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NE40E V800R010C10SPC500 Feature Description - System Monitor 01

This is NE40E V800R010C10SPC500 Feature Description - System Monitor
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Huawei uses machine translation combined with human proofreading to translate this document to different languages in order to help you better understand the content of this document. Note: Even the most advanced machine translation cannot match the quality of professional translators. Huawei shall not bear any responsibility for translation accuracy and it is recommended that you refer to the English document (a link for which has been provided).
NQA Detection on an IP Network

NQA Detection on an IP Network

DNS Test

An NQA DNS test instance measures the speed at which an NQA client sends UDP packets to resolve a specified DNS name to an IP address. Figure 4-2 shows the DNS test process.

  1. Device A (source end) sends a DNS request packet to the DNS server, requesting the DNS server to resolve a specified DNS name (Server.com).

  2. The DNS server receives and parses the DNS request packet, and then constructs a DNS response packet and sends it to Device A.

  3. After receiving the DNS response packet, Device A computes the delay between the DNS response packet receiving time and the DNS request packet sending time to obtain the DNS name resolving duration, which can reflect the network DNS protocol performance.

Figure 4-2 DNS test application scenario

ICMP Test

An NQA Internet Control Message Protocol (ICMP) test checks whether the route between an NQA source and a destination is reachable. The ICMP test functions similarly to the ping command. The difference is that the ICMP test can provide detailed output information:

  • By default, the ping command output contains the results of the five latest tests.

  • The test results contain information about the average delay time, packet loss ratio, and the time when the last packet was correctly received.

Figure 4-3 illustrates a network on which an NQA ICMP test is performed. The NQA ICMP process is as follows:
  1. The NQA source (Device A) constructs an ICMP Echo Request message, sends it to destination router B, and adds timestamp t1.

  2. Upon receipt, the destination responds to the NQA source with an ICMP Echo Reply message and adds timestamp t2 to calculate the time it takes to communicate between the NQA source and the destination by subtracting the time when the NQA source received the ICMP Echo Reply message from the time the NQA source sent the ICMP Echo Request message.

    The data obtained is used to evaluate the network status.

Figure 4-3 ICMP test networking

Delay = t2 – t1

If the delay is longer than the specified timeout period, the network is congested and ICMP packets will be counted as lost packets.

An ICMP test can also measure the packet loss rate using the following formula: Packet loss rate = Number of lost ICMP packets/Number of sent ICMP packets

The packet loss rate further reflects network status.

TCP Test

An NQA TCP test uses a three-way handshake to measure the time it takes to set up a TCP connection between an NQA client and a TCP server. Figure 4-4 illustrates a network on which an NQA TCP test is performed. The NQA TCP test process is as follows:

  1. The NQA client (Device A) sends a TCP SYN message to the TCP server (Device B) to set up a TCP connection.

  2. Upon receipt, the TCP server accepts the request and responds to the NQA client with a TCP SYN Ack message.

  3. The NQA client returns an Ack message to the TCP server, which indicates that a TCP connection has been successfully set up.

    The NQA client can calculate the time used to perform the three-way handshake and set up the TCP connection to the TCP server by subtracting the time when the NQA client received the TCP SYN message from the time when the NQA client sent the TCP SYN message and Ack message. The data obtained is used to evaluate the performance of the TCP protocol on the network.

Figure 4-4 TCP test networking

UDP Test

Many services on networks use the User Datagram Protocol (UDP). Should the quality of a service deteriorate, users are unable to determine whether the deterioration arises from a faulty service or UDP performance. Network quality analysis (NQA) UDP tests can help solve this problem. UDP performance is checked, and users can identify the cause of the service quality deterioration.

To this end, NQA UDP tests measure the communication speed between a host and an NQA server, which are both Huawei products. Figure 4-5 demonstrates the UDP test process.

  1. Device A constructs a UDP packet, sends it to the NQA server, Device C, and adds timestamp t1.
  2. Once the UDP packet is received, Device C returns the packet to Device A and adds timestamp t2.
  3. Upon receipt, Device A calculates the duration between the time Device A sent the UDP packet and the time Device A received it. The time taken reflects the UDP performance on the network.

Figure 4-5 UDP test networking

If the delay is longer than the specified timeout period, the network is congested and UDP packets will be counted as lost packets.

