# Transparent CoAP Services to IoT Endpoints through ICN Operator Networks +
## 2 Background
### The POINT Architecture  
The POINT architecture allows the legacy IP traffic to be run over an ICN core network; the ICN is mainly deployed at a single network operator [4]. The core ICN in the POINT network follows the publish/subscribe principle originally developed in the PSIRP/PURSUIT projects [13]. This architecture divides the core network functions into a control and data plane. At the Control plane, the architecture has Topology manager (TM) which creates a distributed awareness of the local network topology. The TM discovers the network topology by executing a distributed routing protocol, e.g., Open Shortest Path First (OSPF) [14]. On top the topology management, the architecture has Rendezvous (RV) system which takes the responsibility of matching between the publishers and subscribers. Whenever the RV finds a matching between the publisher(s) and subscriber(s), it requests the topology manager to create a logical information delivery tree from the publisher(s) to the subscriber(s). The Data plane finally takes the responsibility of Forwarding (F) functionality to perform the actual data transfer between subscriber and publisher.  
The POINT architecture follows a gateway based approach where the first link from the user endpoint (UE) to the network is based on IP-based protocols. The Network Attachment Point (NAP) serves as the entry point into the ICN network as shown in Figure 1. NAP provides a number of handlers for existing IP-based protocols (e.g., HTTP, CoAP, and basic IP) that map the underlying protocols onto appropriate named objects within the ICN core. The communication between user equipment (UE) and NAP follows the standard IP-based protocols. The other communication interfaces between NAP and ICN are publisher-rendezvous (PR), subscriber-rendezvous (SR) and Topology manager-publisher (TP).  
Every content item in the POINT architecture is identified by a flat identifier known as the Rendezvous Identifier (RId). Moreover, every content item belongs to at least one scope. The purpose of a scope is to group \"similar\" content items and to give a hint about content location. Scopes are hierarchically organized and identified by a Scope Identifier (SId). Scopes are managed by specialized Rendezvous Nodes (RNs), which form an overlay Rendezvous Network. The rendezvous network provides a lookup service, which routes a \"subscription\" to a RN that \"knows\" (at least) one publisher for the requested item. A typical ICN transaction in POINT involves the following steps. A content item is assigned a RId and stored in (at least) one publisher that advertises its availability in one or more scopes. With this advertisement, the RId is stored in the RNs that manage these scopes. Subscribers send subscriptions for specific (SId, RId) pairs, which are routed by the rendezvous network to an appropriate RN. Upon receiving a subscription message, and provided that at least one publisher exists, the RN instructs a Topology Manager to create a forwarding path from a publisher to the subscriber, which is included in the notification message to the publisher. Finally, the content item is transferred from the publisher to the subscriber.