DTN/VDTN Architecture VDTN Fragmentation Experimental evaluation - PDF document

technology from seed Bundles Fragmentation in Vehicular Delay-Tolerant Networks Naércio Magaia, Paulo Rogério Pereira , Augusto Casaca, (Inesc-ID, Portugal), Joel J. P. C. Rodrigues, João A. Dias, João N. Isento, (IT, Portugal) Cristina Cervelló-Pastor, Javier Gallego (UPC, Spain). Instituto de Engenharia de Sistemas e Computadores Investigação e Desenvolvimento em Lisboa 111 NGI'2011: Bundles Fragmentation in Vehicular Delay-Tolerant Networks 27-06-2011 Summary technology from seed • DTN/VDTN Architecture • VDTN Fragmentation • Experimental evaluation • Conclusion Instituto de Engenharia de Sistemas e Computadores Investigação e Desenvolvimento em Lisboa 222 NGI'2011: Bundles Fragmentation in Vehicular Delay-Tolerant Networks 27-06-2011

Summary technology from seed • DTN/VDTN Architecture • VDTN Fragmentation • Experimental evaluation • Conclusion Instituto de Engenharia de Sistemas e Computadores Investigação e Desenvolvimento em Lisboa 3333 NGI'2011: Bundles Fragmentation in Vehicular Delay-Tolerant Networks 27-06-2011 Introduction technology from seed • Delay/Disruption Tolerant Networks (DTNs) are networks that may experience frequent and long duration partitions. • Examples: military communications in the battlefield, deep space communications, some forms of ad-hoc sensor/actuator networks, rescue actions in catastrophe sensor/actuator networks, rescue actions in catastrophe hit areas, wild life monitoring, offering Internet connectivity in developing regions, vehicular networks. Instituto de Engenharia de Sistemas e Computadores Investigação e Desenvolvimento em Lisboa 4 4 NGI'2011: Bundles Fragmentation in Vehicular Delay-Tolerant Networks 27-06-2011

Bundle Layer technology from seed • Link disruptions are not properly handled by the Internet protocols, due to high delays and high packet loss. • The DTN Research Group, which was chartered as part of the Internet Research Task Force (IRTF), has proposed an architecture (RFC 4838) and a communication protocol for DTNs (RFC 5050). DTNs (RFC 5050). • “Bundle Layer” added on top of the Application Application transport layer for the end-to-end Bundle end point Bundle end point Bundle end point Bundle end point exchange of messages (called Transport Transport Transport Transport bundles) taking advantage of Network Network Network Network scheduled, predicted, opportunistic or permanent connectivity. Instituto de Engenharia de Sistemas e Computadores Investigação e Desenvolvimento em Lisboa 555 NGI'2011: Bundles Fragmentation in Vehicular Delay-Tolerant Networks 27-06-2011 DTN characteristics technology from seed • Random and predictable node mobility • Intermittent/Scheduled/Opportunistic Links • Large or variable delays • High Error Rates / Low Usable Capacity • Limited node uptime (e.g. to save power) • Limited node uptime (e.g. to save power) • Link bandwidth/loss/delay asymmetry • Heterogeneous Network Architectures • End-to-end path may not exist Instituto de Engenharia de Sistemas e Computadores Investigação e Desenvolvimento em Lisboa 666 NGI'2011: Bundles Fragmentation in Vehicular Delay-Tolerant Networks 27-06-2011

technology Delay-Tolerant Networking from seed Architecture • Goals – Support interoperability across ‘radically heterogeneous’ networks – Tolerate delay and disruption • Acceptable performance in high loss/delay/error/disconnected environments • Decent performance for low loss/delay/errors Instituto de Engenharia de Sistemas e Computadores Investigação e Desenvolvimento em Lisboa 7 NGI'2011: Bundles Fragmentation in Vehicular Delay-Tolerant Networks 27-06-2011 Message Abstraction technology from seed • Network protocol data unit: bundles – “postal-like” message delivery – origination and useful life time -assumes synchronized clocks – source, destination, and respond-to EIDs (Endpoint Identifiers) – Options : return receipt, “traceroute”-like function, alternative reply-to field, custody transfer – fragmentation capability – fragmentation capability – overlay atop TCP/IP or other (link) layers: layer ‘agnostic’ • Applications send/receive messages – “Application data units” ( ADUs ) of possibly-large size – Applications should “bundle” together all data concerning a transaction that is sent asynchronously, to minimize interactions with large RTT – Adaptation to underlying protocols via ‘convergence layer’ Instituto de Engenharia de Sistemas e Computadores Investigação e Desenvolvimento em Lisboa 8 NGI'2011: Bundles Fragmentation in Vehicular Delay-Tolerant Networks 27-06-2011

