ts. RTCP provides feedback on the quality of the data distribution. This is an integral part of RTCP's role as a transport protocol and is related to the flow and congestion control functions of other transport protocols. SRTP-There is considerable interest in the use of SRTP, a relatively new protocol, to prevent eavesdropping on VoIP calls. SRTP permits the voice packet payload to be encrypted. It also allows other protocol messages, such as RTCP messages, to be protected. Encryption protects privacy. How- ever, diagnostic troubleshooting tools cannot analyze encrypted voice pay- load. That's where RTCP Reporting Extension (RTCP XR) comes in. It Chapter 9 IP Services allows information hidden by SRTP to be extracted directly from the digital signal processing software, IP phones, and gateways and reported directly in the RTCP XR message. Of course, this assumes that the RTCP XR mes- sages themselves are not encrypted. The advantages of SRTP are that it provides both privacy via encryption and authentication via message integrity checking. It uses very little bandwidth for overhead, and it uses modern and strong cryptology suites, such as Advanced Encryption Standard (AES) countermode for encryption and Keyed Hashing for Message Authentication for message integrity. IPT QoS QoS is managed unfairness because some users purposely get better service than others. As discussed further in Chapter 10, QoS is needed to address the stringent delay requirements of voice traffic. Several techniques, including the following, can be used to improve various aspects of a network's QoS: Random Early Detection (RED)-RED is a queue management algorithm and a congestion avoidence algorithm. RED monitors the average queue size and drops packets based on statistical probabilities. If the buffer is almost empty, all incoming packets are accepted. As the queue grows, the probability for dropping an incoming packet grows, too. On a shared voice/data queue, RED does not prevent large delay and jitter for voice. RED is primarily effectiv