EDITED DATA REQ. N-EXPEDITED DATA IND. Routing MTP-TRANSFER REQ. N-RESET REQ. control MTP-TRANSFER IND. N-RESET IND (SCRC) N-RESET RESP. N-RESET CONF. Connection N-UNIT DATA REQ. N-UNIT DATA IND. transfer control (SCLC) MTP-PAUSE IND. MTP-RESUME IND. Management control N-NOTICE IND. (SCMB) Figure 14.9 General SCCP overview block diagram. Note the listing under user, left side; we find a listing of SCCP primitives. For a discussion of primitives, consult Ref. 18. [From ITU-T Rec. Q.714, Figure 1/Q.714, page 307, CCITT Red Books, Vol. VI, Fascicle VI.7 (Ref. 15).] 14.12 USER PARTS 4. SCCP Routing. On receipt of the message from the MTP or from the functions listed previously, SCCP routing either forwards the message to the MTP for transfer or passes the message to the functions listed. A message whose called party address is a local user is passed to functions 1, 2, or 3, whereas one destined for a remote user is forwarded to the MTP for transfer to the distant SCCP (Ref. 13). 14.12 USER PARTS 14.12.1 Introduction SS No. 7 user parts, along with the routing label, carry out the basic signaling functions. Turn again to Figure 14.5. There are two fields in the figure we will now discuss: the SIO (service information octet) and the SIF (signaling information field). In the paragraphs that follow, we briefly cover one of the user parts, the TUP (telephone user part). As shown in Figure 14.10, the user part, OSI layer 4, is contained in the signaling information field to the left of the routing label. ITU-T Rec. Q.723 (Ref. 14) deals with the sequence of three sectors (fields and subfields of the standard basic message signal unit shown in Figure 14.5). Turning now to Figure 14.10, we have from right to left the service information octet (SIO), the routing label, and the user information subfields (after the routing label in the SIF). The SIO is an octet in length made up of two subfields: the service indicator (4 bits) and the subservice field (4 bits). The service indicator, being 4 bits long, has 16 bit combinations 