneity
  in loads, delays, technologies, topologies, and
  traffic
• bringing storage/content squarely into the set of
  resources managed by the network (including at
  Layer 3), whereas traditionally managing storage
  and content has been an application layer concern
• a confluence of networking and databases (e.g.,
  declarative networking)
• a confluence of networking and logistics (e.g.,
  scheduled data mules)
• challenging the end-to-end principles, or if you
  prefer causing a reapplication of those
  principles under changing resource tradeoffs
• something else, ...
• What if any is really new and fundamental about
  DTN?
• What can DTN do that cannot be done just as
  easily or well in the application layer over the
  Internet?
• Is DTN just the new fad?

4
DTN What is Fundamentally New?Discussion (1/3)

• Demmer disconnections are expected, storage
  enables dealing with those
• Mostly a combination of b and c. It's an
  approach to bring link disruption into the
  expected from the exceptional. In other words,
  alink going up and down does not represent a
  network failure, but a characteristic. Storage is
  a necessary tool to handle these.
• Fall heterogeneity and flexible naming
• DTN is also targeted to handle highly
  heterogeneous networks and their protocol
  architectures (to tie them together). This
  relates to the way flexible naming is conceived.
  Maybe this is (g), as I don't really see it being
  brought out in the question.
• Demmer, Fall more than just multiplier, BP
  works over a wide range of nets
• Obviously we're biased, but we don't think the
  value of DTN/BP is just the multiplier effect. We
  spent a lot of time designing for a wide range of
  networks with input from several different
  sources and the architecture/protocol reflects
  this input.
• Matta Reinventing email?, DTN is for niche
  Internet stubs
• I think DTNs/sensor nets/MANETs will remain as
  (small) islands within the bigger Internet.
  Regarding DTN, it's not new -- email has been a
  DTN application )

5
DTN What is Fundamentally New?Discussion (2/3)

• Brown support both well/ill connected, storage
  is central to DTN, logistics is a special case,
  DTN routers determine network functionality while
  apps do not have that kind of control
• This (b) is a must. It seems that many DTNs will
  be well-connected a lot of the time so good
  behavior when the network is well-connected is
  important. Users will want networks that
  transparently move between both well-connected
  and disrupted domains, and behave well in both.
  It will also enable network designers to
  specifically provision for different link types
  intermittent, scheduled, opportunistic.
• This (c) seems to be a primary aspect of the DTN
  architecture. In E2E connected networks, storage
  is not the concern of routers they can just drop
  packets according to their own storage policies
  and resources, with only marginal performance
  impact (since at maximum powerbandwidth/delay,
  no storage is used anyways). In DTN, this isn't
  possible maximum power requires optimal storage
  allocation.
• This (e) seems like a special case of (a). (a)
  is an important first step in DTNs but would be a
  limited result if that was all we could
  accomplish. Eventually, we should be able to
  provision for different types of mobility,
  random, deterministic (scheduled), controlled.
  Mobility would be come a first-class resource
  within networks.
• Yes. In DTN, the routers (custodians) determine
  the functionality of the network whereas an app
  on top of the internet approach can only achieve
  what the connectedness of the Internet allows,
  assuming that app support isn't possible on
  routers. The eventually transportable networks
  are not amenable to apps on top of the internet.

6
DTN What is Fundamentally New?Discussion (3/3)

• Dai change the TCP paradigm, proactive relays,
  reduce delay
• Changing the TCP paradigm Mechanism to
  differentiate between network congestion and
  network disruptions.
• Opportunity to incorporate additional
  communication infrastructures If there are
  relays/data mules available, the trajectories of
  these relays can be controlled to reduce/mitigate
  delay. Under the DARPA Proactive Mobile Wireless
  Network program, we are looking at algorithms to
  proactively insert relay nodes and control their
  trajectories to improve probability of network
  connectivity. DTN protocols can be used
  synergistically to reduce delay during rare
  disconnection events.
• Reduce delay at the expense of using more
  communication and storage resources If I have a
  message to send, I can either wait for end-to-end
  connectivity (storing information at source) or
  send now and hope that at least one of the
  intermediate nodes can forward information to
  destination before I can.

7
DTN/BP as a Unifying FrameworkQuestion/Propositio
n

• Current mobile network, system, or application
  solutions are insular and do not interoperate.
  Due to a lack of common abstractions and
  implementations, it is often not possible to do
  fair comparisons of alternative solutions or to
  easily build upon each others' work to create a
  multiplier effect.
• Why not use the Bundle Protocol (BP) as the focal
  point for RD in mobile and nomadic computing, ad
  hoc networking, and content-oriented networking?
• What are the limitations if any of the BP and its
  implementations in terms of supporting your
  research vision?
• Are there good alternatives that could serve this
  role?
• What might be an alternative MANET
  interoperability layer?

