/mcpQuality of Service for Voice over IP VoIP QoS over Leased Lines (Using PPP) 34 QoSVoIP.mif – RED is specifically designed for TCP traffic. VoIP rides on top of UDP. Therefore, whenever possible, voice and data traffic should be classified into separate categories and RED should be applied to data but not to voice. In addition, each link and piece of equipment in the VoIP path adds delay to voice packet transmission. The possibility of voice packet loss also increases as voice traffic travels a longer distance and over more hops in the network. Low speed WAN connections usually are the weakest links. VoIP over Leased Line (Using PPP) Recommended Solution Under normal conditions, network equipment and end stations cannot differentiate between the requirements of real-time voice packets and standard data traffic. This could result in serious speech degradation. To ensure voice quality, you must classify data and voice traffic into different categories and give voice traffic priority handling across a shared data network backbone. Giving voice traffic priority handling minimizes delays and drops, and whenever possible, gives voice traffic predictable transmission performance. For PPP links, we recommend the following QoS features: • Packet classification through MQC • Class-based marking (at the DS edge) • Priority handling though LLQ • CRTP—Needed only on low speed links with a low number of calls for bandwidth optimization • MP LFI—Needed only on low speed links (below 1.2 Mbps) to ensure that one fragment transmission time is less than 10 ms