delay toleran network

A Delay-Tolerant Network Architecturefor Challenged InternetsNov. 26, 2003Presented by Sookhyun, YangKevin Fall ([email protected])Intel Research, BerkeleySIGCOMM03

Computer Network LabLab Seminar 2003

*ContentsIntroduction

Background

Challenges for Internetworking

Delay Tolerant Networking (DTN)

Application Interface

Conclusion


*Introduction (1/2)TCP/IP based InternetPacket-switched modelImplicit assumptionEnd-to-end path between source and destination node exitsMaximum round-trip time between any node pairs in the network is not excessiveEnd-to-end packet drop probability is small

Challenged networkViolate one or more of Internets assumptionsVery long delay pathFrequent network partitions, etc..Have their own specialized protocol stacksHave naming semantics for their particular application domainNot be well served by the current end-to-end TCP/IP


*Introduction (2/2)Challenged network (contd)ExamplesTerrestrial mobile networksExotic media networksMilitary ad-hoc networkssensor/actuator networks

In this paperAchieve interoperability between very diverse networksPropose a network architecture and application interfaceForm an internetworking of challenged internets


*Challenges for InternetworkingPath and link characteristicsHigh latency, low data ratesDisconnectionFaultyNon-faulty : motion and low-duty-cycle operationLong queuing timesNeed to be stored for potentially long periods of time at routers

Network architecturesInteroperability considerationsSecurityEndpoint involving security is not very attractive

End system characteristicsLimited longevityConventional end-to-end acknowledgement for reliable delivery should be delegatedLow duty cycle operationScheduling a-priori in concert with path selectionLimited resourcesDo not necessarily have to wait for an end-to-end acknowledgement


*Delay Tolerant Networking (1/3)CharacteristicsOperate as an overlay above the existing transport layersBased on an abstraction of message switchingBundleBundle forwarder (DTN gateway)Store-and-forward gateway function between different networks

Constituent of DTN architectureRegionSimilar network stack and addressingDTN gatewayInterconnection point between region boundariesLogically two of halvesName Tuple{Region name, Entity name}


*Delay Tolerant Networking (2/3)ArchitectureRegion C - IntranetRegion A - InternetRegion B Sensor networkdatadatadatadata{A, UserHost}{A, R1}{B, R2}{B, R3}{D, R4}{A, R2}{C, R3}{C, R4}


*DTN Gateway (1/5)Routing (path scheduling) and message schedulingEnd-to-end routing path cannot be assumed to existRouteCascade of time-dependent contacts (communication opportunity) from source to destination Contact = {start_time, end_time, }Measure contacts predictabilitySelect the next message to be sentChoose next-hop forwardersDelay Tolerant Networking


*DTN Gateway (2/5)Class of service (CoS)Priority-based resource allocationUS Postal ServiceNon-interactiveCoarse granularity and intuitive character : low, ordinary, highOption of reliable deliveryHandled differently by the routing systemPersistent storageCustody transfer

Custody transfer and reliabilityTwo distinct types of message routing nodesPersistent (P)Non-persistent (NP)Hop-by-hop reliabilityAcknowledged delivery of message from one DTN hop to nextDelegate reliable delivery responsibility

Delay Tolerant Networking


*DTN Gateway (3/5)Supplementary function for transport layerBundle forwarding functionTransport-protocol-specific convergence layerWithin the regions containing a DTN P nodeReliable delivery capability with message boundaries

Failure detectionRetransmission timer

Congestion controlHandle of contention for the persistent storageBuffer space as a function of CoSShared priority queue for custody transferMessages are spooled based on priority and useful lifetimePriority inversion & head-of-line blocking problemDelay Tolerant Networking


*DTN Gateway (4/5)Time synchronizationIdentify message fragmentsPurge messages that have exceeded their source-specified lifetimeDTNs scheduling and path selectionDTNs congestion management technique

SecurityVerifiable access to the carriage of traffic at a particular class of serviceAvoid carrying traffic long distances later found to be prohibitedPostage stampID of sender || Class of service || Cryptographic material

Delay Tolerant Networking


*DTN Gateway (5/5)Security (contd)

Sender AdestinationDTN gateway BDTN gateway CEKRA(M || CA)DKUA(EKRA(M || CA)) = M || CAEKRB(M || CB)DKUB(EKRB(M || CB)) = M || CBEKRC(M || CC)Delay Tolerant Networking


*Application InterfaceBe 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 functionName tuple creation, manipulation, and registrationClass of service classifierAuthentication information

Continue operate in the face of reboots or network partitioning as much as possible


*ConclusionDTNs contributionProvide interoperable communications between a wide range of networksAdvocate 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

DTNs different choices in the architectural designMessages vs. packetsHop-by-hop reliability and security vs. end-to-endName-based routing vs. address-based routingPartially-connected routing vs. fully-connected network graph


*DTN GatewayFileStoreSockets

TDP UDP SCTP

IP

802.3 802.11 OtherFileStoreScheduling and Message ForwardingBundledataBundledataRPC ServerDTNApplicationDTN library+RPCOther Transport OrRaw Protocols(TBD)Sensor Net API

Sensor NetworkStack(TBD)

SerialPort< DTN (Bundle) Gateway >


*DTN GatewayFileStoreSockets

TDP UDP SCTP

IP

802.3 802.11 OtherFileStoreScheduling and Message ForwardingBundledataBundledataRPC ServerDTNApplicationDTN library+RPCOther Transport OrRaw Protocols(TBD)Sensor Net API

Sensor NetworkStack(TBD)

SerialPort< DTN (Bundle) Gateway >

*Challenged network ! ( assumption .. TCP/IP ) example Challenged network.Very significant link delaynon-existence of end-to-end routing pathsLack of continuous power and large memory at end node*Path and link, network architecture, end system Challenged internetwork network architecture

delay toleran network

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end path

end routing path

existroutecascade of

long periods of time

end packet

routing path scheduling

message schedulingend

forward gateway function