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Hello everyone my name is vijay kumar Devireddy and i am glad to have you back on my episode 56 today we are discussing about Telephony devices.Telephony is a term that's used for a device that provides voice communication to your end users.Originally, telephony was used in networks to make connections with the outside world such us through your modem.So a modem was this old device that we used to use that would allow us to modulate and demodulate digital information into an analog signal that could transmit over a standard dial-up connection. So if you used AOL as a dial-up connection way back in the day,you would put your phone line into your computer,it would take your ones and zeros,convert them into signals of sound and transmit that over the phone line.Now, modems were a great attack vector though from the security perspective.And for the Security you need to know the concept of war dialing.War dialing is simply when an attacker starts dialing random phone numbers to see if any modems would answer on the other side. So a lot of servers back in those days will have dial-up modems so that remote technicians could dial into the server,gain access and make changes to due support.Well, if I was an attacker and I started dialing random numbers like 555-1234,nobody there.555-1235 and just keep adding numbers,eventually, I'll find some server that answers.And if they do, I now have a way into that network. So how do we protect modems in our systems for any dialog resources that we may have from this type of thing like war dialing?Well, one of the main things to do is use a callback feature.If you still have modems, which most of us don't in our networks anymore, but if you do,you want to make them set so that when somebody calls in,they would then hang up and the modem, if it recognize that phone number based on caller ID will then call them back and initiate the connection.This will verify that the person is who they think they are and who they say they are.Now, you always want to also use some form of authentication,like a username or password.But preferably, you want to use something more complex like two factor or multi-factor authentication.The best practice though is to do what most of us have done,and that's eliminate modems where possible and switch to remote access to using things like an SSH connection over VPN tunnels.Now, while it's great to try to eliminate all your modems,sometimes, you still have old systems and you simply can't do that.If you have to maintain a dial-up modem for some reason,you want to make sure you keep that dial-up number a secret.And so somebody's going to have to work hard to be able to find it and be able to get into your system.Again, if you have a dial-up modem,you want to use good authentication.You want to be able to use things that will help prevent it like callbacks and other things to help secure it,because these are prime targets for attackers.Now, the next type of telephony equipment I want to talk about is a PBX system. A PBX equipment is something you're going to find much more often in your networks than you are going to find modems.A PBX system stands for a Public Branch Exchange.Essentially, this is the telephone system that runs all of the internal phone lines for your company.If you're sitting in your office and you want to call your accountant inside the office and you dial the last four digits of his phone number only to get him, that internal call is being routed through your PBX system,through that public branch exchange.