Performance Comparison of Content-oriented Networking Alternatives : A Hierarchical Tree versus A Flat Distributed Hash Table

The internet was designed with host-oriented networking applications such as file transfer and remote login. However, recent internet statistics show that content-oriented traffic (e.g. web pages, multimedia clips) becomes more and more dominant. Even though content-oriented networking has received increasing attention, there have been few comprehensive and quantitative studies on how to realize a content-oriented networking framework. In this paper, we focus on the operational issues of the new networking framework: (i) how to locate contents, (ii) how to deliver contents, and (iii) how to cache contents. There are two major infrastructure alternatives in substantiating these mechanisms: a tree and a distributed hash table (DHT). We carry out comprehensive simulation experiments to compare these alternatives in terms of content transfer latency, cache effectiveness, and failure resilience. I. I NTRODUCTION The Internet has evolved from a small-scale academic testbed into a crucial social infrastructure. For 40 years since its inception, the Internet has tried to accommodate new and unanticipated requirements. However, its rigid design based on TCP/IP, internet service providers’ exclusive control of networks and so on have ossified the Internet [6]. One of the Internet design principles that hinders the current Internet evolution is the host-oriented communications. That is, the early stage Internet applications, such as remote login, file transfer, and e-mail, focused strictly on host-to-host communications, where an end user explicitly directs his/her host to communicate with another host. Over the past several years, however, the vast majority of Internet usage has become data retrieval and service access [23], [3], [16] (i.e.,data-orientedusage), where an end user cares about contents 1 but is oblivious to or less aware of the host (or its location) [16]. For example, (i) many people often use search engines like Google from which they jump to the data or service page irrespective of the location in which the desired data/service resides, (ii) web intermediaries such as web caches and content delivery networks (CDNs) [18] transparently redirect web clients to a nearby copy of the requested data without contacting the original Web server, and (iii) peer-to-peer (P2P) applications enable users to search and 1In this paper, we use “data” and “contents” almost interchangeably. In the literature, “contents” often have more semantics than “data”. retrieve the data without making them know the location or identity of the host. The common viable contribution of search engines, web caching, CDNs, and P2P applications is that they all seek to support data-oriented applications. They improve the data availability, ease-of-use, performance, and scalability of applications by overcoming the limitations of the host-oriented principles of the legacy Internet by manipulating DNS naming and/or name resolution. In other words, they decouple content files from their locations (or hosts) using various techniques such as caching, replication with transparent request redirection, maintenance of a searching infrastructure, etc. [16]. Recently, lessons from these several application/servicedependent ad-hoc solutions, have motivated “clean-slate” efforts [1], [16], [10], termed data-oriented or content-centric networking, which strive to redesign the host-oriented Internet to accommodate more and more dominant data-oriented Internet usage at the architectural level. The essence of contentoriented networking lies in decoupling contents from the service host/location not at application levels, but at networking levels. That is, content-oriented networking shifts the focus from transmitting data between two hosts (or their locations) to delivering data via a content identifier 2. The content-oriented networking architecture is expected to (i) free application/service developers from re-inventing the necessary mechanisms, and (ii) provide scalable and efficient delivery of the requested contents. However, there have been few studies that how to substantiate the content-oriented networking infrastructure in terms of performance metrics. In order to address the operational issues that are missing in the recent architectural studies on content-oriented networking in the literature, this paper explores two alternatives for content-oriented network infrastructures: a hierarchical tree and a flat distributed hash table (DHT). Whether we choose a tree or a DHT for the infrastructure affects almost every aspect of network operations: name resolution, content delivery, caching, and so on. We will compare these two alternatives in terms of scalability, robustness, transfer latency thoroughly. 2As an example, the Data-Oriented Network Architecture (DONA) [16] r places endpoint-based DNS by a new name resolution mechanism using flat, certifying names and name-based anycast primitives above the IP layer.