Vehicular Contact Times technology from seed Contact times between vehicles crossing each other are rather short • Results for UDP with packet size 1460 bytes over IEEE 802.11a/g • [6]: Car speed Transferred data Contact Time Goodput 20 Km/h 13.0 MB 38.48 s 2.75 Mbps 40 Km/h 3.6 MB 14.90 s 1.90 Mbps 60 Km/h 1.6 MB 10.83 s 1.15 Mbps For TCP, the performance is very low: average of 80 KB transferred • in a crossing at 60 Km/h (relative speed 120 Km/h), in 4 out of 10 experiments no data is transferred at all. Motivates the study of fragmentation, necessary for large bundles. • Instituto de Engenharia de Sistemas e Computadores Investigação e Desenvolvimento em Lisboa 9 NGI'2011: Bundles Fragmentation in Vehicular Delay-Tolerant Networks 27-06-2011 VDTN technology from seed • Vehicular networks may benefit from DTN concepts – especially in regions with no communications infrastructure or with few vehicles, such as: rural and mountainous regions. – non real-time applications, such as: traffic information, meteorological information – the use of fixed relay nodes in cross-roads may improve the – the use of fixed relay nodes in cross-roads may improve the delivery ratio Instituto de Engenharia de Sistemas e Computadores Investigação e Desenvolvimento em Lisboa 10 NGI'2011: Bundles Fragmentation in Vehicular Delay-Tolerant Networks 27-06-2011

VDTN Architecture technology from seed • Bundle layer below the network layer – objective is to route large size messages instead of small size IP packets – results in fewer packets processing and routing decisions, which can be translated to less complexity, lower cost and energy savings • BAD layer: Bundle Aggregation and De-aggregation BAD layer: Bundle Aggregation and De-aggregation • BSC layer: Bundle Signaling Control Application Layer • Persistent storage to avoid data loss Transport Layer • Relay nodes only have the lower Persistent Network Layer Storage BAD Layer BSC Layer layers MAC Layer MAC Layer PHY Layer PHY Layer Data Plane Control Plane Instituto de Engenharia de Sistemas e Computadores Investigação e Desenvolvimento em Lisboa 11 NGI'2011: Bundles Fragmentation in Vehicular Delay-Tolerant Networks 27-06-2011 Summary technology from seed • DTN/VDTN Architecture • VDTN Fragmentation • Experimental evaluation • Conclusion Instituto de Engenharia de Sistemas e Computadores Investigação e Desenvolvimento em Lisboa 12 12 12 12 NGI'2011: Bundles Fragmentation in Vehicular Delay-Tolerant Networks 27-06-2011

IP fragmentation technology from seed • Fragmentation in IP networks has been considered harmful – poor performance or complete communication failure – additional headers, additional bandwidth, additional processing – complex reassembly mechanisms at the receiver – loss of fragments requires retransmission of the entire original datagram • IPv6 disallows fragmentation inside the network, requiring that fragmentation is done in the source node • HTTP protocol allows byte ranges of objects to be individually retrieved: useful to resume partial file transfers Instituto de Engenharia de Sistemas e Computadores Investigação e Desenvolvimento em Lisboa 13 NGI'2011: Bundles Fragmentation in Vehicular Delay-Tolerant Networks 27-06-2011 DTN Fragmentation Types technology from seed • Two types of fragmentation • Proactive : a node divides a bundle in fragments before transmission – used primarily when the contact duration is known (or predicted) in advance, e.g. satellite networks • Reactive : nodes in communication fragment a bundle when • Reactive : nodes in communication fragment a bundle when a contact is broken – the received part is a fragment – the undelivered part is another fragment – “toilet paper” variant allows fragmentation only at predefined boundaries • Fragments reassembled at the destination only. • Any fragment loss results in the entire bundle loss. Instituto de Engenharia de Sistemas e Computadores Investigação e Desenvolvimento em Lisboa 14 NGI'2011: Bundles Fragmentation in Vehicular Delay-Tolerant Networks 27-06-2011