This chapter covers
- Enabling IP telephony with voice VLANs
- Powering IP phones and other devices with Power over Ethernet
- Prioritizing important network traffic in times of congestion with quality of service
Network resources—bandwidth, in particular—are not unlimited. This means that networks can become congested, and bottlenecks can occur, negatively affecting network performance and the experience of the network’s users. Some types of network communications are more sensitive to these problems. For example, users in a voice/video call, due to their real-time nature, are more likely to notice a network slowdown than users communicating via email.
Quality of service (QoS) is a set of technologies that enable the prioritization of more important traffic (and the de-prioritization of less important traffic) in times of network congestion. In this chapter, we will cover QoS and its various components. Before covering QoS itself, we will cover the topic of IP telephony, also called Voice over IP (VoIP)—telephones that communicate over a network using IP packets. Voice traffic is particularly sensitive to poor network performance and is usually prioritized in a QoS policy. We’ll also cover Power over Ethernet (PoE), which is used to power IP phones (and other devices) over Ethernet cables. Here are the exam topics we’ll cover: