This Technical Specification (TS) specifies minimum performance requirements, test procedures and digital test sequences to be used for conformance testing of implementations of the eCall in-band modem. The eCall in-band modem PSAP and IVS transmitters and receivers are specified in TS 26.267. The reference fixed point ANSI-C implementation for the specified eCall modem is provided in TS 26.268. The eCall in-band modem is a technology that transmits data reliably over the speech channel of the cellular and PSTN networks. It is specifically designed for transmission of the Minimum Set of Data (MSD) from IVS to PSAP for the Pan-European eCall initiative. For the purpose of the present specification, conformance is determined for the transmission of one single MSD of length 140 bytes. Other applications of the eCall in-band modem are out of scope of this document.