Traffic Flow Design Considerations

Traffic engineering involves the measurement and control of traffic. Main VoIP traffic sources are IP phones and VoIP Trunks. We need to be able to perform traffic engineering on individual nodes and consider the traffic between nodes. Traffic measurement is an analysis of existing traffic flow and the patterns of a network. This will help us to determine how many users and calls a VoIP network can support. Some operational metrics from the system include the number of calls and users, the duration of calls, the number of concurrent calls, call volume profiles, location and call flow, and the number and length of faxes sent and received. In order to assemble this traffic information and make a judgment we need to look at a number of design considerations:
1. System capacity for busy hour
2. Interfaces for critical connections
3. Single points of failure at critical points in the network
4. Is there sufficient power
5. If a device fails, does network design provide redundant paths?

Once again, I will reiterate that we should ONLY use switched media Ethernet networks with VoIP. Shared media, such as hubs, will cause problems. We need to ensure that QoS is being used, such as 802.1p, VLANs, port prioritization, and the rest. If we are fortunate enough to be using Layer 3 switching, we should try to use DiffServ to manage applications with different types of QoS services. And, of course, we should look to increase bandwidth as necessary.

When considering routing across a WAN, we have some additional factors to consider. WANs can require a large amount of memory and processing capacity. When designing WAN traffic flow, we should consider performance, resiliency, stability, and route cost. As always, performance is a large part of WAN design. When considering performance, we should:
1. Be aware of CPU utilization required for router intelligence
2. Move the heavy burden of processing routers to out-of-band processors
3. Use network routers for packet forwarding and handling
4. Deploy Layer 2 QoS Switching between policy switch stacks to reduce policy switch stack and router CPU utilization for LAN-Side traffic
5. Reduce the number of router zones (or areas)
The complexity of a network will dramatically affect its resiliency. Network instability, or Route Flapping, can occur on a more complex network. In addition, we need to consider route cost or metrics that will be applied to a route. In order to guarantee a scalable and reliable enterprise WAN service providers should offer a competitive Service Level Agreement (SLA). The SLA should clearly guarantee the maximum latency and available bandwidth. Increased reliability and performance requirements of converged networks put added pressures for the establishment of strong SLAs with our service providers. If our service provider of choice will not give us an acceptable SLA we should begin the process of looking for another service provider!

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