# Hybrid Zoning Algorithm to Optimize Overhead in Smart Mobile Communication
## 5 Zone Geographic Forwarding Rules
### Second Strategy: Acting on Transmissions: Geographic Forwarding Rules  
The MPR concept guarantees that a shortest path exists between every two nodes in the network. However, the default forwarding technique, summarized in Figure 5, takes into consideration the source of the message without caring about the destination nodes. Nodes may receive the same TC message more than once, which lowers the network efficiency. Considering the destination nodes in the flooding process may help to reduce the redundant transmissions and enhance the reliability of the network.  
In the network illustrated in Figure 9(a), both \(h\) and \(g\) will rebroadcast the \(TC_{o}\) message generated by node \(o\). Both of them will receive the \(TC_{o}\) message twice. These redundant retransmissions consume resources on all nodes in \(N1(g)\cap N1(h)\). The geographic forwarding rules, illustrated in Figure 11, use the location information of nodes to divide the network into virtual zones and delete useless transmissions between these zones. Upon receiving the \(TC_{o}\) message, node \(h\) divides the network based on the position of the originator \(o\) into two vertical zones. The border line goes through the position \((X_{o},Y_{o})\) of node \(o\) and it is perpendicular to the x-axis. Figure 9(b) shows the virtual zones and the border line inferred from the coordinates introduced in the \(TC_{o}\) message. Node \(h\) computes \(X_{h}<X_{o}\) and \(X_{g}>X_{o}\) according to the Cartesian coordinate system of origin \((X_{o},Y_{o})\). \(h\) locates itself and \(g\) in the east and west zones, respectively. Node \(h\) detects that node \(g\) is located in another zone and tries to avoid the transmission of the \(TC_{o}\). Node \(h\) checks the topology \(G^{\prime}{}_{h}=(V(h),E(h))\) to find another path formed by MPRs located in the same zone as \(g\), which connects node \(g\) to the originator \(o\). Node \(h\) computes the path \(P_{g}=\{g,e,c,a,o\}\) and abstains from rebroadcasting \(TC_{o}\). The same procedure applies on node \(g\). It computes the path \(P_{h}=\{h,f,d,b,o\}\) and it abstains from rebroadcasting the \(TC_{o}\). Thus, the GFR avoids redundant transmissions between zones and saves resources such as bandwidth and delay, which makes the network more reliable. There are as many groups of zone \(|Z|\) as there are TC messages circulating in the network. Every group is related to the position of the MPR at the time it sends the TC message. Algorithm 1 describes the the geographic forwarding rules in OLSR.  
Figure 10: Difference between DFR and GFR.  
Figure 9: Zone MPR computation of modified OLSR.  
Figure 11: Geographic forwarding rules of OLSR.  
```
1:Initial: \(u\), \(s\), \(TC_{o}\), \(N1(u)\), \(N1(s)\), \(G^{\prime}_{u}\), sendTC = \(false\), \(notexist=false\)
2:Begin
3:if\(TC_{o}\) is already sent then
4: break
5:else if\(s=o\)then
6: sendTC=true
7: break
8:else if\(s\) is MPR selector of \(u\)then
9:if\((\forall w\in N1(u),Z_{u}=Z_{w})\) or \((\exists w,X_{w}=X_{o})\)then
10: sendTC=true
11: break
12:else
13: compute \(N^{s}_{s}=\{N1(u)\backslash\{s,N1(s)\}\}\)
14:for all\(v\in N^{s}_{u}\)do
15: compute \(G^{o}_{u}=\{o,v,M(o),M_{v}\}\), \(M_{v}\) is a set of MPR \(m\) where \(Z_{v}=Z_{m}\)
16:if a path \(P_{v}\) doesn't exist in \(G^{p}_{u}\) that connect \(v\) to \(o\)then
17: notexist=true
18: break
19:endif
20:endfor
21:endif
22:endif
23:if sendTC or notexist then
24: send \(TC_{o}\)
25:endif
```  
**Algorithm 1** Geographic forwarding rules of modified OLSR.