list of connected nodes and the connected timestamp does not exceed two beacon intervals, then the node ignores the `BEACON`. However, every data packet and control packet other than `BEACON`s update the connection timestamp. A `BEACON` changes the timestamp only when the timestamp exceeds two beacon intervals because it is considered as a new connection.

[24]{}\
&\

Epidemic Logic {#sec:EpidemicDTN}
==============

The Epidemic control logic performs four main steps as shown in Figure \[fig:EpidemicDTNConM\]. After receiving a `BEACON`, nodes exchange `REPLY` and `REPLY_BACK` control packets. `REPLY` and `REPLY_BACK` control packets are the summary vectors discussed in [@vahdat:2000:ERF]. The goal of sending message summaries is to avoid sending messages that the other node already contains in its buffer. Since both nodes are likely to send a response to a beacon at the same time, an anti-entropy session prevents node responses from colliding. The node with the lower address sends its message summary first as a `REPLY` packet. When the node with the higher address receives the `REPLY` packet, it sends a response using the `REPLY_BACK` packet. After a node receives the list of messages that the other node contains, the node sends messages that the other node does not have in 