Location-aware routing for Delay Tolerant Networks
Summary (3 min read)
Introduction
- With advance of wireless technologies and prevalent usage of portable wireless devices, in recent years, the idea of Delay Tolerant Networks (DTN[1]) has been proposed.
- In their work, the authors also labeled the inherited structure of the network explicitly, but unlike the previous work, they labeled the nodes based on their location visiting information as well as their contact information to make forwarding decisions.
- Motivated by these observations, the authors proposed a location aware routing scheme for DTN networks.
- In addition, the authors demonstrated the superiority of the proposed scheme over other representative schemes via extensive simulation experiments using the contact trace from real-world dataset.
B. Connectivity and isolation
- For DTN networks, how to avoid the message delivery failure and reduce the delay is the major concern.
- When the threshold gets increased, more nodes are isolated from the giant component but the giant component still exists.
- To define the metrics, the authors modified the contact graph into a weighted contact graph Gw(d), where for each edge on the graph, its weight is defined as the averaged inter-contact time between the two corresponding nodes.
- The authors show the calculated intra- and the inter-component delays under different thresholds in Fig.
- The observation suggests that node isolation is the major reason for the latency and the failure in DTN’s message delivery, and should be their focus in designing the routing scheme.
C. Contact-location relationship
- The authors studied the locations where nodes make their contacts.
- With each node’s home location identified, the authors also counted how many times an AP becomes a node’s home location and plotted the histograms over all the APs for each group in Fig. 2(b-d) respectively.
- For each node in UCSD, the authors identified the AP where it could meet the largest number of distinct nodes, as well as its 2nd, 3rd, and 4th popular APs for comparison.
- It is surprising to see that overall there are nearly half of the nodes having one location, i.e. AP 173, as their pub location, and AP 173 is the most and the only popular pub location candidate for both component nodes and isolated nodes.
- The authors omit the detailed statistical results here for space reason, interested readers can refer to their technical report [15].
IV. ROUTING SCHEME
- Motivated by the observations made in the previous section, the authors propose a message routing scheme for DTN networks to avoid the failures and reduce the delays in message delivery.
- As in many message forwarding algorithms (e.g., [7], [19]), a node holding a message can forward the message to a non-destination node only once, after that, the node becomes forwarding inactive and can only pass the message to the destination.
- The message routing procedure in Location is divided into two phases: the first phase happens when the forwarding active node is outside the component of the destination or the destination node is isolated; the second phase happens when the forwarding active node is in the same component of the destination.
- For their experimental evaluation, the authors chose the Greedy strategy used in [19].
- In the Location routing scheme, the authors exploited the location information as well as the social network structure (i.e. components) in the first routing phase.
V. PERFORMANCE EVALUATION
- The authors evaluated the performance of the proposed location-aware approach, and compared it with other four representative DTN routing schemes, which are named Epidemic, Wait, Greedy and Social.
- In particular, the Social routing scheme applies exactly the same strategy used in BUBBLE Rap[7] when routing messages outside of the destination’s component.
- For details of these schemes, please refer to their technical report[15].
- For each routing scheme under study, given a message delivery task between a source and a destination node within a delay constraint, the authors are interested in 1) whether the message can be successfully delivered within the constraint; 2) how many times the message is copied and transferred during the routing procedure.
- The former metric regards the effectiveness of the routing scheme while the latter indicates the cost of bandwidths and storages paid for delivering the message.
A. Overall comparison
- The authors evaluated and compared performances of the five schemes above mentioned using the contact trace from the UCSD dataset.
- The averaged number of successfully delivered messages and the averaged number of message copies are listed in Table II.
- For the message copies, Epidemic duplicates and transfers much more copies than the other schemes, making it impractical under the context of DTN networks.
- Among the three forwarding-style schemes, Location has more copies than the other two.
- As Social and Location perform much better than Greedy, in their following study, the authors only focus on comparing the two schemes.
B. Detailed study
- In Section III, the authors point out that node isolation is the main reason for message delivery failures and delays, they testify this argument in this experiment.
- In addition, for each case the authors only select the infrequent visitors to its pub location.
- Moreover, by comparing the two routing schemes, one can see that although the Location scheme suffers node isolation as well, it outperforms Social all the time.
- In particular, under “Component → Component”, “Component → Isolated”, and “Isolated → Isolated”, when the delay constraint is stringent, say, 5 days, Location delivers much more messages than Social.
VI. CONCLUSION
- The authors considered the message routing problem under Delay Tolerant Networks (DTN).
- By analyzing realworld datasets , the authors found that node isolation is prevalent, and it is the major reason for message delivery failures and long delays in DTN networks.
- The authors also investigated the nodes’ contact-location relationship, and found that there exist pub locations which are of system-wide importance.
- The authors demonstrated the scheme’s effectiveness by comparing it with a number of representative solutions via simulation-based experiments, where real-world contact traces is used to drive the simulator.
- In particular, the authors show that with the awareness of contactlocation relationship, message delivery jobs involved with isolated nodes could be better accomplished, comparing with the schemes without such concern (e.g., Bubble Rap[7]).
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Citations
77 citations
6 citations
Cites methods from "Location-aware routing for Delay To..."
...The few location-based routing protocols [7]–[11] designed in DTN networks assumed delay tolerant network as the 2-plane network to make use of 2-dimensional(2D) position information to route messages, such as (x, y) planar coordinates....
