Delay-tolerant Networking at TKK Comnet

NEW: Various DTN applications now available
NEW: The ONE simulator for DTNs v1.2.0
NEW: DASM v0.3: DTN Implementation for Symbian

Delay-tolerant Networking (DTN)

DTN in an emerging research area that takes a different approach to (inter)networking and allows to work in stressed as well as in highly heterogeneous environments. DTN features a number of unique properties which make this concept applicable to challenged networking environments in which traditional communication paradigms would fail or perform rather poorly:

Communication based upon asynchronous messaging
No reliance on end-to-end path at any point in time
Store-and-forward delivery as well as physical data carriage
Deterministic and/or probabilistic routing

For encompassing information on DTN in general look at the DTN Research Group in the Internet Research Task Force (IRTF)

DTN RG Architecture

The DTNRG has developed an architecture for Delay-tolerant networking that has emerged from the efforts on Interplanetary Internet (IPI). The basic concepts find their application in sensor networks, interpersonal communication (people or "pocket-switched" networks), and in mobile Internet access.

Exchange of Bundles hop-by-hop via Bundle Protocol Agents
Bundle Protocol across different internetworks
Convergence layer provides mapping to lower layer
Custody transfer for reliability
Support for end-to-end semantics at the application layer

Working with DTNs requires reconsidering the way in which application protocols operate since delays and disruptions have to be considered the default. This means that highly interactive application protocols do not operate well in DTN environments, nor do security or reliability mechanisms that require multiple end-to-end handshakes. And the otherwise ubiquitously available Internet infrastructure services (DHCP-based autoconfiguration, DNS lookups, certification validations, etc.) are likely out of reach or at least not directly accessible. At the same time, store-carry-and-forward operation of DTNs offers unique properties for enabling communication in challenged environments and for efficient cooperation between mobile nodes.

In our DTN research, we focus on applications run by (mobile) human users, with different degrees of mobility and changing mobility patterns. We specifically look at

protocol design in general,
applications for DTN-based communications,
ways of exploiting DTN characteristics for communication and cooperation in mobility communities,
mobility models and DTNs in mobile ad-hoc networking, and
enabling DTN communication for embedded devices as part of daily life and work routine.

General Publications

Mikko Pitkänen, Jörg Ott: Enabling Opportunistic Storage for Mobile DTNs. Journal on Pervasive and Mobile Computing, Elsevier, to appear.

Mikko Pitkänen, Ari Keränen, Jörg Ott: Message Fragmentation in Opportunistic DTNs. Proceedings of the Second WoWMoM Workshop on Autonomic and Opportunistic Communications (AOC) 2008. [PDF]

Mikko Pitkänen, Jörg Ott: Redundancy and Distributed Caching in Mobile DTNs. Second ACM SIGCOMM Workshop on Mobility in the Evolving Internet Architecture (MobiArch), Kyoto, August 2007. [PDF]

Jörg Ott, Mikko Pitkänen: DTN-based Content Storage and Retrieval. Accepted for publication at the First WoWMoM Workshop on Autonomic and Opportunistic Communications (AOC) 2007. [PDF]

Jörg Ott: Application Protocol Design Considerations for a Mobile Internet. 1st ACM MobiArch Workshop, San Francisco, December 2006. [PDF] [Slides]

DTN in Support of general application (e.g., for Drive-thru Internet)

In the Drive-thru Internet Project, we have developed a dedicated protocol architecture to support users potentially moving at high speeds and experiencing opportunistic intermittent connectivity in accessing Internet services. We have performed experiments with mail transmission and reception, with interactive web access, and are also looking into aspects of interactive services.

Code

A DTN-enabled web server will shortly be available for download here. It uses the Ruby DTN2 bindings developed Uni Bremen for the DTN Reference Implementation.

Publications

Jörg Ott, Dirk Kutscher: From Drive-thru Internet to Delay-tolerant Ad-hoc Networking. Book chapter in Marco Conti, Jon Crowcroft, Andrea Passarella (eds): "Mobile Ad-hoc Networks: From Theory to Reality." Nova Science Publishers, Inc., ISBN 978-60021-605-3, 2007.

