What is different about phone registration between SCCP and SIP signaling?
During registration, SEP file contains CUCM server, TCP Ports for SCCP signaling and firmware version. SCCP signaling then sends DNs, softkeys and speed dial info.
SIP sends all that info in the SEP file. SIP has no extra signaling to send the DNs and Speed dials so the SIP files are larger than SCCP.