Previous chapters discussed satellite links from the perspective of providing a physical transmission path, either in a point-to-point mode or in a point-to-multipoint (broadcast) mode. As is the case with other transmission links, users of satellite links typically utilize a data link layer protocol to define framing mechanisms to support communications over a single such link, as well as a network layer protocol to route packets (datagrams) over a number of such links (some of which could also be terrestrial hops). Modern-day communication is characterized by the use of the Internet Protocol (IP) at the network layer. At this time, most of the systems deployed in the field or just about being ready for deployment make use of IP version 4 (IPv4), which has been around for about two decades. However, the expectation is that by 2010 and beyond there will be increased use of IP version 6 (IPv6). Hence, this chapter shifts the focus to the topic of IPv6; the chapter that follows will cover the topic of Transmission Control Protocol (TCP). IPv6 offers the potential of achieving the scalability, reachability, end-to-end interworking, quality of service (QoS), and commercial-grade robustness for data communication, as well as for VoIP/triple-pay networks. IPv6 is now gaining momentum globally, with major interest and activity in Europe and Asia, and there also is some traction in the United States. For example, the U.S. Department of Defense (DoD) announced in 2003 that from October 1, 2003, all new developments and procurements need to be IPv6-capable. The DoD’s goal is to complete the transition to IPv6 for all intra-and internetworking across the agency by June of 2008. In 2005 the U.S. Government Accountability Office (GAO) recommended that all agencies become proactive in planning a coherent transition to IPv6*. Corporations

and institutions need to start planning at this time how to kick off the transition planning process and determining how coexistence can best be maintained during the 3 to 6-year window that will likely be required to achieve the global transition. This book addresses the migration and macro-level scalability requirements for this transition.