Overview#Telex has an OID of 126.96.36.199 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 188.8.131.52.4.1.14184.108.40.206.15 syntax.
Telex is, as far as Ldapwiki can determine, exclusively used in Microsoft Active Directory.