Shulou(Shulou.com)06/03 Report--

In this issue, the editor will bring you about what is the Ethernet frame format. The article is rich in content and analyzes and narrates it from a professional point of view. I hope you can get something after reading this article.

Ethernet frame format

Packets on an Ethernet link are called Ethernet frames. The beginning of the Ethernet frame consists of a preamble and a frame start character. This is followed by an Ethernet header that indicates the destination and source addresses with a MAC address. In the middle of the frame is a packet loaded with other protocol headers (such as the IP protocol). The Ethernet frame ends with a 32-bit redundancy check code, which is used to verify that the data transmission is corrupted.

structure

A binary packet from a line is called a frame. The preamble and the start of the frame can be seen, among other things, from the frame seen on the physical line. This information is required for any physical hardware.

The following table shows the full frame format for MTU transmissions with 1500 octets (some Gigabit Ethernet or even higher Speed Ethernet supports larger frames, called jumbo frames). An octet is eight bits of data (that is, a byte of a modern computer).

Ethernet | | Type Ethernet frame structure preamble frame start MAC destination address MAC source address 802.1Q tag (optional) Ethernet type load redundancy check frame spacing 10101010 7 octet10101011 1 octet6 octets6 octets (4 octets) 2 octets46-1500 octets4 octets12 octets

64-1522 octets

72-1530 octets

84-1542 octets

Preamble and frame start character

See: Syncword

A frame begins with a 7-byte preamble and a 1-byte frame start character. Before Fast Ethernet, the bit pattern for this part of the frame on the line was 10101010 10101010 10101010 10101010101010101010101010101011. Because the lowest bit is transferred first (LSB) when a byte is transferred, its corresponding hexadecimal representation is 0x55 0x55 0x55 0x55 0x55 0x55 0x55 0xD5.

The 10thumb 100m network card (MIIPHY) transmits 4 bits (one half word) at a time. Because previously, the leader will become seven sets of 0x5+0x5, and the frame start character will become 0x5+0xD. 1000m network card (GMII) transmits 8 bits at a time, while 10Gbit/s (XGMII) PHY chip transmits 32 bits at a time. Note that when described in octet, seven 01010101 is transmitted first and then 11010101. Since the lower 4 bits of the 8-bit data are sent first, 0101 of the frame start character is sent first, followed by 1101.

Header

The header contains the MAC addresses of the source and destination addresses, an Ethernet type field, and an optional IEEE 802.1QVLAN tag that describes VLAN membership and transport priority.

Frame check code

The frame check code is a 32-bit cyclic redundancy check code to verify whether the frame data is corrupted.

Frame spacing

Main entry: en:Interframe gap

When a frame is sent, the sender needs to send at least 12 octet idle line status codes before the next frame is sent.

The above is what the editor shares for you what is the Ethernet frame format, if you happen to have similar doubts, you might as well refer to the above analysis to understand. If you want to know more about it, you are welcome to follow the industry information channel.

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