IP Telephony Thing

VoIP (Voice over Internet Protocol) or, in English, how to use the Web to transmit voice.

new stuff.

The Internet has come full circle from its inception over 50 years ago as a resiliant means of routing communications in the event of a nuclear attack on an entire city.

Reliable communications is the key to holding society together and cordinating government, etc. Radio and telephone systems can be badly interupted when key parts of the infrastructure are damaged. So, when computers became powerful enough to route communication in real-time, the Internet was invented by some boffins working for the USA. The plans for this communication system were also made freely available to the USA's Cold War Antagonists so that each of the Superpowers would know that the other side possesed the means for uninterupted communications in the event of a nuclear strike. Computers were able, to re-route communications around a damaged communications centre, taking a longer router, but getting to the destination automatically even though the system may be damaged. This is how the Internet Work today too.

SIP

Session Initiated Protocol

SIP is techno mumbo jumbo for 'making telephones interface with each other'.

How Does SIP Work

Our experience of using SIP for remotely located telephone handsets is not good. Because most users are behind firewalls, SIP does not alwasy work correctly. Partly due to the firewall not knowing about SIP, and partly because SIP was not designed to travel through NAT-type firewalls.

NAT Firewalls

NAT Firewalls enable more than one computer to share a single internet connection. Unfortunately, this is the bane of SIP and the voice data that travels between two telephone calls.

NAT stands for 'Network Address Translation'. This is a bit like having a receptionist answer the phone for an office full of workers. They all have their individual names or extension numbers, but have to share a single telephone number. The receptionist figures out which person to put the call through to based on what the caller asks. When a cold caller attempts to gain access to a worker, the receptionist can refuse to put the caller through. And that is pretty much how a firewall works.

Unfortunately with SIP and the voice data, they don't work well when trying to get past our NAT Receptionist. First of all, the SIP (first contact) part might ask for someone that does not even work in the office (a wrong number), and secondly, a completely different caller will attempt to call in if the first contact goes smoothly but doesn't even mention that they are calling due to the first contact. It's a mess. And we need to sort it out somehow.