Hybrid Architectures: Networks Exuding both DTN and MANET Characteristics

1. Darien Hirotsu UC Santa Cruz Hybrid Architectures:Networks Exuding both DTN and MANET Characteristics

2. Introduction • Gregg Bachmeyer • Integrating UMTS and Bluetooth • Integrating Infrastructure-based and Infrastructure-less Networks • Darien Hirotsu • Integrating DTN and MANET Paradigms

3. A Brief Delay/Disruption Tolerant Network (DTN) Introduction

4. An Introduction to Delay/Disruption Tolerant Networks (DTN’s) • My apologies to Rance and Philip… • I hope I don’t steal your thunder here (I promise to keep this short) • Feel free to interrupt/augment any explanations at any time • What constitutes a DTN? • Traditional IP networks (both wired and even MANET) suffer in performance when seeing certain qualities: • Large delays • Frequent disruptions • Disconnected network graphs • The DTN architecture attempts to address these issues

5. An Introduction to Delay/Disruption Tolerant Networks (DTN’s) • Examples where a DTN architecture helps: • Sparsely connected sensor networks • Networks with frequent disconnections due to node mobility (interplanetary networks)

6. An Introduction to Delay/Disruption Tolerant Networks (DTN’s) • The DTN protocol stack provides a bundle layer • This allows for a DTN overlay network to be built over the existing architecture • DTN nodes typically use spray-and-wait between hops • Note that internet routers can be integrated between existing DTN nodes

7. Why do we need a hybrid MANET and DTN architecture?

8. Why is there a need for this “hybrid architecture?” • DTN Assumptions: • Connectivity is typically achieved without fixed infrastructure • Nodes move independently and freely • Nodes are typically NOT CONNECTED due to node mobility or sparse node density • The topology that a node sees is limited to ONLY what is “locally connected” • Aroute typically does NOT exist between the sender and receiver • As a result,a persistent store and forward model is needed to allow traffic to be routed and forwarded to the end destination

9. Why is there a need for this “hybrid architecture?” • MANET Assumptions: • Connectivity is typically achieved without fixed infrastructure • Nodes move independently and freely (although only moderate movement is tolerable) • Nodes are inherently CONNECTED via a reasonably dense or stable topology or redundancy of routes • A full topology of the network is maintained by each node • If a route to an end-node does not exist with protocols like AODV or DSR, packets are not routed or forwarded to the next-hop • If a stale route exists, packets are “black-holed”

10. Why is there a need for this “hybrid architecture?” • There are many scenarios in which a MANET would benefit from DTN capability • Sensors in a densely connected MANET may experience battery failure causing sparse connectivity • Failed sensors may cause A to become disconnected from B • If A and B were DTN nodes, A could “save” the data until a path to B became available again • In the MANET, scenario all may be lost A X X X D X X X C X X B

11. Why is there a need for this “hybrid architecture?” • There are many scenarios in which a DTN may benefit from MANET features • DTN’s typically make forwarding decisions based on node availability rather than optimal paths 2 • Suppose C moves at a constant rate with slight pauses between points 1, 2 • At point 1, C can forward traffic between A, B • A MANET could p0tentially discover the more optimal path (A-C-B) over the typical one (A-D-E-B) A C 1 D E B

12. What types of solutions are available to account for this?

13. Methods to account for DTN and MANET like qualities • Connectivity-focused routing solutions • Implement a routing protocol that can build BOTH optimal end-to-end paths when available but also leverage store-and-forward if needed • HYMAD • HYbridMANET-DTN routing protocol • DTN-AODV • “Cooperative” routing solutions • Allow nodes to cooperate to use available bandwidth optimally • TIL • Transient Information Level based routing

14. HYMAD Routing Protocol

15. An Illustration to Show the Need for a Hybrid Architecture • Higher node density makes a strong case for MANET since a path likely exists end-to-end • High node mobility makes a strong case for DTN since the network is likely to become disconnected • A hybrid network that falls in between the extremes could benefit from both paradigms • Also, networks can flip-flop between the two types to have characteristics of both

16. HYMAD • The goal of HYMAD is to group individual nodes such that only groups need to exchange data between each other Inter-group routing can be achieved via DTN. Intra-group routing can be achieved via MANET. This simplifies the topology from 12 connected nodes to 3 connected groups.

17. HYMAD • Intra-group routing (control plane) • Distance vector routing messages to achieve mesh like connectivity Nodes within a group exchange distance vector routing messages much like AODV.

18. HYMAD • Inter-group routing (control plane) • Border nodes are elected for the group • Border nodes use a flag in the routing messages to discover each other • Spray-and-wait routing of data between border nodes B A Nodes A and B are border nodes use a spray-and-wait type routing to forward messages between groups.

