# Location-Based Deferred Broadcast for Ad-Hoc Named Data Networking
## 3 Location-Based Deferred Broadcast Scheme
### Ad-Hoc NDN Basic Scheme  
NDN is a proposed future Internet architecture that adopts data-oriented communication paradigm [2]. In NDN, all communications are based on the names of data. There are two types of packets in NDN: (1) interest packets that include the requested data name; (2) data packets that contain a data name, metadata and data. Consumers initiate communication by sending an interest packet. Producers reply the requested data upon receiving an interest packet with the same name. The data name field uses the naming structure introduced earlier. Thus, LBDB can retrieve the the location information directly from the received interest packets. Each node maintains three data structures in NDN: (1) Content Store (CS): it caches generated or cached data. The content store is managed based on the local cache policy and replacement policy; (2) Forwarding Information Table (FIB): it guides the interest request to the next forwarder towards the provider. The FIB table is constructed by routing protocols, where the data providers advertise name prefixes; (3) Pending Interest Table (PIT): it keeps track of the received and forwarded interest packets that are not yet satisfied by a returned data packet. The NDN data retrieval process has two phases: forwarding interest and flowing data. In the first phase, a consumer initiates the data retrieval by sending an interest packet containing data name. When a node receives an interest packet, it will first check the CS using prefix matching. If it already has the requested data, it will reply by sending back the data. If the match is missed, it will check the PIT to see if this node has sent a request with the same name. If yes, it will discard the interest packet because the same request packet has been forwarded. Otherwise, it will forward the interest packet according to the matched entry in FIB. In the flowing data phase, when a node receives a data packet, its name is used to look up the PIT. If a matching entry is found, the node sends the data packet to the interface according to the PIT entry. Then it will delete the entry in PIT. In addition, it will cache the data packet in CS if desired. If there is no matching entry in PIT, the data packet is considered unsolicited and will be dropped.  
Wireless networks, such as vehicular networks, differ from wired Internet in these aspects: the ad-hoc connection, the intermittent connectivity and the ability of physically store, carry and forward data. Thus, V-NDN [3] has some modifications to the baseline NDN operations for the vehicular environment. First, to take advantage of the nature of wireless broadcast, a vehicle caches all received data regardless of whether it has a matching PIT entry or whether it needs the data for itself. This opportunistic caching strategy can be advantageous in facilitating rapid data dissemination in highly dynamic environments. Secondly, to take advantage of vehicles' physical movement, packets can be carried by moving vehicles when there is no network connectivity. It enlarges data spreading areas and increases rendezvous opportunity between consumers looking for a specific piece of data. Finally, due to the dynamics of connectivity among moving vehicles, it is infeasible to run a routing protocol to build and maintain the FIB. Therefore, V-NDN adopts an interest flooding strategy instead of following FIB when forwarding interest packets. Our work targets ad-hoc NDN, which is based on V-NDN but can be further applied to multiple scenarios including vehicular networks and underwater sensor networks.