How to idenfity the ethernet frame data belong to which frame ?

[123zxc123]

I have a project which convert E1 signal to ethernet signal, use FIFO to buffer data portion of ethernet frame, i have a question on how to idendify the data read from FIFO belong to which ethernet frame.

eg. When read 1st frame data, at these time 2nd frame,3rd frame,4th frame may be written into FIFO, and the length is different, so when i read next data i don`t know how to idendify it belong to which frame.

 

[ebuddy]

Make the FIFO one bit wider. The extra bit serves as the frame "tag". The first byte of a frame from E1 side will be tagged with this "SOF" (Start of Frame) bit when it is written into FIFO. On the Ethernet side, you will know the byte you are reading out belongs to the previous frame or it is the first byte of a new frame. Hope this helps.

 

[kornukhin]

Or you can use FIFO to store packet length. Put it in FIFO before the frame.
It doesn't require additional FIFO bits, but need addintional logic to calculate length of packet and write it to FIFO.