A Delay-Tolerant Network Architecture for 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 Challenged network 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 Challenged network의 예를 그림으로 넣을것! (왜 assumption을 위배하는지..왜 현재의 TCP/IP컨셉만으로는 불가능한지에 대해서 이유넣으면서 각 네트웍 설명) 그림을 넣게 되면 example은 그림에 캡션으로 달고 글자로 쳐넣은 것은 없앤다 Challenged network은…. Very significant link delay non-existence of end-to-end routing paths Lack of continuous power and large memory at end node

Introduction (2/2) Challenged network (cont’d) In this paper 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 Path and link, network architecture, end system의 크게 세부분으로 나누어 Challenged internetwork에 대한 특징과 이들 특징이 network architecture 디자인에 영향을 미치는 점을 알아본다

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} source destination DTN gateway

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

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

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) EKRA(M || CA) EKRB(M || CB) EKRC(M || CC) 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

Scheduling and Message Forwarding < DTN (Bundle) Gateway > DTN Gateway DTN Application RPC Server Scheduling and Message Forwarding Internet Convergence Layer SensorNet Other Database Manager 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 >

Scheduling and Message Forwarding < DTN (Bundle) Gateway > DTN Gateway DTN Application RPC Server Scheduling and Message Forwarding Internet Convergence Layer SensorNet Other Database Manager 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 >