Port Address Translation, using transport layer port numbers to identify the local host, theoretically allows up to about 65,000 hosts share one public IP address, and the router should be able to determine the returned data stream sent to which hosts.
R3 and R4 are the following routes within the network port mapping the external network through R1 PC2 fixed IP plus port number different to remotely access and control. 
R1>
enable
the configure Terminal
interface FA 1/0
NO the shutdown
ip address 12.1.1.1 255.0.0.0
interface FA 0/0
NO the shutdown
ip address 192.160.2.254 255.255.255.0
ip route 192.160.1.0 255.255.255.0 12.1.1.2 to access 192.160. routing network training and preparation 1.0 12.1.1.2
R2>
enable
Configure Terminal
interface 1/0 FA
NO the shutdown
IP address 12.1.1.2 255.0.0.0
interface 0/0 FA
NO the shutdown
IP address 192.160.1.254 255.255.255.0
IP route 0.0.0.0 0.0.0.0 12.1.1.1 all access routes to the external network of training and preparation 12.1.1.1 
R3>
enable
the configure Terminal
hostname host name change R3 R3
enable password xxwj set privileged password xxwj
Line vty 0 4 to enter the virtual port number 0-4
password xxwj password xxwj
the Login Save
Exit
interface FA 0/0
NO the shutdown
ip address 192.160.2.3 255.255. 255.0
Exit
IP route 0.0.0.0 0.0.0.0 192.160.2.254
R4>
enable
Configure Terminal
hostname R4
enable password xxwj
Line VTY 0. 4
password xxwj
Login
Exit
interface 1/0 FA
NO the shutdown
IP address 192.160.2.4 255.255.255.0
Exit
IP route 0.0 192.160.2.254 0.0.0.0 .0.0 
Rl>
ip nat inside source static tcp 192.160.2.3 23 12.1.1.1 5033 mapped into port 23 192.160.2.3 12.1.1.1 port 5033
ip nat inside source static tcp 192.160.2.4 23 12.1.1.1 5044 to port 23 of 192.160.2.4 12.1.1.1 port 5044 is mapped to
interface 1/0 FA
IP interface marked outside NAT external network
interface 0/0 FA
IP NAT internal network interface labeled inside 
then tested PC2
Telnet 12.1.1.1 5033
password: xxwj
R3> enable
password: xxwj
Show IP interface Brief
found 12.1.1.1 5033 is port access router R3, and R3 192.160.2.3 only the IP
Telnet 12.1.1.1 5044
password: xxwj
R4> enable
password: xxwj
Show IP interface Brief
found 12.1. 1.1 5044 into the port of the router is R4 and R4 IP 192.160.2.4 only
prove successful port mapping.
Enter R1> enable
Show Translations' show ip NAT conversion activity