A Survey on Security in Mobile Peer-to-Peer Architectures—Overlay-Based vs. Underlay-Based Approaches <s> Integrated <s> We argue that there exists a synergy between peer-to-peer (p2p) overlay networks for the Internet and mobile ad hoc networks (MANETs) connecting mobile nodes communicating with each other via multi-hop wireless links-both share the key characteristics of self-organization and decentralization, and both need to solve the same fundamental problem, that is, how to provide connectivity in a decentralized, dynamic environment. We propose Dynamic P2P Source Routing (DPSR), a new routing protocol for MANETs that exploits the synergy between p2p and MANETs for increased scalability. By integrating Dynamic Source Routing (DSR) and a proximity-aware structured p2p overlay routing protocol, DPSR limits the number of the source routes that each node has to discover and rediscover to O(logN), while retaining all the attributes of DSR for dealing with the specifics of ad hoc networks. This is in contrast to the maximum of N source routes each node has to maintain in DSR. Thus DPSR has the potential to be more scalable than previous routing protocols for MANETs, such as DSR and AODV. ::: ::: In addition to being a network layer multi-hop routing protocol, DPSR simultaneously implements a distributed hash table (DHT) in MANETs; it implements the same functionalities as CAN, Chord, Pastry, and Tapestry, which can be exposed to the applications built on top of it via a set of common p2p APIs. <s> BIB001 </s> A Survey on Security in Mobile Peer-to-Peer Architectures—Overlay-Based vs. Underlay-Based Approaches <s> Integrated <s> Distributed hash tables (DHTs) have proven to be a novel and efficient platform for building a variety of scalable and robust distributed applications like content sharing and location in the Internet. Similar to those in the Internet, distributed applications and network services in mobile ad hoc networks (MANETs) can potentially benefit from the deployment of a DHT. However, bandwidth limitations, node mobility, and multi access interference pose unique challenges to deploying such DHTs in MANETs. In this paper, we first study how to efficiently implement DHTs in MANETs. We explore two disparate design options: the simple approach of directly overlaying a DHT on top of a MANET multi-hop routing protocol, and Ekta which integrates a DHT with a multi-hop routing protocol at the network layer. Second, we examine the efficiency of DHT substrates in supporting applications in MANETs by examining the performance of a resource discovery application built on top of Ekta with one that directly uses physical layer broadcast. Such a study answers the fundamental question of whether a DHT substrate can be more efficient in supporting applications than a physical layer broadcast-based protocol, since in MANETs, DHT protocols effectively rely on physical layer broadcast to discover and maintain routes. <s> BIB002 </s> A Survey on Security in Mobile Peer-to-Peer Architectures—Overlay-Based vs. Underlay-Based Approaches <s> Integrated <s> This paper presents Virtual Ring Routing (VRR), a new network routing protocol that occupies a unique point in the design space. VRR is inspired by overlay routing algorithms in Distributed Hash Tables (DHTs) but it does not rely on an underlying network routing protocol. It is implemented directly on top of the link layer. VRR provides both raditional point-to-point network routing and DHT routing to the node responsible for a hash table key.VRR can be used with any link layer technology but this paper describes a design and several implementations of VRR that are tuned for wireless networks. We evaluate the performance of VRR using simulations and measurements from a sensor network and an 802.11a testbed. The experimental results show that VRR provides robust performance across a wide range of environments and workloads. It performs comparably to, or better than, the best wireless routing protocol in each experiment. VRR performs well because of its unique features: it does not require network flooding or trans-lation between fixed identifiers and location-dependent addresses. <s> BIB003 </s> A Survey on Security in Mobile Peer-to-Peer Architectures—Overlay-Based vs. Underlay-Based Approaches <s> Integrated <s> Scalable source routing (SSR) is a novel routing approach for large unstructured networks such as mobile ad hoc networks, mesh networks, or sensor-actuator networks. It is especially suited for organically growing networks of many resource-limited mobile devices supported by a few fixed-wired nodes. SSR is a full-fledged network layer routing protocol that directly provides the semantics of a structured peer-to-peer network. Hence, it can serve as an efficient basis for fully decentralized applications on mobile devices. SSR combines source routing in the physical network with Chord-like routing in the virtual ring formed by the address space. Message forwarding greedily decreases the distance in the virtual ring while preferring physically short paths. Thereby, scalability is achieved without imposing artificial hierarchies or assigning location-dependent addresses <s> BIB004
Integrated approaches reduce routing overhead by combining the MANET and P2P protocols at the network layer as shown in Figure 6 (c). This way, the number of required routing tables is reduced as no separate MANET and P2P routing tables are required. Further, the routing algorithm may benefit from synergy effects such as updating overlay routing tables based on overheard underlay messages as described below. By reducing the complexity and the number of required entries in the routing table, routing and maintenance overhead may be reduced. Further, knowledge of the physical neighborhood may improve the routing efficiency of the routing protocol. Scalable Source Routing (SSR) proposed by Fuhrmann BIB004 introduces an MP2P architecture based on Chord. Similar to Chord, SSR is based on a ring architecture. However, SSR simplifies routing maintenance as no finger tables are used but only direct virtual neighbors. Further, physical neighbors are listed in the routing table. During routing, a node decides whether a virtual or physical neighbor is closer to the destination. Due to the simplified routing table, maintenance overhead is reduced. Further, by combining MANET and P2P routing tables, the route length can be reduced without increasing the complexity or the routing maintenance required. Additionally, awareness of physical neighbors at intermediate nodes between source and destination in the underlay can improve the efficiency of the routing protocol. The Virtual Ring Routing (VRR) algorithm presented in BIB003 combines the set of virtual and physical neighbors in a single routing table at the network layer. As VRR is based on a Ring architecture, the set of virtual neighbors consists of r nodes with a node-ID next to the node-ID of the routing table owner. Those r nodes consist of the r/2 virtual neighbors clockwise and the r/2 virtual neighbors counter-clockwise. VRR provides bidirectional links to the neighbors and maintains them proactively. The physical node set consists of the nodes in direct transmission range. The routing table provides the next underlay hop with an endpoint closest to the requested ID when an object is requested. As each intermediate node checks its own routing table before forwarding the request, requests may be rerouted when intermediate nodes are aware of shorter routes. This way, routing is simplified and overhead is reduced. As a further optimization, every overheard or forwarded packet may be harnessed to update the routing tables in order to reduce maintenance overhead. This is the basic concept of EKTA BIB002 and DPSR BIB001 . Both integrated approaches implement a Pastry DHT on the network layer. Similar to Pastry, a primary and a leafset routing table are provided. Complete multi-hop routes are stored at these routing tables to avoid underlay flooding during overlay routing. Shortest routes are preferred to reduce overhead. Whenever a message is overheard, the routing table is updated by routing information obtained from the message. Due to this, overhead generated by routing table maintenance is strongly reduced.