Here's how PAT distinguishes between multiple devices:
Device A sends request:
- Original: 192.168.1.100:54321 to 93.184.216.34:80
- After PAT: 203.0.113.5:40001 to 93.184.216.34:80
Device B sends request:
- Original: 192.168.1.101:54321 to 93.184.216.34:80
- After PAT: 203.0.113.5:40002 to 93.184.216.34:80
Response to Device A:
- Arrives at 203.0.113.5:40001
- Router looks up port 40001
- Translates to 192.168.1.100:54321
The port number on the public side routes responses to the correct internal device.