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BITS PilaniPilani Campus

Advanced Computer

Networks (CS ZG525)Virendra S Shekhawat

Department of Computer Science and Information Systems

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BITS PilaniPilani Campus

First Semester 2015-2016Lecture-14 [10th Oct 2015]

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BITS Pilani, Pilani CampusFirst Sem 2015-16

Agenda

• History of Delay Tolerant Networking [CH-25]

– Lecture Slides

• DTN Architecture and Bundle Protocol [CH-26] – Reading

• A Delay-Tolerant Network Architecture for Challenged Internets [K Fall,

2003]

•

www.kevinfall.com/seipage/papers/p27-fall.pdf

3Advanced Computer Networks CS G525

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Topics…

• Challenged Networks and their Limitations

• Solutions

– Fixing Internet Protocols

– Delay Tolerant Networks (DTNs)

• DTN Architecture

– Bundle Protocol

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Introduction

• In 2002, Kevin Fall started to design terrestrial

networks, called as IPN

– termed this new architecture as Delay/Disruption Tolerant

Networks

• Initial efforts have been focused on combining the

solutions for MANETs and Sensor networks

• Later, such networks have also been termed as

challenged networks

Advanced Computer Networks CS G525

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Challenged Networks

• Characteristics

– Latency

– Bandwidth Limitations

– Error Probability

– Node Longevity (aka life time)

– Path Stability


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Path and Link Characteristics[1]

• High Latency Low Data Rate

– Transmission and propagation delay is proportional

to transmission medium (ignoring queuing delay)

– For transmission rates of 10 Kbps having delays in

the order of few seconds

• e.g. Underwater acoustic modems and low power radios

for sensor nodes

– Asymmetric data rates (downlink and uplink)

• e.g. Remote instruments, Military assets


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• Disconnection

– Disconnection due to fault (may occur in

conventional networks as well)

– Non-faulty disconnections occur due to motion

and low-duty-cycle system operation

– Disconnection due to low-duty-cycle is common

among low capacity devices (e.g. sensor networks)


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• Long Queuing Times

– Queuing delay is significant in multi hop paths (in sec)

– Due to disconnection queuing delay may become

large (hours, even in days)

• Problem:

– Source initiated retransmission becomes costly in

such networks


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Network Architectures

• Interoperability Considerations – Challenged networks are not designed with

consideration of interoperability as such

–

Getting communication between nodes itself isbiggest challenge!

• Security

– In challenged n/w bandwidth is a precious resource

hence uses should be authenticated – End to end authentication approaches are not

worth… Why?


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End System Characteristics

• Limited Longevity

– Nodes are placed in hostile environment like militarynetworks, sensor networks in coal mines etc.

– Node life is limited and long periods of disconnections

• Low Duty Cycle Operation

– To increase longevity for battery power operated nodes, lowduty-cycle is desirable

• Limited Resources

– Limited memory and processing power

– Implication: Previous data should be transmitted before newdata is produced otherwise node will loose the data


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Solutions

• Fixing Internet Protocols

– PEP, Boosters and Proxies

– E-mail

• Come up with an Additional Architecture

– Delay Tolerant Message Based Overlay

Architecture


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Fixing Internet Protocols

• PEP, Boosters and Proxies (aka middle boxes) – Discouraged by the IETF as violating the fate sharing

principle (connection state should reside only in endhosts)

– They may keep some information for connection state

– Proxies are application specific . Inter Proxycommunication is not exists at this point of time

• E-mail (aka asynchronous message delivery system) – Positives: Flexible naming, asynchronous message based

operation, and in-band error reporting

– Negatives: Lack of dynamic routing, Weakly defineddelivery semantics, lack of consistent applicationinterface


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Problems With TCP/IP Network

• IP routing drops a packet if next hop route is notavailable immediately

– Problematic with frequently disconnected links

• Internet’s fate sharing does not hold for many such

networks

– It may be quite useful to hand-off its end node connectionstate if it has other tasks to accomplish, particularly forpower or memory limited nodes

• Usually Internet applications are designed for lowdelay that may not be suitable for challengednetworks


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What is DTN…?

