Call encryption with voip.ms, using OBi200 series

On voip.ms website

1.  Login
2. Go to Main Menu -> Account Settings -> Advanced
3. Encrypted SIP Traffic: Yes.

Obi20x

1. Login
2. Go to Service Providers -> ITSP Profile A -> SIP
   ProxyServerPort: 5061 (from 5060)
   ProxyServerTransport: TLS (from UDP)
   RegistrarServerPort: 5061 (from 5060)
   OutboundProxyPort: 5061 (from 5060)
3. Voice Services -> SP1 Service -> Calling Features
   X_SRTP: Use SRTP Only (from Disable SRTP)

Troubleshooting

After making the changes, I got an error message when placing a call: The number you dialed **** has not received a response from the service provider.

The reason is that I was using the Local DNS Records feature (System Management -> WAN Settings). According to voip.ms(https://wiki.voip.ms/article/Call_Encryption_-_TLS/SRTP#Configuration_on_SIP_Client), to use the encryption feature, one must specify the exact server name with a number at the end. It seems that a local DNS would not work either.

I fixed it by picking and setting up a specific server:
1. Use "ping" to check the latency of the voip.ms servers listed here: https://wiki.voip.ms/article/Choosing_Server
2. Find a fastest server to you, e.g. newyork2.voip.ms

Obi20x

Go to Service Providers -> ITSP Profile A -> SIP
ProxyServer: newyork2.voip.ms

On voip.ms website

DID Numbers -> Manage DID -> Edit DID
DID Point of Presence: newyork2.voip.ms