Section: 10.1 Overview
Content: Within the Layer 3 protocols defined in 3GPP TS 24.008[ Mobile radio interface Layer 3 specification; Core network protocols; Stage 3 ] , every message is a standard L3 message as defined in 3GPP TS 24.007[ Mobile radio interface signalling layer 3; General Aspects ]  [20]. This means that the message consists of the following parts: a) protocol discriminator; b) transaction identifier; c) message type; d) other information elements, as required. This organization is illustrated in the example shown in figure 10.1/3GPP TS 24.008[ Mobile radio interface Layer 3 specification; Core network protocols; Stage 3 ] . Figure 10.1/3GPP TS 24.008[ Mobile radio interface Layer 3 specification; Core network protocols; Stage 3 ]  General message organization example Unless specified otherwise in the message descriptions of clause 9, a particular information element shall not be present more than once in a given message. The term "default" implies that the value defined shall be used in the absence of any assignment, or that this value allows negotiation of alternative values in between the two peer entities. When a field extends over more than one octet, the order of bit values progressively decreases as the octet number increases. The least significant bit of the field is represented by the lowest numbered bit of the highest numbered octet of the field.