This International Standard specifies a connection-less and a connection oriented transport layer (TL) for DLMS/COSEM communication profiles used on IP networks. These TLs provide OSI-style services to the service user DLMS/COSEM AL. The connection less TL is based on the Internet Standard User Datagram Protocol (UDP). The connection- oriented TL is based on the Internet Standard Transmission Control Protocol (TCP). Although the major part of the DLMS/COSEM TLs is the UDP and TCP as they are specified in the relevant Internet Standards, they include an additional sublayer, called wrapper. Annex A shows how the OSI-style TL services can be converted to and from UDP and TCP function calls.