Linksys SPA921 Cisco SPA9000 Voice System Web-UI Based Product Installation an - Page 37

Preparation System Design Considerations 3 Codec G.72616 G.729 Approximate bandwidth budget for each side of conversation 63 kbps 55 kbps 2 calls 126 kbps 110 kbps 4 calls 252 kbps 220 kbps 6 calls 378 kbps 330 kbps 8 calls 504 kbps 440 kbps For more information about bandwidth calculation, refer to the following web sites: www.erlang.com/calculator/lipb/ www.bandcalc.com/ Wide Area Network (WAN) Quality of Service You can choose from several types of broadband access technologies to provide symmetric or asymmetric connectivity to a small business. These technologies vary on the available bandwidth and on the quality of service. It is generally recommended that you use broadband access with a Service Level Agreement that provides quality of service. If there is not a Service Level Agreement with regard to the broadband connection quality of service, the downstream audio quality may be affected negatively under heavy load conditions (bandwidth utilization beyond 80%). To eliminate or minimize this effect, Cisco recommends one of the following actions: • For broadband connections with a bandwidth lower than 2 Mbps, perform the call capacity calculations by assuming a bandwidth value of 50% of the existing broadband bandwidth. For example, in the case of a 2 Mbps uplink broadband connection, assume 1 Mbps. Limit the uplink bandwidth in the Integrated Access Device to this value. This setting helps to maintain the utilization levels below 60%, thus reducing jitter and packet loss. • Use an additional broadband connection for voice services only. A separate connection is required when the broadband connection services do not offer quality of service and when it is not possible to apply the above mentioned utilization mechanism. SPA9000 Voice System Installation and Configuration Guide for Web UI 35