connect your shiro modem and type 192.168.1.1 in Internet Explorer (IE)
Type admin as both login and password and then go through all of the pages and copy all the settings on a notepad. You will only need a couple such as DNS setting and Gateway etc but since you have no idea what you are looking for, copy all.
Then go through manual of your cisco modem on how to access its settings. Copy all the settings you can and then try. Btw you would also need your login/pass for the PTCL DSL. Login is your phone number and they email or text you the password at the time of registeration.
Do let us know the progress!