Summary

This chapter has described the on-the-wire aspects of the RTP data transfer protocol in some detail. We considered the format of the RTP header and its use, including the payload type for identification of the format of the data, sequence number to detect loss, timestamp to show when to play out data, and synchronization source as a participant identifier. We also discussed the minor header fields: marker, padding, and version number.

The concept of the payload format, and its mapping onto payload type identifier and payload header, should now be apparent, showing how RTP is tailored to different types of media. This is an important topic, to which we will return in later chapters.

Finally, we discussed RTP translators and mixers: intermediate systems that extend the reach of RTP in a controlled manner, allowing sessions to bridge heterogeneity of the network.

Associated with the RTP data transfer protocol is a control channel, RTCP, which has been mentioned several times in this chapter. The next chapter focuses on this control channel in some depth, completing our discussion of the network aspects of RTP.