Routing in Delay Tolerant Network Qing Ye EDIFY

Routing in Delay Tolerant Network Qing Ye EDIFY Group of Lehigh University

Outline n n n Introduction Routing Issue and the Model DTN Routing Approaches q q n Gossiping-like Shortest-path-like Summary and Our view

Introduction – Concept n Delay Tolerant Networks: networks suffer from frequent, long duration partitioning and the lack of guaranteed end-to-end path n Examples: q q Low Earth Orbiting Satellites Interplanetary networks by satellites, spaceships, and base stations Special Military Networks Groups of Handheld devices for search and rescue teams

Introduction – Characteristics n Heterogeneity: q q n n n A hybrid of wired and wireless links Bandwidth, delay and capacity of links may vary Different types end-devices Node may move or not Is DTN a Mobile Ad hoc Networks ? ? Larger end-to-end delay No fixed stable end-to-end path Up and down of links may be predictable, periodic, or opportunistic

Routing Issue n n Conventional Routing: q Internet: distance vector and link state q Wireless Ad hoc networks: table-driven and source-initiated ondemand q Find and take advantage of the best current available end-to-end path between source and destination DTN Routing: what if no end-to-end path exist in the network q q So-called message ferry becomes important Buffer size in the intermediate nodes become a precious system resource Reliability (eventual packet delivery in lifetime) become a research goal Hop-by-hop scheme becomes dominant, rather than end-to-end methods

DTN Routing Model n n n DTN a multigraph G(E, N), multiple paths may exist according to different types of links Contact: point-to-point opportunity, (src, dst, uptime, downtime, delay, capacity) Message: (src, dst, creationtime, lifetime, size) Storage: finite buffer in intermediate nodes, infinite buffer in destinations Routing: hop-by-hop store-and-forward approach, how to select the next hop

DTN Routing Approaches – First Contact (FC) n n n Basic idea: a message is forwarded along a contact chosen randomly among all current available contacts. Or the first available contact is selected Similar approach: Gossiping Routing Properties: q q Simple: routing is based on a local view Small control overhead Not a loop-free approach Unreliable: routing decision may be incorrect

DTN Routing Approaches – Minimum Expected Delay (MED) n n n Assumptions: q the up and down schedules as well as the delays of overall contacts between the source and the destination are known q the overall message sizes are known q Next-hop delay = waiting delay + average propagation delay + average transmission delay Basic idea: q Dijkstra’s shortest path algorithm is applied q choose the path with the overall smallest next-hop delays Properties: q Achieve the minimum average delays q Loop-free q Superior contact happens later would be ignored q Congestion may happen since the route is fixed, no load balancing

DTN Routing Approaches – Earliest Delivery (ED) n n Assumptions: same as the MED approach Basic idea: q q n calculate the next-hop delay in a real-time manner always pick up the current contact with smallest delays as the next hop Properties: q q Loop-free May achieve the minimum delay Good for new contact Not consider the queuing delay and the constraints of finite storage space in nodes

DTN Routing Approaches – Earliest Delivery with Local Queuing (EDLQ) n Assumptions: q q n Basic idea: q q n same as the MED the local queue/buffer information is also known next-hop delay = waiting delay + queuing delay + propagation delay + transmission delay same as the ED approach Properties: q q take the local buffer into account can not avoid buffer overload in next few hops

DTN Routing Approaches – Earliest Delivery with All Queues (EDAQ) n Assumptions: q q n Basic idea: q n same as the MED the info of overall queue/buffer usage is known same as EDLQ Properties: q q is able to avoid the buffer overload problem may not be the optimal route since the future traffic info is unknown

DTN Routing Approaches – Linear Programming n n n What if we know everything of DTN? DTN Routing “Quickest delivery Problem” Minimum Cost Maximum Flow Problem Linear Programming approach is good But q q too strong assumptions centralized appraoch

DTN Routing Approaches – Simulation Results n dtnsim: a java based DTN simulator

DTN Routing Approaches – Simulation Results

DTN Routing Approaches

Summary n Pros: q q n Cons: the optimal routing have to be decided with strong assumptions, which may not be study the basic DTN scenarios discuss the DTN routing issues and model propose two type of DTN routing approaches: gossipinglike and shortest-path like design a new DTN simulator Cons: q q the optimal routing have to be decided with strong assumptions, which are not true in the real world centralized approaches the problem of none end-to-end path in DTN is not studied No Qo. S support