Vehicular Content Centric Network (VCCN): A Survey and Research Challenges Safdar H. Bouk1 , Syed Hassan Ahmed2 and Dongkyun Kim3 School of Computer Science & Engineering, Kyungpook National University, Daegu, Republic of Korea.
{1 bouk,2 hassan,3 dongkyun}@knu.ac.kr ABSTRACT Recently, Content Centric Networking (CCN) has been proposed for the Future Internet. Since CCN is at an early bud stage, many issues are still unidentified and open. In this paper, we investigate the feasibility of applying the CCN concept to vehicular communications (named as Vehicular CCN, VCCN in this work). In addition, we identify a number of VCCN challenges such as naming, name resolution, routing or forwarding strategies, content storing, management and policy of forwarding information base and pending interest table management, security and trust issues, etc.
Categories and Subject Descriptors C.2.1 [Network Architecture and Design]: Distributed Networks, Network Communications, Wireless Communications.
General Terms Design, Performance, Reliability, Security.
Keywords VANETs, CCN, VCCN.
1.
INTRODUCTION
From the past decades, Vehicular Ad hoc Networks (VANETs) have been extensively investigated by researchers, academia and industries. Vehicular ad hoc networks (VANETs) are getting closer and closer to reality in everyday life by providing vehicles and roadside units (RSUs) with communication capabilities. Although initially designed to improve road safety, VANETs can additionally offer commercial, informative, and entertainment services to drivers and passengers [1], thus also providing revenues to the car manufacturers and service providers. However, for a deep market penetration of VANETs, much effort is still required to deal with some issues typical of vehicular environments such as the fast changing topology, the Permission to make digital or hard copies of all or part of this work for personal or classroom use is granted without fee provided that copies are not made or distributed for profit or commercial advantage and that copies bear this notice and the full citation on the first page. To copy otherwise, or republish, to post on servers or to redistribute to lists, requires prior specific permission and/or a fee. Request permissions from
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shorten intermittent connectivity, the unique set of applications, and the harsh propagation conditions. Such distinguishing features demand the design of new emerging networking solutions to replace the traditional end-to-end hostcentric Internet paradigm depending on its TCP/IP protocol stack, which is mostly ineffective in mobile wireless environments. The typical location-based and time-dependent vehicular applications would rather have benefit of in-network and decentralized data caching and replication mechanisms, as also acknowledged in [2]. As a matter of fact, the Wireless Access in Vehicular Environments (WAVE) protocol stack [3], which has been considered for VANETs, supports data exchange without the TCP/IP overhead, by means of the WAVE Short Message Protocol (WSMP) designed for safety critical and control messages. For instance, there are two main communication paradigms in VANETs, namely infrastructure-less and infrastructurebased ones. In the former, vehicles communicate with each other (i.e. vehicle to vehicle or V2V communication) regardless of any support from infrastructure element. In the infrastructure-based one, communications involve infrastructure based elements, i.e. Road Side Units or RSUs (vehicle to Infrastructure or V2I communication). Mobility is an intrinsic feature of the VANETs, resulting in a highly dynamic vehicular network topology. Therefore, the information communication in an extremely dynamic topology is challenging. Recently, Content Centric Networks (CCNs) has been adapted in VANETs by several researchers, which is an emerging trend for future communications [4]. CCN mainly shifts the communication concept from host-based to the information centric. In traditional communication networks, it is mandatory that a node in the network must be assigned its unique ID (e.g. IP address). The source node(s) use(s) this/these unique IDs to locate destination node(s) to perform information communication. Similarly, both the source and destination nodes must establish and secure the communication channel before routing any sensitive information between each other. One of the most challenging task that traditional networks had been facing is the mobility management of hosts. In presence of mobility (e.g. change in a source or destination host’s topological and/physical location), it is difficult to retain the same host IDs as well as to maintain the ongoing communication path(s). In contrast, CCN assigns an unique ID (called name) to the information instead of a host, which attempts to relinquish information from host’s physical location and supports node mobility. In a content-centric network, each content unit is self-identifying and self-authenticating and can be retrieved by its name regardless of its location. This is a particularly
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Motivation
The need of emerging CCNs for vehicular networks is also investigated in [6] to improve information-rich applications. However, only a few works have focused on CCN for VANETs, despite the recent interest in research projects targeting the CCN paradigm. Thus, more attention is required to cope with the performance and deployment issues for Vehicular Content Centric Networks (VCCNs). More specifically in this paper, we would like to summarize the recent research and efforts made for advancements in VCCNs. Likewise traditional networks, VCCNs are also facing several basic issues such as content naming, name resolution, transport issues, forwarding, congestion control and so on. We therefore provide a road-map to be followed by the CCN research community. Moreover, we aim to provide readers with salient differences between conventional VANETs and forthcoming paradigm, VCCNs. The rest of this article is organized as follows. In Section II, we provide details of VANETs and CCN. Section III includes description of VCCNs along with its components. Section IV discusses the open issues and future research directions. Finally, we conclude this survey in Section V.
