(off−ACS) database to store the user names and passwords for the badges, Cisco does not recommend this practice. Because the ACS must be queried whenever the badge roams between access points, the unpredictable delay to access an off−ACS database could cause excessive delay and poor voice quality.
Wireless Network Infrastructure
The wireless IP Telephony network, just like a wired IP Telephony network, requires careful planning for VLAN configuration, network sizing, multicast transport, and equipment choices. For both wired and wireless IP Telephony networks, separate voice and data VLANs is often the most effective way of suggested deployment to ensure sufficient network bandwidth and ease of troubleshooting.
Voice, Data and Vocera VLANs
VLANs provide a mechanism for segmenting networks into one or more broadcast domains. VLANs are especially important for IP Telephony networks, where the typical recommendation is to separate voice and data traffic into different Layer 2 domains. Cisco recommends that you configure separate VLANs for the Vocera Badges from other voice and data traffic: a native VLAN for access point management traffic, data VLAN for data traffic, a voice or auxiliary VLAN for voice traffic, and a VLAN for the Vocera Badges. A separate voice VLAN enables the network to take advantage of Layer 2 marking and provides priority queuing at the Layer 2 access switch port. This ensures that appropriate QoS is provided for various classes of traffic and helps to resolve addressing issues such as IP addressing, security, and network dimensioning. The Vocera Badges use a broadcast feature that utilizes multicast to deliver. This common VLAN ensures that when a badge roams between controllers, it remains part of the multicast group. This last process is discussed in detail when multicast is addressed later in this document.
Network Sizing
IP Telephony network sizing is essential to ensure that adequate bandwidth and resources are available to meet the demands presented by the presence of voice traffic. In addition to the usual IP Telephony design guidelines for sizing components such as PSTN gateway ports, transcoders, WAN bandwidth, and so forth, also consider these 802.11b issues when you size your wireless IP Telephony network. The Vocera Badges are a specialized application that stretch the number of wired clients beyond our typical deployment recommendations.
Number of 802.11b Devices per Access Point
Cisco recommends that you have no more than 15 to 25 802.11b devices per access point.
Number of Active Calls per Access Point
Vocera uses two different codecs based on if it is a badge−to−badge (proprietary low−bit rate codec) call or a badge−to−phone (G.711 codec) call. This table shows a percentage of available bandwidth by data rates and gives you a clearer picture of the expected throughput:
Call Process | 1 |
| 2 |
| 5.5 |
| 11 |
|
| Mbps |
| Mbps |
| Mbps |
| Mbps |
|
Badge−to−Phone (G.711) | 20.7% |
| 11.8% |
| 6.3% |
| 4.7% |
|
|
|
|
|
| ||||
Badge−to−Badge |
|
|
|
|
|
|
|
|
(Proprietary Low−bit rate |
|
|
|
|
|
|
|
|
codec) | 9.4% |
| 6.1% |
| 4.2% |
| 3.6% |
|
|
|
|
|
|