# Flooding Message Mitigation of Wireless Content Centric Networking for Last-Mile Smart-Grid +
## 3 Proposed Scheme
### Efficient CCN Packet Dissemination by MPR Devices  
TOP-CCN defines the two tables for maintaining 1-hop and 2-hop neighbor information, respectively. The 1-hop neighbor table contains ID and lifetime of the device, whereas the 2-hop neighbor table includes 2-hop neighbor ID, connected 1-hop neighbor ID, and lifetime of the 2-hop neighbor. Both tables are periodically updated from the information of the received CA packets. The lifetime of the neighbor information is periodically initialized by CA message from the neighbor. When a lifetime of neighbor is expired, then the relative 1-hop and 2-hop neighbor information  
Figure 4: Frame format of the TOP-CCN, *: extended or new elements of the TOP-CCN compared to pure CCN [2]. is removed. In addition, face information in the FIB and PIT is removed to prevent any wrong content delivery. In CSMA/CA based wireless environments, broadcast transmissions may induce potential problems such as data congestion and packet collision due to shared medium characteristics [16]. However, CCN only considers the broadcasting approach to transmit packets, which is regarded to be especially error-prone to these environments. To mitigate the collision and congestion problem in CCN over wireless environment, TOP-CCN selects a MPR set that can disseminate its received packets such as interest, content, and multi-hop CA packets. If a device that is not elected to MPR or PMPR then cannot rebroadcast of dissemination packets. The MPR is elected by neighbor devices. To select a MPR, every device periodically calculates _MPRcost_ using Equation (1),  
\[\text{MPRcost}_{\text{i}}=(1-\text{a})\ 2\text{hRatio}_{\text{i}}+\text{CacheHit Ratio}_{\text{i}}\ (0\leq\text{a}\leq 1) \tag{1}\]  
where i is the neighbor number index, 2 hRatio\({}_{\text{i}}\) represents the ratio of the 2-hop neighbor connectivity ratio of the neighbor\({}_{\text{i}}\). For example, a device has six 2-hop neighbors and its neighbor\({}_{\text{i}}\) has three neighbors, then 2 hRatio of interface\({}_{\text{i}}\) is 0.5. If a neighbor\({}_{\text{i}}\) has the same number of neighbors as the number of 2-hop neighbors of the device, 2 hRatio\({}_{\text{i}}\) is 1. CachehitRatio\({}_{\text{i}}\) is given by CA packet from the neighbor\({}_{\text{i}}\). We use an exponential weighted moving average (EWMA) method to reflect not only network connectivity but also cache effect in MPRcost [17]. The MPR selection algorithm is shown in the Algorithm 1: MPR selection. When a device needs to remove or add an entry in the 1-hop and 2-hop neighbor tables, then the MPR selection procedure is invoked. Foremost, MPR devices are elected among 1-hop neighbors of the device. Then, a device selects its MPR device that has the highest MPRcost between neighbors. After selection of the MPR, all 2-hop neighbors that are connected through MPR are removed from the 2-hop neighbor list. When a device finds a remaining 2-hop neighbor, then additional MPR devices are elected until the 2-hop neighbor list is empty. If the device does not have any remaining 2-hop neighbors, then the selected MPR list is notified through NBR-TL in the CA message. Thus, every device in the network can decide the device type, which can be a MPR or PMPR through the NBR-TL of the CA message from the neighbor(s). Figure 3 shows an example of the MPR selection using CA packets. In Figure 5a, device 0 selects MPR devices 1 and 4 to cover its 2-hop neighbors of devices 2, 3, 7, and C. Following the same reason, every device selects its own MPR set as Figure 5b,c, respectively. After MPR selection, the entire MPR set of the topology is selected as Figure 5d. All broadcast messages are relayed only by the MPR devices. As a result, TOP-CCN can alleviate broadcast storming and duplicated transmission problems. Figure 5: An example of Multiple Point Relay (MPR) selection for reducing packet flooding of the CCN.