# Quality-of-Service-Linked Privileged Content-Caching Mechanism for Named Data Networks
###### Abstract
QLPCC proposes the calculation of an eviction score for a given priority content entry, for eviction from a saturated PIT. Content store management consists of an admission-control phase, where heuristics decide whether or not to cache the content. Each content belongs to a traffic flow, and each QoS node adopts a Flow ID. If the content belongs to the adopted Flow ID, then it is cached by the CS; otherwise, the content is forwarded without caching. The admission-control algorithm defines the steps to adopt new Flow IDs and to drop the old ones. The second phase of CS management is content eviction for the better utilization of limited available memory. QLPCC proposes a novel heuristic-based content-eviction algorithm by considering their QoS priorities, usage frequency, and content freshness. Time-expired content is evicted first, followed by prompt-priority content which was overlapped by Least Frequently Used (LFU) and Least Fresh First (LFF) algorithms. If such an overlapping was not found, then LFU prompt-priority content is evicted. If a memory requirement still persists, then the content-eviction strategy applies LFU and LFF algorithms on reliable priority content. Content that is overlapped by LFU and LFF is evicted first, followed by LFU reliable-priority content. The proposed QLPCC designates dedicated NDN nodes as QoS nodes for implementing the proposed strategies. QoS nodes are resourceful NDN nodes that handle QoS traffic flows as per the QLPCC strategy. A QoS node can be any resourceful NDN node, including routers. The unique feature of the proposed QLPCC is that it provides support for privileged content through both PIT management and CS management. The distinguishing features of QLPCC, when compared with other schemes, are provided in Table 1.  
QLPCC is simulated on an ndnSIM [30] platform, and results are compared with EQPR [28], PRR [29], probability cache, and LFU and LFF schemes. QLPCC outperformed the previously mentioned schemes in terms of content store hit rate, response time, and hop count reduction from the perspective of priority traffic and overall traffic. QLPCC is also evaluated in terms of content store hit rate vs. the percentage of QoS nodes in the network. The contributions of the proposed QLPCC strategy are listed as follows:  
* The QLPCC strategy to manage QoS content in NDN-based networks;
* A QoS-based PIT management scheme through a novel Flow Table involving the calculation of eviction scores;
* A QoS-based content store management scheme, which proposes the content store admission-control and content-eviction heuristics;
* A priority flow adoption method for caching QoS-linked privileged content among QoS nodes;
* A reduction in hop count, an increase in content store hit rate, and an improvement in response time. The paper is organized as follows. Section 1, above, provided an introduction to the work, and will be followed by a brief discussion of the QoS guidelines published by the IETF, with respect to ICN, in Section 2. Section 3 overviews the related works in terms of NDN traffic classification, content store management policies, and PIT management policies. Section 4 provides a description of the QLPCC strategy in terms of Flow Table description, the QoS table, eviction score calculation, PIT management, content store management, and finally, an illustration through a case example. Results and discussions are provided in Section 5, followed by a conclusion in Section 6.