Kevin Lee & Adam Piechowicz 10/10/2009 Delay Tolerant Mobility Aware Routing/Mobility Dissemination Protocol for the Airborne Network Kevin Lee & Adam Piechowicz 10/10/2009

Problem Statement An end-to-end path is not always guaranteed Packets have to be delivered in a delay-tolerant fashion How to use planned AN backbones’ trajectories to deliver packets to minimize: Packet failure rate Delay Local buffer

Contributions Provide best next forwarding hop in the delay tolerant network based on current network condition Provide congestion avoidance and load balancing by local queuing awareness mechanism

MARP/MDP+DTN Design Think of the topology as a time-varying graph We can select the best next hop given a specified metric (minimum delay) Use modified Dijkstra’s algorithm with time-varying edge costs w(e(u,v), t) indicates the cost of using edge (u, v) after time time t The cost is predominantly the time after t that (u, v) is up Propagation delay negligible Transmission rate not considered Will say something about the disadvantage of this scheme (unawareness of congestion), but will mention it’s not so bad at all because it compares favorably with all-knowledge oracles

Example 1 Source node at 1 and each edge cost is 1 N Node 1, Pre {1,2,3,4} 0,1 ∞ {2,3,4} 1,1 5,1 {3,4} 5 < 1 + w(e(2,3), 1) = 1 + (4+1) = 6 1 < 1 + w(e(2,4),1) = 1 + (2 + 1) = 4 {3} {} Node 1, Pre: Node 1’s delay and its predecessor.

Example 2 N Node 1, Pre Node 2, Pre Node 3, Pre Node 4, Pre {1,2,3,4,5} 0,1 1,1 ∞ 7,1 4,1 {2,3,4,5} 2,2 {3,4,5} 7 > 2 + w(e(3,4),2) = 2 + (0 + 1) = 3,3 {5} 3,3 4 < 3 + w(e(4,5), 3) = 3 + ∞ {0}

Predecessor Computation Take Node 3 from Example 2 2, 2 means: It will take Node 1 to reach Node 3 with cost of 2 (the first 2) The predecessor of Node 3 is Node 2 (the second 2) One can then trace back to get the complete route traversal and the time at which the packet should be sent

Local Queuing Aware Scheduling Network disconnectivity increases queuing delay Queuing delay increases congestion Route around congestion by considering neighbors’ queue size w(e, L[u] + T) will incorporate: The cost of sending packets already in the queue plus, The cost of sending the last packet scheduled to use u to deliver to v

Importance of Encountering for Queuing Awareness The more frequently a node encounters with another node, the more packets the node can offload to that node Intuitively, the link between these two nodes provide lower delay to the destination Two types of encountering: Single Multiple

Single Encountering A node A single encounters another node B if node A meets node B only once in a period Where time(1,e,L[u]+T) indicates the time Node u meets Node v at which time one packet in Node u’s queue is delivered since L[u] + T P is the period of the time-varying graph Qsize is the queue size at Node u

Single Queuing Example Assume there are 2 messages in Node 2’s queue N Node 1, Pre Node 2, Pre Node 3, Pre Node 4, Pre {1,2,3,4} 0,1 ∞ {2,3,4} 1,1 5,1 {3,4} 5 < 1 + w(e(2,3), 1) = 1 + 5 + 6 + 6 = 18 1 < 1 + w(e(2,4),1) = 1 + 3 + 6 + 6 = 16 {3} {} Node 1, Pre: Node 1’s delay and its predecessor.

Single Queuing Example (cont.) w(e(2,3), 1) = 5 + 6 + 6 because it takes 5 more seconds to dequeue the first packet, 6 seconds to dequeue the second packet, another 6 seconds to dequeue the last packet By the eqn, w(e(2,3), 1) = 5 + 6 * 2 = 17 Packets in Node 2’s queue will use the same edge in consideration, e.g., w(e(2,3),1) considers first two packets going to Node 3 w(e(2,4),1) considers first two packets go to Node 4

Multiple Encountering A node A multiple encounters another node B if node A meets node B more than once in a period Tx(e,P-(L[u]+T)): the number of times e is up during P-(L[u]+T time Tx(e,t) is the # of times e is up during the remaining time t of one period

Multiple-Encounter Queuing Example Assume there are 2 messages in Node 2’s queue N Node 1, Pre Node 2, Pre Node 3, Pre Node 4, Pre {1,2,3,4} 0,1 ∞ {2,3,4} 1,1 5,1 {3,4} 5 < 1 + w(e(2,3), 1) = 1 + 3 + 2 + 4 = 10 1 < 1 + w(e(2,4),1) = 1 + 3 + 6 + 6 = 16 {3} {} Node 1, Pre: Node 1’s delay and its predecessor.

Multiple-Encounter Queuing Example (cont.) w(e(2,3), 1) = 3 + 2 + 4 because it takes 3 more seconds to dequeue the first packet, 2 more seconds to dequeue the second packet, 4 seconds to dequeue the last packet Since Qsize (=3) > Tx (=2), eqn (2) is used: w(e(2,3), 1) = (6 – 1) + 0 + 4 = 10

Handling Multiple-Traffic Flows Contacts (the time-varying at any given point in time) is known Local queuing is known; approximate global queuing by keeping track of messages along each routing path Traffic demand is known, It is a set of messages Each message is a tuple (u,v,t,m), where u is the source of the msg, v is the destination, t is the time the msg is sent, m is size Buffer constraints are given THE ORACLE HAS COMPLETE KNOWLEDGE! – A linear programming exercise

Approximate Optimality LP is computationally expensive! – Computation become too large for practical example Use contacts and queuing oracle (EDAQ) instead “EDAQ compares favorably, in terms of average delay, with the optimal solution.” However, Global knowledge may not be required for good performance in many cases Implementing the queuing oracle, in particular, may not be worthwhile EDAQ: Earlier delivery with all queues

Approximate Optimality (contd.) Contact oracles (ED) might just be enough for our scenarios! Lesson: TOO MUCH KNOWLEDGE MAY NOT ALWAYS BE GOOD! Didn’t God say not to eat the wrong tree?

Evaluation

MARP/MDP vs. MARP/MDP+DTN Network Flow from GlobalHawk to AWACs 2 Solid arrow shows the desired network flow Dotted lines shows current available connections 3 experimental variables Radio range Delay tolerance Flow volume

Results Delay tolerance represents largest improvement in packet delivery, 52% (col1 &2) Fixed range: Low flow has higher delivery and lower latency (col 1 & 3) Fixed flow: High radio range has higher delivery ratio and lower latency than low radio range

MARP/MDP+DTN vs. MARP/MDP+DTN+QC Two separate rate flows from 1 and 2 to 5 Transmission rates range from 2.048 Mbps to 1024 kbps

Results When transmission rate is high, PDR for MARP/MDP+DTN is 0%

Packet Difference between Node 3 and 4 Both flow forward to Node 3 heavily in MARP/MDP+DTN MARP/MDP+DTN+QC is able to divert traffic and achieve load balancing

Latency Delay extremely long in MARP/MDP+DTN Result indicates the need for local queuing awareness

Conclusion & Future Work MARP/MDP+DTN shows the benefit of delay tolerance MARP/MDP+DTN+QC shows the benefit of local queuing awareness Congestion scenario configuration to verify local queuing aware scheduling Tune parameters/routing metrics of MARP/MDP+DTN+QC protocol in accordance with flight and link data obtained from real flight tests like Capstone II