A UDP test can also measure the packet loss rate using the following formula:

Packet loss rate = Number of lost UDP packets/Number of sent UDP packets

The packet loss rate further reflects network status.

Path Jitter Test

An NQA UDP jitter test instance can accurately measure the delay and jitter along the path from the client to the server, but cannot figure out the faulty location if the jitter value is too great. An NQA path jitter test instance, however, can identify the router whose jitter value is great.

The NQA path jitter test first identifies the IP address of each hop from the client to the server by initiating a trace test, and then initiates an ICMP jitter test from the client to obtain the jitter value of each hop along the path. Figure 4-6 shows the process of a path jitter test:

  1. Device A initiates a trace test to obtain the IP address of each hop along the path to DeviceC.

  2. Device A initiates an ICMP jitter test to the IP address of each hop to obtain the jitter value of each hop.

Figure 4-6 Application scenario of a Path Jitter test

Path MTU Test

A path MTU test instance is used to obtain the maximum MTU value that does not require packet fragmentation during the packet transmission on the link.

When one host sends a large number of IP packets to another host, the IP packets are fragmented according to the maximum acceptable packet length. This affect forwarding efficiency. It is preferable that these packets be of the largest size that does not requires fragmentation anywhere along the path from the client to the server. This packet size is referred to as the path MTU.

Usually, the path MTU is equal to the minimum of the MTUs of each hop along the sub-paths.

As shown in Figure 4-7, the MTU value between DeviceA and DeviceB is 100 bytes and between DeviceB and DeviceC is 200 bytes. Therefore, the path MTU value between DeviceA and DeviceC is 100 bytes.

An NQA path MTU test is initiated from the client to the server. It requires several incremental steps to estimate the maximum path MTU. Figure 4-7 shows the process of a path MTU test:
  1. DeviceA sends an ICMP probe packet to DeviceC, with the packet size as the minimum range (The value is configurable and the default value is 48 bytes).

  2. When the first probe packet successfully hits the destination, DeviceA continues to send ICMP probe packets with incremental steps (which is configurable and the default value is 10 bytes) to DeviceC until three consecutive packets time out. This indicates that the MTU of the sent packet is greater than the minimum path MTU.

  3. DeviceA sends a 48-byte detection packet to DeviceC to check the connectivity of the network. If the connectivity of the network is normal, the size of the last successful probe packet before the timeout in step 2 is the maximum path MTU.

NOTE:
The packet header contains a Don't Fragment (DF) flag, indicating whether a packet can be fragmented. The DF field should be set to 1, indicating that the device cannot fragment the packet.
Figure 4-7 Application scenario of a Path MTU test

SNMP Test

The Simple Network Management Protocol (SNMP) is used for network management on TCP/IP networks. SNMP uses a central computer that functions as a network management station (NMS). This central computer runs network management software to manage network elements (NEs). On the network shown in Figure 4-8, the NMS manages Devices A, B, and C.

NQA SNMP tests use UDP packets to measure the communication speed and SNMP connectivity between a host and an SNMP agent. If a faulty NE is detected when the network management software is deployed on the NMS, an NQA SNMP test instance can be configured on another NE to detect an NE failure or a communication failure between the NMS and the NE. Figure 4-8 demonstrates the SNMP test process.

  1. Device A sends an SNMP request packet to the SNMP agent Device C to request the system time. Because Device A does not know which SNMP versions Device C runs, it sends an SNMPv1 request packet, SNMPv2c request packet, and SNMPv3 request packet to Device C.
  2. Once the SNMP request packets are received, Device C queries the system time, constructs SNMP response packets, and sends the SNMP response packets to Device A. If SNMPv1, SNMPv2c, and SNMPv3 are all enabled on Device C, Device C constructs all three SNMP response packet versions.
  3. After receiving the first SNMP response packet, Device A calculates the duration between the time Device A sent the SNMP request packet and the time Device A received the SNMP response packet. The time taken reflects the SNMP connectivity and SNMP performance on the network.
Figure 4-8 SNMP test networking

Trace Test

The NQA trace test monitors the forwarding path between the NQA client and a destination and collects statistics about devices along the forwarding path. The trace test functions similarly to the tracert command. The difference is that the trace test provides detailed output information. For example, information about each hop contains the average delay time, packet loss ratio, and the time when the last packet was received. Figure 4-9 illustrates a network on which an NQA trace test is performed. The NQA trace test process is as follows:

  1. The NQA client (Device A) constructs a UDP packet with a TTL of 1 and sends the packet to destinationDevice B.

  2. After Device C at the first hop receives the UDP packet, it finds that the TTL of the packet expires. Then, Device C discards the packet and replies with an ICMP Time Exceeded message.

