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 TCP and UDP transport layers. The relation between IP and ATM is still an open issue. Classical IP and ARP over ATM  is an initial standards 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 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, however it is still in draft form, and there may be better solutions, more amenable to a mobile environment, which are proposed before NHRP becomes a standard. Figure 11 shows the relationship of the IP standards in regard to the wireless link, fixed link, and address resolution on both links.