Lauri Peltola: Enabling DTN-based Web Access: the Server Side. Msater Thesis, Helsinki University of Technology, Department of Communications and Networking, April 2008. [PDF]

Jörg Ott, Dirk Kutscher: Bundling the Web: HTTP over DTN. WNEPT Workshop 2006. [PDF]

Jörg Ott, Dirk Kutscher: Applying DTN to Mobile Internet Access: An Experiment with HTTP. Technical Report TR-TZI-050701, Technologiezentrum Informatik, Universität Bremen, July 2005. [PDF]

DTN for Mobile and Ad-hoc Networking

Mobile communication services rely on wireless infrastructure provided by third party operators even if communicating peers are in reasonable geographical proximity. Ad-hoc networking between powerful mobile devices may allow bypassing such infrastructure or partly replacing as a backup where no such infrastructure is available or the infrastructure is temporarily not (fully) operational.

However, mobile ad-hoc networking usually seeks to mimic IP-style connectivity because present applications require end-to-end communications. In practice, the limited effective node density makes the existence of an end-to-end (for a sufficient period of time) unlikely because

Number of mobile users with mobile devices in an area
Only some of them are actually in communication range
Not all devices are interoperable
Users may not be willing to cooperate (battery, memory)

The DTN approach may provide one suitable mechanism to allow operation also in sparse (mostly or often disconnected) environments, provided that applications and application protocols are adapted to deal with the different conditions.

This research is carried out in close cooperating with Uni Bremen TZI where the Kasuari emulation framework has been developed which we have used for our joint work on DTN-MANET integration.

Publications

N. Asokan, Kari Kostiainen, Philip Ginzboorg, Jörg Ott, Cheng Luo: Applicability of Identity-based Cryptography for Disruption-Tolerant Networking. Proceedings of the First International MobiSys Workshop on Mobile Opportunistic Networking (MobiOpp), June 2007. [PDF]

Jörg Ott, Dirk Kutscher, Christoph Dwertmann: Integrating DTN and MANET Routing. Proceedings of the SIGCOMM CHANTS Workshop, September 2006. [PDF] [Slides]

Mobility Models and Simulations

We have designed the Opportunistic Network Environment (ONE) Simulator which provides a powerful tool for generating mobility traces, running DTN messaging simulations with different routing protocols, and visualizing both simulations interactively in real-time and results after their completion. The ONE simulator comprises three major components:

The mobility generator which provides a flexible means to create group mobility on a surface. Nodes may be subdivided into different groups with different movement attributes and other properties (e.g., storage space, radio range) per group. This allows distinguishing between pedestrians, vehicles, stationary devices, among others. The space may be organized according to city maps derived from GPS data; these maps may further augmented using map editors to define, e.g., bus/tram stops, park areas, etc.
The mobility generator produces a text-based mobility trace file as output which can be fed into the ONE simulation engines or exported to be used with other simulators (such as ns2 and dtnsim2).
The DTN simulation engine is a discrete event based simulator for DTN messaging. It takes the mobility trace file from the mobility generator as input (but also accepts other mobility files and real-world traces, such as those archived by the CRAWDAD project at Dartmouth). An externally generated message pattern file is used to control transmission of messages (size, source, destination), and the engine can additionally generate replies to incoming messages (which can also be specified in the external file).
The current release of the engine implements four different DTN routing protocols (flooding, epidemic, spray-and-wait, PRoPHET), with further ones being under development.
The engine generates a set of output files containing many details as well as aggregated statistics about the simulation runs.
The visualizer operates on the output of the simulation engine. It comes essentially in two parts: the real-time visualizer instantly analyzes the simulation engine output and shows how nodes mode on the defined surface, how many messages they carry, and many details about the communications going on. Interactive controls allow focusing on selected nodes or selected events and even support breakpoints in the simulations when predefined events occur.
The non-real-time components consists of a set of scripts for postprocessing and visualizing the simulation results.

The ONE Simulator Code

The ONE simulator is written in Java. Design and implementation are by Ari Keränen. It is published under GPL and its version 1.2.0x is now available for download here.

Publications

Frans Ekman, Ari Keränen, Jouni Karvo, and Jörg Ott: Working Day Movement Model. 1st SIGMOBILE Workshop on Mobility Models for Networking Research, Hong Kong, May 2008. [PDF]

Frans Ekman: Mobility Models for Mobile Ad Hoc Network Simulations. Master Thesis, Helsinki University of Technology, Department of Communications and Networking, May 2008. [PDF]

Ari Keränen and Jörg Ott: Increasing Reality for DTN Protocol Simulations. Technical Report, Helsinki University of Technology, Networking Laboratory, July 2007. [prelimenary PDF] (official PDF with ISBN to come)

DTN for embedded mobile personal devices

To support DTN-based mobile (inter)personal communications, we are investigating, in addition to our aforementioned work on Drive-thru Internet, DTN for embedded mobile devices.

