24x7 describes the access to TAC, x2/4 describes the amount of business hours before an advanced hardware is replacement part is sent, once it is confirmed defective by TAC. This service is only available within major metropolitan areas http://www.ci...
Take a look at the quick start guide for the MGBSX, your answer are in there. http://www.cisco.com/c/dam/en/us/td/docs/interfaces_modules/csbna/mgb/quick_start/guide/Optical_Module_QSG_en-US.pdf
