RTP is the protocol that supports the transport layer services for real-time applications. Each RTP packet contains a RTP header and a RTP payload that contains a small sample of the voice conversation. The size of the voice sample encapsulated within the RTP packet will depend on the CODEC used. The following diagram shows the RTP stack. Fig. 2.2. RTP stack
RTP uses UDP as its basic transport protocol to avoid the retransmission of lost or dropped packets. So that a user would not experiences a long pause or delay in the conversation due to the retransmission of lost packets. The network should be designed, though, so that few packets are lost in transmission.
RTP Header: The RTP frame contains information related to handling individual…show more content… CSRC Count – Provides the number of CSRC headers that follow the fixed header.
Marker – The marker field allows the marking of significant events, such as frame boundaries, in the packet stream.
Payload Type – This field identifies the format of the RTP payload and determines its interpretation by the application.
Sequence Number –For each RTP data packet sent, this number increment by one. In addition, the receiver may be used this number to detect packet loss and to restore packet sequence. The initial value of the sequence number is chosen randomly.
Timestamp – The sampling instant of the first octet in the RTP data packet reflects the RTP Timestamp. The sampling instant must be derived from a clock that increments monotonically and linearly in time to allow synchronization and jitter calculations. The resolution of the clock must be adequate for the preferred synchronization accuracy and for computing packet arrival jitter. The initial value of the timestamp is random, as is the sequence number.
SSRC – Identifies the synchronization source. The value is chosen randomly, with the objective that no two synchronization sources within the same RTP session will have the same
