Your experience when making any phone call begins when you pick up the handset. Traditionally, you would pick up the handset and you would listen for a dial tone. However, as new unified applications rolled out, you might find yourself just clicking on an icon on a website to place a call to another person or company through your PC and headset. However, your likely experience can be summarized with the following basic criteria:
- Did you get a dial tone when you pick up the phone?
- Did the call connect successfully?
- If so, does it connect within a reasonable amount of time?
These are the basic criteria for call set up within VoIP.
For example if you do not get this:
- If you pick up the phone and you don’t receive a dial tone within several seconds, then you’ll hang up, thinking the phone isn’t working.
- If you dial a phone number and don’t hear ringing or a busy signal within several seconds, then you’ll hang up, thinking the phone isn’t working.
- If the call fails to connect and you hear a fast busy signal then you’ll hang up, thinking the phone isn’t working.
All of these experiences – getting a dial tone, connecting the call, ringing the other party – are dependent on the performance of the call setup protocols in a VoIP system. The PSTN is excellent, tried and tested, and that is how we have come to judge, telephone call setup performance, PSTN is high quality, Mobile medium and VoIP sometimes low.
However, we’ve come to expect high performance for call setup from the PSTN, after all it is developed over a hundred years on a fixed line network but what happens with call setup on a VoIP network?
There are special protocols that enable call set up in VoIP some of the key call setup protocols are SIP, MGCP, H.323, and SCCP. These protocols have been developed in order to deliver higher quality voice call set up, and although still not comparable to PSTN over long distance have come a long way to bridging the gap on national calls.