DTN for Nokia 770, N800, N810 Internet Tablets

We have done a simple and straightforward port to the Linux-based Nokia 770/800 Internet tablets. The Berkeley DTN reference implementation compiles quite nicely in the Scratchbox development environment. As applications, we are looking an email gatewaying and have a prototype of our dtntcp DTN-based web proxy/gateway working on a 770/800.

Running the DTN reference implementation (UC Berkeley)
Sample application for HTTP-over-DTN
Further applications under development
Interacts with PC-based peer applications via WLAN

DTN for Symbian Mobile Phones

We have developed a Symbian-based implementation of the DTNRG bundle protocol and the TCP convergence layer spec from the DTN reference implementation. We have also include a Bluetooth convergence layer. Some characteristics:

Plug-in concepts for convergence layers and routing
Interoperable with DTN reference implementation
Sample application for multimedia messaging
Interacts with PC- and 770/800-based applications

DTN communication is presently restricted to WLAN and Bluetooth but we are working on convergence layers for GPRS and multimedia messaging, too. We are presenting the implementation at a demo at the RealMAN 2006 Workshop for which the paper and the poster are available.

Publications

Tuomo Hyyryläinen, Teemu Kärkkäinen, Cheng Luo, Valdas Jaspertas, Jouni Karvo, Jörg Ott: Opportunistic Email Distribution and Access in Challenged Heterogeneous Environments. Demo at the Second ACM SIGCOMM Workshop on Challenged Networks (CHANTS), Montreal, September 2007. [PDF]

N. Asokan, Kari Kostiainen, Philip Ginzboorg, Jörg Ott, Cheng Luo: Applicability of Identity-based Cryptography for Disruption-Tolerant Networking. First International MobiSys Workshop on Mobile Opportunistic Networking (MobiOpp) 2007. [PDF]

Omar Mukhtar: Design and Implementation of Bundle Protocol Stack for Delay-Tolerant Networking. Master Thesis, Helsinki University of Technology, 2006. [pdf]

Omar Mukhtar, Jörg Ott: Backup and Bypass: Introducing DTN-based Ad-hoc Networking to Mobile Phones. Demonstration (short paper) at the RealMAN Workshop 2006. [pdf]

DASM Code

The code of the DTN Symbian implementation is available for download. Tuomo Hyyryläinen is maintaining and enhancing the code now.

(Mobile) DTN Applications

We have developed a couple of DTN applications mostly for use with the DTN reference implementation.

DTN-enabled Blogger

A proxy for a mobile device which is contacted by the mobile user's web browser and then encapsulates blog-postings (with optional attachments) in DTN bundles and transfers them to a backend which unpacks them and posts them to a regular blogging site.

Publication

Lauri Peltola: DTN-based Blogging. Special Assignment, TKK Networking Laboratory, 2007. [PDF].

The code release is yet to come.

DTN-enabled Web Server

As an MSc thesis project, we have developed an open source DTN-capable web server. See the DTN web server project page for details and download.

Publication

Lauri Peltola: Enabling DTN-based Web Access: the Server Side. Msater Thesis, Helsinki University of Technology, Department of Communications and Networking, April 2008. [PDF]

DTN Mail

We have developed a set of mail applications in support of DTN-based communications. This includes a personal mail proxy connecting existing mail clients (such as Thunderbird) via SMTP and POP3, a simple native DTN mail client for the Nokia Internet tablet, and an infrastructure mail gateway to translate between traditional SMTP and DTN-based mail traffic.

Publication

All components are open source under an Apache-style license. The code release is yet to come.

The DT-Talkie

The DT-Talkie is a push-to-talk-style application for the Nokia N800 and N810 Internet tablets. It allows holding (delay-tolerant) conversations over a DTN network (e.g., using a WLAN) by encapsulating talk spurts into bundles and exchanging them between peers. Simple conversations can make use of the hardware buttons of the N810; a GUI allows managing contacts and maintaining multiple conversation contexts.

For further information see the DT-Talkie project web page.

Publication

Md. Tarikul Islam: DT-Talkie: Push-to-Talk in Challenged Networks. Demo presentation at ACM MobiCom 2008. [PDF]