Description: This object shall be used to select a user plane layer 3 protocol (or user plane layer 2 bridging). The first octet of this object shall be encoded as follows. Bits 5-7 (i.e., the three most significant bits) shall be set to 0; any other values shall be ignored. Bits 0-4 (i.e., the five least significant bits) shall be encoded as shown in the entry for 'User information layer 3 protocol (octet 7)' in Table 4-10/Q.2931. However, if no user plane layer 3 protocol is specified, then the first (and only) octet shall be encoded as '0b00000000'. a) If ISO TR9577 network layer protocol identification is to be used, then the first octet shall be encoded to indicate 'ISO/IEC TR9577'. In this case, either: i) the user plane layer 3 protocol is to be selected in the management plane. The second octet of this object shall contain the ISO/IEC TR9577 Initial Protocol Identifier (IPI). - For layer 3 protocols for which ISO/IEC has assigned a Network Layer Protocol Identifier (NLPID), then this NLPID shall be used as the IPI, and the length of the octet string shall be 2. - For layer 3 protocols for which ISO/IEC has not assigned an NLPID, the IPI shall be encoded to indicate 'IEEE 802.1a SNAP identifier' (see Annex D of ISO/IEC 9577). The following five octets (octets 3 through 7) of this object shall then contain a SNAP identifier, which consists of a 3-octet organization unique identifier (OUI) and a 2-octet protocol identifier (PID). This SNAP coding shall be used only if ISO/IEC has not assigned a Network Layer Protocol Identifier for the layer 3 or layer 2 protocol. The octet string shall thus be 7 octets long. - If an IME wishes to indicate that bridged LAN frames are to be carried in the user plane then the IPI shall be encoded to indicate 'IEEE 802.1a SNAP identifier'. The following five octets of this object shall contain a SNAP identifier, which indicates the bridged protocol. For consistency with SIG 4.0, use of the ISO/IEC subsequent protocol identifier (SPI) is not recommended but not explicitly prohibited as one can envision scenarios where it has utility. or ii) the user plane layer 3 protocol is to be selected using network layer protocol identification in the user plane. The octet-string shall be one octet long. The first octet(s) of each layer 3 protocol data unit shall contain layer 3 protocol identification according to ISO/IEC TR9577.

b)If bits 0-4 of the first octet of the octet string are set to any value other than 'ISO/IEC TR9577', then any subsequent octets shall be encoded as follows. Bit 7 (i.e., the most significant bit) of each of these octets shall be set to 0; however, if it is set to 1, it shall be ignored. Bits 0-6 shall be encoded according to the codings for octet 7a, octet 7b and octet 7c specified in table 4- 10/Q.2931. If more than one subsequent octet is needed, then octets shall appear in the order shown in figure 4-16/Q.2931.