# An Efficient Probe-Based Routing for Content-Centric Networking
## 2 Related Work
### Content Exploration in CCN  
One solution to fully exploit in-network cache is to explore the distribution of cached content [3; 4; 5; 7; 24; 25; 33]. They can be categorized into _content share_ and _content query_.  
_(1) Content Share_ indicates that the router regularly broadcasts cache information to other routers.  
[PERSON] et al. [5] discussed the necessity and feasibility of routers advertising cached information in the network. [PERSON] et al. [12] proposed an intra-Autonomous Systems (intra-AS) cache cooperation scheme. The router periodically advertises the cache \"summary\" of its currently cached information to neighboring routers. [PERSON] et al. [21] proposed a cooperative caching strategy to handle the distribution of large video streams. This method can make each Content Routers (CR) cache different data and avoid caching the same data on neighboring CRs. [PERSON] et al. [11] proposed a cooperative scheme that is a cached-bit strategy informing other routers along the path whether a given content has already been cached in the network or not through a bit set. [PERSON] et al. [34] and [PERSON] et al. [35] proposed a hash-based cooperative caching strategy, which uses hash values to map content names to router IDs. [PERSON] et al. [24] also proposed an effective hash-based cache distribution and search scheme. The CS of all routers in the network is managed by an independent autonomous system. When cached content is updated, all neighboring routers are notified to update FIB by broadcast. [PERSON] et al. [36] proposed a Pull-based Bloom Filter-based Routing (BFR) method, which only advertises the required file name. It is better than the original BFR in terms of overhead, latency, and memory. The notion of SDN has been integrated into CCN in some studies [30; 37]. To solve the problem of estimating the location of the cache server in the centralized cache management of SDN-based ICN, [PERSON] et al. [37] used singular value decomposition (SVD) and QR-factorization with column pivoting methods. The _probe_-based approach is designed to improve the precision of FIB, especially for the peer-to-peer distributed networks. Compared to peer-to-peer distributes networks, SDN has a controller to manage the routing tables and data storage so it is less significant to apply a probe-based approach in SDN.  
_(2) Content Query_ indicates that the router asks for other routers' cache information by sending an extra packet.  
[PERSON] et al. [4] proposed a hybrid forwarding solution to exploit the known routing information and explore the unknown cache content. They also [26] proposed a dynamic INterest FORwarding Mechanism (INFORM) based on a reinforcement learning framework that is a distributed Q-leaning. [PERSON] et al. [38] proposed an ideal Nearest Replica Routing (iNRR) forwarding policy. This policy can explore a meta-request that only needs to respond to true or false. [PERSON] et al. [3] proposed a Diversity-based Search-and-Routing (DIVER) approach, which uses a probe packet with \(\varepsilon\) probability to search for copies of cached content on surrounding routers. To make full use of multipath forwarding and in-network caching, [PERSON] et al. [7,33] proposed an on-demand off-path Cache Exploration-based Multipath Forwarding strategy (O2 CEMF).  
However, extra-packet is the significant burden for all of the above methods, which increases redundant traffic, computational complexity, and network overhead [1, 3, 7]. Moreover, several content query approaches have an additional table to manage the candidate exploration object. Compared to those approaches, our approach fully utilizes the advantages of in-network cache and effectively improves these problems.