 Some of these are proprietary protocols and some are implementations of the ECMA CSTA standard.Some of these manufacturers also offer their own CTI servers (such as Nortel's Contact Center Manager Server), but those servers generally operate only with that single manufacturer's telephone system.By contrast, the companies that have owned and marketed CT Connect over the years (see the CT Connect history below) have made arrangements with most major PBX manufacturers to get access to their protocol specifications and implement their CTI link protocols.