A Delay-Tolerant Network Architecture for Challenged Internets

A Delay-Tolerant Network Architecturefor Challenged Internets SIGCOMM’03 Kevin Fall (kfall@intel-research.net) Intel Research, Berkeley Nov. 26, 2003 Presented by Sookhyun, Yang

Contents • Introduction • Background • Challenges for Internetworking • Delay Tolerant Networking (DTN) • Application Interface • Conclusion

Introduction (1/2) • TCP/IP based Internet • Packet-switched model • Implicit assumption • End-to-end path between source and destination node exits • Maximum round-trip time between any node pairs in the network is not excessive • End-to-end packet drop probability is small • Challenged network • Violate one or more of Internet’s assumptions • Very long delay path • Frequent network partitions, etc.. • Have their own specialized protocol stacks • Have naming semantics for their particular application domain • Not be well served by the current end-to-end TCP/IP

Introduction (2/2) • Challenged network (cont’d) • Examples • Terrestrial mobile networks • Exotic media networks • Military ad-hoc networks • sensor/actuator networks • In this paper • Achieve interoperability between very diverse networks • Propose a network architecture and application interface • Form an “internetworking of challenged internets”

Background • Overview of Challenged networks Mobile network Ad hoc network MH FA Movement FA Sink MH FA Sensor field Sensor network

Challenges for Internetworking • Path and link characteristics • High latency, low data rates • Disconnection • Faulty • Non-faulty : motion and low-duty-cycle operation • Long queuing times • Need to be stored for potentially long periods of time at routers • Network architectures • Interoperability considerations • Security • Endpoint involving security is not very attractive • End system characteristics • Limited longevity • Conventional end-to-end acknowledgement for reliable delivery should be delegated • Low duty cycle operation • Scheduling a-priori in concert with path selection • Limited resources • Do not necessarily have to wait for an end-to-end acknowledgement

source DTN gateway DTN gateway destination Delay Tolerant Networking (1/3) • Characteristics • Operate as an overlay above the existing transport layers • Based on an abstraction of message switching • Bundle • Bundle forwarder (DTN gateway) • Store-and-forward gateway function between different networks • Constituent of DTN architecture • Region • Similar network stack and addressing • DTN gateway • Interconnection point between region boundaries • Logically two of halves • Name Tuple • {Region name, Entity name}

UserHost DTN gateway Delay Tolerant Networking (2/3) • Architecture Region A - Internet data Region D {B, R2} data {A, R2} {A, R1} data {D, R4} Region B – Sensor network {C, R4} Region C - Intranet {C, R3} {B, R3} {A, UserHost} data

Internet Convergence Layer SensorNet Convergence Layer Other Convergence Layer Database Manager RPC Server Scheduling and Message Forwarding DTN Application DTN library+RPC File Store Sockets TDP UDP SCTP IP 802.3 802.11 Other Sensor Net API Sensor Network Stack (TBD) Serial Port Other Transport Or Raw Protocols (TBD) File Store Bundle data Bundle data Delay Tolerant Networking DTN Gateway (1/5) • Routing (path scheduling) and message scheduling • End-to-end routing path cannot be assumed to exist • Route • Cascade of time-dependent contacts (communication opportunity) from source to destination • Contact = {start_time, end_time, …} • Measure contact’s predictability • Select the next message to be sent • Choose next-hop forwarders

Delay Tolerant Networking DTN Gateway (2/5) • Class of service (CoS) • Priority-based resource allocation • US Postal Service • Non-interactive • Coarse granularity and intuitive character : low, ordinary, high • Option of reliable delivery • Handled differently by the routing system • Persistent storage • Custody transfer • Custody transfer and reliability • Two distinct types of message routing nodes • Persistent (P) • Non-persistent (NP) • Hop-by-hop reliability • Acknowledged delivery of message from one DTN hop to next • Delegate reliable delivery responsibility

Delay Tolerant Networking DTN Gateway (3/5) • Supplementary function for transport layer • Bundle forwarding function • Transport-protocol-specific convergence layer • Within the regions containing a DTN P node • Reliable delivery capability with message boundaries • Failure detection • Retransmission timer • Congestion control • Handle of contention for the persistent storage • Buffer space as a function of CoS • Shared priority queue for custody transfer • Messages are spooled based on priority and useful lifetime • Priority inversion & head-of-line blocking problem

Delay Tolerant Networking DTN Gateway (4/5) • Time synchronization • Identify message fragments • Purge messages that have exceeded their source-specified lifetime • DTN’s scheduling and path selection • DTN’s congestion management technique • Security • Verifiable access to the carriage of traffic at a particular class of service • Avoid carrying traffic long distances later found to be prohibited • Postage stamp • ID of sender || Class of service || Cryptographic material

Delay Tolerant Networking DTN Gateway (5/5) • Security (cont’d) EKRB(M || CB) EKRC(M || CC) EKRA(M || CA) Sender A DTN gateway B DTN gateway C destination DKUA(EKRA(M || CA)) = M || CA DKUB(EKRB(M || CB)) = M || CB

Application Interface • Be careful not to expect timely response • Generally operate where a request/response turn-around time exceeds the expected longevity of the client and server processes • Supported function • Name tuple creation, manipulation, and registration • Class of service classifier • Authentication information • Continue operate in the face of reboots or network partitioning as much as possible

Conclusion • DTN’s contribution • Provide interoperable communications between a wide range of networks • Advocate a change to the basic service model and system interface, mostly accustomed Internet-style applications • Suggest model while keeping the current service model and existing TCP/IP based protocols constant • DTN’s different choices in the architectural design • Messages vs. packets • Hop-by-hop reliability and security vs. end-to-end • Name-based routing vs. address-based routing • Partially-connected routing vs. fully-connected network graph

Internet Convergence Layer SensorNet Convergence Layer Other Convergence Layer Database Manager DTN Gateway Scheduling and Message Forwarding DTN Application RPC Server DTN library+RPC File Store Sockets TDP UDP SCTP IP 802.3 802.11 Other Sensor Net API Sensor Network Stack (TBD) Serial Port Other Transport Or Raw Protocols (TBD) File Store Bundle data Bundle data < DTN (Bundle) Gateway >

A Delay-Tolerant Network Architecture for Challenged Internets