2.1
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attractive solution for highly mobile and dynamic environments like VANETs. In addition, CCN uses simple RequestReply based communication model, where a requesting node sends Interest messages and the Provider sends a Response message with a requested data in response. According to the recent literature [5], CCN is known to be a key enabling paradigm for upcoming Vehicular Ad hoc NETworks (VANETs). Due to no dependency on IP address, it can potentially eliminate issues related to IP allocation, setup and maintenance of delivery paths and session establishment before data transfer. However, applying the CCN model to vehicular environments is not straightforward. More specific functionalities have to be introduced in the content naming, forwarding and transport mechanisms to cope with the hostile propagation environment, the limited and intermittent connectivity, the broadcast nature of the radio channel, and the node mobility.
2.
IP
Figure 2. VANET vs CCN: Overview
Figure 1. VANETs Overview
1.1
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CCN IN VANETS CCN: Basics
Information Centric Networking (ICN) has become one of the main potential architectures for the Future Internet and several related projects are active worldwide [7]. In this scope of research, the Content-Centric Networking (CCN) architecture proposed by Jacobson et al. [8] has rapidly
gained interest and it is now the ground of many research initiatives running worldwide, including Named-Data Networking (NDN). Generally, each content or data in CCN is associated with a location independent name that is directly used by the applications for content search and retrieval. Communication is driven by the receiver, which uses an Interest packet to request a content by name. The content provider, or any other network node that stores the requested content, replies with a packet that contains the required content along with additional authentication and data integrity information. From recent literature [9], it has been noticed that CCN is an effective networking paradigm that well matches the features of wireless environments. Indeed, CCN can overstep the inefficiencies of TCP/IP while handling node mobility, unreliable wireless links, and resource-constrained devices by relaxing the need of creating and maintaining stable end-end sessions. Moreover, CCN may leverage the broadcast channel nature and help the content sharing between neighboring nodes. Some good surveys have addressed information-centric solutions [10] [11] and focused on topics such as naming, mobility management and caching, e.g., [12][13]. However, our discussions in this paper differs from the previous ones since it focuses specifically on the CCN paradigm for VANETs, and it provides a comprehensive overview and clearly identifies a number of challenges currently faced by CCN.
2.2 CCN in VANETs: Applications Perspective Figure 1 provides an overview of VANETs, where vehicles can communicate with each other using V2V architecture and V2I infrastructures are also explored in the literature [14]. In addition to safety applications, a large variety of applications are anticipated for VANETs. Numerous car manufacturers are taking information dissemination into account for upcoming vehicles. Those applications include parking lots, traffic/weather conditions, fuel prices, points of interest, bus times, etc. In addition, an entertainment applications (e.g., file sharing, web browsing, gaming, etc.) are also the part of future cars. Most of the applications specifically in vehicular environments consider vehicles in a given area, regardless of their identity or IP address. In Figure 2, we therefore show the network layers supporting CCN in VANETs, where CCN takes over the TCP/IP layer. For example, the push-based dissemination and pull-based querying techniques, focusing on the content and the temporal and spatial scope of information, are both advocated in [15] to tackle the demands of information-rich vehicular applications. They can be considered as a form of content-based communications, thus overlapping the traditional host-centric paradigm since messages
are routed based on their content name rather than on their destination address. Publish-subscribe (pub/sub) event notification belongs to push-based communication, where senders publish messages and receivers subscribe for different contents provided within a network. Examples of pub/sub approaches for VANETs can be found in the literature such as [16]. The pub/sub paradigm is well-suited for some VANET applications where drivers/ vehicles indicate their interests about certain types of notifications (e.g., warnings concerning traffic jams only within 1 km from the vehicle’s current location) announced by the publishers. Since the other vehicular applications could get benefit from pull-based approaches that deliver content upon demand (e.g., map download, file sharing). The CCN framework well suits pull-based applications where a given content, which might be available from multiple providers, is transmitted on demand in reply to an Interest. Due to the data caching available in on-board units of every vehicle, contents can be spread into the network as vehicles move around, without being tied to a specific node. This nature of CCN somehow solves provider mobility issues and content availability is increased. Moreover, vehicles (and adjacent infrastructures such as RSUs) themselves could generate data on demand in response to a particular interest, without conventional publishing procedures. Both pub/sub event notification and on-demand content delivery is based on asynchronous communication. However, they have some conceptual differences, mainly in terms of a source of the content flow and content validity over time, as discussed in [17]. Therefore, we can conclude that in CCN, each content is self-authenticated, identical and can be retrieved regardless of its location, thus providing an attractive solution for highly dynamic and mobile environments such as VANETs.
