This read-only value is a globally sequential session number assigned across the entire chassis, starting at 1 for the first modem on the first module of the first board and continuing in order through every modem on every module and board. Admins use this single flat numbering scheme as a simple way to enumerate or reference any modem in the entire chassis without needing to combine board, module, and modem IDs. For example, a monitoring tool could iterate cmmSessionNum from 1 upward to poll every modem's status across the whole chassis in one consistent sequence.