  3. After the NQA client receives the ICMP Time Exceeded message, it records the first-hop IP address, increases the TTL of the same UDP packet to 2, and sends the UDP packet.

  4. After Device D at the second hop receives the UDP packet with a TTL of 2, it finds that the TTL of the packet expires. Device D discards the packet and replies with an ICMP Time Exceeded message.

  5. This process continues until the packet reaches the last hop router, which replies with an ICMP Port Unreachable message to the NQA client.

    Based on the ICMP message returned from each hop, the NQA client collects information about the forwarding path between the NQA client and the destination and statistics about each router along the forwarding path. The data obtained is used to evaluate the network status.

Figure 4-9 Trace test networking

UDP Jitter Test

Implementation Principle

A UDP jitter test is used to calculate the packet delay, jitter, and packet loss ratio using timestamps carried in UDP packets. Jitter is time offset of the interval between the receipts of two consecutive packets minus the interval between the transmissions of the two packets. Figure 4-10 illustrates a network on which a UDP jitter test is performed. The UDP jitter test process is as follows:

Figure 4-10 UDP jitter test networking

  1. The NQA source (Device A) sends packets to the NQA destination (Device B) at a specified interval. Timestamp t1 is added when a packet is sent.

  2. Upon receipt of the packet, the destination adds timestamp t1' to the packet.

  3. After processing the packet, the destination adds timestamp t2' to the packet and forwards it back to the source.

  4. Upon receipt of the packet, the source adds timestamp t2 to the packet.Timestamps t3/t3' and t4/t4' are similar.

    NOTE:

    In a UDP jitter test, the maximum number of packets to be sent each time is equal to the configured probe-count value and jitter-packetnum value.

    The following indexes can be calculated by the source:

    • Maximum, minimum, and average jitter values of the packets exchanged between the source and destination.

    • Maximum one-way delay time of the packets that the source sends to the destination or the destination sends to the source.

    The jitter time reflects the network status.

Related Concepts

RTT=(t2–t1)-(t2'-t1')

If the RTT is longer than the specified timeout period, the network is congested and UDP packets will be counted as lost packets.

Packet loss rate = Number of lost UDP packets/Number of sent UDP packets (Number of lost UDP packets = Number of sent UDP packets – Number of received UDP packets).

A UDP jitter test can measure jitter either unidirectionally or bidirectionally:

  • Source-to-destination jitter=(t3'-t1')-(t3-t1)

    A larger absolute jitter value indicates poorer link quality, no matter whether the jitter value is positive or negative.

  • Destination-to-source jitter=(t4–t2)-(t4'-t2')

    A larger absolute jitter value indicates poorer link quality, no matter whether the jitter value is positive or negative.

In a UDP jitter test, you can set the number of packets to be sent at one time in each test instance to simulate a specific service. For example, configure the source to send 3,000 UDP packets every 20 ms to simulate G.711 traffic.

A UDP jitter test can also measure the packet loss rate unidirectionally. On the network shown in the Figure 4-10, destination (DeviceB) collects statistics about received packets. After source (DeviceA) finds that the number of packets sent by itself is different from the number of packets received by itself, source (DeviceA) initiates a unidirectional packet loss query to learn the number of packets received by destination (DeviceB).

  • Source-to-destination packet loss rate = Number of packets sent by source (DeviceA) – Number of packets received by destination B

  • Destination-to-source packet loss rate = Number of packets received by destination (DeviceB) – Number of packets received by source (DeviceA)

  • If the source (DeviceA) does not receive any query packet, it records Packet Loss Unknown in the NQA structure table.
Hardware-based UDP Jitter Test
A hardware-based UDP jitter test, a supplement to a UDP jitter test, enables the hardware forwarding engine to transmit packets and add timestamps to packets. The hardware-based UDP jitter test has the following advantages:
  • Reduces the interval at which packets are sent. The minimum interval is 10 ms.

