## 3 ICN Architecture
### 3N Architecture
#### 3.3.1 3 NA Forwarding Strategies  
3 NA utilizes a set of PDUs called data transmission PDUs to make use of 3N name information in the architecture's forwarding strategies. These PDUs include 3N name information in its fields and permits the encapsulation of ICN PDUs. The encapsulation allows the inter-operation of 3 NA networks with other ICN implementations. The data transmission PDUs defined in 3 NA are summarized in Table 2. More details about the data transmission PDUs are available in [27; 28].  
3 NA relies on SF to forward Interest PDUs. Compared to a pure ICN, the 3 NA gives all nodes participating in the network a name, permitting the aggregation of those 3N names within the PIT. When a Data PDU is sent downstream, a 3 NA node will trigger a search for the aggregated 3N names  
\begin{table}
\begin{tabular}{c c} \hline
**PDU Name** & **Description** \\ \hline EN & Enrolls nodes into a sector \\ OEN & Offers a name to an enrolling node \\ AEN & Acknowledges the enrollment of a node into a sector \\ REN & Re-enrolls a node into a new sector while the node still has a valid 3N name \\ DEN & Dis-enrolls a node a from a sector \\ ADEN & Acknowledges the dis-enrollment of a node from a sector \\ INF & Informs sectors about nodes obtaining new 3N names \\ \hline \end{tabular}
\end{table}
Table 1: 3N architecture mechanism PDUs.  
\begin{table}
\begin{tabular}{c c} \hline
**PDU Name** & **Description** \\ \hline SO & Includes only Source node’s 3N name \\ DO & Includes only Destination node’s 3N name \\ DU & Includes the Source node’s along with the Destination node’s 3N name \\ \hline \end{tabular}
\end{table}
Table 2: 3N architecture data transmission PDUs.  
in the PIT entry. Before the 3N name is used in the delivery of a Data PDU, a check in the NNPT is performed to make sure that the 3N name being used is the newest available 3N name. The NNST is then used to figure out which path to use for the forwarding process by comparing the destination 3N name with the PoA to 3N mapping maintained in the structure. This search results in a PoA name and an associated interface that would best fit the requirements. The use of 3N names in the Data PDU means that, in 3 NA, one is routing directly on the 3N names and can leverage the mathematical properties of the namespace. The resulting forwarding strategy is called Smart Flooding with 3N names (SF 3N). If 3N names are not used when using SF 3N, the forwarding strategy performs exactly like SF (Section 3.1).  
One very important use case that 3 NA can support is forwarding Data PDUs without the need of PIT entries. When nodes using 3 NA enroll into the network, they are given a 3N name. Due to the properties of 3N names, if the offered name is (5.0.0), one knows that the node who offered it is (5.0). With this information, a 3 NA node is capable of creating a DO or a DU PDU to encapsulate Data PDUs to reach specific named nodes. Normally, the CS in ICN is updated only when a related PIT entry is available. The usage of DO or DU PDUs offers the possibility of a different trigger flow which can be used for producers to push the desired Data PDUs to a given node. This easily enables the support for push producers.