RFC2544 standard test

Hello!

This time, it was time to consider the standard RFC2544 test: what it is used for, how it is performed, its advantages and disadvantages.

Introduction

RFC2544 was developed in 1999 and adopted by the IETF . There is a translation into Russian. Now this recommendation is practically a de facto standard, thanks to its wide distribution and free access. The recommendation “describes and defines a set of tests for determining the characteristics of interconnection devices”, describes the formats for the presentation of test results.
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Method structure

Testing according to the RFC2544 methodology is reduced to the execution of a set of tests, four of which are present in most manufacturers of measuring equipment, and two are quite rare (the latter are on the list).

• Throughput
  
  • determines the bandwidth of the DUT as recommended by RFC1242
  • determines the load at which there is no packet loss
  
  
• Latency
  
  • determines the delay, as recommended by RFC1242
  • measures frame delay selectively
  
  
• Frame loss
  
  • determines the frame loss rate, as recommended by RFC1242, over the entire range of data rates and frame sizes
  • determines the dependence of losses on the load
  
  
• Back-to-back
  
  • determines the ability of the DUT to handle back-to-back frames, as recommended by RFC1242
  • measures the duration of work at a given load
  
  
• System Restore
  
  • determines the speed of DUT recovery after traffic overload
  
  
• Reboot
  
  • determines the speed of DUT recovery after a software or hardware reset
  
  

Bandwidth

The maximum number of frames per second, which the device can transmit without errors, is determined. Speed ​​is determined by bisection method. The test starts at maximum speed. In case of losses, the speed is halved. If there is no loss, then the speed is doubled compared to the previous one. And so on. The maximum speed is determined by the stability of work (no loss) for 60 seconds. Testing is carried out for each frame size. Dimensions are specified in RFC2544 test parameters before launch.

Delay

The test relies on previous bandwidth measurement. For each packet size with a corresponding maximum speed, a data stream is generated. The stream must have a duration of at least 120 seconds. A timestamp is inserted into 1 packet after 60 seconds. The transmission time is recorded on the sending side. At the receiving side, the sender's mark is determined and the packet reception time is recorded. Delay is the difference between the time of receipt and the time of dispatch. The test must be repeated at least 20 times. Based on the measurement results, the average delay is calculated.

Packet loss

Calculates the percentage of packet loss (the ratio of lost to sent). The measurement starts at maximum speed and decreases by 10% (or less) with each subsequent attempt. The speed is reduced until two measurements in a row do not pass without loss.

Back-to-back

The test is to check the equipment to process frames with a minimum interframe interval, i.e. back to back (back-to-back). It starts with the number of frames set in the RFC2544 test parameters. If no losses are observed (for at least 2 seconds), then the number of frames increases, if present, then decreases. According to the results of at least 50 measurements, an average value is calculated.

The disadvantages of the technique

The testing methodology is old (developed in 1999) and today it no longer meets the requirements of the market. Of the disadvantages stand out:
impossible to measure latency (Frame Transfer Delay, FTD)
no delay variation measurement (Frame Delay Variation, FDV)
no multithreading, everything is done in turn
long test (based on the previous paragraph)

Additions to the method

To extend the functionality and compensate for the shortcomings of the developed supplement:

• jitter measurement
• complex traffic

Jitter

Packet jitter is the absolute difference in propagation delays between two consecutively received packets belonging to the same data stream.
Ideal - the complete absence of jitter:

A possible option is a different delay between adjacent packets:

Complex traffic

The test allows you to generate and receive multiple streams of test traffic.
It measures throughput and frame loss (Frame Loss Rate, FLR), but does not measure the constant delay (FTD) and delay variation (FDV).

Conclusion

The RFC2544 technique is now present in the equipment of most manufacturers, primarily historically, and it can be said that today it is the same basic test for packet Ethernet as BERT for TDM networks. But it is worth remembering that RFC2544 does not conduct extensive testing, and even with the successful completion of all tests, a situation may arise that the network will not function as expected.
In place of the RFC2544 methodology comes Y1564, which I am going to devote to the next article.

My other articles

1. The quality of data networks. Software and hardware measurements
2. The quality of data networks. Transport