Abstract: This paper briefly introduces the routing protocols commonly used in ad hoc networks, and uses the network simulation software NS2 to simulate the DSDV, DSR and AODV routing protocols, and calculates the first packet receiving time and average delay of the routing protocol through different simulation scenarios. And package delivery rate. The results show that the DSDV routing protocol is suitable for the network scenario where the node is stationary. The AODV and DSR routing protocols have better network performance in the mobile environment.
Keywords: ad hoc network; DSD; DSR; AODV
introduction
An ad hoc network is an autonomous system consisting of a group of mobile nodes with radio transceivers. It is characterized by self-organizing, multi-hop, and temporary establishment of links. In this network, the environment of the channel, the topology of the network, and the mode of the service are dynamically changed with the movement of the node. Self-organizing networks provide a better solution for communication in any environment, and are widely used in military fields and civil communications. At present, the self-organizing network and the 2.5G and 3G mobile communication are effectively combined, and the large-scale broadband wireless ad hoc network will become an important form of broadband wireless communication or future mobile communication.
In the ad hoc network environment, because the wireless communication coverage of the node is limited, two mobile nodes that cannot communicate directly can forward packets through the intermediate node to implement data communication. Therefore, the process requires a routing protocol to perform packet forwarding decisions. It is important to adopt what kind of strategy to forward messages to get good communication results. Routing protocols are hotspots and difficulties in recent years. Routing protocols need to adapt to topology changes quickly, complete route establishment and maintenance, and minimize control overhead to improve network throughput. Currently, new protocols for ad hoc networks generally establish network routes in broadcast or multicast mode. Representative protocols that are generally accepted are DSDV (DesTInaTIon sequenced distance vector), DSR (Dynamic Sou rce RouTIng), and AODV (Ad hoc On-). Demand Distance Vector RouTIng).
1 Wireless Network Routing Protocol
According to the route discovery policy, the ad hoc network routing protocol can be divided into active routing and on-demand routing. The active routing protocol is that the node periodically broadcasts routing information packets, exchanges routing information between routers, and calculates related routes. The node maintains routes to all nodes of the entire network, and the discovery strategy is similar to the traditional routing protocol. Active routing protocols mainly include protocols such as DSDV, GSR, and WRP. The on-demand routing protocol initiates route lookups as needed. When a node needs to send data and there is no valid routing information in the routing table, the source node floods the entire network and finds the route to the destination node. Topology and routing table information are built on demand and may be just part of the overall topology information. The on-demand routing protocol maintains the route during the communication process, and maintenance is not performed after the communication is completed. On-demand routing protocols mainly include DSR, AODV, TORA, and so on.
1.1 DSDV
The DSDV protocol is a point-to-point distance vector routing protocol, which requires each node to periodically broadcast routing information to neighboring nodes, and each node maintains a routing table. When the network topology changes so that the routing table changes, the node will also actively send updated routes to neighboring nodes. The DSDV protocol is basically the same as the DV protocol on the Internet, except that the routing information has more records of the destination node serial number. After the destination node serial number is introduced, the routing information can be distinguished from the old and new, and the routing loop and infinite counting can be effectively avoided. The problem is suitable for wireless ad hoc networks such as the fast-changing network of nodes required. When a node receives multiple different vector table data packets, it uses the routing information with a larger serial number to calculate. If the serial number is the same, the path is short.
1.2 DSR
The DSR protocol is an on-demand routing protocol based on source routing. In the DSR protocol, when the source node sends a packet, it carries the routing information to the destination node in the datagram header. The routing information is composed of several node addresses in the network, and the data packets of the source node pass through the nodes. Followed by forwarding to the destination node. The DSR routing protocol mainly includes route discovery and route maintenance procedures. The route discovery process is mainly used to help the source node obtain the route to the destination node. The node obtains routes to other nodes in the network through the route discovery process. In the route discovery process, the source node first broadcasts a "routing request" data message to the neighboring node. The data packet includes fields such as "Request ID", "Destination Node Address", and "Route Record". The “Route Record†field is used to record the address of the intermediate node in the route from the source node to the destination node. When the route request message reaches the destination node, all the node addresses in the field constitute the route from the source node to the destination node. . When a node in a route cannot be guaranteed to reach the destination node due to shutdown, movement, etc., the current route is no longer valid. The route maintenance process monitors the availability of the current route. When a route failure is detected, a new round of route discovery process is invoked.
1.3 AODV
The AODV protocol draws on the on-demand routing mechanism of the DSR protocol and the point-to-point routing mechanism of the DSDV protocol. The AODV protocol forwards data packets in a hop-by-hop manner. It does not need to carry complete routing messages in the packets. The AODV protocol route discovery process is initiated by the source node. When a node needs to send a data packet, it first checks whether the routing table of the node has a valid route to the destination node. If not, the routing request data packet needs to be broadcast to the neighboring node, where the address of the source node and the destination node are recorded, and the neighboring node receives the routing request data packet, and first determines whether the destination node is the local node, if No, look in the routing table for a route to the destination node. Each route corresponds to a serial number, and the serial number is updated as the route is updated. The route maintenance of the AODV protocol is implemented by periodically broadcasting hello packets. When a link is disconnected, the node sends a route error message to notify the nodes that are disconnected due to link disconnection and delete the corresponding route. recording.
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