? Greedy peripheral stateless routing protocols mainly include two methods of forwarding packets: greedy forwarding and peripheral forwarding. Greedy forwarding is the core of the algorithm. Simply put, the greedy forwarding method is to find the nearest one-hop neighbor node and then forward the packet to this node; The peripheral forwarding mode is a supplement to the greedy forwarding mode, which solves the packet forwarding dilemma in the greedy forwarding failure area.
? The advantage of GPSR is that it only needs to save the state information of one-hop neighbor nodes, and the routing overhead is small; And with the increase of the number of network nodes, it is more scalable than distance vector routing (DV) or link state routing (LS). Even if the nodes in the network move frequently, GPSR protocol can quickly find alternative routes according to the information of one-hop neighbors.
Each node periodically broadcasts beacon data packets, the main components of which are unique identification and location information. The position information is encoded as two 32-bit floating-point numbers, which respectively represent the horizontal (longitude) and vertical (latitude) coordinate values of the node. The beacon transmission period is b by default, but in order to reduce the signal conflict with neighboring nodes, the beacon transmission period will be randomly dithered by 50%, that is, the beacon transmission period will be evenly distributed in the interval [0.5B, 1.5B]. Neighboring nodes receiving beacon broadcast only need to save the received identification and location information into the routing table. The routing table stores the information of a node's one-hop neighbor nodes. The data in the routing table will be used to make next-hop routing decisions.
? The routing information in the routing table will also be deleted. When the time interval of not receiving the routing information of the neighbor node exceeds t, it can be considered that the neighbor routing node failed to send or the node is no longer in the signal radiation range of the neighbor node, and the neighbor node is deleted from the routing table. In the GPSR protocol, T=4.5B, which is three times the maximum beacon transmission period.
Due to the mobility of nodes, the location information in the routing table may not be up-to-date during the beacon transmission period. This may be because: 1. Old nodes may leave the signal coverage; 2. The new node may enter the signal coverage area; 3. The accuracy of obtaining the position may decrease, and so on.
? From these reasons, the relative movement rate between nodes and the signal radiation range of nodes determine the accuracy of the routing table, and also represent whether the beacon transmission cycle is suitable for this network environment. Packet forwarding needs to ensure that the network topology within one hop is up-to-date, because there is no available routing and forwarding strategy to deal with the situation that the forwarding node does not know the topology information of one or more hop neighbor nodes. This is the minimum standard for packet forwarding.
In the implementation of GPSR, the following measures are taken to reduce beacon overhead:
? (1) The location information of the local node is appended to all packets forwarded by the node.
? (2) Set the network interfaces of all nodes to run in promiscuous mode.
? By adopting the above measures, all nodes within the signal radiation range can receive the location information of the node. Because the location information only needs the overhead of 12 bytes, all data packets can carry beacons. Any node can restart the internal beacon timer after sending a packet. This optimization strategy reduces the beacon traffic in the packet forwarding area of the network.
Detailed explanation of GPSR protocol (II) —— Greedy forwarding
Detailed explanation of GPSR protocol (3)- Peripheral forwarding
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