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6 citations
Cites background from "Location-aware routing for Delay To..."
...While Bubble and similar algorithms successfully leverage social context, they do not specifically account for spatial variations that underlie the cliqued network graphs upon which the algorithms are based....
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5 citations
Cites background from "Location-aware routing for Delay To..."
...Analysis on real-world movement traces show that nodes spend about 90% of their time in just one geographic region [11]....
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Cites background from "Location-aware routing for Delay To..."
...Controlledflooding protocols [13], [9], [10], [2], [6], [5], [14] prevent nodes from unconditionally exchanging messages with other nodes to avoid excessive message exchanges....
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References
4,355 citations
"Location-aware routing for Delay To..." refers background in this paper
...scheme[11] based on flooding makes use of every device contact, it is regarded as impractical due to the large number of message duplicates generated during the routing procedure....
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2,712 citations
"Location-aware routing for Delay To..." refers background in this paper
...The Spray and Wait routing[12] makes an effort on reducing the duplicates by assigning certain limitation on message...
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1,854 citations
"Location-aware routing for Delay To..." refers methods in this paper
...Using the weighted contact graph, the intra-component delay is defined as the mean distance between any two nodes in a same component using the MED algorithm[2], and the inter-component delay is defined as the mean distance between one component and one isolated node....
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...Examples of such flat network routing schemes include MED[2], FRESH[3], PRoPHET[4], MobySpace[5], and SimBet[6]....
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...Examples of this forwarding-style schemes include MED[2], FRESH[3], PRoPHET[4], MobySpace[5], SimBet[6], and delegation forwarding[13]....
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...In the second phase, many message routing strategies such as the ones used in MED[2], FRESH[3], PRoPHET[4], and MobySpace[5] can be applied....
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...Examples of this forwarding-style schemes include MED[2], FRESH[3], PRoPHET[4], MobySpace[5], SimBet[6], and del-...
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1,750 citations
"Location-aware routing for Delay To..." refers methods in this paper
...Examples of this forwarding-style schemes include MED[2], FRESH[3], PRoPHET[4], MobySpace[5], SimBet[6], and del-...
[...]
...as the ones used in MED[2], FRESH[3], PRoPHET[4], and MobySpace[5] can be applied....
[...]
...Examples of such flat network routing schemes include MED[2], FRESH[3], PRoPHET[4], MobySpace[5], and SimBet[6]....
[...]
...Examples of this forwarding-style schemes include MED[2], FRESH[3], PRoPHET[4], MobySpace[5], SimBet[6], and delegation forwarding[13]....
[...]
...In the second phase, many message routing strategies such as the ones used in MED[2], FRESH[3], PRoPHET[4], and MobySpace[5] can be applied....
[...]
1,666 citations
"Location-aware routing for Delay To..." refers background or methods in this paper
...For example, in the Bubble Rap routing[7], nodes are explicitly grouped into communities, and different routing strategies are applied based on the community structure....
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...the destination’s component: in Social, the message is forwarded to popular nodes which have met more distinct nodes, and this is exactly the strategy used in BUBBLE Rap [7]; while for Location, information of pub locations is exploited, and the message is forwarded to popular nodes associated with a same pub location....
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..., [7], [20]), a node holding a message can forward the message to a non-destination node only once, after that, the node becomes forwarding inactive and can only pass the message to the destination when encountered....
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...Our work is different from previous works: the difference between our work and BUBBLE Rap is that in our work, in addition to label the social structure, we use a twodimensional labeling by incorporating nodes’ contact-location information; and our work differs with MobySpace in that unlike the simple message forwarding based on the destination dependent location similarity, we use the location information in addition to the social information to structure the network and accelerate the message delivery....
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...In the recent proposed BUBBLE Rap routing scheme[7], communities among the nodes are detected and explicitly labeled, and different forwarding strategies are applied for different routing phases based on the community structure....
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Frequently Asked Questions (8)
Q2. What is the definition of a contact graph?
Given a dataset d, a contact graph G(d, t) = (V,E) is defined as an undirected graph, with V as the vertex set where each node in the dataset corresponds to a vertex.
Q3. What is the definition of the intercomponent delay?
With the weighted contact graph, the intra-component delay is defined as the mean distance between any two nodes in a same component using the MED algorithm[2], and the intercomponent delay is defined as the mean distance between one component and one isolated node.
Q4. What are the two metrics of a contact graph?
With node isolation widely observed, to investigate its implication on the DTN routing problem, the authors studied two metrics of a contact graph, namely the intra-component delay and the inter-component delay.
Q5. Why do the authors believe that Location is the route for message delivery?
The authors believe this is because by the replicating operation in the Location scheme, the source node has more chances to forward the message into the destination node’s component.
Q6. What is the main reason for the latency and the failure in DTN’s message delivery?
The observation suggeststhat node isolation is the major reason for the latency and the failure in DTN’s message delivery, and should be their focus in designing the routing scheme.
Q7. How many source/destination pairs did the authors randomly select for each routing scheme?
In their first experiment, for each routing scheme, the authors randomly selected one hundred source/destination pairs for message delivery, and the authors did not restrict the delay constraint.
Q8. What is the metric for the inter-contact delay?
To define the metrics, the authors modified the contact graph into a weighted contact graph Gw(d), where for each edge on the graph, its weight is defined as the averaged inter-contact time between the two corresponding nodes.