19. HYMAD • Data plane operation • Suppose A wants to send a “bundle” of data to B • A forwards the message to the border node C A Group 3 C Group 2 Group 1 The data from A is first forwarded to C which is the border node. C notes that A is the “custodian” for the bundle. C being a border node has routing knowledge of both Group 1 and 2. B

20. HYMAD • Data plane operation • Suppose A wants to send a “bundle” of data to B • C forwards the bundle to node D which is a border node for Group 2 A Group 3 D C Group 2 Group 1 Border nodes maintain a “messages-in-group-list” which contains a list of data needing to be delivered. C compares its list with D and sees that D does not have the bundle from A, so it’s forwarded from C to D. B

21. HYMAD • Data plane operation • Suppose A wants to send a “bundle” of data to B • D randomly elects E as the “custodian” of the bundle and forwards it A E Group 3 D C Group 2 Group 1 D sees that the destination B is not within its group. D elects E randomly to be the “custodian” of the DTN bundle from “A” and forwards it accordingly. D adds the bundle to its “messages-in-group-list.” B

22. HYMAD • Data plane operation • Suppose A wants to send a “bundle” of data to B • E happens to be a border node as well to Group 3 A E Group 3 F D C Group 2 Group 1 E references its “messages-in-group-list” and sees F is missing the bundle in A. E forwards the “bundle” accordingly via “spray-and-pray.” B

23. HYMAD • Data plane operation • Suppose A wants to send a “bundle” of data to B • F sees B is in its group and forwards the “bundle” as needed A E Group 3 F D C Group 2 Group 1 F sees that B is a member of its group. F forwards the datagram to B using distance vector like routing. B

24. HYMAD • Group formation (control plane revisited) • Intra-group disconnections may cause new groups to form • Border nodes are re-elected • “Messages-in-group” list allows “bundles” to be re-forwarded as needed • Dmax is a group diameter that represents the maximum number of allowable hops to reach the farthest node of a group (restricts group membership) • When routes are lost due to disconnections, data is stored by the “custodian” rather than dropped Group 1 may disconnect into different groups should node mobility cause link disconnections A B If Dmax=2, node B cannot join the adjacent group since it’s 3 hops away from node A.

25. HYMAD • Benefits of HYMAD: • Outperforms a standard spray-and-wait forwarding scheme in terms of delay and delivery-ratio over a variety of mobility scenarios • Random Waypoint (synthetic) • Rollernet (trace-based group movement) • Performance in terms of overhead is NOT dependent on Dmax • Increasing Dmax increases the group size which increases the amount of control plane messages within the group • As a tradeoff, this also decreases the amount of control messages between groups

26. HYMAD • Detriments of HYMAD: • Over a wide variety of scenarios, Epidemic routing still outperforms HYMAD in terms of delay and delivery-ratio • In Epidemic routing, random pairs of nodes that establish connectivity exchange information as needed • Performance is strongly tied to timer values of the control plane messages • All nodes need to be DTN nodes • All nodes need to have storage for the batch layer • Assumes that the “custodian” of data can store data for a period long enough for delivery • How does it deal with storage failure?

27. DTN-AODV

28. DTN-AODV • The goal of AODV with DTN capability is to extend the reach of AODV by discovering DTN nodes If DTN nodes (D) are able to speak AODV at the IP layer, DTN nodes can extend the reach of AODV to allow nodes such as originator (O) to reach targets that would be unreachable (T) under typical circumstances.

29. DTN-AODV • Integrating AODV with DTN: • Need to expand the route discovery process and processing of RREQ/RREP messages • Add a flag in the AODV header to tell nodes to check for the DTN header shown below

30. DTN-AODV • Integrating AODV with DTN (RREQ): • O wants to send data to T • O generates a RREQ as per usual O A O generates a RREQ and forwards it to adjacent nodes. Node A is a non-DTN AODV speaker, so it does not toggle the DTN flag in the header, but still forwards the RREQ accordingly. T

31. DTN-AODV • Integrating AODV with DTN (RREQ): • O wants to send data to T • B is a DTN speaker so it toggles DTN bit in the header and adds its DTN header telling AODV nodes it has DTN capability O B A B toggles the DTN bit in the AODV header. B also adds the DTN Router Info extension to the RREQ including a hop count to O. The RREQ is then forwarded normally. T

32. DTN-AODV • Integrating AODV with DTN (RREQ): • O wants to send data to T • D also is a DTN node so it adds another Router Info. Extension header to the RREQ and adds B to its list of DTN nodes O C B A D C is a non-DTN node, so it forwards the RREQ per normal AODV. D sees the DTN bit toggled already, but it still needs to add its Router Info header to the RREQ. It also adds node B to its list of DTN aware nodes establishing a full DTN overlay topology. T

33. DTN-AODV • Integrating AODV with DTN (RREP): • O wants to send data to T • T sees that it’s the target for node O so it generates an RREP O C B A D T generates the RREP and copies all Router Info extension headers from the RREQ onto the RREP and forwards it normally. If node T does not understand the DTN extension, all Router Info extension headers are dropped. T

34. DTN-AODV • Integrating AODV with DTN (RREP): • O wants to send data to T • Nodes may also learn about DTN information based on RREP O E C B A D Node E can also see RREP packets and also learn about DTN nodes B and D through that process. This ensures robustness for nodes in learning the DTN overlay network. T

