# Geo-DMP: A DTN-Based Mobile Prototype for Geospatial Data Retrieval
## 2 Literature Review
### Named Content Retrieval  
Indisputably, an evolution has taken place in the way of network usage, as several recent reports [42; 43] suggest that data traffic is overwhelmingly dominated by digitized contents. Such a new trend indicates that, instead of \"end-to-end\" conversations, now users are more concerned with obtaining desired contents efficiently.  
Disappointingly, Internet-related protocols are not really good at this aspect: The \"link rot\" problem [44; 45] often causes inaccessibility, and target host-centric requests result in repeated transmissions and significant waste on bandwidth [46]. Though remedial measures such as content distribution network (CDN) and peer-to-peer (P2P) overlays have been proposed, these patching methods inevitably introduce extra complexity and unexpected problems, as the high financial cost for content publishers and maintenance cost for service providers in CDN [47]; and a massive amount of cross-ISP traffic which is contradictory to policies of ISPs in P2P [48].  
This is what prompts the academic communities to reconsider clean-slate content-centric designs for the next generation of inter-networking. Among all proposals, information-centric networking (ICN) [49] is a representative solution that attracts much attention. Unlike conventional IP-based networking, ICN natively privileges contents and their unique names to serve the purpose of efficient dissemination and reduction on network load.  
Interestingly, despite some dissimilarities in applicable scenarios, DTN shares many commonalities with ICN in respect of in-network caching, late-binding technique, hop-by-hop transport, and asynchronous interaction model. Therefore, it is plausible to borrow the main ideas of ICN to tackle with the inefficiency of content acquisition and resource utilization in DTN. Lately, several research works attempt to directly extend ICN approaches to DTN [50; 51; 52; 53]. However, such migration is neither effortless nor seamless. For one thing, studies of ICN are still in its nascent stage and lots of problems remain unsolved. For another, it should be noticed that ICN and DTN have essential architectural differences.  
To gain the synergy with less investment, the Delay-Tolerant Networking Research Group (DTNRG) proposes the bundle protocol query (BPQ) mechanism [54]. BPQ enables content naming as well as name-based matching, caching, and routing. More importantly, it is compatible with antecedent DTN standards, which means modifications on the basic framework can be minimized and existing works in DTN still have their values. Even though BPQ is often mentioned in past papers [55; 56; 57; 58], it is not fully exploited in research work. As far as we know, only two papers put BPQ into practice: in [59], BPQ is adopted to mingle the protocol stack of DTN and named data networking (NDN) [60]. Ref. [61] presents an architecture for offloading contents that are bulky and do not have a tight delivery deadline from cellular network to local DTN network, in which BPQ works for content lookup among DTN nodes. To further explore the possibilities of BPQ, in this paper, we apply BPQ to the dissemination of geospatial data. Additionally, location indicators are incorporated in BPQ-enabled bundles to supplement more information for routing decisions.