It divides the group divided into subgroups, each maintain its subgroup using Group Diffie-Hellman
(GDH) and links with other subgroups using Tree-based Group Diffie-Hellman
While STR uses unbalanced key tree for group key computation, tree-based group Diffie-Hellman
(TGDH) leverages balanced tree structure.
As its name indicates, TGDH is built upon the well-known Diffie-Hellman key exchange protocol  and its extension, the Group Diffie-Hellman
(GDH) key agreement protocol  that enables provably secure, fully distributed GK generation .
Pointcheval, "Dynamic Group Diffie-Hellman
Key Exchange under Standard Assumptions", in Proc.
Quisquater, "Provably Authenticated Group Diffie-Hellman
Key Exchange," in P.
The group controller is the last member to join the group in the Enhanced Tree-based Group Diffie-Hellman (ETGDH) protocol.
The Enhanced Tree-based Group Diffie-Hellman (ETGDH) functions include member authentication, group key generation, and distribution of the group key to all members.
The tests designed were run on the testbed in order to measure the average response times of computing a group key and the communication overhead of sending and delivering messages under the selected protocols, which included GDH (Group Diffie-Hellman) , BD (Burmester and Desmedt) , STR (Skinny Tree) , and TGDH (Tree-based Group Diffie-Hellman) .