Port Forwarding BSNL VMC AN1020-21 Modem (Type WT) for Transmission

Transmission is a bittorrent client like utorrent, for linux.
It uses a default port 51413 to make connections.
You can go to Edit-->Preferences-->Network and look at the Port for Incoming Connections option.
Click Test port under it, and if it shows Port is Open, you have to do nothing.

If it shows Port is Closed, follows these instructions.
Note down the port number (51413 in this case, you can change it if you want, but not all ports are allowed)
Now, go to 192.168.1.1 in your browser. (this is your router's home page)
Enter username and password as admin
On the left pane, under the security tab, select Port Forwarding.
If it asks for password again, type admin as username and admin as password as earlier
Now, you have to add a port forwarding rule.
Click on the Add button

Select user-defined instead of pre-defined
Give some trivial name. I gave Transmission.
WAN interface, the default one. (pppoe_0_35)
Forward to internal host ip address:
Now this setting is what requires caution.
Bring up command prompt or terminal and type ifconfig or ipconfig and find inet address.
Mine was 192.168.1.2
Type that in.
Now in the protocol type select TCP
For External Packet Port Start, Port End and Internal Port Port Start, Port End,
for all 4 of them, type 51413 (the transmission port)
Now in the protocol type (second row) select UDP. And type 51413 for all the ports as we did for TCP.

Click apply and if everything goes well you'll have added two port forwarding rule.

Now, you may have to reboot the router. But if you want you can go to Transmission Preferences and click Test Port to see if it shows up Port is Open now without rebooting.
 If it still doesn't try rebooting the router.
If it still doesn't show port is open, my friend, I can't help you.

(BTW, I set Use UPnP or NAT checked in transmission preferences)