Introduction

Proliferation of networked digital devices, communication networks, online communications and services is creating massive and heterogeneous network traffic. Monitoring and analysing this network traffic is essential for different purposes including enhancing the quality of service of the underlying systems and networks, providing security and handling related issues. With the rapid growth of network traffic over the Internet, monitoring and analysing this traffic is becoming a challenging task. Further, this task is complicated when the traffic is encrypted. Communications over the Internet are supported by the protocols arranged in logical, hierarchical layers. Higher layers in the hierarchy provide security to the communications through encryption, anonymisation, etc. This encryption provides security and privacy but also gives away most of the information to analyse the traffic. This chapter provides basic understanding and foundations of security in Transmission Control Protocol /Internet Protocol (TCP/IP) protocol stack. It discusses how encryption achieves security in network, transport and application layers. Further, this chapter also provides how communications are secured in other TCP/IP networks. This analysis provides a basis to understand the source of encrypted network traffic. Also, this chapter discusses the network traffic analysis and the challenges involved in it.