3.
VCCN: BASIC OPERATIONS
In this section, we describe the CCN concepts emerging into vehicular networks and its operations. We collectively name this paradigm shift as a Vehicular Centric Content Network (VCCN). In future networks1 , each vehicle expects to be equipped with multiple interfaces for communication such as 802.11, LTE, WiMax and so on. Due to the increasing interest for a network paradigm shift such as ICN, multiple architectures supporting content-centric have been recently proposed [19]. Most of them are based on some pre-defined set of rules but they differ in the way their operations are performed. For instance, we target the CCN architecture for VANETs (VCCN), whose ideas are now the main focus of many European and US research projects. The main VCCN building blocks are as follows:
3.1
Naming
Each content packet is associated with a unique, hierarchically or hash-based name that is directly used by the VCCN applications for content search and retrieval. This content name is independent of any transport connections.
3.2
Security
Data authentication and integrity are considered as the pillars of network security. Thus, they are included into 1
CCN is one of the promising solution to the Future Networks [18]
every content/data packet containing a signature piggyback with provider information. Different Encryption/Decryption techniques can be used to provide access control, but not applied to contents available for public use.
3.3 Caching Since each content packet is a self-consistent (i.e. selfidentifying and self-authenticating) unit, caching operation is facilitated. Each network node can provide content caching that is limited only by resource availability. Various caching policies can be implemented in order to speed up data retrieval and delivery, depending on the features of the nodes and the requirements of applications.
3.4 Communication model As shown in Figure 3, most VCCN communications have receiver-driven process based on two types of packets: the Interest, which carries the request for a content unit identified by its name. Each node2 propagating an interest is named a Consumer and similarly a vehicle providing that content is called a Provider. A consumer requests a DATA/Content3 by broadcasting an Interest packet over all available connectivity interfaces, where any node with the content can be a provider.
3.5 Node model Similar to CCN, each node in VCCN maintains three data structures: (i) a Content Store (CS) storing the produced and incoming contents; (ii) a routing table named Forwarding Information Base (FIB), which stores the outgoing interface(s) to forward the Interests; (iii) a Pending Interest Table (PIT), which keeps track of forwarded Interests so that received content can be sent back to the consumer(s).
3.6 Retrieval process A prefix-based name searching is done for each content by each node in its CS after receiving an Interest. If a node finds a matching, it sends the requested content back to the same interface from which the Interest was received. Otherwise, if there is a match in PIT, the arrival interface of the Interest is added to the PIT and the Interest is discarded to avoid duplicated interest. Otherwise, if there is an interest matching in FIB, the Interest is sent towards the data provider (or source) and it is recorded in PIT. If there is no match for the Interest, it is discarded. Contents are required to follow the chain of PIT entries back to the consumer(s).
3.7 Transport In order to provide a reliable transport, Interests that are not satisfied in a specified time period must be retransmitted by the original consumer. However, alternative transport services can be specified, depending on application requirements and network constraints.
4. VCCN: RESEARCH CHALLENGES Although CCN provides promising solution for VANETs in the future, extending the model to support vehicular communications is not straightforward. Many open issues must be properly addressed. Therefore, in this section, we identify a number of challenges in VCCN/CCN domain, which 2
Generally a ”node” refers to a ”vehicle” in VANETs. The terms DATA and CONTENT are interchangeable in the context of this manuscript 3
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of VCCN topologies coupled with the channel unreliable and congestion rises many challenges in the application of such a mechanism.
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The basic operation of VCCN requires one Interest to be sent per packet, which may result in high signalling overhead [16, 17]. Because of the broadcast shared medium, packets using the same route, or close routes, in opposite directions may severely affect each other: Interests on the forward path may contend with the related content on the reverse path and cause interference between interest and content packets.
4.5 Naming Schemes and Name Resolution
Figure 3. VCCN: Communication Model
to the best of our knowledge are new to grab attention from the research community (See Fig. 4).
Information naming is the most important issue in VCCN because all the basic CCN functionalities also depend on this feature [18]. There are different naming schemes that have been proposed for VCCN that are categorized into different categories including flat, hierarchical, human-readable, hash-based, attribute-based, and hybrid-naming schemes. Which scheme is more suitable for VCCN is still an open issue. Thus, in-depth and potential evaluation of each naming approach should be made. Routing of the information can be achieved purely on the basis of the content name or it may require name resolution. Name resolution service is required for the overlay architecture i.e. NetInf, to resolve name into a locator that is used for information communication. The current Domain Name System is not suitable for name resolution system. Therefore, a new resolution technique is required for VCCN.
