Section: 19.4.2.3 Tracking Area Identity (TAI)
Content: The Tracking Area Identity (TAI) consists of a Mobile Country Code (MCC), Mobile Network Code (MNC), and Tracking Area Code (TAC). It is composed as shown in figure 19.4.2.3.1. Figure 19.4.2.3.1: Structure of the Tracking Area Identity (TAI) The TAI is composed of the following elements: - Mobile Country Code (MCC) identifies the country in which the PLMN is located. The value of the MCC is the same as the three digit MCC contained in the IMSI; - Mobile Network Code (MNC) is a code identifying the PLMN in that country. The value of the MNC is the same as the two or three digit MNC contained in the IMSI; - Tracking Area Code (TAC) is a fixed length code (of 2 octets) identifying a Tracking Area within a PLMN. This part of the tracking area identification shall be coded using a full hexadecimal representation. The following are reserved hexadecimal values of the TAC: - 0000, and - FFFE. NOTE: The above reserved values are used in some special cases when no valid TAI exists in the MS (see 3GPP TS 24.301[ Non-Access-Stratum (NAS) protocol for Evolved Packet System (EPS); Stage 3 ]  [90] for more information). A subdomain name can be derived from the TAI. This shall be done by adding the label "tac" to the beginning of the Home Network Realm/Domain (see clause 19.2) and encoding the TAC as a sub-domain. This is called the TAI FQDN.. The TAI FQDN shall be constructed as follows: tac-lb<TAC-low-byte>.tac-hb<TAC-high-byte>.tac.epc.mnc<MNC>.mcc<MCC>.3gppnetwork.org The TAC is a 16-bit integer. The <TAC-high-byte> is the hexadecimal string of the most significant byte in the TAC and the <TAC-low-byte > is the hexadecimal string of the least significant byte. If there are less than 2 significant digits in <TAC-high-byte> or <TAC-low-byte >, "0" digit(s) shall be inserted at the left side to fill the 2 digit coding.