ew of Internet Technology Protocols Internet technology protocols are placed in the upper layers of the protocol layering model, covering the range from the network layer (layer 3) up to the application layer QoS for Fixed and Mobile Ultra-Broadband, First Edition. Toni Janevski. © 2019 John Wiley & Sons Ltd. Published 2019 by John Wiley & Sons Ltd. 2 Internet QoS (layer 7). However, the main protocols are those implemented at the network layer and the transport layer (layer 4). The main protocol is the IP, which currently is standardized in two versions, IPv4 [1] and IPv6 [2]. The main transport layer protocols are the user datagram protocol [3] and the transmission control protocol [4]. However, there are others that may exist in layer 4, such as SCTP (stream control transmission protocol) [5] and DCCP (datagram congestion control protocol) [6]. 2.1.1 Internet Network Layer Protocols: IPv4 and IPv6 IP is the main communication protocol in the IP stack. It is positioned on the network protocol layer (layer 3) and provides functions for transmission of datagrams (i.e. blocks of data) over interconnected systems of packet-switched networks from any source to any destination. IP is a connectionless protocol because it does not require a connection to be estab- lished between the source host and the destination host prior to the datagrams' trans- mission. When the IP first appeared (at the beginning of the 1980s) it was completely different from the traditional telecommunication approach in PSTNs where connec- tions were established (prior to the transfer, such as voice transfer) by using signaling between the two end devices and the network. Internet datagrams are also called IP packets, SO the terms are used interchangeably throughout this book. In general, a datagram is a variable length packet consisting of two parts: IP header and data (in the payload of the packet). The IP has exactly two versions (not more, not less): IPv4, standardized in 1981 by the IETF [1]; IPv6, standardized in 1998 by the IETF [2]. The 