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Figure 4. Hive view of Research Challenges in VCCN
Channel Constraints
As discussed earlier, the Content retrieval starts with Interest broadcasting over the available network interfaces at the consumer node (e.g., the IEEE 802.11p interface in case of current vehicular devices) and the Interest forwarding is repeated by intermediate relays on the path to the content provider. However, due to the broadcast nature of wireless medium, two conclusions are made: firstly the broadcasting enables packets overhearing, thus helping to cache the content packets and to take decisions about packet forwarding; secondly, it can lead to the well-known broadcast storm problem [20], thus leading us to consequent scalability issues. A robust and bandwidth efficient transport solution is needed to enforce broadcast storm mitigation techniques and also cope with unreliable and maximum error-free wireless links.
4.2
Dynamic Network Topologies
Since a node in VCCN communicates without the need to obtain the IP address, mobility can be natively supported in this domain as shown in [20]. However, because of connected links only for limited time and extremely fast connectivity dynamics, VCCN represents a very unique and challenging environment for mobility management. More demanding approaches should be implemented in order to reduce disruption periods under intermittent connectivity.
4.3
Interest Flooding
In VCCN, multiple Interests asking for successive contents may be pipelined in the shape of sliding window flow control. By properly tuning the Interests transmission rate, traffic flow can be controlled according to the available network resources. However, as aforementioned, the high dynamics
The content routing is one of the actively researched parts of VCCN [19]. Request and Response forwarding between consumer and provider nodes is the responsibility of the routing scheme. The simplest routing scheme that has been used in the CCN is the breads-crumb technique. However, to achieve QoS in dynamic topologies such as VANETs, we need an efficient routing scheme to fulfill requests effectively and efficiently.
4.7 CS, FIB and PIT Management The contents generated or received by any node in the VCCN are stored in the CS. It requires cache management policies to effectively utilize the memory space and provide correct and timely content to the requesting node. The storage time of contents inside the CS should be based on the information priority, usability, arrival time, size and many other factors. Each Request or Response message received or forwarded via any interface, must go through FIB and PIT structures of the VCCN. There can be thousands of entries that are entered, removed or searched within the FIB and PIT structures. To provide timely communication in VCCN, FIB and PIT management, maintenance and searching strategies should be fast and efficient.
4.8 Security in VCCN Many issues related to security are completely open. It is worth mentioning that many wireless nodes are resource constrained devices and signature and authentication operations can be computationally expensive in terms of time and energy resources consumption. This further complicates the management of the wireless security framework. Therefore, the use of public key cryptography claims for two open tasks:
(i) definition of an efficient key management methodology that works both with and without infrastructure environment, and (ii) development of computation and bandwidth efficient signature schemes.
4.9
Caching in VCCN
One of important concerns in VCCN is content caching [20]. Currently, the storage is becoming cheaper and portable and many devices such as modern smart phones and tablets have significant storage capacity often reaching several gigabytes. Thus, caching space would not be a big matter, unless considering battery-constrained devices and sensors typically equipped with a few kilobytes memory. Several design options shall be considered to decide where, what, and how long to cache data. For instance, in an environment with nodes equipped with heterogeneous capabilities, data storage could be distributed in a few nodes which are more powerful than the others. In a more general case, the popularity, the priority, and the type of contents could make the difference to decide what and how long to cache data.
5.
CONCLUSION
In this paper, we have discussed recent advancements in the new emerging paradigm for vehicular networks known as Content Centric Networks (CCN). CCN recently gained popularity among other Information Centric Network (ICN) architectures. Since CCN nodes communicate regardless of location-dependency and host centric approaches (IPs), thus providing promising solution for upcoming vehicular networks. We collectively named this emerging technology as Vehicular Content Centric Network (VCCN). However, applying CCN to VANETs is not straightforward. Therefore, we provided an overview of CCN with respect of VANETs and its applications. Although some good surveys were presented for information-centric networks and focused on topics such as naming, mobility management and caching, e.g. [12][13]. However, our contribution in this paper differed from the previous ones since it focused specifically on the CCN paradigm for VANETs. Moreover, we provided readers with many research challenges connected with VCCN, needing the attention from research community working for VANETs and CCN domains.
Acknowledgment This research was supported by the MSIP(Ministry of Science, ICT & Future Planning), Korea, under the C-ITRC (Convergence Information Technology Research Center) support program (NIPA-2014-H0401-14-1004) supervised by the NIPA(National IT Industry Promotion Agency). This research was also supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology (2012R1A1A4A01009954).
6.
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