def dial(session_id, token, sip_uri, opts)
      response = @client.dial(session_id, token, sip_uri, opts)
    end
def dial(session_id, token, sip_uri, opts)
      response = @client.dial(session_id, token, sip_uri, opts)
    end
Dials a SIP gateway to input an audio-only stream into your OpenTok session.
 See the {https://tokbox.com/developer/guides/sip/ OpenTok SIP developer guide}.

 @example
    opts = { "from" => "14155550101@example.com",
      "auth" => { "username" => sip_username,
        "password" => sip_password },
      "headers" => { "X-KEY1" => "value1",
        "X-KEY1" => "value2" },
      "secure" => "true"
    }
    response = opentok.sip.dial(session_id, token, "sip:+15128675309@acme.pstn.example.com;transport=tls", opts)
 @param [String] session_id The session ID corresponding to the session to which
   the SIP gateway will connect.
 @param [String] token The token for the session ID with which the SIP user
   will use to connect.
 @param [String] sip_uri The SIP URI the OpenTok SIP gateway will dial.
 @param [Hash] opts A hash defining options for the SIP call. For example:
 @option opts [String] :from The number or string that will be sent to the final
   SIP number as the caller. It must be a string in the form of "from@example.com",
   where from can be a string or a number. If from is set to a number
   (for example, "14155550101@example.com"), it will show up as the incoming
   number on PSTN phones. If from is undefined or set to a string (for example,
   "joe@example.com"), +00000000 will show up as the incoming number on
   PSTN phones.
 @option opts [Hash] :headers This hash defines custom headers to be added
   to the SIP ​INVITE​ request initiated from OpenTok to the your SIP platform.
   Each of the custom headers must start with the ​"X-"​ prefix, or the call
   will result in a Bad Request (400) response.
 @option opts [Hash] :auth This object contains the username and password
   to be used in the the SIP INVITE​ request for HTTP digest authentication,
   if it is required by your SIP platform.
 @option opts  [true, false] :secure Wether the media must be transmitted
   encrypted (​true​) or not (​false​, the default).