to manage. It copes by borrowing several different protocols from the Internet Engineering Task Force (IETF). These include the Real-Time Transport Protocol (RTP), User Datagram Protocol (UDP), the Transmission Control Protocol (TCP) and the Internet Protocol (IP). Although H.323 is not aimed exclusively at them, implementations generally traverse IP networks. On IP networks, H.323 audio and video use UDP. When compared to the Transmission Control Protocol (TCP), UDP lacks sophistication. It is a unidirectional protocol that simply divides data into IP packets that it sends with checksums. UDP is better suited to real-time data types than is TCP. TCP strives for reliable delivery and thereby retransmits if it detects corrupted packets or dos not receive acknowledgement of packets. UDP does not retransmit. It discards packets that are corrupted; otherwise, it simply forwards them. To bolster UDP's lack of reliability, H.323 uses RTP (RTP is also used on the Internet's Multicast Backbone-the MBONE). RTP appends a 10-byte header (that contains a time stamp and a sequence number) to each UDP packet. At the receiving end, H.323 implementations buffer and process UDP packets to capture timing and sequence information and to guard against duplicate and out-of-order packets. Thus, audio, video, and data are generally resynchronized and presented to the user in a coherent stream. While audio and video use the UDP, H.323 does specify TCP for data conferencing, which is not time sensitive. H.323 also uses TCP for conference control and signaling. Standards for Videoconferencing Another IETF protocol, the Resource Reservation Protocol (RSVP), is not an official part of H.323 but products without it may suffer from network congestion problems. The RSVP allows a conference participant to reserve bandwidth for a particular real- time data stream. The reservation is made in the network (in which RSVP-compliant routers receive and grant requests). Although users can ask for bandwidth, there is no guarantee (at the time of this wr