When looking at a WiFi Audio system, there are several potential bandwidth bottlenecks.
- The Ethernet Switch
- The Venue Server
- The Wi-Fi Access Points
- IP Address space
In a technical blog, here, we looked at the Wi-Fi access points. Access points must be added to reach the total number of clients (smart phones and tablets) that will be listening at one time.
Doing some quick calculations on data rates and bandwidth, assume 150 kbps for the communication to each phone and a 50% load capacity on the Ethernet, then 100 baseT (100 MHz) Ethernet can support about 300 phones and Gigabit Ethernet can support about 3000 phones, assuming no other significant traffic. Note, you should use a cut-through switch for minimum latency.
Audio Everywhere offers two types of venue servers (ExXtractors), the MX3 (basic) and MX3-plus. The MX3 basic can handle about 150 phones and the MX3-plus about 500. It is a soft roll over, so one can push the plus, for instance, to 600 phones, but there will be an occasional extra packet drop, more important for music than speech. Note that this capacity is no longer a function of the number of channels per ExXtractor. For instance, an MX3-1 and MX3-16 can service the same number of smart phones. Of course more ExXtractors create more capacity.
Finally, one does need to get enough IP address space in the network so that each phone can grab one from DHCP. The usual netmask of 255.255.255.0, for instance, only provides for about 250 addresses. And don’t forget about the impact of DHCP lease times (we recommend 120 minutes). An IP address for a phone that has left the building cannot be reused until it is released.
The proper system deployment considers all of these potential bottlenecks.