A.8 Packet delay, drop rate and loss rate related performance

32.4533GPPPerformance Management (PM)Performance measurements Home enhanced Node B (HeNB) Subsystem (HeNS)Release 17Telecommunication managementTS

Latency is of prime concern for some services, particularly conversational services like speech and instant messaging. A counter is added to measure the mean delay for IP packets incurred within the HeNB. Separate counters are provided per QCI which are particularly useful when the QCI is used by very few services and the packet sizes vary little. It is only practical to measure packet delays on the downlink.

When a cell is heavily loaded congestion can take place. When congestion is not severe the impact is typically the incurrence of additional delay for non-GBR radio bearers. However, when congestion is severe the HeNB may be forced to discard packets. It is important for the operator to have visibility of packet discard so that corrective action can be instigated (for example, by adjusting admission control settings in the network). It is only practical to measure packet discards on the downlink. Packet discards on handover should not be included in the count.

The downlink air interface packet loss can be directly compared with the PELR value of a QCI to see if the packet loss (over the air interface) aspect of quality of service is being met within the cell. On the downlink this measurement can be added to the congestion losses (see DL packet drop rate) to determine the total packet loss rate at the HeNB. Consequently, the downlink useful bit-rate can be estimated by scaling the measurement of the downlink PDCP ingress bit-rate by (1 – DL packet drop rate) (1 – air interface packet loss rate).

The uplink air interface packet loss rate (per QCI) can be compared directly with the PELR defined for that QCI. An estimate of the uplink air interface packet loss may be provided by the “Uplink PDCP SDU loss rate”. This uplink measurement is based on PDCP sequence numbers and cannot precisely measure the air interface losses. Any packets discarded by the UE within the protocol stack (i.e. at layer 2) are also counted since they will have been given a PDCP sequence number. Discards at layer 3 are not counted.