The Quality of Service (QoS) features mentioned in this section apply only to the Customer’s LAN and private WAN (i.e. MPLS) networks. Internet connections do not apply or use any QoS features, since US laws prohibit the preferential treatment of traffic on Internet connections.
Voice, as a class of IP network traffic, has strict requirements concerning packet loss, delay, and delay variation (also known as jitter) to maintain high voice quality. To meet voice traffic requirements, many vendor solutions include the following QoS features:
Traffic classification
Queuing
Traffic shaping
Compressed Real-Time Transport Protocol (CRTP) *
Transmission Control Protocol (TCP) header compression *
46 Labs monitors and sizes the Network to Network Interfaces (NNIs) (the connections between the MPLS, Internet, and the PSTN network) to prevent oversubscription. However, in MPLS networks, the Provider Edge (PE) to Customer Edge (CE) MPLS connections are a common place where oversubscription can occur. The proper QoS configuration of the PE and CE routers is often the most important consideration in maintaining high voice quality on MPLS networks.
46 Labs recommends that Peeredge Switch follow the industry best practice design approach and mark all SIP signaling traffic with a Differentiated Services Code Point (DSCP) marking of 24 (PHB CS3) and all RTP/SRTP traffic with a DSCP marking of 46 (PHB EF).