With the increase of smart devices and demand for new networking applications (i.e., online games, social networking services, and high definition multimedia), Internet has been explosively grown in terms of data traffic and the number of connected devices in recent years (Saleh and Simmons, 2011). However, current Internet routing and addressing systems are facing various challenges such as routing scalability, mobility support, multihoming support, etc., due to the use of an IP address as a single namespace simultaneously expressing an identifier and a location of a mobile node (MN) (Meyer et al., 2007). In order to address the single namespace issue in the Internet, several ID/locator separation architectures have been proposed and widely recognized as a promising technology for the Future Internet (Kafle and Inoue, 2012).
ID/locator separation architectures can be categorized into two approaches: host-based approach and network-based approach. Host-based approaches, such as host identify protocol (HIP) (Moskowitz et al., 2008), Shim6 (Nordmark and Bagnulo, 2009), and identifier-locator network protocol (ILNP) (Atkinson et al., 2010), decouple IDs from locators in the host's protocol stack. On the other hand, network-based approaches separate core networks and edge networks by means of routers. Locator/identifier separation protocol (LISP) (Farinacci et al., 2012) is a representative example of network-based ID/locator separation architectures. Mobile-oriented Future Internet (MOFI) is another proposal for network-based ID/locator separation protocol in mobile environments (http://www.mofi.re.kr/). As reported in Kim et al. (2008), since network-based approaches have some advantages (e.g., low implementation cost and easy deployment) over host-based approaches, a network-based approach similar to LISP is assumed throughout this paper.
Figure 1 shows a LISP architecture where ingress tunnel routers (ITRs) and egress tunnel routers (ETRs) are gateways between core and edge networks. When an MN moves to ITR/ETR2 from ITR/ETR1, ITR/ETR2 registers the ID/locator binding of the MN to a mapping system. If a packet destined to the MN arrives at ITR/ETR0, ITR/ETR0 requests the MN's location information from the ID/locator mapping system. After obtaining the location information, ITR/ETR0 can transmit the packet to the MN through ITR/ETR2.
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Fig. 1.
ID/locator separation architecture.
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As shown in Fig. 1, an ID/locator mapping system consisting of one or multiple mobility agents (MAs) is indispensable to register and retrieve the location information of MNs.1 The ID/locator mapping system can be organized in centralized and distributed manners. A centralized mapping system (CMS) employs only one MA and thus the MA can be a single point of failure and bottleneck. On the contrary, several MAs are employed in a distributed mapping system (DMS) and thus an additional mechanism is needed to find out the serving MA for a specific MN. In the literature, DMS with multicast and DMS with distributed hash table (DHT) have been suggested (Fischer et al., 2008, Zhai et al., 2011 and Gohar and Koh, 2012). However, to the best of our knowledge, no works on comparative study among these mapping systems have been reported.
In Kim et al. (2012), we developed analytical models for evaluating CMS, DMS with multicast, and DMS with DHT in ID/locator separation architectures. The analytical models evaluate the signaling and processing overheads for location update and location query procedures. Two well-known topologies (i.e., mesh and tree) are considered to represent the both ends of network deployments. By extending out previous work (Kim et al., 2012), we propose an enhanced DHT to reduce the signaling overhead incurred in DMS with DHT and develop its analytical model. We also present a new analytical model on the processing latency at the mobility agent to assess the scalability of the mobility agent. Numerical results demonstrate that DMS with enhanced DHT provides higher scalability with comparable or low signaling overhead compared with other mapping systems (i.e., CMS, DMS with multicast, and DMS with DHT).
The remainder of this paper is organized as follows. Related works and the detailed descriptions of CMS and DMS are described in 2 and 3, respectively. Section 4 describes the analytical models for CMS, DMS with multicast, DMS with DHT, and DMS with enhanced DHT. Numerical results and concluding remarks are given in 5 and 6, respectively.
In this work, we have conducted a comparative study of centralized mapping system (CMS) and distributed mapping system (DMS) in ID/locator separation architecture. Specifically, analytical models on location update cost, location query cost, and processing latency are developed. Numerical results demonstrate that CMS and DMS with enhanced DHT are tolerant to the scale of networks in terms of signaling overhead compared with DMS with multicast. On the other hand, CMS has several weak points such as higher processing overhead. DMS with DHT can mitigate the overhead incurred in CMS at the expense of the increased signaling cost. In particular, DMS with enhanced DHT can reduce the signaling cost by extending the finger table. Consequently, DMS with enhanced DHT is a more attractive solution for scalable and fault-tolerant mapping systems in ID/locator separation architecture. Currently, we are building a testbed for DMS with (enhanced) DHT under the MOFI project (http://www.mofi.re.kr/), and thus an experimental study over the testbed will be conducted in the future. We will also investigate how to use efficient caching strategies in DMS schemes for better performance.
