4.1.1 Initiating Sessions

Initiating RTP sessions with ccRTP involves the construction of an object of the class RTPSession and calling some optional initialization methods. RTPSession constructors take two mandatory arguments: local network address and local transport port (where incoming packets are expected). There are two constructors, one of them takes a host address as first parameter, while the other takes a multicast address. In the latter case, the application will join to a multicast group.

General purpose RTP stacks of ccRTP, such as RTPSession objects, must be signaled to start execution. This is done calling the startRunning() method. Note there is also a enableStack() method, this only activates the stack but does not start the execution of the stack thread.

After the steps above, the application can receive data, but will not transmit to any destination. This and other session parameters can be set as follows:

• Add destinations: calling the method addDestination.

• Set payload format. Method setPayloadFormat. By default, the static payload type 0 is assumed (PCMU format at 8Khz).

• Set local SDES Items. For common applications, the CNAME item value is automatically guessed as user@host. Other items have no default value and are not sent in RTCP packets unless a value is specified by the application. For those items that should be sent in RTCP packets along with the mandatory CNAME, its values can be set calling the setSDESItem and setPRIVPrefix methods over the object returned by the defaultApplication global function.

• Enable padding of data packets. Calling setPadding(uint8) on outgoing data queues enables transparent padding of data packets to a multiple of the padding maximum length specified. By default, padding is off (maximum length of padding is 0).
• setting addresses:

• Set session bandwidth calling the setSessionBandwidth method of the session object. If not called, a default bandwidth of 64Kbps is assumed, and 5% of this bandwidth is used for RTCP. This percentage can be changed through the setControlBandwidth method.