# A Survey on Network Optimization Techniques for Blockchain Systems
## 5 Network Optimization Techniques Used in Blockchain Networks
### Network Layer
#### 5.1.1 Gossip Optimization  
Gossip-based optimization frameworks are discussed in this section. These strategies try to limit the amount of duplication introduced by the gossip algorithm or the amount of time spent gossiping. [PERSON] et al. [70] proposed an algorithm accompanied by a modification of the structure of blocks used by peers when gossiping. The modification was introduced to minimize the quantity of duplication caused by the gossip protocol. They introduced a list to keep track of all nodes previously selected for gossiping. Therefore, when a peer receives a block, it does not send the blocks to their neighbors who are already on the history list. Though their approach was effective at minimizing bandwidth wasted on duplicates by about 33%, it was tested on a network consisting of only nine nodes. Their approach may not scale well with the number of peers if the network receives huge volumes of  
\begin{table}
\begin{tabular}{c c c c c c c c c c c c} \hline \hline
**Ref. ** & **PC** & **PR** & **BI** & **CT** & **DT** & **HY** & **DY** & **LY** & **BW** & **Main Contributions** & **Limitations** \\ \hline
[31] & ✓ & & & & & & \(>\)100\% & 40\% & Gossip algorithm with increased speed and reduced bandwidth consumption & Could still be bandwidth inefficient at large scales due to block duplication \\ \hline
[72,73] & & & & & & & & & Goss  
transactions due to the overhead incurred on checking a possibly long history list for every transaction. Therefore, the effectiveness of this approach should be verified by increasing the number of nodes. The authors of [71] used a method similar to [PERSON] et al., except that it also includes the path in the network that the block has traversed. A Distributed Hash Table (DHT) was used for the P2P network. Their approach could reduce bandwidth wastage caused by duplicates by about 33% and also scales well with peers since, for a large network size, their approach still had significant bandwidth savings. Furthermore, the results presented suggested that it had a negligible effect on block verification latency. [PERSON] et al. [31] and [PERSON] et al. [72; 73] altered the steps and communication pattern of the gossip algorithm used by the Hyperledger Framework and Neo Blockchain, respectively, to reduce its bandwidth usage and also to reduce the amount of time it uses. In their approach, whenever a peer receives a new block, it constantly shares it with a new set of uniformly and randomly selected neighbors until the dissemination counter is exhausted. Since this approach increases the probability that all peers get the block in a few gossip rounds, the pull component of gossip (peers requesting blocks they lack) was removed to save bandwidth. The authors minimized the total network bandwidth by about 40%. Their approach realized an improvement in transactional throughput due to its speed and reduction in the number of invalid transactions by 36%. At large scale, their approach might be susceptible to a decrease in bandwidth efficiency due to duplicate transmissions. Therefore, this method can further be improved by minimizing duplicate transmissions. [PERSON] et al. [75] used the INV message and GETDATA response used in bitcoin to calculate a probability that will influence which neighbors will likely receive the new block. A peer sends a number of inventory (INV) messages and measures the number of responses received. The ratio of sent and received forms the probability that is used to decide which neighbor gets the new block. Since all peers will have a variable number of neighbors, peers with more neighbors will most likely respond to INV messages from a lot of their neighbors and will, therefore, respond poorly to each and every neighbor. Peers with few neighbors, however, will respond to INV messages from few peers and will, therefore, respond better, hence gaining a higher probability. Furthermore, a peer with more neighbors will most likely receive a new block from some neighbors, and hence, peers with few neighbors were given a higher priority by the authors.