Actually, you got it wrong, it's like this
20.172.216.4 is mapped to outside interface as 60.10.135.72 like for the host A when wants to connect to host B, host A will try 60.10.135.72 as destination and when inside it will be able to talk directly to it.
I'm getting my information based on the commands that you posted. You posted this:
static (inside,outside) tcp 60.10.135.72 3392 20.172.216.4 3392 netmask 255.255.255.255
static (inside,outside) tcp 60.10.135.72 3394 20.172.216.4 3394 netmask 255.255.255.255
This static command is telling the pix to map 60.10.135.72 tcp 3392 and 3394 on the outside interface to 20.172.216.4 tcp 3392 and 3394 on the internal network.
For Example:
[code:1]
static(inside,outside) xxx.xxx.xxx.xxx xxx.xxx.xxx.xxx netmask 255.255.255.255
| | | |
| +
+ |
+
+
[/code:1]
The diagram above shows the flow of the static command and which portion of the static command represents each address.
