## 3 Concepts for Stimulating Incentives in SocialCode
### SocialCode Guidelines for Distributed Incentive Stimulation
Otherwise, it will issue an ACK packet to the sending node for paying its credit value \(\delta\) to increase that of the sending node. Thus, Table 3 expresses this guideline as Non-duplicate piece: (\(+\delta\), \(-\delta\)), which means SocialCode stimulates the sending node for sending a non-duplicate piece to the intermediate node. If the credit value of the intermediate node is less than \(\delta\), it cannot send any content piece, which may be a duplicate one, to its neighbors or accept any non-duplicate content piece from its neighbors. 4. Because the irrelevant node does not join the SLNC-based CCD process, it just drops the received piece and keeps its credit value unchanged. Hence, Table 3 expresses this guideline as Any piece: (0,0). Please note the value of \(\alpha\) is larger than those of \(\beta\) and \(\delta\), that is, \(\alpha\)\(>\)\(\beta\)\(>\)\(\delta\), which means destination nodes would earn more credits, that is, \(\alpha\), when they broadcast innovative SLNC-coded content pieces to nearby nodes than those, that is, \(\beta\), paid when they broadcast non-innovative pieces. In this way, SocialCode stimulates destination nodes with higher credit values to encourage them to broadcast more innovative content pieces in the SLNC-based cooperative content distribution process, which raises the probability of the receiver to successfully decode all SLNC-coded content pieces and reconstruct original content data. However, SocialCode encourages intermediate nodes with lower credit values, that is, \(\delta\), to forward non-duplicate content pieces. For the example shown in Figure 1, node A and C are destination nodes but node B and D are the overhearing and intermediate one, respectively. Assume the initial credit values of all these nodes are \(\gamma\) Assume node C broadcasts a SLNC-coded content piece to its nearby nodes A, B and D at step 1. If this content piece is non-innovative to destination node A, A must reply an ACK packet with the credit value \(-\beta\) to punish node C at step 2. After that, node A increases its credit value by \(\beta\), which is subtracted from that of C. Overhearing node B has to send back an ACK packet with the credit value \(+\alpha\) to stimulate node C, because it receives an innovative content piece. Similarly, when intermediate node D receives a non-duplicate piece, it will stimulate node C by sending it an ACK packet with the credit value \(+\delta\). Hence, the total revenue of node C is \(\alpha+\delta-\beta\). As node C receives all ACK packets \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Sender** & **Description Node** & **Intermediate Node** & **Overhearing Node** \\ \hline
**Destination Node** & Innovative piece: (\(+\alpha\), \(-\alpha\)) & Duplicate piece: (\(-\delta\), \(+\delta\)) & Innovative piece: (\(+\alpha\), \(-\alpha\)) \\  & Non-innovative piece: (\(-\beta\), \(+\beta\)) & Non-duplicate piece: (\(+\delta\), \(-\delta\)) & Non-innovative piece: (0, 0) \\ \hline
**Intermediate Node** & Innovative piece: (\(+\alpha\), \(-\alpha\)) & Duplicate piece: (\(-\delta\), \(+\delta\)) & Innovative piece: (\(+\alpha\), \(-\alpha\)) \\  & Non-innovative piece: (\(-\beta\), \(+\beta\)) & Non-duplicate piece: (\(+\delta\), \(-\delta\)) & Non-innovative piece: (0, 0) \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Guidelines to modify credit values and stimulate incentives for four types of nodes. after broadcasting this content piece, credit values of node A, B, C and D are \(\gamma+\beta\), \(\gamma-\alpha\), \(\gamma+\alpha+\delta-\beta\) and \(\gamma-\delta\), respectively.