8
DTN/BP as a Unifying FrameworkDiscussion

• Demmer, Fall Sure, BP has got nice features by
  design
• Perhaps not surprisingly, we find that the BP has
  several attractive characteristics for general
  use message-oriented payloads, flexible naming,
  extensible protocol features, and a reasonably
  efficient encoding (i.e. SDNVs Dictionary).
  There's no reason per se why it wouldn't be a
  good glue for mobile and disruption-tolerant
  networking.
• Demmer Could improve some BP features
• For some more self-consistency and protocol
  elegance when used in non-disrupted environments,
  I'd say that some of the DTN-specific features
  that are currently encoded in the primary bundle
  block could be moved into extension blocks, such
  as the alternate reply-to EID, the current
  custodian EID, perhaps the status report
  requesting flags, etc.
• Brown Some improvement to BP possible,
  micro-sensors need special treatment, need
  modular Click-like implementation, network coding
  may pose issues
• Everyone has their niche the BP (like all
  protocols) trades overhead (14 SDNVs in the
  header) for functionality. This is somewhat
  bloated and for a given research task (like our
  work in sensor data collection) it may be faster
  to implement a limited protocol. However, our
  experience is that as the BP has evolved and our
  needs have evolved our protocols have been moving
  closer to BP. At this stage, I think any
  parallel development of an alternative BP would
  only be marginally better (i.e. I don't see any
  killer features missing or poison pills present
  in the current implementation). Sensor nets
  might hack up the BP to fit into small packets,
  with mediators augmenting these bundles to the
  fully-fledged BP but this is a small niche. An
  approach, would be to specify the protocol in a
  more modular implementation (e.g. the Click
  Router) where components could be included or not
  included cleanly. Things like network coding
  might mean that nodes in a DTN receive increasing
  amounts of partial information without ever
  receiving a cleanly-delimited bundle. It's not
  clear what kinds of applications would use this
  network coding, yet.
• Matta DTN is weird, not yet convinced it is an
  elixir
• it seems strange to rely on randomly moving
  vehicles, randomly thrown-from-airplane sensors,
  or randomly .. etc. to do anything serious ) I
  don't know the details of BP, but I can't imagine
  it solves all of our internetworking problems.

9
Achieving Critical Mass for DTN/BPQuestion/Propos
ition

• One way for DTN/BP to be adopted widely and gain
  a critical mass is to create a successful
  application (similar to NCSA Mosaic which caused
  HTTP to become popular). Another way is to vector
  into as many devices as possible (similar to
  Bluetooth and IrDA technologies). A third way is
  to use it as a glue protocol between disparate
  mobile networks.
• What is the killer application for DTN, and if
  there is none, how can we achieve critical mass?

10
Achieving Critical Mass for DTN/BPDiscussion

• Demmer No killer app, DTN will transform but
  become invisible
• There shouldn't ever be a DTN-specific killer app
  -- it should be that the existing killer apps on
  the internet can be made disruption tolerant with
  appropriate shifts in API and protocols.
• Fall Generalized sync
• Generalized 'sync' is the killer app.
  Synchronization of databases, caches, backups,
  etc...
• Brown VANETs, disaster comm, maybe social
  networking
• ... vehicle nets, M2M computing, disaster
  communication.
• ... social networking (but SMS, mobile data, etc.
  are already delivered opportunistically over
  cellular networks. So what's new with DTN?)
• Krishnan Disruption-tolerant caching search
  pub-sub

11
New Agenda for Mobile NetworkingQuestion/Proposit
ion

• Provocative Research in MANETs have so far been
  largely irrelevant as far as commercial
  applications go. MANETs do not scale, do not
  take advantage of infrastructure whenavailable,
  and despite the proliferation of wireless
  devices, there is no hope of interoperability
  yet. MANETs have an inferiority complex and want
  to stay at the edge of the Internet.
• Should we set a new agenda for mobile networking
  research?
• What about rapidly formed high-speed mobile
  wireless transit ASes that can fix Internet
  partitions arising from say, multiple concurrent
  Katrina-scale disasters?
• Should the focus be on vendor-neutral
  interoperability all the way from applications to
  the physical layer?
• What about disruption-tolerant access to content
  (distributed content-flow management including
  caching, search, and publish-subscribe) as a key
  research agenda? What else?

12
New Agenda for Mobile NetworkingDiscussion

• Brown Network support for intelligent localized
  content distribution
• Network support for BitTorrent-like protocols for
  intelligent, localized content distribution.
  However, BitTorrent only worked when people
  started having high-bandwidth free-per-bit
  internet connections. Prior to that, there was
  no way I was going to pay to store-and-forward
  your bits. I think MANETs suffer from that
  problem right now, if I want to join your MANET,
  I have to pay for your bits (either by wasting
  power routing them, or by letting you use my
  EVDO/GPRS backbone). The power problem might get
  incrementally better the backbone problem will
  probably get much better. It seems that more
  work on MANET routing won't really help either.
  We're faced with as much a social problem as
  anything even on the Internet, how often does
  one let a friend have storage/services/processing
  power? People are still happy to rely on big
  service providers (YouTube, Blogspot, Facebook),
  rather than providing their own services.
• Demmer, Fall Content-based DTN
• Again perhaps we're biased, but we definitely
  agree that disruption-tolerant access to content
  is a key research agenda.
• Dai Application design to be delay tolerant
• I think the problem is that many of the key MANET
  application drivers are not delay-tolerant (ie.
  search and rescue, battlefield communication). Is
  there a way we can serve these delay-sensitive
  applications without grossly over-deploy or
  over-design the network? Should this be one of
  the areas of active research? The issue probably
  lies in the network architecture, and cannot be
  adequately resolved no matter how much we improve
  routing, resource allocation, etc.

13
Other QuestionsQuestion/Proposition

• Are there other questions related to mobility and
  interoperability that we should discuss today?

14
Other QuestionsDiscussion

• Demmer Application Interface
• How does DTN affect the programming abstractions
  that networking stacks provide to the application
  developer? For example, it seems clear that
  basing a networked program around an end-to-end
  pipe abstraction (i.e. a TCP socket) is
  inappropriate for frequently disrupted
  environments, but then what is the appropriate
  general alternative. Disclaimer I'm currently
  working on research work to address this exact
  question.
• Fall Security and Net Management
• Is there anything new/different in areas of
  security and management that DTN/BP or something
  similar would affect?
• Brown Standard simulators, GENI-DTN
  integration
• Should we standardize network simulators?
• How should GENI integrate DTN testing needs?