Device-Level Packet Loss Measurement
Device-level packet loss measurement is based on IP Local Performance Measurement (IP LPM). IP LPM can measure network performance indicators, such as packet loss ratio and number of lost packets, on direct links or on devices. Different from IP FPM, IP LPM does not allow target flow definition, and only collects statistics on IP unicast traffic entering/leaving a device or on a direct link. Similar to network-level packet loss measurement, device-level packet loss measurement is also implemented based on packet characteristics bits.
Packet Loss Measurement on a Direct Link
In Figure 1, the link between directly connected devices is considered an independent system. After packet loss measurement is enabled for a direct link, the devices measure packet loss on the link based on packet characteristics bits at measurement intervals.
Within a measurement interval, the number of packets received by an independent system is the sum of the following values:
- PI(1) packets received from Switch_1 interface
- PI(2) packets received from Switch_2 interface
The number of packets sent by the system is the sum of the following values:
- PE(1) packets sent through Switch_1 interface
- PE(2) packets sent through Switch_2 interface
Switch_1 is used as an example here. Within a measurement interval, the number of lost packets from the local device to remote device (LostPacket) is PE(1) - PI(2), and the packet loss ratio (LostPacketRate) is LostPacket/PE(1). The number of lost packets from the remote device to the local device (LostPacket') is PE(2) - PI(1), and the packet loss ratio (LostPacketRate') is LostPacket'/PE(2).
Similar to network-level packet loss measurement, the devices on two ends of a link must follow the same standard to mark the measurement time so that they can obtain their data within the same period of time. Therefore, time synchronization between the two devices is the prerequisite of packet loss measurement on direct links. Before configuring iPCA, configure NTP to allow the two switches to synchronize time with each other.
Packet Loss Measurement on a Device
In Figure 2, the device is an independent system. After the packet loss measurement for a device is enabled, iPCA measures packet loss on the device based on packet characteristics bits at measurement intervals.
Within a measurement interval, the sent and received packets include:
- PI packets are received by all interfaces on the device.
- PE packets are sent out through interfaces on the device.