The figure below is a simplified diagram showing the relationships of the switching frames and the common control equipment (markers, registers, senders,...). It is sized for large displays. This is the "block diagram" of a #5 Crossbar office. For 10K subscriber lines, the Office would have ~825, 200pt, xbars, and up to 50K relays. 

From NO. 5 CROSSBAR SYSTEM GENERAL DESCRIPTIVE INFORMATION, 1975, AT&T DFMP document. This version was redrawn from the original for better resolution. Send me your contact information for access to a 65 MB TIFF version. See Understanding the Crossbar Switch too.