• A Delay Tolerant Networking architecture (DTN) providesinteroperability between different challenged networks

•

End to end message delivery is defined as “bundle layer”

• The “bundle layer” forms an overlay that employs

persistent storage to help combat network interruption

• Devices implementing the “bundle layer” are called DTN

nodes


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Delay Tolerant Message Based

Overlay Architecture

• DTN Architecture composed of regions and gateways• DTN Gateways are point which can serve as a basis for both

translation (region specific encodings) as well as enforce policy andcontrol information


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The Bundle Protocol

• The bundle protocol tiestogether the lower-layerprotocols

• Application programs can

communicate across the sameor different sets of lower-layerprotocols

• A bundle-protocol agent stores

and forwards entire bundles(or bundle fragments) betweennodes


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DTN Nodes


Source: Delay- and Disruption-Tolerant Networks (DTNs): A Tutorial - Version 3.2, Sept 2015

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Delay Isolation via Transport

Protocol Termination


Source: Delay- and Disruption-Tolerant Networks (DTNs): A Tutorial - Version 3.2, Sept 2015

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Custody Transfers

• The bundle protocol supports node-to-node

retransmission (at both the transport and the

bundle layers) by means of custody transfers

• A bundle custodian must store a bundle untileither

– another node accepts custody (ack is required here)

– expiration of the bundle’s time-to-live

• Points of retransmission progressively forward

toward the destination using Custody Transfers


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Classes of Bundle Service

• Custody Transfer – Delegation of retransmission responsibility

• Return Receipt – Confirmation by the destination to the source

• Priority of Delivery – Bulk, Normal, or Expedited

• Time to Live –

Congestion control is the main purpose of thisfunction

– Notion of congestion in DTN is insufficient memory tostore the bundle at DTN node


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End Points

• A bundle endpoint is a set of zero or more nodesthat all identify themselves by the same

endpoint ID

• An endpoint ID is a uniform resource identifier(URI) text string using the syntax

– :

–ex. dtn://abc/file1


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Path Selection and Scheduling

• Routes are made of contacts which arecommunication opportunities

• A contact has a number of parameters:

– Start & end times

– Capacity (aka buffer at nodes)

– Latency

– Endpoints

–

Direction• Problems include determining existence of

contacts, knowing the state of pending messagesand efficiently assigning messages to contacts


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Convergence Layer

• The bundle forwarding function requires anunderlying reliable delivery mechanism withmessage boundaries.

• An implementation of DTN would requiretransport-layer specific convergence layers

– For example, TCP would require a convergence layerto add message boundaries

• Reliable delivery can, at worst, be implementedwith timeouts and retransmission


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Time Synchronization

• DTN requires a form of time synchronization.

• It is used for:

– Identifying message fragments.

– Purging messages which have exceeded their lifetimes.

• The paper recommends time synchronization to on

the order of 1ms.

• It is questionable whether this would be possible inthe varied networks that DTN is supposed to work

with


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DTN Applications[1]

• Military and Intelligence – Mobile ad-hoc networks (MANETs) for wireless

communication and monitoring, cargo tracking, search and

rescue communication, unmanned aerial vehicle (UAV)

communication and control

• Public Service and Safety:

– Security and disaster communication, search and rescue

communication, humanitarian relief monitoring, smart-city

event-response, smart transportation networks, smartelectric-power networks, global airport-traffic control,

infrastructure-integrity monitoring, unmanned aerial vehicle

(UAV) communication and control, remote learning


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DTN Applications[2]

• Environmental Monitoring: – Animal migration, soil properties and stability,

atmospheric and oceanographic conditions,

seismological events• Undersea Communication:

– Submarines, unmanned undersea vehicles, oil and

mining undersurface sensors. Beneath the surface of

water, only sound is effective for communication over

distance, and the speed of sound in water is only

about 1 km/sec


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DTN Applications[3]

• Commercial

– Cargo and vehicle tracking (by road, rail, sea, and air),

in-store and in-warehouse asset tracking, data

transactions (e.g., financial, reservations),agricultural crop monitoring, processing-plant

monitoring, communication in underground mines

• Space Agencies

– International Space Station communication

(currently operational for research), interplanetary

communication, future space-debris monitoring.


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Thank You !

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Documents

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