These days, the interests in challenged networks are increasing and many researches are performed to seek a reliable end-to-end connectivity under harsh environments, which have a long propagation delay, high error rates, low data rate, and intermittent connectivity. Delay Tolerant Network was introduced to provide challenged networks with reliable transmission and interoperability with an overlay network concept. In this paper, we present comprehensive overview of Delay Tolerant Network and introduce a study case about the implementation of this network. This paper is designed to encourage the exploration of this field by giving basic concept and also motivate to investigate this area by presenting a study case at the end section. --- Please contact to lailiaidi@gmail.com for download request

1. LailiAidi (aidi@kth.se)
Jung Changsu (changsu@kth.se)

2.  Many evolving wireless networks have
characteristics different from the Internet.
• The instability of the link
• Long propagation and queuing delays
• Extremely asymmetric data rate
• High link error rates
 Delay Tolerant networks are designed to provide
• reliable transmission
• Interoperable communications between wide range of
networks
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3.  The Interplanetary Internet initiative: find a solution
& suggestion network architecture, support reliable
transmission between a station on the Earth and
satellites, with an overlay network concept
 IRTF DTN Research Group: Interplanetary Internet
under challenged networks
 DARPA Disruption Tolerant Networking program:
Protocols for transmitting bundles to DTN nodes
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4.  Path and Link
• High Error and Asymmetric Rate
• Disconnection
• Long and Variable Delay
 Network
• Intermittent Connectivity
• Security
 End System
• Limited Longevity
• Low Duty Cycle Operation
• Limited Resources
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5.  Link-repair approach
Maintaining the end-to-end reliability and fate-sharing
model of Internet
 Network-specific proxy agent
Accessing internet from challenged networks, vice versa
 Message-oriented reliable overlay architecture:
Interoperability properties + Robust non-
interactive delivery semantics + CoS
 Store-and-Forward message switching:
Gateway concept - Hold data until it has a scheduled
transfer, In-network storage
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6.  Region
• Regional network concept
• Interconnect different networks
• Own communication protocol
• Unique ID
 Node
• Host: Sends or receives bundles and requires storage for
queuing bundles.
• Router: Forwards each bundles in the same DTN
region, requires storage to store incoming packets
• Gateway - support interoperability: interconnection
point, forwards bundles to other DTN regions with different
protocol stacks.
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7.  Bundle: message
• Bundle header: Fragmentation
• Control information: handling, storing, disposing
• Source-application’s user data
 Fragmentation
• To increase the possibility of delivery & increase
performance
• Proactive fragmentation
• Predicted Contact volume + Optimize its usage
• Reactive fragmentation
• disconnection while transmitting fragmented bundles + Send
smaller fragments
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8.  Bundle Layer
(2)
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9.  Class of Service
(2)
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10.  Name Tuple :
• Region: Globally unique, reduce forwarding tables size
• Entity Name: Identifier in specified region, not globally
unique
 Contact Knowledge Oracle:encapsulate particular
knowledge of network (Null, Contact Summary, Complete
Contact, Queuing, Traffic On Demand)
 Group Membership Oracle:encapsulate particular
knowledge of group dynamic (Local, Delay, Complete)
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11.  Objective: Maximize the probability of message delivery
• time-varying multi-graph: no guarantee of the availability
of the next hops link
• Asymmetric data rate sender vs. receiver
• high error rate link: retransmission
• Contact intervals and volumes: unknown precisely ahead
of time
 Routing Algorithm Class
• Zero Knowledge: Poor performance
• Complete Knowledge: Complete knowledge
• Partial Knowledge: Route message independently based
on the future traffic demand.
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12.  Single-copy technique:
• EMDDA: evaluating different routing metrics, no network
traffic consideration
• Deterministic node mobility assumption
 Multi-copy techniques:
• Flooding-based protocols: non resource-constrained
environments
• Quota-based protocols: resource-constrained
environments (quota flag to every message )
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13.  Unicast-based routing (UBR)
 Broadcast-Based Routing (BBR)
 Tree-Based Routing (TBR)
 Group-Based Routing (GBR)
 Context Aware Multicast Routing
 Static tree-based routing (STBR)
 Dynamic Tree-Based Multicasting Algorithm
(DTBR)
 Context Aware Multicast Routing (CAMR)
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14.  Issues in bundle layer
• Vulnerable to attack because it is an overlay network
• Bundles can be modified
• Unauthorized insertion of bundles.
• Accept only authenticated messages
 Bundle Security
• Authentication is carried out in routers and gateways
• Public-key cryptography
• both users and forwarders have their own key-pairs and certificates
• A sender uses its private key to sign bundles and create
bundle-specific signature.
• A forwarding node replaces the sender’s signature with its
own.
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15.  Open Issues in Bundle Security
• The level of flexibility
 The bundle security protocol prevents insecure combination of
application such as including plain-text signatures.
 Can support VPN but the complexity can cause high cost
• Key Management
 No key management schemes exist in DTN deployments
 Existing schemes need hard coding.
• Canonicalization of bundles
 Requires the same bytes of bundle of signature for integrity
 Bundles may be changed during traversal between nodes
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16.  Analyticalresearch, Mobility model
 Free-space Optical Communications: smart
mobile phone-based mobile ad-hoc networks
(MANETs)
 Radio Frequency (RF)
 Ultra-Wide Band (UWB)
 Acoustic (Sonar, Ultrasonic)
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17.  Outer Space / Deep-Space Networks
Inter Planetary Networks: communication
network robustness, timeliness data return
 Terrestrial Civilian Network
Mule Networks (ZebraNet), Challenge Links
(SenDT)
 Acoustic underwater networks
 Battlefield networks
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18.  Overview
• Developed by the University of Waterloo
• Providing low cost Internet services to the poorest villages
• Vehicles are used to deliver data
• Services:
 birth, marriage, and death certificates
 Medical consultation and agricultural problems
• Key concepts for a robust system
 Low-cost(70$/kiosk/month)
 low-power kiosk controller (6~8W)
 Using refurbished PCs without hard disks
 Free software
Figure 11. KioskNet overview
S.Guo, M.H. Falaki, U.Ismail, E.A. Oliver, S.UrRahman, A. Seth, M.A. Zaharia, and S.Keshav.
“Design and Implementation of the KioskNet System (Extended Version)”. [Online].
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19.  Components
• Kiosk
 Kiosk controller provide a network boot function, a network file
system, user management, and network connectivity
• Ferries
 a car, buses, motorcycles or trains
 contact with kiosk controllers and gateways using opportunistic ways
• Gateway
 connected to the Internet through DSL or broadband
 receives data from a ferry and uploads the data to the proxy
• Proxy
 Support communication between kiosk users and a legacy server
• Legacy Server
 Typical servers supporting applications such as IMAP, SMTP and HTTP
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20.  Security Architecture
• Entities
 KioskNet Franchisers, Franchisees, Users, Application Service providers
• Certificate
 All entities have a 2048-bit RSA key and a public key
 Proxy broadcasts a public key for users, franchisees and ASPs
• Infrastructure Integrity
 Digital signatures are used on all remote commands and software updates
from franchiser
• User data protection
 This system offers encrypted virtual space for each user’s home directory
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21.  The main goal of a DTN
• Interoperability
 between different kinds of networks in wide-ranging regions even
though many limitations
• Reliable transmission based on overlay network
 The implementation of DTNs will be a good solution for
challenged networks
• For example: KioskNet
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22. Questions?
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