# Quality-of-Service-Linked Privileged Content-Caching Mechanism for Named Data Networks
## 6 Conclusions  
QoS-linked privileged content caching (QLPCC) is a Pending Interest Table (PIT) and content store (CS) management strategy for NDN-based networks for the scenarios of Quality-of-Service (QoS) implementation. QLPCC proposes a QoS node as an intermediate resourceful NDN node which handles only QoS traffic in the network. QoS traffic receives regular treatment in other NDN nodes, which ensures that regular traffic is not starved. QLPCC proposes a Flow Table-based PIT management scheme, which categorizes each QoS traffic into (prompt, reliable), prompt, reliable, and regular service categories [14; 15; 16], and calculates an eviction score for the content of the traffic identified by a Flow ID. The PIT entry with the highest eviction score is pre-empted when the need arises. QLPCC proposes a QoS Table-based content store management scheme for content-admission-control and content-eviction operations. The QoS Table maintains a record of content expiry times, Flow IDs, and paths for QoS nodes which have adopted other Flow IDs. Using QoS Tables, the QLPCC strategy decides whether to cache the content or to forward the content towards other QoS nodes. QLPCC proposes a content store eviction algorithm to free the limited memory. The content-eviction algorithm evicts the content in the order of obsolete content, prompt-privileged content, and reliable-privileged content, respectively. The proposed QLPCC strategy is simulated on an ndnSIM [30] platform for 500 nodes and 1000 nodes as a proof of scalability. The results are compared with EQPR [28], PRR [29], probability cache, and Least Frequently Used (LFU) and Least Fresh First (LFF) schemes, and are analyzed from the viewpoint of content store size vs. hit rate, response time vs. QoS-node content store size, and hop count vs. content store size. QLPCC has outperformed all of the previously mentioned measures.  
For NDN-based ad hoc networks, NDN nodes should be dynamically designated as QoS nodes. Future work explores this challenge and the heuristics required to solve this problem.  
**Author Contributions:** Conceptualization, S.H.S.; methodology, S.H.S. and U.B.; software, S.H.S.; validation, S.H.S. and U.B.; formal analysis, S.H.S.; investigation, S.H.S.; resources, U.B.; data curation, S.H.S. and U.B.; writing--original draft preparation, S.H.S.; writing--review and editing, S.H.S. and U.B.; visualization, S.H.S.; supervision, U.B.; project administration, U.B. All authors have read and agreed to the published version of the manuscript.  
**Funding:** This research received no external funding.  
**Institutional Review Board Statement:** Not applicable.  
**Informed Consent Statement:** Not applicable.  
**Data Availability Statement:** Not Applicable, the study does not report any data.  
**Conflicts of Interest:** The authors declare no conflict of interest.  
**Abbreviations**  
Please refer to the CRediT taxonomy for term explanations. The following abbreviations are used in this manuscript:  
MDPI  
Multidisciplinary Digital Publishing Institute  
DOAJ  
Directory of open-access journals  
NDN  
Named Data Networks  
CS  
Content store  
PIT  
Pending Interest Table  
IOT  
Internet Of Things  
ICN  
Information-centric networking  
QoS  
Quality of service  
QLPCC  
Quality of service-linked privileged content caching  
IETF  
Internet Engineering Task Force  
LFF  
Least Fresh First  
LFU  
Least Frequently Used  
ECNCT  
Equivalence class name component type