35. DTN-AODV • Integrating AODV with DTN (RREP): • O wants to send data to T • Node O can make in intelligent decision on how to forward traffic to T based on the DTN information it has received O E C B A D Node O processes RREP normally. All intermediate nodes may now make “optimal” forwarding decisions based on the knowledge of both the AODV network and the DTN overlay network. The DTN Router Info. header has a “metric” field which potentially could indicate how trustworthy a DTN route is. T

36. DTN-AODV • Integrating AODV with DTN (RREP): • Failure of RREQ • The first DTN node in a path for an RREQ is responsible for ensuring the RREQ reaches the destination O E C B A D B is the first DTN node in the path from O to T. It maintains a timer that kicks off after getting the RREQ and listens for an RREP from T. If node T fails and does not send an RREP before B’s timer expires, B sends a special “DTN-Only” RREP to allow nodes to still learn the DTN overlay network. T X

37. DTN-AODV • Benefits of DTN-AODV • Allows for the dynamic establishment of the DTN overlay network over the AODV network • Normally overlay networks requires static configuration • BGP is an example • Allows for the learning of a granular view of the network to provide optimal forwarding decisions • Knowing both AODV and DTN nodes allows the mobile node to intelligently determine an optimal next-hop

38. DTN-AODV • Benefits of DTN-AODV • Evaluation of a similar implementation shows performance improvement over Epidemic routing in terms of delivery-ratio and delay • Implementation (called adaptive routing) was slightly different but still integrated AODV and DTN capability • Not all nodes have to be DTN speakers • Not all nodes even have to understand the DTN extensions

39. DTN-AODV • Detriments of DTN-AODV • Overhead increases with the number of DTN nodes • Since each DTN node adds its Router Info header to the RREQ, more DTN nodes yields higher protocol overhead • DTN-AODV results in a lot of queueing • DTN-AODV results in far more queuing on average per node compared to Epidemic routing • Route cacheing may cause issues with AODV-only speakers • If an AODV-only node receives an RREQ and responds via route-cache, it will only send AODV routes limiting the full realization of the DTN network

40. TIL: Transient Information Level Routing

41. TIL • Created for directional tactical networks using RF and optical links (free-space optical networks)

42. TIL • Directional networks • Sometimes nodes can’t transmit data in the optimal path due to interference or physical conditions • A satellite may not be pointing the optimal direction Node A needs to transmit to D, but it can’t send data directly due to the direction of the antennae. Instead, it takes a suboptimal path through B and C. C B D A

43. TIL • The goal of TIL is to have nodes coordinate together and share bandwidth optimally based on a “DTN algorithm” using a called TIL • An individual node in a network is typically selfish • Since bandwidth is finite, there is some benefit for nodes to “cooperate” and share to maximize bandwidth • Built primarily for DTN’s, but the paper claims that the solution works for directional MANET’s as well

44. TIL • Consider the scenario where Gregg and Darien see an 802.11n and 802.11a access point • Both of us knowing 802.11n is faster, we both join that access point and potentially contend over the available bandwidth • If we played nicer and coordinated, we could work together and join different access points to potentially maximize our perceived service 802.11n 802.11a X Darien Gregg

45. TIL • Assumes the following: • All nodes have perfect knowledge of: • Location of nodes in the network • Amount of network traffic at each node • Connectivity of the network • If all nodes have this complete information, an algorithm can be used by each node to minimize the amount of work needed to move data from source to destination

46. TIL • The goal is to forward traffic based on the lowest TIL value for all nodes i and j • T(i, j) : amount of traffic needing to be delivered from node i to node j • D(i, j) : distance between node i and node j • h(i, j) : amount of traffic being retained via DTN on the path from node i to j

47. TIL • Detriments: • Impractical • Is it even possible for to get this granular information AND disperse it through a network? • All nodes have to be DTN nodes • Benefits: • Novel solution • Cooperation makes sense when “fighting” over a shared resource • Simulations show the protocol shows correctness in delivering data over an RF, optical network

48. Issues in General with Integration of DTN and MANET • Varying simulation tools • Different simulators have different capabilities • Comparing performance of unlike protocols in unlike tools is inefficient • Congestion control mechanisms • The possibility exists for congestion to occur at DTN capable nodes • Does the bundle layer need additional congestion control mechanisms? • Security • DTN nodes present a natural target for DoS

49. Finishing Up • Thanks for listening

50. Why is there a need for this “hybrid architecture?” • Why not use MANET only? • MANET routing protocols use Hellos for neighbor discovery which could be wasteful if nodes are rarely connected • MANET forwarding is based on availability, so if an end-to-end path does not exist, traffic is dropped • This is not optimal if the network graph is typically disconnected or constantly changing • Why not use DTN only? • DTN forwarding is often based on a per-encounter basis (the node that is connected the “most” based frequency of connectivity may become the best hop) • This means the most optimal path through the network is not always utilized (DTN nodes don’t know the full topology) • Without constant topology discovery, suboptimal forwarding/routing is a possibility