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Nowadays, voice transmission over data networks has become of wide spread. However data networks always suffer from packet loss, delay, and delay jitter that greatly affect the quality of the perceived voice quality. Delay jitter can be cured through using playout buffers. However delay can cause further loss for voice packets. Many recovery techni...
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Context 1
... can be used for media on demand, as well as for interactive services such as Internet telephony. RTP (refer to figure 2.2) consists of a data part and a control part, the latter called RTP Control Protocol (RTCP). The data part of RTP is a thin protocol that provides support for applications with real-time properties, such as continuous media (for example, audio and video), including timing reconstruction, loss detection, and content identification. RTCP provides support for real-time conferencing of groups of any size within an Internet. This support includes source identification and support for gateways, such as audio and video bridges as well as multicast-to-unicast translators. It also offers QoS feedback from receivers to the multicast group, as well as support for the synchronization of different media streams. Using RTP is important for real-time traffic, but a few drawbacks exist. The IP/RTP/UDP headers are 20, 8, and 12 bytes, respectively. This adds up to a 40-byte header, which is big compared to the payload for packetized voice. Large RTP header can be compressed to 2 or 4 bytes by using RTP Header Compression ...
Context 2
... main types of traffic ride upon Internet Protocol (IP): User Datagram Protocol (UDP) and Transmission Control Protocol (TCP). In general, TCP is used when a reliable but not delay sensitive connection is needed, and UDP when simplicity and reliability is not a main concern. Due to the time-sensitive nature of voice traffic, UDP/IP is the logical choice to carry voice. More information is needed on a packet-by-packet basis than UDP offers, however. So, for real-time or delay-sensitive traffic, the Internet Engineering Task Force (IETF) adopted the RTP (Real Time Protocol). VoIP rides on top of RTP, which rides on top of UDP. Therefore, VoIP is carried with an RTP/UDP/IP packet header. RTP is the standard for transmitting delay-sensitive traffic across packet-based networks. RTP rides on top of UDP and IP. RTP gives receiving stations information that is not in the connectionless UDP/IP streams. As shown in figure 2.2, two important bits of information are sequence information and timestamping. RTP uses the sequence information to determine whether the packets are arriving in order and if a packet is lost, and it uses the time-stamping information to determine the interarrival packet time ...
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