The next and last step before we can perform the actual calculations is to populate the tool with the site-based parameters we identified earlier.
Browse the Sites sheet and populate the relevant fields as follows:
For the Central Sites section:
- Add the Datacenter site.
- Set the Local PSTN breakout value to Yes. This tells the tool that there is a PSTN gateway in the data center site (later in our configuration, we will set the same parameters for the branch sites to No, and this will indicate that our PSTN gateway is centralized in the data center).
- Set the WAN Link speed and WAN link BW allocated to RTC traffic options as per the table in the previous recipe.
- For the Personas option, we have assigned no user. This tells the tool that it is a pure datacenter site.
For the Branch Sites section:
- Add all identified sites
- Set the Central site that provides the user services parameter to the data center. This tells the tool that all the branch site users are hosted in the Lync deployment in the datacenter site.
- Leave the Number of sites like this value as 1 (default). This option comes in handy when we have numerous sites with identical values.
- Set the Local PSTN breakout value to No for all branch sites. This tells the tool that the PSTN gateway in the datacenter's site will be used (if you had a local PSTN gateway on a site, and you set it to Yes, the tool would assume that the calls for that site are routed through the local gateway, and therefore, they would not use the WAN link).
- Set the Low delay WAN for all branch sites value to Yes (the default is No). A No value is applied if we know that the latency will be 25 ms or more. This will instruct the tool to consider different codecs (which have a different bandwidth requirement) or introduce FEC (forward error correction) to account for potentially less-than-optimal network conditions at the cost of incremental bandwidth usage for FEC redundancy data.
- Set the WAN Link speed and WAN link BW allocated to RTC traffic options for all branch sites as per the table in the previous recipe.
- Finally, set the Restrict Audio codecs using CAC option to Yes. This instructs the tool to change the codecs used in calculations, assuming CAC is restricting the usage to less bandwidth-intensive codecs with the purpose of allowing for more sessions (for example, without CAC, the calculator will consider the RTAudio Wideband codec for P2P calls using 45 Kbps for typical usage, whereas with CAC, the tool will calculate based on the RTAudio Narrowband codec typically using 27.8 Kbps).
- For the Persona option, we have assigned no user. This tells the tool that it is a pure datacenter site.
Next, let's populate the Persona fields in the Branch Sites section, as shown in the following image:
This way, we have assigned a given number of users for each persona and for each site to sum up to the total user count in our initial table.
The tool is now ready to perform the calculations.
For an overview of codecs used by Lync and the typical bandwidth usage for each, please refer to http://technet.microsoft.com/en-gb/library/jj688118.aspx. You can also refer to the Codecs sheet in the Bandwidth Calculator tool and even change them (although we do not recommend it unless you know exactly what you are doing).