The connection between the sub-ITL and the telex exchange is over the Internet. The connection is authenticated as well as encrypted using standard X.509 certificates (issued by SwissTelex) and the Secure Socket Layer (SSL 128) protocol. The encryption (128 bits) is the same as that used for e- banking and e-commerce.
The connection is established in the direction of client (sub-ITL at the customer site) to server (hub-ITL at the telex exchange). Consequently, there is no requirement to open any port in the customer firewall to unsolicited incoming connections.
The sub-ITL is essentially a dumb transmission medium – it performs no message storage or switching functions. Telex messages are sent and received in real time under control of the customer system and the telex exchange. In particular, responsibility for answerback tripping and response lies outside the sub-ITL.

Singapore Customer systems currently connect to the telex network in Singapore by means of standard V21 telex line(s).

The sub-ITL is a PC-based unit, which can be connected to the customer system via its existing V21 telex line(s). One sub-ITL can handle up to 8 telex lines.
The Unit converts V21 signalling to V28 and connects to a multi-port async card in the sub-ITL. The sub-ITL connects to a corresponding hub-ITL in the SwissTelex exchange via a permanent SSL connection.
The sub-ITL effectively enables long-lining to the telex exchange in Switzerland. Each customer line is assigned a unique virtual line over the internet SSL connection, which is in turn mapped to a unique physical line in a corresponding hub-ITL unit in the Telex Exchange.