Delay measurement


Path delay refers to the time from the source to the sink, which is measured using overheads.
Delay measurement is used to measure the E2E bidirectional delay of ODUk signals. If ODUk SNCP protection is configured on the trail, the measurement result is the delay of the current working trail.
The measurement process automatically inserts PM-layer delay measurement overhead bytes to the OTU board at the source end. The intermediate NEs transparently transmit the overhead bytes and the sink end loops back the overhead bytes. After the measurement is complete, the related configurations are automatically restored.

Other related questions:
SIP message delay of the U1930
The delay of the INVITE message cannot exceed 10s.

Is it normal if the VRRP preemption delay configured on an AR router is different from actual delay
Is it normal if the VRRP preemption delay configured on an AR router is different from actual delay? It is normal. The backup-to-master conversion procedure for VRRP devices is as follows: Backup device: If the backup device receives packets with priority being 0 (lower than the priority of its own packets), the timer is set to Skew_time (offset time). If the packet priority is not 0, the packets are discarded and the backup device changes to the master state immediately. Master device: The master device sends VRRP advertisement packets regularly, and publicizes its configuration information (priority, for example) and working state in the VRRP group. Based on the VRRP packets, the backup device determines whether the master device works normally. - If the master device drops its master state (for example, it quits the backup group), it sends an advertisement packet with priority set to 0, to enable the backup device to change to the master state quickly without waiting for the timer specified by Master_Down_Interval to expire. This switchover time is referred to as the skew time, and is calculated based on the formula: �?56 - Backup device priority)/256 (unit: second). - If the master device encounters a network fault and cannot send an advertisement packet, the backup device will not know the status of the master device immediately and is notified of the fault until the timer specified by Master_Down_Interval expires. In this case, the backup device considers that the master device cannot work normally and switches over to the master state. The value of Master_Down_Interval is calculated based on the formula: 3 x Advertisement_Interval + Skew_time (unit: second). Note: In a performance-unstable network, network congestion may result in a backup device failure to receive packets from the master device within the time specified by Master_Down_Interval. In this case, the backup device will automatically switch over to the master state. If the packets from the master device arrive then, the device switches back to the backup state. This is likely to cause frequent switchover between VRRP devices. To relieve this phenomenon, a preemption delay can be configured to enable the backup device to wait for the preemption delay time after the timer specified by Master_Down_Interval expires. Before this relay time expires, the backup device will not switch over to the master state even if it does not receive an advertisement packet.

How to check ping packet loss on S series switches
For S series switches (except the S1700), you can run the ping command to check ping packet loss directly. For example: [HUAWEI] ping -c 100 PING 56 data bytes, press CTRL_C to break Reply from bytes=56 Sequence=1 ttl=124 time=1 ms ... --- ping statistics --- 100 packet(s) transmitted //Total number of sent packets 91 packet(s) received //Total number of received packets 9.00% packet loss //Packet loss ratio round-trip min/avg/max = 1/1/19 ms You can also perform the following steps to configure traffic statistics collection to check ping packet loss: Configure traffic statistics collection for packets received by a switch. 1. Configure an ACL rule. [HUAWEI] acl number 3000 [HUAWEI-acl-adv-3000] rule permit icmp source 0 destination 0 [HUAWEI-acl-adv-3000] quit 2. Configure a traffic classifier. [HUAWEI] traffic classifier 3000 [HUAWEI-classifier-3000] if-match acl 3000 [HUAWEI-classifier-3000] quit3. Configure a traffic behavior. [HUAWEI] traffic behavior 3000 [HUAWEI-behavior-3000] statistic enable [HUAWEI-behavior-3000] quit 4. Configure a traffic policy. [HUAWEI] traffic policy 3000 [HUAWEI-trafficpolicy-3000] classifier 3000 behavior 3000 [HUAWEI-trafficpolicy-3000] quit 5. Apply the traffic policy to an interface. [HUAWEI] interface gigabitethernet 0/0/2 [HUAWEI-GigabitEthernet0/0/2] traffic-policy 3000 inbound [HUAWEI-GigabitEthernet0/0/2] quit 6. Check traffic statistics of packets received by the switch. [HUAWEI] display traffic policy statistics interface gigabitethernet 0/0/2 inbound verbose rule-base //The output is omitted. For more information about ping packet loss, see "Ping Failure Troubleshooting" or "S Series Switches packet Loss Troubleshooting" in "Maintenance Topics" in the Huawei S Series Campus Switches Maintenance Guide.

Long ping latency on S series switches
Network latency indicates the round-trip period of time during which a source device sends a packet to the destination device and then the destination device returns a packet to the source device. Possible causes of long network latency are as follows: 1. Multiple hops on the packet forwarding path. The transmission time of packets in the physical medium can be ignored because optical and electrical signals are transmitted at a high speed. However, the time that a switch spends processing packets cannot be ignored. When packets are transmitted through too many hops, the network latency is long. 2. Insufficient network bandwidth. When the network through which packets are transmitted does not have sufficient bandwidth, network congestion occurs and packets need to wait in queues, resulting in long network latency. 3. Insufficient memory space. When a switch receives a large number of packets, the switch does not have sufficient memory space to process these packets, resulting in slow packet processing speed and long network latency. You can run the ping command to test network latency. The test results are only for reference and cannot be used as an absolute value of network latency measurement. No reference value is available for determining whether the ping latency is normal because requirement for network latency varies depending on network status. Other measurement methods such as network quality analysis (NQA) are also required to accurately measure network latency. Pay attention to the following points when analyzing a ping latency: 1. When a switch forwards packets through the hardware at a high speed, network latency is short. For example, ping a PC connected to the switch. When packets need to be processed by the CPU, network latency is long. For example, ping a gateway. Through network latency is long when the switch pings the gateway, packets are normally forwarded because the packets are processed by the underlying chip rather than the CPU. You can run the icmp-reply fast command to enable the fast ICMP reply function on the switch to shorten network latency when the switch pings the gateway. After the function is enabled, the switch quickly responds to received Echo Request packets destined for its own IP address. The CPU of the LPU directly responds to the received ICMP packets, improving the processing speed of ICMP packets and shortening network latency. 2. The processing priority of ICMP packets has been minimized to prevent impacts of common ping attacks on the switch, so that ICMP packets are the last to be transmitted and processed. Therefore, the network latency is long.

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