Other VoIP Protocols
Internet data transmissions are composed of several layers and the most commonly used Application Layers for VoIP are SIP and RTP.
Real-time Transport Protocol (RTP) was originally developed for delivering multimedia over the Internet and is often used for streaming audio and video content. It always uses UDP (User Datagram Protocol) as its transport layer, and can be used in conjunction with both SIP and H.323 for delivering voice data.
Quality of Service (QOS) in VoIP refers to the likelihood that voice data will be delivered quickly and to the required standard. It is used for VoIP, multimedia streaming, and applications that require a high degree of reliability.
Essentially, QOS is provided by ensuring enough bandwidth has been reserved for a particular application - either through ringfencing bandwidth to meet all needs at all times or reserving it only when it needed.
VoIP often uses RSVP (Resource ReSerVation Protocol) to reserve bandwidth, which manages QOS by requesting minimum bandwidth and latency from every router between two endpoints.
When a reservation is accepted, the routers have to carry data as specified and reserve the resources necessary to guarantee bandwidth. The data path is then monitored to make certain data travels along the path as expected and, if it doesn't, the request times out to free the resources.