ranslation (NAT) intended to work. CIR is a committed and reliable rate, whereas burst is a bonus when network conditions VoIP does not work well with networks that use NAT permit it without infringing on any user's CIR. For this because most NAT implementations do not support reason, burst frames are marked Discard Eligible (DE) H.323 protocols. The destination IP address is encapsu- and are queued or discarded when network congestion lated in more than one header: the Q.931, H.225, and IP exists. Although experience has shown that customers headers. NAT changes only the address in the IP header, can achieve significant burst throughput, it is unreliable resulting in a mismatch that prohibits the control of calls. and unpredictable and not suitable for real-time appli- Using a firewall to guard against intruders is often cations such as VoIP. suggested, but the firewall should not provide NAT Therefore, the objective is to prevent voice traffic functions for VoIP packets unless it is Q.931 friendly. from entering the burst range and being marked DE. One way to accomplish this is to prohibit bursting by shaping Network design recommendations the traffic to the CIR and setting the excess burst size (Be-determines the burst range) to zero. However, this also prevents data traffic from using the burst range as This section is an amalgam of various converged network well. Another possible alternative is to size the CIR above vendors' recommendations for best practices in designing the peak voice traffic level, and then prioritize the voice a converged IP network. traffic SO that it is always delivered first. The underlying A network should be designed with the following factors in mind: assumption here is that the network administrator has an expectation of peak voice traffic. By sizing the CIR to Reliability/redundancy meet or exceed the peak voice traffic and then applying Scalability priority queuing on the interface SO that VoIP is serviced Manageability first, we can intuitively assure that voice traffic will no