# A Dual-Connectivity Mobility Link Service for Producer Mobility in the Named Data Networking
## 4 System Overview  
When a consumer wants certain content, it sends an Interest to the NAR to which it is attached. The NAR then searches through the routing information at its FIB to forward the Interest to the producer. The routing information is generated by the NLSR of the reference implementation [16]. When the producer moves its location while the Interest is being forwarded, the routing information for the forwarding path within the FIB of the NDN router becomes out-of-date.  
The proposed scheme attempts to extend the period in which the routing information within the FIBs of the NDN routers on the forwarding path is relevant. Out-of-date forwarding paths occur when the link connecting the pNAR with a producer is broken due to the movement of the producer. When the producer attaches to a new NAR (nNAR) after it moves, a new Face is created to connect the producer with the nNAR. This allows the transport module of the new Face to communicate with its network. Therefore, the old Face may reconnect the pNAR using the same transport technology used at the transport module of the nNAR. This restores the connectivity between the pNAR and the producer to avoid invalidation of the forwarding path using the pNAR. The old Face removes itself gracefully after the new forwarding path made using nNAR is disseminated over the NDN network. The proposed scheme introduces PMLS, which is a subtype of the link service defined at the NDN specification. The PLMS conceals the link breakage from the NDN forwarding plane and repairs the broken link without needing to introduce a fixed anchor node.  
As shown in Figure 1, only two types of NDN nodes, NDN Mobile Producers (NMPs) and NARs, are involved in the proposed scheme. An NMP is a producer NDN node that stores content and provides it to the consumers requesting the content. It can move randomly. The NMP does not have a name-based routing protocol like NLSR, but its RIB includes an APP module. The NAR is the NDN router at which the NMP is currently attached. The NAR has an NLSR as the name-based routing protocol, and the NLSR is responsible for advertising the content name prefixes registered at the RIB of the NAR. The APP at the NMP delegates the content name announcement process to the NAR. It also propagates the content name prefixes of the contents stored in the NMP to the NLSR via the RIB at the NAR. Both the NMP and the NAR create their own Faces when they are connected, and these Faces use the producer mobility link service as their link service. When the NMP changes its point of attachment from pNAR to nNAR, it maintains dual connectivity: one with pNAR and the other one with nNAR until a new forwarding path using nNAR is stabilized.  
Since NDN can run directly over layer 2, Internet Protocol (IP) is not the only layer that should be used as the underlying layer of NDN. Tunneling technology implemented at the data link layer such as Layer 2 Tunneling Protocol (L2 TP) can be used as the underlying layer of NDN. However, the proposed scheme assumes that the NDN network employs the IP network as the transport network. It is because that the current IP network is the most popular transport network and it is used at the NDN reference implementation as well.