of tech- nologies, such as Ethernet, WiFi, mobile RANs, and optical links. Higher protocol layers (above IP) include the transport protocol layer and above (e.g. presentation, session, and application layers, usually treated on the best-effort Internet as a single application layer), which include protocols (on those layers) such as TCP, UDP, RTP on the transport layer, HTTP, FTP, SMTP, POP3, and proprietary (not standardized) applications on the application layer. Higher layers may also influence the end-to-end performance (e.g. TCP provides congestion control end-to-end by the end-hosts, while RTP provides two-way control information needed for real-time services). Transport and network layer protocols are implemented in the OSs of the end-user equipment, SO their implementation (e.g. TCP implementation) may influ- ence the behavior of applications and services on the top. For example, different OSs may provide different user experiences at the same network conditions (throughput, congestion, etc.) due to different versions of TCP. There are interrelationships of the QoS parameters on different layers, such as the link layer, network layer, and application layer (Figure 2.8). For example, link layer per- formance influences QoS, including the technology used for the given link (e.g. whether it is Ethernet or mobile access, and SO on), as well as its QoS mechanisms and congestion occurrence at a given time period. Network factors, such as packet loss, jitter, or delay, in different networks as packets travel between the end-hosts influence the application factors, which may include overall packet loss, overall delay, end-to-end average jitter, 2.5 Traffic Management Techniques Perceived quality by the end-user QoS service level Application available bitrate Overall Codec delay performances Overall packet losses Jitter Application buffer parameters Network Network available bitrate Network packet delay Network jitter Network losses parameters Figure 2.8 Interrelationship of QoS parameters. and codec performance (