/mcpQuality of Service for Voice over IP VoIP QoS over Leased Lines (Using PPP) 35 QoSVoIP.mif The following configuration example shows a complete configuration with all of the listed QoS features enabled: Configuration Example 15: QoS for VoIP over PPP WAN Links Commands Description class-map voip match ip precedence 5 ! Creates the class voip for voice traffic that has been marked with IP Precedence 5 using one of the available marking methods. class-map webtraffic match ip precedence 3 ! Creates the class webtraffic for web traffic that has been marked with IP Precedence 3 using one of the available marking methods. policy-map llq class voip priority 64 class webtraffic bandwidth 64 class class-default fair-queue ! Defines the QoS policy map llq: Class voip traffic gets priority and is limited to 64 kbps during congestion; class webtraffic packets are guaranteed 64 kbps. All other traffic shares the remaining bandwidth. interface Serial1/0 bandwidth 256 encapsulation ppp no fair-queue ppp multilink multilink-group 1 ! Attaches the serial interface 1/0 to multilink interface in group 1. (For link bandwidths over 1.2 Mbps, Multilink PPP LFI and cRTP are not needed. In that case, the IP address and service-policy statement would go under the serial interface configuration.) interface Multilink1 ip address 10.1.1.1 255.255.255.252 bandwidth 256 ! Configures Multilink PPP LFI for links less than 1.2 Mbps. ip rtp header-compression iphc-format ip tcp header-compression iphc-format ! Configures cRTP to reduce bandwidth requirements of each voice call. ppp multilink ppp multilink fragment-delay 10 Enables a fragmentation size of 10 ms. ppp multilink interleave Enables packet and fragment interleaving. multilink-group 1 service-policy output llq ! Attaches the multilink interface to group 1. Attaches the llq QoS policy to outgoing traffic on the multilink interface. In this example, Multilink PPP LFI prevents VoIP packets from getting delayed behind large data packets, cRTP reduces VoIP bandwidth requirements, and LLQ provides priority to VoIP traffic and guaranteed bandwidth to another class. You need to configure these features on both ends of the PPP link. Multilink PPP LFI is needed only for links less than 1.2 Mbps, and cRTP is recommended only on links with a low number of VoIP calls and if the CPU is not running too high.