Network managers generally focus on quality of service (QoS) as the only means of monitoring and managing the quality of IP services. But while managing packets for loss, jitter, or delay is important for VoIP networks, today's successful VoIP providers must go farther; they must ensure a high-quality customer experience by monitoring and managing voice quality levels.

In fact, the quality of voice reproduction and transmission can often make or break customer satisfaction and service renewals. In this article, we'll look at IP voice quality challenges along with a new class of solutions for this challenge.

 

Why Standard QoS Isn't Sufficient for Voice Service providers typically use three techniques to control and enhance QoS in packet-based networks: class of service (CoS), differentiated services (DiffServ), and Multi-Protocol Label Switching (MPLS).

 

All three have one thing in common: they all attempt to minimize packet loss and jitter of the voice transport. While this is one piece of the puzzle, controlling packet loss and jitter does not prevent other impairments from degrading the voice. CoS (IEEE 802.1p) is the usual means for providing QoS in Ethernet networks. With CoS, all packets are assigned a priority, and VoIP traffic generally receives the highest priority; thus, using CoS prioritization can minimize VoIP traffic packet loss.

 

DiffServ is a class-based IP QoS technique specified by the Internet Engineering Task Force (IETF). The DiffServ Control Point contained in the IP header is used to control the Per-Hop Behavior (PHB) of routers along the traffic's path from end to end. With VoIP traffic, the PHB is normally set for "Expedited Forwarding" to minimize latency and packet loss.

 

MPLS adds a separate 32-bit header to each packet which is used to create virtual label switched paths (LSPs). With LSPs, providers can segment, prioritize, and expedite traffic. Originally created as a means to implement virtual private networks (VPNs), the MPLS header also has a 3-bit QoS field that can be used to minimize packet loss and latency with VoIP traffic.