  • Increases the number of concurrent test instances. To increase the number of concurrent test instances, install more line processing units on a device.

  • Increases the accuracy of the calculated delay and jitter time.

The advantages helps users learn about accurate network status and improve the efficiency of devices.

NOTE:

By default, UDP jitter (hardware-based) is not enabled. To implement a hardware-based UDP jitter test, enable the interface board to send packets.

Table 4-3 Differences between the UDP jitter test and hardware-based UDP jitter test

Item

UDP Jitter Test

Hardware-based UDP Jitter Test

Minimum interval at which test packets are sent

20 ms

10 ms

Maximum number of concurrent test instances

100 concurrent test instances on each device

The number of concurrent test instances increases with the number of boards

Jitter calculation

A main processing unit (MPU) timestamps packets.

Every LPU timestamps packets more precisely

ICMP Jitter Test

Implementation Principle

An Internet Control Message Protocol (ICMP) jitter test calculates the delay, jitter, and packet loss ratio using timestamps carried in ICMP packets. Jitter time is the time offset of the interval between packet receipts minus the interval between packet transmissions. Figure 4-11 illustrates a network on which an ICMP jitter test is performed. The Internet Group Management Protocol (IGMP) jitter test process is as follows:

Figure 4-11 ICMP jitter test networking

  1. Source (DeviceA) adds timestamp t1 to an ICMP packet and sends the packet to Destination (DeviceB).

  2. Upon receipt of the packet, Destination (DeviceB) adds timestamp t1' to the packet.

  3. After processing the packet, Destination (DeviceB) adds timestamp t2' to the packet and forwards it back to Source (DeviceA).

  4. Upon receipt of the packet, Source (DeviceA) adds timestamp t2 to the packet. Timestamps t3/t3' and t4/t4' are similar.

The NQA source can calculate the following indexes:

  • Maximum, minimum, and average jitter values of the packets exchanged between the NQA source and destination.

  • Maximum one-way delay time of the packets that the source sends to the destination or the destination sends to the source.

The data obtained is used to evaluate the network status.

Related Concepts

An ICMP jitter test can measure jitter either unidirectionally or bidirectionally:

  • Source-to-destination jitter=(t3'-t1')-(t3-t1)

    A larger absolute jitter value indicates poorer link quality, no matter whether the jitter value is positive or negative.

  • Destination-to-source jitter=(t4–t2)-(t4'-t2')

    A larger absolute jitter value indicates poorer link quality, no matter whether the jitter value is positive or negative.

RTT=(t2–t1)-(t2'-t1')

If the RTT is longer than the specified timeout period, the network is congested and ICMP packets will be counted as lost packets.

Packet loss rate = Number of lost ICMP packets/Number of sent ICMP packets (Number of lost ICMP packets = Number of sent ICMP packets – Number of received ICMP packets).

In an ICMP jitter test, you can set the number of packets to be sent consecutively in a single test instance to simulate a certain type of traffic.

Hardware-based ICMP Jitter Test
A hardware-based ICMP jitter test, a supplement to the ICMP jitter test, enables the hardware forwarding engine to transmit packets and add timestamps to packets. The hardware-based UDP jitter test has the following advantages:
  • Reduces the interval at which packets are sent. The minimum interval is 10 ms.

  • Increases the number of concurrent test instances. To increase the number of concurrent test instances, install more line processing units (LPUs) on a device.

  • Increases the calculation accuracy of the delay and jitter time.

The NQA source can calculate the following indexes:
  • Maximum, minimum, and average jitter values of the packets exchanged between the source and destination

  • Maximum one-way delay time of the packets that the source sends to the destination or the destination sends to the source

The obtained jitter value reflects the network status. Table 4-4 compares the ICMP jitter test and hardware-based ICMP jitter test.

Table 4-4 Differences between the ICMP jitter test and hardware-based ICMP jitter test

Items Compared

ICMP Jitter

ICMP Jitter (hardware-based)

Minimum interval at which test packets are sent

20 ms

10 ms

Maximum number of concurrent test instances

100 concurrent test instances on each device

The number of concurrent test instances increases with the number of boards

Jitter calculation

An MPU timestamps packets.

Every MPU timestamps packets more precisely.

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Updated: 2019-01-03

Document ID: EDOC1100055050

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