eMDI Monitoring Indicators

An eMDI-enabled switch obtains monitoring indicator statistics from devices at a specified monitoring interval, and periodically sends the statistics to the NMS. eMDI supports quality monitoring and fault demarcation for services transmitted over TCP and UDP. The methods of collecting monitoring indicator statistics differ between UDP and TCP services.

UDP services

Monitoring indicator statistics about UDP services are calculated based on Real-time Transport Protocol (RTP) packets. RTP is a transport layer protocol designed for end-to-end and real-time transmission of services. It is widely used in communication and entertainment systems that involve streaming media, such as live video, streaming television, and video teleconference applications. An RTP packet consists of a header and a payload. The PT field in the RTP header is analyzed to determine the service type. The packet loss rate and out-of-order packet rate are calculated based on the sequence number in the RTP header. The jitter is calculated based on the timestamp in the RTP header.
TCP services

TCP is a connection-oriented transport layer protocol that provides reliable, ordered, and error-checked delivery of a stream of bytes. Monitoring indicator statistics about TCP services are calculated based on TCP packets. The average rate is calculated based on the length of TCP packets transmitted within a monitoring interval. The upstream and downstream packet loss rate is calculated based on the sequence number in the TCP header. The average upstream and downstream two-way delay is calculated based on the timestamp and serial number in the TCP header.

Table 1 and Table 2 list the eMDI monitoring indicators.

**Table 1** UDP service monitoring indicators
Indicator	Description	Calculation
RTP-LR	Packet loss rate within a monitoring interval	RTP-LR = Number of lost packets/(Number of received packets + Number of lost packets - Number of out-of-order packets) If the different between sequence numbers of consecutive RTP packets is greater than 1, packet loss has occurred. If the sequence number of an RTP packet is less than the largest sequence number of all previously received packets, the packet is an out-of-order packet.
RTP-SER	Out-of-order packet rate within a monitoring interval	RTP-SER = Number of out-of-order packets/(Number of received packets + Number of lost packets - Number of out-of-order packets)
Jitter	Jitter within a monitoring interval	Jitter = T2 - T1 T1 indicates the interval between the sender sending the first and last packets. T2 indicates the interval between the receiver receiving the first and last packets.

**Table 2** TCP service monitoring indicators
Indicator	Description	Calculation
MFR	Average bitrate within a monitoring interval, in kbit/s	MFR = Total length of packets received within a monitoring interval/Monitoring interval
UPLR	Upstream packet loss rate within a monitoring interval	If no packets are lost, the sequence number of the current packet plus the packet length is the expected sequence number of the next packet. If the sequence number of the next packet is greater than the expected sequence number, packet loss has occurred on an upstream device. The number of lost packets can be calculated based on the average packet size. UPLR = Number of the lost upstream packets/(Total number of received packets + Total number of lost packets)
DPLR	Downstream packet loss rate within a monitoring interval	If no packets are lost, the sequence number of the current packet plus the packet length is the expected sequence number of the next packet. If the sequence number of the next packet is less than the expected sequence number, the packet is considered to be a retransmitted packet. The number of retransmitted packets is considered to be the total number of lost packets. Number of the lost downstream packets = Total number of the lost packets - Number of the lost upstream packets DPLR = Number of the lost downstream packets/(Total number of received packets + Total number of lost packets)
DRTT	Average downstream two-way delay within a monitoring interval	DRTT = T2 - T1 A received non-retransmitted packet is randomly selected, and its timestamp is recorded as T1. The sequence number of the current packet plus the packet length is the expected sequence number of the next packet. When the sequence number of an upstream packet sent from a downstream device is greater than or equal to the expected sequence number, the timestamp of this packet is recorded as T2.