Overview#Telex has an OID of 184.108.40.206 and is as far as Ldapwiki can find the same as CaseIgnoreString
Telex is found in the schema for the regarding attribute. This OID is described in the Microsoft Active Directory Technical Specification MSADTS. Telex corresponds with the basic 220.127.116.11.4.1.1418.104.22.168.15 syntax.
Telex is, as far as Ldapwiki can determine, exclusively used in Microsoft Active Directory.