The Rebel spy network is structured like a pyramid. At the top is a single unknown person who has recruited three others. These three then each recruited three more members, and so on down the chain.
Each trio of operatives is called a cell. Each cell member knows the identity of the other two members, and sometimes also the identity of the handler who recruited him. He is also aware of the identities of the three operatives he recruits into the cell below him, but not the identities of the operatives who his colleagues recruit into their own cells.
This compartmentalization insulates the network from compromises. If one operative is discovered by the Empire or decides to betray the Rebellion, he can only reveal the names of six others, limiting the damage done. If a subordinate cell is compromised, its handler can cut off communication and recruit a new cell in order to rebuild the network.
The levels are lettered beginning with Aurek and proceeding through the Aurebesh Alphabet. Each member of a cell chooses a codename that begins with the letter corresponding to his cell’s level. For example, “Dewback”’s cell is on the fourth level from the top, and so his codename begins with Dorn.