transport with acknowledg- ments (DCCP never retransmits data), reliable handshake and negotiation of fea- tures, and support for TCP-like or TCP-friendly rate control for congestion control. SCTP and DCCP are designed to address the growing range of voice, video, and multimedia applications being introduced on the Internet and IP networks and will provide for improved performance, but so far they have seen little deployment. ICMP provides error-handling and control functions. It is tightly integrated with IP. ICMP messages, delivered in IP packets, are used for control messages related to network operation or misoperation. Because ICMP uses IP, ICMP packet delivery is best-effort delivery. ICMP functions include announcing network errors, network congestion, and timeouts, as well as assisting in troubleshooting. IGMP is a Layer 3 (network layer) protocol whose primary purpose is to allow Internet hosts to participate in multicasting. The IGMP standard describes the basics of multicasting IP traffic, including the format of multicast IP addresses, multicast Ethernet encapsulation, and the concept of a host group (i.e., a set of hosts interested in traffic for a particular multicast address). IGMP enables a router to determine which host groups have members on a given network segment, but IGMP does not address the exchange of multicast packets between routers. ARP and RARP Layer 3 (the network layer) is home to the protocols ARP and RARP. ARP deter- mines the physical address of a node, given that node's IP address. ARP is the map- ping link between IP addresses and the underlying physical address, known as the Media Access Control (MAC) address. RARP enables a host to discover its own IP address by broadcasting its physical address. When the broadcast occurs, another node on the LAN answers with the IP address of the requesting node. Routing Protocols Routing protocols are protocols that allow routers to communicate with each other. They include Routing Information Protocol (RIP), interior gateway protocols (IGPs