Like mentioned above, Elan is used for signaling purposes. Keep it seperate from your Telephony/Customer Lan by VLanning or a whole seperate LAN.
The TLAN and the CLAN can be the same.
TLAN being the Telephony LAN, just a name used for the Network you will/have your telephone system on.
CLAN is the exisiting Network your customer has it's Server/Clients are on.
Pro refers to my company, not my status