Discussion on the IFG Technology of frame spacing

1. What is IFG? (What)

IFG (interframe
GAP), frame spacing, and time disconnection between two adjacent Ethernet frames. The Ethernet transmission mode is one frame and one frame, and the gap between frames is required, that is, the frame spacing IFG can also be called IPG (interpacket gap ). IFG refers to a period of time, not a distance, usually in microseconds (μs) or nanoseconds (NS ). As shown in:

"Times New Roman" '> Figure 1; MSO-ascii-font-family: "Times New Roman"; MSO-Hansi-font-family: "Times New Roman" '> frame spacing

2. Why IFG? (Why)

Font-family: "yahei consolas hybrid" '> after a network device or component receives a frame, it takes a short period of time to recover and prepare for receiving the next frame.

3. What is the IFG size? (Importance)

The minimum value of IFG is 96 bit time, that is, the time required to send 96-bit raw data in the media. The minimum value of IFG in different media is different:

12.0pt; font-family:; color: black; MSO-Fareast-language: ZH-CN; MSO-no-proof: yes "> NO MATTER 10 m / 100 m / 1000 m At least 96bit; font-family:; MSO-Fareast-language: ZH-CN; MSO-no-proof: yes "> ifgmin = 96bit/Speed
(S)

12.0pt; font-family:; MSO-Fareast-language: ZH-CN; MSO-no-proof: yes "> then: 10 mmin: 9600 NS

Yes "> ZH-CN; MSO-no-proof: yes"> 100 mmin: 960 NS

ZH-CN; MSO-no-proof: yes "> 1000 mmin: 96 NS

MSO-ANSI-language: Fr '> 4. How to Use fr'> ifgmso-ANSI-language: Fr '>? (How)

For example, IFG solves the speed matching problem in the Ethernet traffic control mechanism;

Font-family: "yahei consolas hybrid" '> here the Ethernet traffic control mechanism is involved, for example:

"Times New Roman" '> Figure 2; MSO-ascii-font-family: "Times New Roman"; MSO-Hansi-font-family: "Times New Roman" '> Ethernet transmission example

 

12.0pt; font-family: "yahei consolas hybrid"; MSO-bidi-font-family: "yahei consolas hybrid" '> 1)
Device 1 sends data to device 2 with its own working clock (osc1;

12.0pt; font-family: "yahei consolas hybrid"; MSO-bidi-font-family: "yahei consolas hybrid" '> 2)
Data Packets enter device 2:

12.0pt; font-family: "yahei consolas hybrid"; MSO-bidi-font-family: "yahei consolas hybrid" '>)
After processing by the clock data recovery device (CDR), extract the clock from the data and store the data packets into the receiving cache based on the extracted clock (clk2). At this time, clk2 and osc1 are synchronized;

12.0pt; font-family: "yahei consolas hybrid"; MSO-bidi-font-family: "yahei consolas hybrid" '> B)
Data is stored in the sending cache after receiving and processing by the upper-layer protocol;

12.0pt; font-family: "yahei consolas hybrid"; MSO-bidi-font-family: "yahei consolas hybrid" '> 3)
The sending cache uses the working clock (osc2) of device 2 to send data. Because Ethernet works asynchronously, osc1 and osc2 act as the local clock of different devices, it cannot be exactly the same frequency (the working clock of the Ethernet device can have a frequency difference of plus or minus 50ppm). If osc1 is greater than osc2, the receiving speed of device 2 will be greater than the sending speed, if the receiving buffer is full, packet loss will occur;

How can we solve the packet loss problem?

On the sending side of device 2, IFG (frame spacing) is reduced to speed up the transmission of valid data packets, so that the transmission speed can keep up with the receiving speed.

5. What is the application of IFG in our actual work?

Smartbit 6000c Use in production testing.

Usage principle:

When the IFG increases, the effective speed of the device decreases, which can solve the problem of packet loss due to the high speed;

IFG is reduced (but must be greater than 96 bit time), and the effective speed of the device increases, which can solve the problem of testing timeout caused by slow speed.

MSO-Hansi-font-family: "Times New Roman" '> references:

[1] MSO-ascii-font-family: "Times New Roman"; MSO-Hansi-font-family: "Times New Roman" '> Ethernet traffic control mechanism and its Implementation Based on vsc7323 "Times New Roman"; MSO-Hansi-font-family: "Times New Roman"'>. http://tech.c114.net/169/a266942.html

[2] interframe gap Wikipedia. http://en.wikipedia.org/wiki/Interframe_gap

Thernet. http://www.cisco.com/en/US/docs/internetworking/technology/handbook/Ethernet.pdf