Named Data Networking design to cope up with machine dependability issues where content is strongly bounded by machine address. The user requests are considered as interests and the response to the requests are called as content objects. The interests are routed based on the routers in Forwarding Information Base (FIB).
In addition, the interests are sent back to the same path which generates the respective interests in reverse direction. This method is assured by a data structure called as Pending Interest Table (PIT), which holds a list of interests. Every item of PIT contains a name (key) and a collection of faces (value). Since the entry counts are very large in many routers, it is a big challenge for routers to finish the fast forwarding when the PIT is archived in larger as well as slower storage spaces. Based on 2, the interests are arriving at a rate of 125million/sec and every packet requires 80ms as the average for its round trip time. For the process of fast forwarding, it is highly recommended to compress PIT.
The forwarding model 3 of NDN node is given in Fig. 1. When a face receives an interest and the node fails to fulfil the interest, it adds the CCN name into the interest and its succeeding face in the PIT. Next, the interest is transmitted to the next hop in the direction of the source of content. The direction is decided based on the data available at FIB. When some faces to the content are available, routers will choose the correct one by executing an algorithm which selects the best next hop.PIT keeps an entry for every receiving I_pkt till its respective D_pkt reaches or timeout occurs. The entries are utilized to send D_pkt downstream to the end user.
They can be searched by looking for exact name matching. NDN forwarding is defined as stateful as an NDN router holds an entry for each I_pkt. Every individual PIT entry comprises 5 fields as shown in Fig. 2 4. The fields are CN, nonce, incoming and outgoing interface(s), and timer. The nonce is 4-octet long which is used to identify an I_pkt and eliminates duplicate packet forwarding. The outgoing interface(s), send-time> tuple are used to calculate the respective name prefix’s Round Trip Time (RTT).
When an I_pkt is pass through NDN router, a timer based on RTT time is associated with respective PIT entry. When none of the D_pkt is received corresponding to I_pkt timer expires and entry is removed from PIT. PIT Three essential function perform over PIT: adding incoming name prefixes, eliminate existing entry by defined constrained over PIT, and updating entry.