Traffic Path for IP Telephony

Consider complete traffic path when placing equipment and configuring VLANs.

The size of an enterprise network drives the design and placement of certain types of devices. If the network is designed according to the ECNM, there will be distinct devices separating the access, distribution, and backbone areas of the network. The network design and the types of applications supported will determine where certain traffic sources are located. In the case of multicast and IP telephony applications, they do share some common traffic types. Specifically, if a Cisco CallManager is providing music on hold, it may need to multicast that traffic stream.

Consider these points when determining where to place the servers:

■ Cisco CallManager servers must be accessible throughout the network at all times. Ensure that there are redundant NICs in the publisher and subscriber servers and redundant connections between those NICs and the upstream switch from the server. It is recommended that voice traffic be configured on its own VLAN. Cisco CallManager servers are typically located within the Server Farm block in the ECNM design.

■ VLAN trunks must be configured appropriately to carry IP telephony traffic throughout the network or to specific destinations.

When you deploy voice, Cisco recommends that you enable two VLANs at the access layer: a native VLAN for data traffic and a voice VLAN.

Separate voice and data VLANs are recommended for these reasons:

■ Address space conservation and voice device protection from external networks

■ QoS trust boundary extension to voice devices

■ Protection from malicious network attacks

■ Ease of management and configuration

2-16 Building Cisco Multilayer Switched Networks (BCMSN) v3.0 © 2006 Cisco Systems, Inc.

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