This section of the architecture is concerned with the Internet Protocol and how it relates to ATM and mobility. This layer provides a well known and widely used network layer, whose primary purpose is to provide routing between subnetworks and service for the Transmission Control Protocol (TCP) and User Datagram Protocol (UDP) transport layers. The relation between IP and ATM is still an open issue. Classical IP and ARP over ATM  (CLIP) is an initial standard solution. However, it has several weak points such as requiring a router to connect Logical IP Subnetworks (LIS) even when they are directly connected at the ATM level, and requiring an ATM Address Resolution Protocol (ARP) server to provide address resolution for a single LIS. The Non-Broadcast Multiple Access (NBMA) Next Hop Resolution Protocol (NHRP) provides a better solution but it is still in draft form. The RDRN architecture has implemented CLIP and supports both PVCs and SVCs via ATMARP.