# Quality-of-Service-Linked Privileged Content-Caching Mechanism for Named Data Networks
###### Abstract
In an IP network, QoS involves managing network resources such as bandwidth, buffer allocation, and transmission priority [10]. An NDN-based network adds an additional dimension of resource management, i.e., CS management and PIT management. The implementation of QoS for a network involves assuring resource priority to the qualified content stream over the regular content stream. Flow-based QoS guarantees the priority for a content stream based on the application of origin, and class-based QoS guarantees the priority for a content stream based on traffic classes such as telephony, network control packets, etc. [11]. In NDNs, content may have originated from multiple sources, and may be consumed by multiple destinations. For this reason, content-forwarding resources are distributed, and these NDN properties make QoS enforcement difficult. The request-response sequence in an NDN navigates in a hop-to-hop manner, which may trigger an unforeseen amount of data packets and quickly exhaust the resources. Pre  
Figure 1: NDN operational scenario [4]. empting pending interests, dropping data packets, and prioritizing the interests of QoS by differentiating regular traffic without a proper strategy may lead to a burst in interest packet volume, and resources may become underutilized [12]. For NDNs, QoS strategies can leverage the inherent advantages of a CS. A CS improves turn-around time, reduces traffic congestion by availing the content in demand through multiple NDN nodes, and acts as a re-transmission buffer. QoS strategies should consider managing PITs, which indicate pending interests to be satisfied. As priority interests become satisfied by data packets, regular interests recorded in a PIT may be starved. In another situation, a CS and PIT may become saturated with QoS traffic and become unable to cache further content and maintain the record of pending QoS content interests, respectively. In such situations, heuristic mechanisms are needed to manage the CS and the PIT with proper service balance for the regular and competing QoS content. While managing distributed resources such as PITs and CS, coordination between NDN nodes are essential. Identical content in a cluster of NDN nodes decreases the potential of the network [13]. The overall CS capacity of the NDN may be efficiently used if a cooperative caching scheme is implemented. In the context of PITs, a saturated PIT may pre-emptively remove entries and terminate the path for the content flow. This wastes the content-forwarding resources of preceding NDN nodes. This is unacceptable in cases where the traffic is QoS guaranteed. In this light, this proposal explores ways to manage the PITs and CS of NDNs to implement QoS in NDNs. The Internet Engineering Task Force (IETF) has published guidelines on tackling QoS issues in information-centric networks using the techniques of flow classification, PIT management, and content store management from a resource-management point of view [14; 15; 16]. The traffic flows are identified as, and in the order of \((prompt,reliable)>prompt>reliable>regular\), for \"prompt\" QoS, which aims to minimize the delay for QoS traffic by providing a content-forwarding priority. For \"reliable\" services, the priority order is \((prompt,reliable)>reliable>prompt>regular\), with the intention of guaranteeing the reliable delivery of data packets to consumers. The nomenclature \"prompt\", \"reliable\", and their priority orders are preserved in QLPCC, as proposed by the IETF publication. The flow classification introduces the concept of embedding name components to establish equivalence among different traffic flow priorities [14; 15; 16]. The proposed QoS-linked privileged content-caching (QLPCC) mechanism employs this concept to facilitate the assignment of priorities for different traffic flows indicated by the Flow ID. A Flow ID is a name component which uniquely identifies a priority traffic flow for the implementation of flow differentiation.