What is SIP?
SIP is a signaling protocol used for communication over IP (Internet Protocol). This communication includes not only VoIP, but video calls, instant messaging, file transfer, and online gaming.
SIP identifies the caller and recipient by address in a format like sip:username:password@host:port. The address is registered with a SIP server registrar, and the caller requests access from the SIP server to contact the recipient.
SIP has standard telephony functions like dial, answer, reject, hold/unhold, and call transfer. A SIP phone can be either an actual phone or a softphone on a computer.
What is SIP Trunking?
SIP trunking is a way in which VoIP providers deliver telephone service to customers. SIP trunking is useful to businesses with a legacy PBX. The SIP line replaces the conventional telephone trunk, allowing connection to the outside world via the Internet.
SIP trunking blends both data and voice into a single line. Having all communication (voice, video, data) on one line is more efficient technologically and monetarily. Because virtually every business has Internet, the service that carries VoIP and data should already be in place.
SIP trunks cost $20-$30 per user a month, and you need to match the number of trunks with the expected amount of simultaneous calls your business has. Luckily, you can purchase additional SIP trunk lines from VoIP providers one at a time, as and when you need new SIP trunks to make more calls. Plus, SIP trunking phone lines can support many more special features that current analog phone lines (which cost $40-$50 a month and include only local calls). With a SIP trunk, long distance rates cost the same as local minutes and international calls are very cheap.
Even more on SIP Trunking
SIP Trunking and Bandwidth Efficiency
Think of SIP trunking as consolidating all of your communication into one physical type of line. A conventional phone line sees a high range (from no/few calls to many calls at peak hour) of bandwidth usage over the course of a day. Internet bandwidth is used in bursts.
Both Internet bandwidth and conventional phone lines use an amount of bandwidth far under the maximum capacity of a PBX and its network. If you combine the two communications methods of Internet and telephony, you are more efficient in your bandwidth usage.
A QoS device (Quality of Service device) can manage data and voice, prioritizing bandwidth for VoIP and leaving the extra capacity for Internet usage and other data.