CAN’T ABLE TO TELNET to CISCO 1841 Router

Hai Guys … i have a issue in telnetting my router 1841.
I configured NAT in my router
I can able to telnet from my private networks . I can able to ping but i can’t able to access my router from external network.
I configured telnet password and login command in my router …configuration as follows

SRP(config)#line vty 0 4
SRP(config-line)#password cisco
SRP(config-line)#login

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