Section: 10.5.4.18 Low layer compatibility
Content: The purpose of the low layer compatibility information element is to provide a means which should be used for compatibility checking by an addressed entity (e.g., a remote user or an interworking unit or a high layer function network node addressed by the calling user). The low layer compatibility information element is transferred transparently by a PLMN between the call originating entity (e.g. the calling user) and the addressed entity. Except for the information element identifier, the low layer compatibility information element is coded as in ITU recommendation Q.931. For backward compatibility reasons coding of the modem type field according to ETS 300 102-1 (12-90) shall also be supported. The low layer compatibility is a type 4 information element with a minimum length of 2 octets and a maximum length of 18 octets. Figure 10.5.104/3GPP TS 24.008[ Mobile radio interface Layer 3 specification; Core network protocols; Stage 3 ]  Low layer compatibility information element If the value part of the IE is empty, the IE indicates "not applicable".