This section describes the following SRTP call flows:

• Centralized SIP phone to IP Office PSTN trunk in Sunny day and Rainy day.
• IP Office user with IP phone to headquarters (HQ) user outside the branch in Sunny day. This call flow option is not available in Rainy day.

This section highlights a few key SRTP call flow examples. Other call flow scenarios not directly described in this section are also possible.