Advanced Computing Techonologies

1. KARPAGA VINAYAGA COLLEGE OF ENGINEERING & TECHNOLOGY
G.S.T Road, Madhuranthagam Taluk, Kanchipuram – 603 308
Seminar on
Advanced Computing Techonologies
Dr.A.Kathirvel
Professor & HoD M.E-CSE
13.12.2011

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Delay-Tolerant Network

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Outline
 Introduction
 Challenged Internet
 Fixed The Internet Protocols
 A Delay Tolerant Message Based Overlay
Architecture
 Application Interface
 Related Work
 Conclusion

4. DTN - Introduction
 Delay-tolerant networking (DTN) is an approach to computer
network architecture that seeks to address the technical issues in
heterogeneous networks that may lack continuous network
connectivity. Examples of such networks are those operating in
mobile or extreme terrestrial environments, or planned networks in
space.
 Recently, the term disruption-tolerant networking has gained
currency in the United States due to support from DARPA, which
has funded many DTN projects. Disruption may occur because of
the limits of wireless radio range, sparsity of mobile nodes, energy
resources, attack, and noise.

5. DTN Status
 Spring of 2002: Internet Research Task Force research group
DTNRG formed to articulate DTN concepts.
 Summer of 2002: first demonstration of initial Bundling
implementation.
 March 2003: peer review of DTN architecture Internet Draft.
 May 2004: DARPA issues BAA (Broad Agency Announcement) for its
DTN research program.
 July 2004: version 01 of LTP Internet Draft published.
 Version 02 editing is in progress.
 Stephen Farrell is working on the first implementation.
 September 2004: version 03 of Bundling protocol spec Internet
Draft published.
 November 2004: initial meeting of CCSDS DTN BOF.

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Introduction (cont.)
 Three key assumption to achieve today’s end-to-
end inter-process communication
1.An end-to-end path exists between a data
source and its peer(s).
2.The maximum round-trip time between any node
pairs in the network is not excessive.
3.The end-to-end packet drop probaility is small.

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Introduction ( cont.)
 Challenged network :
1.Terrestrial Mobile Networks:
2.Exotic Media Networks:
3.Military Ad-Hoc Networks:
4.Sensor/Actuator Networks:

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Introduction ( cont.)
 Some approaches to adapt Internet to unusual
evironments:
1.Link-repair approaches : engineer problem
links to appear more similar to the types of links
for which TCP/IP war designed.
2.To attach them to only the edge of the
Internet by means of a special proxy agent.(but
does not provide a general way to use such
networks for data transit.

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Introduction
 We suggest a general purpose message-oriented
reliable overlay architecture as the appropriate
approach to tie together such networks, forming
an”internetwork of challenged internets.”
 Its design is influenced by the internet
design( interoperability),the roust noninteractive
delivery semantics of electronic mail, and
USPostal System.

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CHALLENGED INTERNETS(cont.)
 Path and Link Characteristic
1.High Latency, Low Data Rate.
2.Disconnection: Non-faulty disconnections
A. Motion:
B. Low-duty-cycle
3.Long Queuing Times

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CHALLENGED INTERNETS(cont.)
 Network Architectures
1.Interoperability Considerations: Some network
tend to be comparatively simple and local in scope, and
may fail to provide even the baseline abstractions that
are well-match for supporting layered protocol families
(such as Internet).
2.Security: end-to-end-only approaches typically
require some exchange of challenges or keys ,which
would be undesirable for high-delay and disconnection-
prone networks.

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CHALLENGED INTERNETS
 End System Charateristics
1.Limited Longevity : sensor network
2.Low Duty Cycle Operation
• Motion
• Low-duty-cycle
3.limited Resources

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FIX THE INTERNET
PROTOCOLS?(cont.)
 Two limits of PEPs (Performance
Enhancing Proxies), Boosters and Proxies :
 Specific command to specific network: Limits
the ability to re-use the proxies for different
applications.
 Fails to take advantage of any special
resources the proxy node may have to offer .

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FIX THE INTERNET
PROTOCOLS?(cont.)
 Electronic Mail
 Provides an abstractions that comes close to
addressing many of the problems posed by
challenged networks. Such as its flexible
naming ,asynchronous message-based
operation, and in-band error reporting.
 Email falls short due to its lack of dynamic
routing, weakly-defined semantics, and
consistent application interface.

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FIX THE INTERNET PROTOCOLS?
 Motivation for an Additional Architecture
Such a system should combine:
 Overlay routing capability such as is present in
peer-to-peer system with delay-tolerant and
disconnection-tolerant properties of electronic mail.
 Provide a gateway function between radically
dissimilar networks

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A DELAY TOLERANT MESSAGE
BASED OVERLAY
ARCHITECTURE(cont.)
 Regions and DTN Gatways

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A DELAY TOLERANT MESSAGE
BASED OVERLAY ARCHITECTURE
(cont.)
 Form of Name Tuples :
{Region Name, Entity Name}
ex: {internet.icann.int,
http://www.ietf.org/oview.html}

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A DELAY TOLERANT MESSAGE
BASED OVERLAY ARCHITECTURE
(cont.)
 Path Selection and Scheduling
Routes are comprised of a cascade of
time-dependent contacts used to move
messages from their origins toward their
destination.

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A DELAY TOLERANT MESSAGE
BASED OVERLAY ARCHITECTURE
(cont.)
 Custody Transfer and Reliability
 Custody transfer is akin to delegating
responsibility for delivering postal mail to a
person or service that promises (or contracts )
to do so.
 Reliability is depending on end-to-end
reliability.

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A DELAY TOLERANT MESSAGE
BASED OVERLAY ARCHITECTURE
(cont.)
 Convergence Layers and Retransmission:

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A DELAY TOLERANT MESSAGE
BASED OVERLAY ARCHITECTURE
(cont.)
 Time Synchronization
The DTN architecture requires a coarse level of
(relative) time synchronization, which is used for
identifying message fragments and also for
purging messages that have exceeded their
source-specified lifetimes.

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A DELAY TOLERANT MESSAGE
BASED OVERLAY ARCHITECTURE
(cont.)
 Security
 Each message includes an immutable
“postage stamp” containing a verifiable
identity of the sender, an approval of the
requested CoS(class of service).

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A DELAY TOLERANT MESSAGE
BASED OVERLAY ARCHITECTURE
 Congestion and Flow Control
 Proactive method: involve some form of
admission control to avoid the onset of
congestion in the first place.
 Reactive method: used which usually result in
degraded performance

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APPLICATION INTERFACE (cont.)
 The DTN architecture is built as an overlay
network using messages as the primary unit of
data interchange.
 Application making use of the architecture must
be careful not to expect timely responses and
must generally be capable of operating in a
regime where a request/response turn-around
time exceeds the expected longevity of the client
and server processes.

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APPLICATION INTERFACE (cont.)
 Applications must be prepared to handle the
creation and manipulation of name tuples and
their registrations (for demultiplexing received
messages), class of service specifiers, and
authentication information.
 The application interface is non-blocking, and
callback registrations are persistent.
 All DTN applications should be structured to
continue operating in the face of reboots or
network partitioning.

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RELATED WORK (cont.)
 Store-and-forward routing :
 ZebraNet : sensor node (attached to animal).
 DataMules: powepower saving ( traveling
mule).
 The architectural thinking :
Interoperability and layering is guided by
principle of ARPANET/Internet

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CONCLUSION
 The design embraces the notion of
message switching with in-network
storage and retransmission, late binding of
names, and routing tolerant of network
partitioning to construct a system better
suited to operation in challenged
environments than other existing network
architectures.