Traversal zone is for configuring the firewall traversal peer link.
One for traversal client zone which initiate traversal link to specified traversal server address.
Other for traversal server zone which listing the traversal link request from traversal client zone (ideally from VCS-C or GK).
There is keep alive packet between traversal client and traversal server to keep communication link and also have several communication methods define between these two specific zone making H.323/SIP firewall traversal call.