ability problem makes using RSVP on the public Internet impractical, SO it has largely been left to campus and enterprise-type networks. Several other protocols are associated with RSVP (see Figure 10.13). Real-Time Transport Protocol (RTP) is for audio, video, and SO on. It is based on UDP, to cut down on overhead and latency. RTP is specified as the transport for H.323, and receivers can sequence information via the packet headers. Real-Time Transport Control Protocol (RTCP) provides status feedback from senders to receivers. Both RTP and RTCP are standardized by the ITU under H.225. Real-Time Streaming Protocol (RTSP) runs on top of IP Multicast, UDP, RTP, and RTCP. Chapter 10 Next-Generation Networks Table 10.4 IntServ Service Classes Service Guaranteed Controlled Best-Effort Class Service Load Service Service End-to-end behavior Guaranteed Best effort on Best-effort only maximum delay unloaded network Intended applications Real-time Sensitive to Legacy congestion ATM mapping CBR or VBR-RT VBR-NRT or ABR UBR or ABR with MCR Application Application Process Process Routing Policy & Process Policy & Admission Admission Control Control Classifier Packet Classifier Packet Scheduler Scheduler Router (Client) Figure 10.12 RSVP in hosts and routers RSVP is simplex (i.e., it is a reservation for unidirectional data flow), it is receiver driven (i.e., the receiver of data flows initiates and maintains the resource reservation for that flow), and it supports both IPv4 and IPv6. RSVP is not a rout- ing protocol. Key issues regarding RSVP include scalability, security, and assurance that policy-based decisions can be followed. RSVP and related protocols are dis- cussed in more detail in Chapters 8 and 9. DiffServ Today we concentrate more on DiffServ than on its parent, IntServ. The DiffServ approach to providing QoS in networks uses a small, well-defined set of building blocks from which a variety of services can be built (see Figure 10.14). A small bit pattern in each packet in the IPv4 Type of Service (ToS) octet, or t