As described in Chap. 1 , protocols layers 1 and 2 are intra-domain protocols that support the exchange of packets between devices inside a single network. In contrast, higher layer protocols must support communication between any two devices in the Internet. In this section we discuss the network and transport layers. They are by design not aware of, let alone optimized for, the nature of the physical and datalink technologies used in individual networks. In this chapter, we first briefly introduce the Internet Protocol (IP) and Transmission Control Protocol (TCP) and we then elaborate on how wireless links and mobility impact IP, TCP and, indirectly, applications. More detailed information on IP and TCP can be found in several networking textbooks (Kurose and Ross 2021; Peterson and Davie 2020; Tanenbaum et al. 2021).