Explanation of Tx bps L1 and Tx bps L2

[Luca Salvatore]

What does T1 and T2 mean here?  Not sure of the difference here?

This screenshot is from a unidirectional test with a command like: start -f stl/udp_1pkt_simple.py -p 0 -m 100%

[Dominik Tran]

Hi,

by T1 and T2 I assume you mean L1 and L2. You can measure packet size in bits or bytes on different layers of network. Depending on layer, you will get different value.

• L1 is lowest, physical level. It includes interpacket gap (12B), preamble(7B) and SFD(1B). See Ethernet frame.
  
• L2 doesn't include mentioned fields, so on this layer you send/receive 20B less per packet.
  

Example 1: You send 1 packet that has size of 100 bytes on L1. On L2, it will look like you sent packet with size of 80B.
Example 2: You send 1 packet that has size of 1000 bytes on L1. On L2, it will look like you sent packet with size of 980B.

Small packets have bigger percentual difference between L1 and L2 compared to big packets.
In example 1, there is 20% difference in size between L1 and L2.
In example 2, there is only 2% difference in size.

In your screenshot, you can see that L1 is 100Gbps, but L2 is 76Gbps. It means that packets you're sending are small. With big packets, there will be almost no difference. Manufacturers obviously specify max. speeds of their products at L1, because it provides bigger number :)

Dominik

Dne pondělí 18. března 2024 v 21:29:04 UTC+1 uživatel Luca Salvatore napsal:

[Luca Salvatore]

Yes sorry, i did mean L1 and L2.

Thank you for the explanation, this helps a lot.