I want to download iPhone firmware, but I don't know my iPhone is Global or GSM so…
What is difference between "iPhone 5 (Global)" and "iPhone 5 (GSM)"?
How can I recognize if my iPhone is Global or GSM?
The CDMA model presumably has compatibility in more markets than the standard GSM model. According tot he list below, unless you ordered your phone from a Chinese firm, if you have a CDMA model it also supports GSM.
GSM is a European standard and supports the EDGE network. CDMA supports some networks branded as "3G", but YMMV. Both are getting a bit long in the tooth as far as cutting-edge goes (IMO).
You can use this list to help identify if your model includes CDMA (Global) or GSM: http://support.apple.com/kb/ht3939
Check the "Model" at the bottom on the back of the phone and cross-reference it with the model number on that list. Here are the relevant iPhone 5 data: