# Software-Defined Named Data Networking in Literature: A Review
## 3 Overview and Background
### Named Data Networking  
NDN employs an hourglass architecture similar to the TCP/IP protocol stack, as shown in Figure 1. From the figure, one can see that unlike the traditional Internet hourglass model, the NDN architecture introduces a paradigm shift by replacing IP packets in the network layer with content chunks, effectively eliminating the need for a separate transport layer. This transformation is further enhanced by the addition of a security layer on top of the content layer, ensuring data integrity and authenticity. Additionally, a strategy layer is introduced at the bottom of the content layer, which optimizes data retrieval based on network conditions, thus making NDN a more efficient and secure data retrieval system. By maintaining this hourglass structure, NDN acknowledges the successful design of the Internet, which has facilitated significant growth by encouraging innovation across various layers [13]. However, NDN introduces a new shift by redefining the thin waist to prioritize the retrieval of data (contents) over data locations (IP addresses). This shift reflects a profound understanding of the strengths and limitations of the current Internet architecture. NDN fundamentally changes the semantics of network services by moving from delivering packets to specific destination addresses to retrieving data identified by names. Furthermore, NDN addresses security concerns by incorporating basic security measures at the thin waist, ensuring data integrity through the signing of all named data by the data producers. By retrieving data based on names rather than IP addresses, NDN avoids issues related to security and enables seamless mobility, as data names remain unchanged, unlike IP addresses, which must change when users move to a different location. This approach is in line with modern application development trends, where applications prioritize the information they need over specific locations, enhancing the adaptability and functionality of NDN [14]. In NDN, several key terms are used to distinctly identify its various components [4]. Figure 1: Hourglass-shaped NDN architecture (**right**) and hourglass-shaped Internet (**left**). * Packet: A packet refers to a named data object (NDO) that exceeds the network's maximum transmission unit (MTU) in size. When an NDO is broken down at the data link layer, these smaller pieces are known as frames. NDN typically processes two kinds of packets: interest and data (Figure 2). o An interest packet signifies a request for specific data. When a consumer requires certain information, it dispatches an interest packet into the network to find the desired content. o In contrast, a data packet carries the actual content being transmitted. It answers the requests initiated by interest packets, delivering the requested data to consumers. * Consumer: A consumer is an entity capable of generating names and requesting data through interest packets. * Producer: A producer is an entity that produces data packets to meet consumer requests. * NDN node: An NDN node can function as a consumer, producer, or forwarder of cached content. * Forwarding plane: The forwarding plane of NDN is composed of three data structures: CS, PIT, and FIB. The forwarding plane utilizes these structures to forward data using specific forwarding strategies as shown in Figure 3.
* NDN routers: NDN routers are devices that perform fundamental routing and forwarding operations. They contain CS, PIT, and FIB. They can cache content in their CS to fulfill future requests for the same content. Additionally, they forward data according to their forwarding tables. However, they are not to be mistaken for content providers. * Routing plane: The routing plane refers to a collection of NDN protocols used to share information about the accessibility of a namespace. Whereas the routing plane calculates and decides globally on routes' availability, the forwarding plane makes per-node decisions about the preference and use of these routes based on their performance and status.