Cisco Voice over IP (CVoice) (Authorized Self-Study Guide) (2nd Edition)

This chapter introduced the need for quality of service (QoS) in a converged network environment (that is, a network that simultaneously transports voice, data, and/or video). In the absence of QoS mechanisms, voice packets might suffer from packet loss, packet delay, and variable delay (that is, jitter). QoS mechanisms help mitigate such challenges through tools such as classification, marking, low latency queuing (LLQ), RTP Header Compression (cRTP), and Link Fragmentation and Interleaving (LFI).

Even with its relatively high-speed connectivity, local area networks (LANs) also need QoS. For example, an interface speed mismatch for traffic entering (for example, on a 1 Gbps link) and exiting (for example, on a 100 Mbps link) a switch could cause a switch interface queue to fill to capacity and overflow. On the LAN, many Cisco Catalyst switches can use QoS mechanisms, such as weighted round-robin (WRR) and CoS to DSCP remarking.

While the study of how to configure the various aspects of QoS mechanisms is beyond the scope of this book, this chapter did introduce a way to configure QoS on both IOS router platforms and IOS-based Catalyst switch platforms, through a feature called AutoQoS.

In the voice arena, most QoS mechanisms are aimed at protecting voice from data. However, too many simultaneous voice calls can also oversubscribe available WAN bandwidth. Therefore, Call Admission Control (CAC) mechanisms help protect voice from voice. This chapter discussed the configuration of H.323, SIP, MGCP, and Cisco Unified CallManager CAC approaches.