IEEE Std 1702 2011 pdf download – IEEE Standard for Telephone Modem Communication Protocol to Complement the Utility Industry End Device Data Tables.
4. Protocol details Following the guidelines established by the OSI seven-layer model, the protocol described in this standard provides three (3) functions: a) Establishment and modification of the communication channel b) The transport of information to and from the C12.21 Device c) Orderly closure of the communication channel when communications are complete Three (3) layers are used to provide these communication capabilities: the Physical, Data Link, and Application layers. This standard does not specify the implementation requirements of the telephone switched network to the modem, nor does it include definitions for the establishment of the communication channel. The communication channel is considered available once the telephone connection has been successfully established and modems have synchronized. The protocol specification for electric metering (PSEM) Identification Service is required to establish the protocol version and revision in use. Certain communication parameters may be modified through the use of the PSEM Negotiate and Timing Setup services in the Application Layer. These services are optional, and if not implemented in the C12.21 Device or not used during actual communications, the communication channel parameters will remain at the default settings specified by this standard. Implementers are strongly encouraged to implement these optional Application Layer services.
Once the data link is established, the Application Layer provides  Logon, Security, and Logoff services for session activation, access control, and deactivation  Read Service and Write Service for issuing data transmission requests  Authenticate Service for two-way authentication with playback rejection  Terminate Service for returning to the Base State  Disconnect Service for shutdown of the communication channel  A response structure that provides information regarding the success or failure of the service requests. An example of a typical communications session would consist of the following services with appropriate responses, in the order listed: Identification, Negotiate, Logon, Authenticate, Security, Reads or Writes, Logoff, and Disconnect. Note that this brief example does not detail the packet structure or other aspects of the protocol. A more detailed example of a typical communications session is given in Annex A. 4.1 Order of transmission Order of transmission is identical to that specified in ANSI C12.18. 4.2 Layer 7 – Application Layer The Application Layer provides a minimal set of services and data structures required to support C12.21 Devices for purposes of configuration, programming, and information retrieval. Layer 7 shall be defined as in ANSI C12.18 except for the specific items defined in 4.2.1 and 4.2.2.