alerting is verified at the called destination, the network sends the CC Alerting message. When the called party answers, the network sends the CC Connect message. The MS response with the CC Connect Acknowledge message. At this point, the call is active. The TCH+FACCH assignment can occur at any time during the transaction, depending on the configuration of the network. There are three common approaches: Early Assignment. The network assigns the TCH+FACCH after sending CC Call Proceeding and completes call setup on the FACCH. This allows the use of in-band patterns (like the ringing or busy patterns) generated by the network. This is the example shown. Late Assignment. The network does not assign the TCH+FACCH until after alerting has started. This forces the MS itself to generate the patterns locally since the TCH does not yet exist to carry the sound. Very Early Assignment. The network makes an immediate assignment to the TCH+FACCH in the initial RR establishment and performs the entire transaction on the FACCH. The SDCCH is not used. Because immediate assignment starts the FACCH in a signaling-only mode, the network must send the RR Channel Mode Modify message at some point to enable the TCH part of the channel. Mobile-Terminating Call (MTC) establishment This is the transaction for an incoming call to the MS, defined in GSM 04.08 Sections 5.2.2 and 7.3.3, but taken largely from ISDN Q.931. The network initiates the radio channel establishment procedure and assigns the MS to a Dm channel, usually an SDCCH. This establishes the connection in the L3 RR sublayer. The MS sends the first message on the new Dm, which is the RR Paging Response message. This message contains a mobile identity (IMSI or TMSI) and also implies a connection attempt in the MM sublayer. The network verifies the subscriber in the HLR and verifies that the MS was indeed paged for service. The network can initiate authentication and ciphering at this point, but in the simplest case the network can just send the CC Setup message to initiate Q.931-style call control. The MS responds with CC Call Confirmed. The network sends an RR Assignment message to move the transaction off of the SDCCH and onto a TCH+FACCH. Once the MS has acquired the timing on the TCH+FACCH, it responds on the new FACCH with the RR Assignment Complete message. From this point on, all control transactions are on the