a transformer coupling which provides foreign voltage protection between the TCM loop and the digital line. The maximum length of a normal TCM loop is 300 m (1000 ft.) Minimum voltage at telephone 10 V DC and a TCM port should have between 15 and 20 V DC across the Tip and Ring with the phone disconnected. The port connection may be through a Punch-down block or a Modular connector called a TELADAPT plug (or socket) which is Nortel parlance for phone connector. Evolution Path The Nortel Meridian 1 can be upgraded to support VoIP in two forms: VoIP Trunking, the Meridian 1 can have ITG-Trunk cards added to it to support PBX-to-PBX voice trunking using H.323 VoIP Line (VoIP Sets), the Meridian 1 can have IP Line cards added to it to support VoIP sets. The introduction of Release 3.0 for the Meridian 1, otherwise known as the CS1000 Release 3.0 also provides an upgrade path for the existing customer base to upgrade a Meridian 1 to an IP-PBX Introduction of E-MetroTel UCX4.5 MDSE package by leveraging MGC card, line cards and cabinets provides upgrade path for existing customers See also List of telephone switches Nortel business phones Portico TVA References External links Network World. 19 November. 1990 Meridian product group home page Meridian Product Image Library Nortel Meridian / Avaya CS1K Meridian (CS1000) Documentation Telephone exchanges Meridian Computer telephony integration