# A Family of ACO Routing Protocols for Mobile Ad Hoc Networks
## 2 Related Work  
We describe the most important ACO routing protocols, grouping these into proactive, reactive and hybrid. The most representative proactive ACO routing protocols are the following:  
Adaptive swarm-based distributed routing [2], better known as Adaptive-SDR, is inspired by AntNet. This protocol has the property of grouping the nodes in colonies to solve the problems of scalability of other protocols, derived from the fact that each node has to send an ant to others. The grouping of nodes in the colonies is done by a control central entity that becomes aware of their geographical positions. There are two types of ants: colony ants and local ants. The first ones have the mission to find routes from one colony to another. The local ants are internal to the colony, and they find routes within the colony, relying on two routing tables. This protocol has many drawbacks: many colonies are not advisable due to the overheads that occur; to know the optimal number of nodes that should be in a colony is not anything trivial; distributed systems do not always have a control central entity, as is presupposed; large processing of routing tables carried out by the local ants implies a high resources consumption, and it requires devices with important performances, and so on. Mobile ant-based routing [3], better known as MABR, proposes a scheme to tackle the scalability problem of the routing in mobile ad hoc networks. This approach abstracts the network dynamic topology to get logical routers and logical links. These two concepts relate to the set of nodes and created paths among them, respectively. This algorithm uses the geographic partition of the area of the node and the geographical addressing of pheromone exploration. The problem with this proposal is only limited to presenting the theoretical model, not providing experimental results. The probabilistic emergent routing algorithm for mobile ad hoc networks (PERA) [4] is a protocol that adjusts at each node the likelihood that each of its neighbors can receive and forward the data packet. The fact that forward ants are sent in broadcast mode from the source and intermediate nodes causes a multiple broadcast for finding different routes to the destination, causing a great overhead. AntNet ring search and local retransmission (AntNet-RSLR) [5] is an adaptation from AntNet to mobile ad hoc networks through the incorporation of two techniques: Expanding Ring Search (ERS) and Local Retransmission (LR). Using the technique of the expanded ring searching, the request message of the route setup is spread progressively by flood from the source node. Initially, the message is spread to a small neighborhood with a small Time To Live (TTL) value, which is going to increase until you reach the destination. This message is forwarded by the source node if no response is received at a time interval. If the route requesting the TTL value has reached a certain threshold without receiving a response, it assumes that the destination is unreachable. However, this produces a great overhead and can cause loops that reduce the delivered packet ratio. To solve the problem of overhead, it introduces a variant of this technique called blocking-ERS, which does not assume the route search procedure from the source node when a new sending of the message in broadcast mode, generating a rebroadcast from an intermediate node chosen conveniently. A local retransmission technique is used when an intermediate node does not receive the corresponding data packet by expiating the timer value, sending a negative notification control message (Nack) for the intermediate node (and not the source node), returning to retransmit the failed data packet. This has the disadvantage that there is unknown a priori buffer capacity from the node that stores the data for its possible retransmission. Upon being based on a proactive protocol as is AntNet, the overhead should be present as a negative aspect, although the authors claim that it is reduced.