Quality-of-Service

V. Liberatore

Pervasive Computing

RTCP

Control protocol

nWorks in conjunction with RTP

Functions

nQoS monitoring and congestion control

Convey feedback on quality of data delivery and information of membership

Modify transmission rates

Diagnostic

nSource identification

nSession size estimation and scaling

nSession control

E.g., user names to be displayed

Reports

nParticipants periodically send RTCP report packets

nStatistics, e.g.,

Number of packets sent

Number of packets lost

Inter-arrival jitter


	QoS monitoring and congestion control
		Provides feedback to an application about the quality of data distribution
		Sender can adjust its transmission based on the receiver report feedback
		Receivers can know whether a congestion is local, regional or global
	Source identification
		RTCP SDES (source description) packets contain textual information called canonical names as globally unique identifiers of the session participants
		It may include user's name, telephone number, email address and other information
	Session size estimation and scaling
		All participants send periodic RTCP packets
		Transmission rate of RTCP packets must be reduced as the number of participants increases
		RFC 1889 limits RTCP traffic to less than 5% of session bandwidth, divided between sender reports (25%) and receiver reports (75%)
	Session control
		Optional function to convey minimal session control information, for example, participant identification to be displayed in the user interface